Posted by: oikosasa | May 6, 2013

Oikos at INTECOL

INTECOL 2013, takes place in London August 18-23, see http://www.intecol2013.org/

We’ll be there! Will you?

More info on Oikos symposium and other activities will come soon!

The 11th INTECOL Congress, Ecology: Into the next 100 years will be held in London as part of the centenary celebrations of the British Ecological Society.The theme of the Congress is Advancing ecology and making it count.

Early-bird registration closes on 12th May: http://www.intecol2013.org/5_Registration.html

Read about butterflies finding romance in the mountains in the new Early View paper “Simple rules for complex landscapes: the case of hilltopping movements and topography” by Guy Peer and colleagues. here’s Guy’s summary of the paper:

Mating on a hilltop

Mating on a hilltop

You are lost in an unfamiliar, hilly landscape. What shall you do? Most people would ascend the nearest hill and try to get a good overview. Butterflies may have much more limited vision, but they manage quite effectively in aggregating on mountain tops which serve as rendezvous for mating. An individual-based model which focuses on this “hilltopping” phenomenon identifies simple behavioural rules that can optimise mating success, and the success of mated females in finding habitat patches, across landscapes regardless of their complexity. One interesting rule is: when moving uphill, butterflies should respond strongly but not ‘perfectly’ to topography. A perfect response, without occasional random movements, would simply trap them on local summits. If such mild randomness might be adaptive, shall we adopt the rule and accept our imperfections? At least for butterflies, it clearly helps finding a mate.

Fighting overe a female on a hilltop

Fighting overe a female on a hilltop

Guy Pe’er when chasing hilltopping butterflies in Israel, long ago when doing his PhD. While his “hilltopping model” is by now 12 years old, new results continue to emerge.

Guy Pe’er when chasing hilltopping butterflies in Israel, long ago when doing his PhD. While his “hilltopping model” is by now 12 years old, new results continue to emerge.
Posted by: oikosasa | April 23, 2013

The zombie killing spree continues

Look up, zombies are all around us nowadays! Even within science! In the Early View paper  “A critical analysis of the ubiquity of linear local–regional richness relationships“, Thiago Goncales-Souza and colleagues  goes on a zombie-killing adventure. Here is there summary of the paper:

Recently, ecologists have gone on a zombie killing spree, started by a blog post of Jeremy Fox here at the Oikos blog (link here). Dr. Fox defined zombie idea as having “survived decades of attacks from the theoretical and experimental equivalents of chainsaws and shotguns, only to return to feed on the brains of new generations of students.” He featured other zombie ideas such as “neutral = dispersal limitations” and the unimodal diversity productivity relationship. The post on his original zombie idea actually resulted in a peer-reviewed publication (Fox 2013) that, in his own words, has “No zombie jokes or other inflammatory rhetoric in it. I leave it you to judge if that makes the paper better or worse than the blog posts.” (link here).

We think that our publication fits into this zombie killing tradition. One of the most fundamental interests of ecologists since the early development of the ecological theory is the understanding of (potential) processes that drive local community structure. At a fundamental level, communities are structured by a combination of local environmental and regional processes (Ricklefs 1987).  The easiest and most traditional way to test whether regional or local processes affect local community structure consists of regressing local against regional species richness (the famous LSR-RSR relationships). The argument goes that communities controlled by regional processes are considered unsaturated, whereas communities controlled by local processes (such as species interactions) are considered saturated. Sadly enough, this argument survived indeed decades of attack (D. Srivastava, F. He and collaborators, and H. Hillebrand).

Sadder still, this method has kept on feeding on the brains of new generations of students, since it is used and featured prominently in ecology textbooks such as Begon et al. (Ecology: from individuals to ecosystems), Krebs (Ecology: the experimental analysis of distribution and abundance), and Ricklefs (The Economy of Nature and Ecology). Probably every ecology student has heard about the ubiquity of regional processes as drivers of local community structure using this method.

In addition to these fundamental problems, Szava-Kovats and collaborators in Oikos showed that the statistical test for detecting the linearity of the relationship is biased towards linear relationships, and moreover provided an unbiased method (called log-ratio method). In this Forum paper, we reevaluated the evidence for the ubiquity of linear LSR-RSR relationships by comparing the biased conclusions with the unbiased method, and found:

  1. In 113 relationships found in 47 studies, 70% and 30% were considered unsaturated and saturated, respectively, when using the biased method. However, by using the unbiased log-ratio method we found no prevalence of either unsaturated (53%) or saturated (47%) communities (Figure 1);
  2. 40% of the studies using the biased method were misclassified (i.e., mistakenly found an unsaturated pattern when it was saturated or vice-versa) and thus reached wrong conclusions.
  3. 50% of the examples of LSR-RSR relationships used in four (classic) ecology textbooks were misclassified.

Our conclusions thus add a new weapon in the arsenal against the zombie idea of interpreting local-regional relationships based on the linearity of the relationship. We showed that the last argument in favor of the method (its ubiquity) was based on a biased statistical method. We argue instead that future studies should consider the reciprocal interactions between regional and local such as those that take advantage of the metacommunity theory to understand the relative influence of regional and local processes on local community.

While studies of LSR-RSR relationships were instrumental to the development of the ecological curriculum, we hope that we can now finally put this zombie idea to rest and move on. As a final note, one of the reviewers for this manuscript was … non other than Jeremy Fox, zombie slayer par excellence.

Figura1_blog

Posted by: oikosasa | April 18, 2013

Welcome Susan Harrison – new SE

We are very happy to welcome Prof. Susan Harrison from UC Davies, USA, to our editorial board.
 susan at sensitive plant canyon 

My research seeks to understand the processes that shape and maintain plant species diversity at the landscape scale, where small-scale forces such as competition and facilitation interact with large-scale forces such as niche evolution and dispersal.  In the past few years, one particular focus has been to understand what characteristics of plant species and communities make them more or less susceptible to climate change, as well as to other interacting perturbations like fire, grazing, and invasion.  We’ve found that plant communities on nutrient-poor serpentine soils seem to respond less strongly to natural and experimental climatic variation than other communities, but we don’t yet understand the roles of soil properties, plant traits, and emergent community properties in causing this pattern.

Read more:  http://www.des.ucdavis.edu/faculty/Harrison/


GG burn wildflowers 7
Posted by: oikosasa | April 16, 2013

Same, same but oh so different.

They look the same, but perform so differently. And act differently against each other. Cryptic amphipods are dealt with in the Early View paper “Phenotypically similar but ecologically distinct: differences in competitive ability and predation risk among amphipods” by Rickey D. Cothran and colleagues. Read their summary here:

Traditionally, species that look alike were thought to be unlikely co-inhabitants due to competitive exclusion. However, newer theory suggests that a mix of ecological similarity that limits performance asymmetries that lead to competitive exclusion and slight differences in niche use may maintain species diversity. We provide data on the relative competitive ability and predation risk for three amphipod species that co-occur in lakes in North America. Until recently, these species were only differentiated using molecular markers (see picture). We discovered that slight differences in phenotype lead to differences in how well these species compete and deal with predators. We also found that the two species that show the strongest overlap in distribution within lakes are very similar when it comes to their competitive ability and predation risk. Our work suggests that a mix of niche differentiation and ecological similarity are maintaining amphipod species diversity in lakes.

 Cryptic amphipod species before (top) and after (bottom) preservation in 70% ethanol. From left to right: species A, species B, and species C. All animals are females.

Cryptic amphipod species before (top) and after (bottom) preservation in 70% ethanol. From left to right: species A, species B, and species C. All animals are females.

Picture caption: Cryptic amphipod species before (top) and after (bottom) preservation in 70% ethanol. From left to right: species A, species B, and species C. All animals are females.

Posted by: oikosasa | April 11, 2013

Taking metacommunity models to the empirical world

Will the use of “real” connectivity between communities improve metacommunity models? Read more in C.Moritz and colleague’s Early View paper: “Disentangling the role of connectivity, environmental filtering, and spatial structure on metacommunity dynamics”. Here’s their summary of the paper:

For decades, the environment has been proven to structure biodiversity. However, dispersal of organisms is also  a process that helps structuring and maintaining biodiversity in local communities. The problem is that  connectivity between communities (the fact that these communities are linked, resulting from the dispersal  process) is often assessed using a more or less simple function of geographic distance. Theoretical metacommunity models can incorporate both environmental and dispersal processes, but empirical  studies considering real connectivity instead of a function of geographic distance are more scarce. In our work,  we have included real connectivity measures to analyse polychaete community structure in the Gulf of Lions (NW  Mediterranean Sea) at different spatial scales. Our results are not trivial…and equivalent methods should be  applied to other ecosystems (terrestrial or marine) to continue quantifying the importance of dispersal on  biodiversity, either for particular species of interest or for entire communities.

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Posted by: oikosasa | April 9, 2013

When plants help other plants…

Nice to see that nature provides other kinds of interactions than nasty predation, competetion and parasitism! Christian Schöb and coworkers have studied the importance of “nursing” plants – plants that fascilitate for other plants – in community ecology. Read their Early View paper “Direct and indirect interactions co-determine species composition in nurse plant systems”.

Here is a summary of their study:

Our motivation to build a framework based on observational data in order to disentangle direct nurse effects from indirect effects among beneficiary species was twofold:

1) In some very common nurse plant systems, such as alpine cushion plant communities, the removal of the nurse to eliminate the direct effect and unambiguously estimate interactions among beneficiary species is simply not feasible.

Schobe1

The physical removal of the nurse cushion Arenaria tetraquetra ssp. amabilis growing in the Sierra Nevada Mountains in Spain would destroy the beneficiary species growing within the cushion canopy; in particular because beneficiary species often root in the organic matter accrued under the cushion.

2) Even in nurse plant systems where the physical removal of the nurse is feasible, taking away aboveground nurse parts does not remove the permanent effects of the nurse, e.g. the effects on soil properties including texture, resources and microbial communities.

An intact Retama sphaerocarpa nurse plant system in the semi-arid lowland of southeastern Spain with the nurse shrub and its understory community of beneficiary species.

An intact Retama sphaerocarpa nurse plant system in the semi-arid lowland of southeastern Spain with the nurse shrub and its understory community of beneficiary species.

The removal of aboveground parts would not remove the whole effect the nurse shrub, such as accumulation of soil organic matter and its specific communities of soil bacteria and fungi, which all together influence beneficiary species even after the nurse plant has been removed.

Schobe3

In our article we propose a simple but powerful mathematical framework to take apart direct effects of the nurse on its associated community from effects of interactions among beneficiary species. Our results showed facilitative effects of the nurse on its beneficiary species whereas interactions among beneficiary species where mostly competitive. Both interactions contributed significantly to the composition of the beneficiary plant community even though the direct nurse effect was ca. five times stronger than the effect of the interactions among beneficiary species. Interestingly, these patterns where similar in the two nurse plant systems studied even though they differed considerably in abiotic conditions (high alpine vs. semi-arid lowland) and growth form of the nurse (cushion plant vs. shrub). Our data therefore indicate functional parallelism of different nurse plant systems and highlight the complexity of species interactions within plant communities.

Hello everyone, my name is Ross Boucek and I am PhD student at Florida International University. Oikos has asked me to write about our Early View paper “No free lunch: displaced marsh consumers regulate a prey subsidy to an estuarine consumer” where we investigate the value of food subsidies to recipient consumers as well as what controls the amount of food subsidies available to them.  Food subsidies are resources that enter an ecosystem from another place, and add on to the resource base that is already available within the system. Subsidies in some instances can be almost considered a bonus, like getting cash for your birthday in the mail.  If you are on a graduate student stipend, birthday cash subsidies can go a long way! Because of the predictability of birthday cash, many graduate students budget these cash bonuses into their spending well before they arrive.  Therefore, if for some reason these checks get lost in the mail, or they are for less money, we could be in some trouble!

Graduate students and their reliance on birthday money is very similar to how some animals rely on food subsidies to survive.  One particularly charismatic example of consumer-subsidy interaction is bears and salmon in the U.S. Pacific Northwest.  In the fall, these bears congregate around rivers and streams to gorge themselves on salmon that predictably migrate from the oceans to spawn. These salmon subsidies help bears build necessary fat reserves that play a major role in their survival and reproduction over the winter. Because of the importance of food subsidies to consumers, biologists and ecologists have gone to great lengths to identify where subsidies occur in nature, and more importantly what controls how much of the food subsidies reach recipient consumers.

Boucek1

Diagram of the relationship between marine salmon subsidies and bears

Moving back to the bear-salmon subsidy interaction, in some areas of the U.S. Pacific Northwest, sea lions have figured out salmon are easy prey during their spawning migration; such that some sea lions track salmon up rivers, and pig out on these spawning fish, preventing them from reaching bears. The interception of these salmon subsidies by sea lions can be so intense, that they can reduce salmon available to hungry bears waiting upstream by as much as 65%.

Boucek 2

Diagram showing how sea lions reduce salmon subsidies to bears

This brings me to my research.  I work in the Florida Everglades, more specifically, where the iconic Everglades marshes or the “river of grass” joins the beautiful tropical mangrove estuary.

Boucek3

The study area of our research, located at the marsh-estuary interface in the Southwest Everglades

At this interface between the marsh and the estuary, during the winter and spring, rainfall decreases, causing freshwater marshes to dry.  When these marshes dry, large numbers of small-bodied freshwater fishes are forced into the estuary. At the same time that these prey enter the estuary, estuarine fish predators triple in abundance presumably to gorge on the marsh fish prey forced into the estuary.  Thus at the Everglades ecotone, estuarine predators function similarly to the bears in the Pacific Northwest, and small bodied marsh prey are like the salmon. However, similar to the sea lions, these small bodied fishes are accompanied by large-bodied fish predators that also live in the marsh that can intercept and remove or reduce fish prey subsidies to the estuarine consumers.  With all of this in mind, my research questions were 1) how important are marsh prey subsidies to estuarine consumers? And 2) how much of this subsidy is being removed by marsh predators?

Boucek4

Boucek 5

Diagram showing the relationsship between estuarine and marsh predators and marsh prey subsidies at the marsh-estuarine interface of the southwest Everglades

Our results show, like the salmon-bear example, that estuarine predators gorge themselves on these marsh prey subsidies. Consequently, the consumption of this subsidy makes estuarine predators roughly 15% fatter than they were before.

However, like the sea lion example, freshwater marsh predators consume about 60% of the fish prey that enter the estuary, leaving only 40% for the estuarine consumers.   The regulation of this subsidy to snook, the estuarine predator, could influence how much energy snook allocate to reproduction each year.  Snook spawn in the early summer to mid fall. Therefore the weight snook gain from this subsidy in the spring could go to egg production in the summer, thus increasing reproductive output.  If marsh predators decrease in abundance, then the amount of subsidy available to snook could increase, which may allow snook to invest more energy into reproduction and increase spawning success.  My current research is investigating just this question, whether or not larger prey subsidies, facilitated by the loss of marsh predators, result in increased spawning effort by snook.

Understanding the dynamics behind this subsidy could have important implications for South Florida.  In South Florida, snook are an important recreationally sought after fish.  In fact, snook are the 5th most targeted fish in the entire east coast of the United States, despite only occurring in South Florida. The money spent from anglers fishing for snook generates substantial amount of revenue for local businesses.  Therefore, knowing the drivers behind snook population dynamics like the regulation of food subsidies will help us better understand the provisioning of ecosystem services such as fisheries in the Everglades.

Boucek6

Posted by: oikosasa | April 2, 2013

Large-scale testing of Bergman’s rule

The colder, the bigger, suggested Bergman in 1848. In 2013 we publish a paper testing Bergman’s rule on a large data set. Showing…well find out in “Bergmann′s rule in mammals: a cross-species interspecific pattern” by Marcus Clauss and his co-workers. Below is their background story to the study:

I first learnt about ‘Bergmann’s rule’ (that among closely related species, those living at higher latitudes/at colder temperatures are larger) in school. It was one of the biological facts I had always considered a background fact that is unquestioned.  

When preparing a manuscript on the reproductive seasonality of ruminants (Zerbe et al., 2012) we collated various biological data on ruminants, including body mass and mid-latitude of their geographical range, and before testing relationships of these data with our proxy for seasonality, we tested them amongst themselves for potential correlations. We did this without accounting for the phylogenetic structure of the data (ordinary least squares) and with such an accounting (phylogenetic generalized least squares, pgls).

OIK_463_f1

We were not surprised when we found a relationship between latitude and body mass in our phylogenetic analysis – because this simply reflected Bergmann’s rule. The fact that this relationship was not significant in conventional statistics, but significant in pgls, just supported the notion that the rule holds among closely related species, not just any species you lump together. For us, this was a minor side-dish result in our set of analyses, and one we were not excited about, because it simply confirmed what we knew from school. In a quite similar way, our ruminant dataset supported, for example, Rensch’s rule (which was cool for our co-author that had the same name). But when we prepared the manuscript, and searched for other papers to cite in connection with our side result, we realized that Bergmann’s rule had, as far as we could find, not been analysed in this fashion among mammal species, not in ruminants, and surely not in a larger mammal dataset. Literature on Bergmann’s rule in mammals most often dealt with the intra-specific side of the phenomenon or with mammal assemblages, but not on the taxonomic/interspecific level. So we expanded the dataset beyond the ruminant species for which we had seasonality data, to comprise all mammals (based on availability of data in the PanTheria database). Again, we found the same effect: the relationship between latitude and body mass was significant if the phylogenetic structure of the dataset was taken into account. In a sense, we felt like having found a simple proof for a school lesson that had not been provided so far. This does not mean we claim to be first, best, closest, whatever, to proving Bergmann’s rule – we just found a simple, maybe elegant way to demonstrate it. Actually, once you start looking at individual taxonomic subgroups or certain geographic ranges, the picture becomes less simple – but that’s in the paper.  

For us, several lessons came with working on this topic. One is that the statistical procedure (pgls, sometimes called ‘phylogenetically controlled statistics’) is not only a quarrelsome one that one has to apply nowadays to get a paper published, but actually facilitates, in special circumstances, the detection of a pattern that would not be evident from simply plotting the data, or from ‘conventional’ statistics. So we tried to understand how patterns would look that yield different results in conventional and phylogeny-informed statistics, drawing on textbooks on the matter, and produced some schematic graphs to get a mental grasp on this (provided as a supplement to our paper). In my experience, there are quite some examples where a relationship that is significant in conventional statistics is no longer so in phylogenetic statistics (which then needs to be interpreted), but there are very few examples where a relationship is not significant in conventional stats but clearly is in phylo-stats.  

The other lesson came from going through the literature – at some stage, we decided to try to locate the original source itself, Bergmann’s own account, which was sometimes described as ‘hard to get at’ – and were surprised that you could simply download the whole text from the net (it is now part of the google books resource pool). Reading this text was quite some fun, due to the old style it was written in. From other literature, we had gained the impression that Bergmann formulated his rule for mammals, and were therefore surprised to see that he actually developed it, and supported it, using birds. And all the examples Bergmann used himself were between, not within, bird species, so no need to debate whether he meant it on an inter- or intra-specific level. Because the text is written in German, we decided to provide a relatively detailed translation of larger parts of it, so that others could get a picture of how he built his argument. I personally especially cherished his concluding comment, where he cautions the reader that in trying to support his hypothesis, he might have looked at the actual evidence in a biased way, and that therefore independent tests would be welcome.    

Posted by: oikosasa | March 28, 2013

Editor’s choice April 2013

DriesFor the April issue, we chose the following two papers as editor’s choice according to our motto of synthesizing ecology. Mumby et al. (2013) discuss various articles that either support or reject the hypothesis that coral reefs might be able to exist under certain conditions in two alternative stable states (ASS): a coral-dominated and a macroalgae-dominated state. Given the fact that the existence of multiple attractors is controversial, synthesis needs to be created by compiling various forms of evidence. Mumby and colleagues provide such an overview of evidence by providing analyses of the literature and the available empirical and theoretical data. By means of this integrated approach, they conclude that the most compelling evidence, which combines ecological models and field data, is far more consistent with multiple attractors than the competing hypothesis of only a single, coral attractor. This message warns managers that degraded reeds might never be able to be restored once dominated by macro-algae. Read Peter Mumby’s summary of the paper here

The second paper we selected is Baiser et al. (2013) testing the ability of metacommunity models to predict the network structure of the aquatic food web found in the leaves of the northern pitcher plant Sarracenia purpurea. It is the central aim of metacommunity theory to elucidate the relative impact of local and regional processes on local community structure. The structuring processes have, however, been predominately inferred from statistical modelling. The work of Baiser and colleagues takes an elegant approach to formally test to which degree patch-dynamics, species-sorting, mass-effects, and neutral metacommunity models, as well as three hybrid ones are able to predict observed patterns of the aquatic foodweb structure within these plants. By merging empirical data and more mechanistic models they test the probability that dispersal and sorting processes are important mediators of food web structure. While such integrated empirical-theoretical approaches have been developed for other ecological questions, Baiser et al. here demonstrate its usefulness for understanding drivers of food web structure.

Both papers as Open Access.

Posted by: oikosasa | March 26, 2013

New Oikos Cover!!

From the April issue 2013 onwards, Oikos will have a photo illustrating ecology in action on it’s cover.

To find the right photo for this year’s cover, we had a photo competition during winter. The happy winner of the competetion is Sascha Rösner, Marburg, Deutschland. See more of his photos here: www.pixeldiversity.com

And here is our new cover:

OIKOS_122_04_Cover1.indd

And here, Sascha tells us how he took the winning photo:

Wildlife photography often entails long travels to distant and remote landscapes that harbour a particular species of interest. This picture of two sawfly caterpillars (Nematus spec.), however, was taken just three meters of the front door of the photographer’s home. In the front yard, a small willow tree (Salix spec.) was densely populated with hundreds of these caterpillars. An easy opportunity to take the camera from indoors, attach a macro lens to the camera, mount it on a tripod, and take pictures (in fact, still wearing slippers). By chance, two of these guys apparently fed synchronously in the center of a leaf. Within 24 hours, the tree was completely naked, the caterpillars “abseiled” to the ground, and dug into the soil where they would morph into the imago flies some weeks later. Canon EOS 20D, EF 100 mm 2.8 @ f 7.1, ISO 100, tripod, remote control.

Posted by: oikosasa | March 22, 2013

Time to get rid of the males?

It has been debated for a while…are males really necessary? Find out how fish of the genus Chrosomus solve the small problems associated with asexual reproduction, in the Early View paper “Diets of sexual and sperm-dependent asexual dace (Chrosomus spp.): relevance to niche differentiation and mate choice hypotheses for coexistence” by Jonathan A Mee and co-workers.

Here’s a short summary of the study:

In order to persist, sperm-dependent asexuals must be ecologically divergent and/or more sperm-limited compared to their sexually reproducing hosts.

It’s easy to be fascinated by sperm-dependent asexual species – they’re one of those oddities of natural history that, collectively, are the reason many of us became students of biology. These all-female “Amazons” require a male (or just their sperm) of a sexually reproducing host species to provide the trigger for egg development and reproduction, but, in most cases, discard the male’s genome.

In addition to being a fascinating natural oddity, the existence of sperm-dependent asexuals raises an interesting scientific question: how do sperm-dependent asexuals coexist with their host species?  All-female asexuals have a great advantage over sexuals – by producing no males, the asexuals have twice the potential population growth rate relative to the sexuals.  But, in the case of sperm-dependent asexuals, vastly outcompeting the sexuals (i.e., eliminating the source of sperm) would eliminate the ability to reproduce.  There are two general mechanisms by which sperm-dependent asexuals and their sexual hosts can achieve stable coexistence.  First, sufficient ecological divergence between the sexuals and asexuals would avoid competitive exclusion.  Second, if males prefer mating with sexual females rather than asexual females, asexual females would be more sperm limited (and have reduced reproductive output) relative to sexual females.

blog eos

Our contribution to understanding how sperm-dependent asexuals coexist with their sexual hosts examined the combined influence of these two mechanisms (ecological divergence and male mate choice) on the coexistence of sperm-dependent asexual species and their sexual hosts – previous work only considered each mechanism independently. We integrated the insights of mathematical modeling and empirical data on ecological divergence (from two natural populations of the sperm-dependent asexual fish, Chrosomus eos-neogaeus) to conclude that a combination of both mechanisms may be required for coexistence. This integrated approach is valuable to understanding many ecological and evolutionary processes.

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Posted by: oikosasa | March 19, 2013

On the evolution of fruit colour

Ever thought about why an orange is orange while an apple is green? And a blueberry blue and blackberry black, while a raspberry is red? Well, one explanation – seasonality – is studied in the new Early View Paper  “Fruit color and contrast in seasonal habitats – a case study from a cerrado savanna” by Maria Gabriela G. Camargo and co-workers. Here is their short summary of the study:

Fig3

Examples of fruits with different colors. A. green; B. multicolored; C. yellow; D. black; E. multicolored; F. brown; G. multicolored; H. red.

Fruit color is an important signal for diurnal seed dispersers, mainly for birds, and the contrast between the fruit and the background is regarded as more important than the color per se for fruit detectability. However, the contrast between fruit displays and their background are not necessarily constant in seasonal habitats where part of leaves is shed in the dry season.

We thus hypothesized that the contrast between fruit displays and their background vary throughout the year in a seasonal habitat and if this variation is adaptive, we predicted higher contrasts between fruits and foliage during the fruiting season.

To verify our hypotheses we used reflectance measurements of fruits and leaves and contrast analysis. We also accessed a six-year data base of fruit ripening according to the fruit color (red, yellow, black, brown and multicolored) for a woody community in a cerrado-savanna vegetation, southeastern Brazil. The cerrado is subjected to a seasonal climate, with a wet summer between October and March and a dry winter between April and September, when the leaf background get yellowish.

Fig1

Circular histograms for the frequency of fruiting onset dates per fruit colors in a woody cerrado savanna community, southeastern Brazil.

We found that black, and particularly red fruits, that have a high contrast against the leaf background, were highly seasonal, peaking in the wet season. Multicolored and yellow fruits were less seasonal, not limited to one season, with a bimodal pattern for yellow ones, represented by two peaks, one in each season. We further supported the hypothesis that seasonal changes in fruit contrasts can be adaptive because fruits contrasted more strongly against their own foliage in the wet season, when most fruits are ripe. Hence, the seasonal variation in fruit colors observed in the cerrado-savanna may be, at least partly, explicable as an adaptation to ensure high conspicuousness to seed dispersers.

Fig2

Mean leaf reflectance curves during the dry and wet seasons for 49 species of the woody cerrado savanna community, Southeastern Brazil.

To consider at your Friday dinner tonight: Sex-biased diets affect the ecology of other species in the surroundings. Read more in the new early View paper “Antelope mating strategies facilitate invasion of grasslands by a woody weed” by Shivani Jadeja and colleagues. To get a good feeling of the antelope and the seeds that the males eat, read Shivani’s beautiful description of the wildlife reserve in western India, in her summary of the paper:

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Mesquite (Prosopis juliflora) pods

In Velavadar National Park, a grassland wildlife reserve in western India, invasive mesquite trees (Prosopis juliflora) obstruct the horizon, where the land meets the sky. The dominant woody plant in the area, mesquite juts out as green crowns among the drying grasses that give the grassland a hue of yellow, red and olive streaks in the winter and summer. Velavadar is home to a large population of the threatened native antelope, blackbuck (Antilope cervicapra). Male blackbuck defend territories in open grasslands; these territories are either solitary or in clusters called leks. The classical lek in Velavadar, the size of a football field, may have more than ninety rutting males during peak mating season. During this time, the lek turns into a battle field where males perform strenuous displays and engage in fierce fights to defend their territories. Females visit the lek and seem to use a variety of information to choose a male to mate with. Males use urine and dung to create huge scent marks on their territories. These dung-piles can be seen as black dots from outer space (Look at blackbuck dung-piles on Google satellite images at 22° 2’54.82″N and 72° 1’20.78″E).

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Fruit removal by male blackbuck (Antilope cervicapra) captured in a camera trap

3_Seed deposition through dung on a male mating territory- Inset- Large dung-pile on the classical lek

Seed deposition through dung on a male blackbuck mating territory. Inset: A large dung-pile on the classical lek

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Presence of mesquite seeds in blackbuck dung

As blackbuck prefer open habitats, we predict that this concentrated seed dispersal by males will result in a positive feedback process where territories, which are typically in open grasslands, are modified into woodland patches, following which  males shift their territories to more open areas. We also predict that this male-aided conversion of grasslands to mesquite woodlands will negatively affect this open plains antelope species and cause shifts in mating system and social organization and a reduction in population size. Thus, here is one mechanism of spread of a woody invasive in grasslands, where one sex of a disperser, here male blackbuck, through its extreme mating behaviour, is planting seeds in new habitat, and perhaps negatively affecting its own lifestyle.

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Seedling growing in a dung-pile on a blackbuck mating territory

Posted by: oikosasa | March 12, 2013

The little black dress of ecology

Taylor´s power law and bird populations are studied with in the new Early View paper “Interspecific differences in stochastic population dynamics explains variation in Taylor’s temporal power law”, by Marit Linnerud and her coworkers. Here’s Marit’s summary of the study:

Taylor’s power law – an oldie but goodie!

Taylor’s power law is like the little black dress of ecology, a general law that fits every species regardless of size or other personal characteristics.  According to the law the variance of population abundance in either time or space can be described by a function of the mean. A reasonable null expectation following from the definition of the variance is that as the abundance of a population increase by one unit on a logarithmic scale the variance is expected to increase by two logarithmic units, resulting in a slope of two. However, empirically the slope is often less than two, thus revealing some interesting ecological dynamics. Although the causal mechanism behind the law is not agreed upon, it seems likely that several factors are at play. A theoretical framework based on stochastic population dynamics provides testable predictions of what causes the deviations from the expected slope of two.

In our recent study we estimate the temporal mean-variance relationship for a large number of British bird populations. There were two significant challenges. Firstly, we could not ignore that sampling in itself could bias the estimates of the variance and secondly the estimated of variance increases with the number of years the population have been studied. Taking this into account we evaluated how the different deterministic and stochastic factors known to affect temporal population dynamic influenced the slope of the power law. It turns out that differences in demographic stochasticity among species were the main explanation of the variation in the slopes of Taylor’s power law.

Posted by: oikosasa | March 8, 2013

Cocktail mingle ecology

I would so much like to see someone using Hari Sridhar, Ferenc Jordán and Kartik Shankers paper “Species importance in a heterospecific foraging association network” as a basis for a study of humans on cocktail parties. Which small groups may be the core of highly important individuals (instead of species)? Is the same group of people important if they go to a party in another place? Or to a scientific conference in another research area? Or are humans not at all like birds?

Here is Hari’s background story to the study. The beautiful drawing is made by Rangu Narayan.

Chance and luck played a big part in the making of this paper. It was early 2008, and I had just begun my doctoral work on mixed-species bird flocks, when Ferenc visited my department. Ferenc specializes in using network approaches to tackle problems in ecology. In a talk during his visit, he mentioned that ‘network thinking’ was particularly useful in two ecological contexts: (1) to understand interactions among individuals in animal social groups (2) to understand interactions among species in communities, e.g. foodwebs. When we heard this, both Kartik (my PhD supervisor) and I immediately realized the value of network thinking in my doctoral work because mixed-species flocks fit both the contexts that Ferenc highlighted. Each mixed-species flock is a social group built on interactions among individuals of different species; but across multiple such flocks in an area, populations of species are linked in a community-level species interaction network. We spoke to Ferenc and he readily agreed to help us, since he too was keen on trying his hand at a new ecological system.  Given our different geographical locations (Ferenc was based in Trento, Italy, and Kartik and I in Bangalore, India), the plan was to work the collaboration entirely over email. But another lucky break meant that I could go to Ferenc’s institute in Italy to work on the project. My fieldwork was supported by a grant from the International Foundation for Science (IFS), of which a large portion remained unused till the end.  IFS allowed me to use this money to travel to Italy for two weeks in early 2012. Over endless cups of coffee and food at an Indian (!) restaurant in Trento, Ferenc and I built and analysed the flock networks for this paper.

flockpainting_Rangu_Narayan

 This collaboration had other useful spinoffs. Ferenc came back to India in 2012 to conduct a network analysis workshop as part of a student conservation conference in Bangalore that Kartik and I were involved in organizing. Kartik and Ferenc are also putting together a special issue on ecological networks for a conservation magazine called Current Conservation, which will include a non-technical piece based on this Oikos paper.

Posted by: oikosasa | March 7, 2013

Theoretical weed ecology

Do you like trying new food items? I do. And many herbivore insects seem to do so as well. Invading alien species, yummy yummy! How these interactions affect the ecology of the invaders is studied by Matthew L. Forrister and Joseph S. Wilson in “The population ecology of novel plant–herbivore interactions”. Here’s their background to the study:

Everyone knows that weeds are everywhere these days, and most ecologists know that native insects often like to eat exotic plants.  That dynamic (native herbivores utilizing novel hosts) has been very productive for evolutionary biologists (think about the apple maggot fly on apple or the soapberry bug on goldenrain trees), and has become increasingly useful for ecologists who realize that we can watch novel interactions and communities assemble before our eyes.

forOikos

The ubiquity of interactions between native herbivores and novel plants has led to an imbalance in the ratio of empirical to theoretical work.  Moreover, some of the relevant theoretical work (for example on the evolution of niche width) is not always accessible to the average field biologist observing caterpillars eating weeds.  Our motivation in writing this paper was to provide an easily accessible conceptual framework that might serve to organize and focus experimental approaches.  For example, studies are often reported in which the “preference-performance” relationship is examined using native insects reared on native and exotic hosts.  We believe that the focus on that particular relationship demonstrates a certain inertia in the literature that should be overcome, because (for one thing) a rather definitive meta-analysis of that issue has been recently published (Gripenberg et al. 2010 Ecology Letters 13:383-393), and moreover there are many other facets of insect life history that need to be studied, such as interactions with natural enemies, indirect interactions with other herbivores or behavioral factors that affect realized fecundity.

In addition to making the rather fundamental point that our studies need to go beyond the performance of juvenile herbivores and the preference of ovipositing females, we offer some hypotheses to challenge assumptions and spur future work.  We present our hypotheses in qualitative, graphical format in the spirit of the late Robert MacArthur.  Some quantitatively-sophisticated readers might find this approach simplistic, but we hope that other readers will find it useful.  For example, we ask about the shape of the relationship between dispersal ability, population growth rate on a novel host, and the rate at which a new host is utilized.  Also in the spirit of MacArthur, we hope that other researchers will be inspired to propose alternative hypotheses, which is something that we believe the graphical (as opposed to verbal) format encourages.

Posted by: oikosasa | March 5, 2013

Can we trust field-guides in ecological studies?

How consistent are field-guides and atlases? Enough to be used as sources in ecological research studies? Jay Fitzsimmons has checked and has the answer! Find out in his new Early View paper “How consistent are trait data between sources? A quantitative assessment”. Below he tells us what made him conduct the study:

Compare all the sources meme

I compared several field guides and atlases to see whether they were consistent in what they said about species’ traits.  The proximate reason why I did this research is that, given the popularity of trait-based research, I wanted to determine how consistent trait data were among authoritative sources.  The ultimate reason why I did this research is that I’m a paranoid city slicker who worries over how little I know about my study species.

Trait-based ecology is increasingly popular, with researchers evaluating whether species’ traits are related to a variety of ecological factors (e.g., extinction risk, invasiveness).  In my PhD I did such an analysis myself, evaluating the relationship between butterfly species’ traits and their rates of northward range shift in Canada over the 1900s (not yet published – it’s only been two weeks since my PhD ended so give me a break).  The advice given to me on how to obtain species’ trait data was “just use an atlas or a field guide.”  This is when my paranoia alarm started ringing.  Which atlas or field guide should I use?  Do they all say the same thing?

 While I love and respect natural history (I volunteer as Journal Manager for The Canadian Field-Naturalist – www.canadianfieldnaturalist.ca), I am not a great naturalist myself.  I cannot even identify most of Canada’s butterflies, never mind critically evaluate the accuracy of their trait data.  This is a serious problem for macroecology that isn’t given the critical attention it deserves: researchers using fancy models and elaborate analyses can miss critical issues if they don’t know the natural history of their study species.  Non-naturalist macroecologists can miss interesting results that merit follow-up, or wonky results that could indicate coding errors.

 So which source should a paranoid, butterfly-ignorant macroecologist use?  All the sources of course!  Ok, not all the sources (not by a long shot), but I used five authoritative sources authored by recognized experts.  I entered data from each source for 22 traits for 263 Canadian butterfly species.  I compared trait data for species across sources: do different sources say the same things about species?  I found some traits to be very consistent across sources, and others worryingly inconsistent.  In general it seems that subjective traits (e.g., habitat association) were less consistent than more clearly-defined traits (e.g., wingspan, over-winter stage).  This suggests results from single-source trait studies may depend in part on which source was used for trait data.

It was a pleasure to do this work, and to vindicate my paranoia (I can put the tinfoil hat away for another day).  I hope others do similar comparisons of field guides and atlases for other taxa and regions to reveal how general my findings are, and what effect such inconsistency has on trait-based research results.

How do animals decide how to forage? In the new Early View paper “How a simple adaptive foraging strategy can lead to emergent home ranges and increased food intake” Jacob Nabe-Nielsen and colleagues demonstrate that it only requires a few simple behavioural rules to produce most of the complex movement patterns observed for harbour porpoises.

What is it that makes an animal stay within more or less the same area for weeks or months before eventually moving to a new place? Surely it must have been feeding in the area, but how does it decide when it is time to leave? One of the central questions in behavioural ecology is whether animals have evolved many different kinds of behaviour, where each behavioural response is fine-tuned to a particular condition that the animals encounter in nature, or if a few simple mechanisms are sufficient to enable them to respond optimally in a wide range of conditions.

Porpoise in a pound net

The simulated harbour porpoise movements closely corresponded to those of satellite-tracked animals.

Porpoise release after tagging

The harbour porpoise (Phocoena phocoena) is an example of an animal species that displays very complex movement patterns. Porpoises often stay within relatively well-defined areas, or home ranges, where they presumably prey on various species of small fish before moving to new areas. In order to investigate whether a few different cognitive mechanisms could be sufficient to generate this complex behaviour, we developed a simulation model that included only two different kinds of behaviour. In the model the food was distributed in minute, scattered patches. Animals that had recently found plenty of food moved at random, much like cows that walk at their own pace in a field with lots of fresh green grass. Animals that had not been able to find food for some time became increasingly attracted to the patches where they had found food in the past. We let the animals’ ability to find their way back to previously visited food patches be governed by a spatial memory. It turned out that the combination of these two kinds of behaviour enabled home ranges to emerge, and when the animals’ memory about previously visited foraging sites decayed at a particular rate the model was able to produce movement patterns that closely resembled those observed for satellite-tracked porpoises in Danish waters. The right balance between the two kinds of behaviour also allowed animals to maximise their food intake. This suggests that it could be selectively advantageous for animals to base their decision on how to forage on a few, simple behavioural mechanisms.

Posted by: oikosasa | March 1, 2013

Plagiarism in Oikos?

We now check all submitted manuscripts for possible plagiarism using iThenticate.This means that all manuscripts are compared to more than 32 billion webpages, more than 34 million scholarly content items and more than 91 million news pages, books and magazines (and yes, these numbers are “plagiated” from iThenticate’s webpage…).

How similar are manuscripts generally to already published stuff? Most manuscripts show between 5 and 15% similarity.

And where is the limit for plagiarism? When a paper show more than 25-30% similarity with other published material, we do a thorough check for the similarities.

Reference lists, protocols in Methods and author adresslists may generate high similarities that are not really plagiarism. When high similarities are found in Results and Discussion, we act.

So it’s no use trying the copy and paste method for Oikos manuscripts…

Posted by: oikosasa | February 26, 2013

Top of the Pops

One of the most cited papers in Oikos, during 2011 (published 2009 and 2010) is “New perspectives for estimating body condition from mass/length data: the scaled mass index as an alternative method“, by J Peig and AJ Green.

Here, Jordi Peig gives a short summary of the paper and an explanation to it’s impact:

Jordi and Andy

Body condition (physical or nutritional status) is a widespread concept in the ecological literature. Although usually poorly defined, it encapsulates the animal’s health, quality and vigour, and hence its biological fitness. Scientists have used different approaches to estimate BC, but those based on morphometry and particularly on mass-length relationships have been adopted for routine use due to the ease of application and their ‘a priori’ conceptual simplicity. Briefly, morphometric indices attempt to quantify how heavy is an organism for a given body size, because the extra mass indicates more fat and protein reserves to overcome periods of food scarcity or high energy demand in general. However, larger animals will be inherently heavier, and vice versa, so the standardization of body size is the central challenge that underlies all morphometric methods, and is the subject of our paper. Many mathematical formulas and statistical methods have been proposed to standardise body size, yet there is still much debate among scientists as to the most suitable method.

The work published in Oikos has been popular partly because so many studies included attempts to establish the influence of body condition in population ecology. The idea of the paper was born in 2006 when distinct BC indices reported in the literature yielded opposite results when applied to my own data on small mammals. I found that those contradictory results were each scientifically plausible and arguable from an ecological viewpoint, hence the need to rethink the nature of these methods. After reading in and around the subject, including biostatistics, theoretical biology and epidemiology, I conceived the Scaled mass index. Because of the intrinsic tendency within sciences towards specialization, different disciplines have promoted and advocated their own methods (including the Body Mass Index used in medicine), and I searched for a common, unifying approach. With this complexity in mind, and the difficulty of publishing in this area for a PhD student (introducing alternative methods inevitably meets some scepticism and resistance) led me to seek collaboration with my co-author Andy Green, who had previously published in this field. From our first contact by email Andy was enthusiastic, and made substantial improvements to the manuscript. My original draft was prohibitively long for modern journals, and part of it went into a sister paper in Functional Ecology in 2010.

In the Oikos paper we attempt to explain the complexity of the BC issue from the fundamental viewpoint of allometric growth, and develop the Scaled Mass Index from that perspective. Amongst the papers that have cited our work, there are good independent examples of how our index outperforms previous methods. We can only hope that our future contributions on this topic become as successful as the Oikos’ paper.

 

Posted by: oikosasa | February 22, 2013

Mites hitch-hiking with bugs

Thumb’s out when the mite Spadiseius calyptrogynae needs to move to a new host plant. It can’t get their on it’s own, so it simply hitchhikes on bees, bats or beetles. Emanuel H. Fronhofer and co-workes have studied this in the new Early View paper “Picky hitch-hikers: vector choice leads to directed dispersal and fat-tailed kernels in a passively dispersing mite“. Here is Emanuel’s summary of the exciting study:

Tropical species diversity can be so high that while walking through a lowland rainforest it may be difficult to see two individuals of the same tree species. This phenomenon has fascinated generations of naturalists, but at the same time such high diversity represents a considerable challenge for any organism that, because of its biology, has to find another tree of a certain species to feed on, for example. How do specialized mutualists, predators or parasites manage to find their host(s)? This problem is especially relevant and critical for a lot of small, non-mobile species that occupy ephemeral habitats, such as small ponds, dung or, as in this study, flowers.

In this context, we have studied the dispersal strategies of a neotropical phoretic flower mite, that uses a number of different animal vectors – bats, beetles and bees – in order to hitch-hike from one host plant to the next. These mites (Spadiseius calyptrogynae) are specialized to their host plant, an understorey palm (Calyptrogyne ghiesbreghtiana), while the flower visitors and potential dispersal vectors are generalists.

Figure_Blog-1

The long distance disperser (Chasmodia collaris) on a male inflorescence of the palm Calyptrogyne ghiesbreghtiana (left). The detail (right) shows the phoretic mites (Spadiseius calyptrogynae) shortly after boarding their dispersal vector. Photo: E.A. Fronhofer.

Using a dual approach that combines field observations with experiments and individual-based modelling we find that our study species shows a highly developed capacity to discriminate between potential dispersal vectors based on chemical cues. These mites choose their dispersal vectors in order to optimize their dispersal kernel, i.e. the distribution of dispersal distances. The evolutionarily stable dispersal kernel is a mixed kernel resulting from short distance dispersal with bees (Trigona fulviventris) and rare long distance dispersal events with beetles (Chasmodia collaris). This results in a fat-tailed distribution of dispersal distances and additionally guarantees directed dispersal towards especially suitable habitat, as the short distance dispersers prefer young over old flowers.

Besides being an example of information use for making dispersal decisions, we show how passive dispersers may realize directed and long distance dispersal. Furthermore, our study highlights the benefits of combining field work and individual-based modelling or theoretical approaches in general.

 

Posted by: oikosasa | February 20, 2013

New populatin metrics for top-down-bottom up

Here is an interesting essay about measuring top-down-bottom-up effects, written by Leonard Polishchuk. He is also the first author of the Early View paper “How to measure top–down vs bottom–up effects: a new population metric and its calibration on Daphnia“, on which the essay is based.

Arguably, one of the saddest fallacies in ecology is the concept that «Everything is connected to everything else» (known as the first Barry Commoner law of ecology). The key assumption underlying this concept is that all interactions within the system are equally strong. Let’s examine which kind of science this assumption implies. Even in a modest system of 10 species the number of pair interactions between species amounts to 55 (including the effect of a species on itself), and to 5050 for a system of 100 species, leaving aside interactions with the abiotic environment. Such a large number is too big to study the interactions on a one-by-one basis, but probably too small to completely ignore their individuality. The latter is possible if the number of interacting entities is on the order of 1023, the Avogadro constant, but this will lead us to the realm of statistical physics rather than ecology. The Commoner law, if correct, would make our attempts to understand Nature almost hopeless, and turn ecology into hardly more than a casebook of idiosyncratic examples. Or, following Ernest Rutherford’s famous dichotomy, ecology would have been close to stamp collecting rather than hard science. (Rutherford actually said “physics” and was basically right, because physics is a role model for genuine science. But we do not think that “physics envy” can really motivate the ecologist.)

Polishchuk_Daphnia2

The picture is not all gloom, however. Rather than falling into despondency, one could quantify species interactions in order to see whether they are of the same strength or not. The actual problem, as it often happens, is therefore an operational one; it is about how to measure the things of interest. Let us focus our attention on trophic interactions, that is, on bottom-up and top-down effects. One way to assess them dates back to Justus von Liebig and consists of addition of biological nutrients to see which of them elicit a strong response from the pot plant, in terms of its growth, or from the planktonic algae in a water sample, in terms of primary production. These simple experiments, which in the era of ANOVA are called factorial-design experiments, immediately disprove the Commoner law. Liebig’s law of the minimum states that there is a single factor that produces the biggest response in a given species or a set of species with similar requirements, and thus affects them most strongly. Hence, not only the interactions are different in their strength but, under any given circumstances, there is only one that is most important. Clearly, the Liebig law makes a contrast with the Commoner law.

While the factorial-design experiment is a powerful and efficient tool to reduce the number of significant interactions and detect the strongest one, it has its shortcomings. The imposed shifts in food and/or predator abundance, while not completely arbitrary, may not reflect the current situation in the system. Often, for example, one of the treatments completely excludes predators, despite their presence in the environment. In his 2001 review, Mark Hunter sarcastically notes that if we were to completely exclude food, this would have inevitably revealed an “obvious and dramatic bottom-up effect”. Of course, nobody would act that way in regard to food but this reductio-ad-absurdum example shows a general problem: the manipulative (addition / removal) approach does take into account the actual (rather than imposed) dynamics observed in the system. The dynamics is a fundamental feature of natural systems (Pimm 1991), implying that one driving factor, e.g. food, may be quickly replaced by another, e.g. predation, in the course of time and space. The factorial-design experiment is not tuned to track these changes while a truly dynamic approach might be able to make it.

Polishchuk_Daphnia1

These considerations naturally bring us to the field of population dynamics. In the paper, we have focused on zooplankton, in particular Daphnia, a well-known model organism in ecology (Lampert 2011, see Figure), though we do believe that our approach is a general one and may not be limited to zooplankton. The population characteristic we are dealing with is birth rate. In part, this is because planktonologists can take advantage of the Edmondson-Paloheimo model for birth rate. Interestingly, birth rate as a response variable is somewhat similar to growth or production rates often taken as response variable in manipulation experiments, but our use of it is different. The Edmondson-Paloheimo model, being slightly modified (Polishchuk 1995), relates birth rate to fecundity and proportion of adults in the population. Fecundity is closely associated with food conditions and proportion of adults with size-selective predation, the latter being common in zooplankton. Thus, birth rate depends on both bottom-up and top-down effects, which is another reason why it is used here. To quantify the role of fecundity and hence bottom-up effects and that of proportion of adults and hence top-down effects in birth rate dynamics, we employ a mathematical approach called contribution analysis (Caswell 1989, Polishchuk 1995, 1999, Polishchuk and Vijverberg 2005, Hairston et al. 2005, Ellner et al. 2011). This provides us with the ratio of contributions of changes in the proportion of adults and fecundity to birth rate change taken as a measure of the relative strength of top-down vs. bottom-up effects.

We view the ratio of contributions as a kind of measuring instrument, something like a thermometer. The comparison of the ecological instrument to the physical one is, of course, a metaphor – primarily because ecological variables do not obey simple and general quantitative relations such as those used to construct physical instruments; an example is the relation describing the thermal expansion of the physical body, which underlies the functioning of the thermometer. But it is a useful metaphor, for it leads to the next task: calibrating the ratio of contributions as a tool to measure the strength of top-down vs. bottom-up effects. This calibration is based on microcosm and computer experiments, and constitutes a major part of the paper. The main experimental result is that the ratio of contributions allows one to distinguish a strong top-down effect from a strong bottom-up effect.

In the end, we would like to emphasize some points not mentioned in the paper. First, while our approach focuses on population dynamics and, as such, is intended to avoid inappropriate averaging (used, though implicitly, in manipulative experiments), some time-averaging seems necessary. The ratio of contributions is found to be sufficiently robust only when applied to a set of successive sampling intervals rather than an individual interval. (This set covers the second part of the experiments where top-down and bottom-up effects appeared in full strength; see Online Appendix 3 of the paper.) In our experiments, this set was identified by means of ANOVA, the procedure that will not apply to field populations due to lack of “replicate populations”. Hence, we need to understand how to recognize, in natural populations, a set of intervals over which the ratio of contributions remains roughly constant. This will open the way to the use of this approach for natural Daphnia (and other zooplankton) populations.

Second, the Edmondson-Paloheimo model, when appropriately modified, has the potential to estimate birth rate in animals other than Daphnia, such as mammals. If applied to a wider range of organisms, this approach may be a useful supplement to conventional Liebig-style factorial-design experiments.

Posted by: oikosasa | February 18, 2013

Hiding in the litter from the beasty ants

In the new Early View paper “Non-trophic effects of litter reduce ant predation and determine caterpillar survival and distribution”, Richard Karban and co-workers have studied the importance of litter for caterpillars hiding from ants in a hetergenous landscape. Here is Richard’s lay summery of the paper:

cat_pred_by_ant

It is well established that trophic interactions can influence the spatial distribution and abundance of organisms.  What is less well understood is how these interactions vary across space.  In this study, we conducted several observational surveys and manipulative field experiments to examine the role of predators as drivers of caterpillar abundance and distribution across a heterogeneous landscape composed of three predominant habitat types, marsh, coastal grassland, and dune.  Unexpectedly, ants were found to readily prey upon early instar caterpillars.  The intensity of predation varied across habitat types such that caterpillars in marsh habitat had a higher probability of survival than those in drier, upland habitat. Marsh habitat in our study system is characterized by think leaf litter, while less leaf litter is associated with drier habitat.  We hypothesized that habitat substrate complexity may moderate caterpillar predation by ants. This hypothesis was supported by two findings: ant recruitment to baits decreased with litter depth and litter protected caterpillars when ants were present but not when ants were experimentally excluded. Our results show that litter confers a survival advantage to caterpillars by providing habitat, a non-trophic mechanism. In contrast to trophic effects, the importance of spatiotemporal variation of non-trophic effects in mediating species interactions has been underappreciated by many ecologists.

bodegalupine3

Posted by: oikosasa | February 15, 2013

Cascading effects of fish migration

How the anadromous fish alewife affect the whole food-web in it’s ecosystem is studied by Jerome J. Weis and David M. Post in their new Early View paper “Intraspecific variation in a predator drives cascading variation in primary producer community composition”. Below is Jerome’s presentation of the paper:

We know that predation can have a strong influence on the richness, biomass, and composition of prey communities.  We also know that these effects can cascade down a food web to lower trophic levels, including primary producers.  Often, when we design studies to ask how these top-down effects of predators influence lower trophic levels, we focus either on differing densities of a single predator species, or on differences among multiple species.  However, in some cases, variation within a predator species can be an important component of these top-down effects.

YOY AlewifeMesocosms 2

In coastal New England lakes, a species of zooplanktivorous fish, alewife, has a strong influence on zooplankton biomass, diversity, and composition.  Among lakes that support alewife, populations show one of two distinct life histories, an anadromous life history, where ocean residing adults spawn in coastal lakes and young-of-the-year alewife have a substantial impact on zooplankton communities from approximately June until November, and a landlocked life history, where alewife populations are isolated from the ocean and are present through the year.  Differences in the behavior, morphology, and seasonal timing between anadromous and landlocked alewife drive distinct differences in their zooplankton prey communities across the landscape.

In this study we tested the hypothesis that alewife presence and life history will have cascading top-down impacts on phytoplankton density and community composition. We analyzed phytoplankton communities from a mesocosm experiment that manipulated the presence and life history form of alewife and observed lower zooplankton biomass density, average size, and species richness in the anadromous treatment than the landlocked and no-fish treatments.

Mesocosms 1Phytoplankton

We observed a statistically significant shift in phytoplankton community composition among treatments that was consistent with lower zooplankton densities in the anadromous alewife treatment.  The biovolume density of two common single-celled phytoplankton genera, Chlamydomonas and Gymnodinium, was significantly higher in the anadromous treatment than the landlocked and no-fish treatments.  Both of these genera are considered vulnerable to herbivory by zooplankton.  However, these differences in community composition did not result in statistically significant differences in overall phytoplankton biovolume density nor richness among treatments, suggesting that the cascading effect of alewife was relatively small in this study.

Posted by: oikosasa | February 13, 2013

Modelling species interactions

A model to quantify species interactions is proposed in the new Early View paper “Costs, benefits, and loss of vertically transmitted symbionts affect host population dynamics” by Kelsey M. Yule, Tom E.X. Miller and Jennifer A. Rudgers. Below is Kelsey’s background story to the study:

How do we quantify the relationship between two species? When individuals of the two species interact at many points throughout their lifetime, the answer is not as simple as we sometimes assume.  The effect of the interaction at different points in the species’ life history may not affect fitness in the same way. Take, for example, an insect pollinator that greatly increases the reproductive success of its plant partner. We might consider this a classic example of a mutualism, as the presence of the pollinator allows the plant to produce more seeds and the presence of the plant allows the pollinator to produce more eggs.  However, that same pollinator may lay those eggs directly onto the plant, which later suffers significant herbivory damage from the larvae. So, which plant produces more offspring: the one that interacts with that particular pollinator or the one that doesn’t? Without following the plants’ growth, reproduction and survival throughout their lifetimes, it’s difficult to say. Even humans harbor many symbionts of which the varying positive and negative effects are only recently beginning to be understood and debated.  This tension between cooperation and conflict is not uncommon in many of the systems we traditionally call mutualisms or parasitisms. In our paper, we argue that a snapshot at one point in the life history is not sufficient for understanding the population-level effects or evolutionary significance of any interspecific interaction.

Fungal endophytes that produce herbivore-deterring alkaloids are generally considered clear mutualistic partners of their grass hosts in agronomic systems.  Yet, confusion and debate over their role in native systems has arisen due to some documented costs, notably reduction in host survival.  Theory suggests that when these endophytes are vertically transmitted, harming their hosts should doom them to extinction, as the endophytes can only increase their own reproduction by increasing their hosts’ reproduction.  Yet, vertically transmitted endophytes are often present at high frequencies in native systems, despite transmission rates that can be well under 100%. Therefore, we wondered whether an approach that could integrate the effect of endophytes across the entire life history of the host could shed some light on this problem.

To do this, we developed a new modeling approach in which we could structure a native grass host’s population both continuously by size and discretely by the presence or absence of endophyte symbionts.  With our integral projection model (IPM) megamatrix, which we parameterized with experimental field data, we were able to show that endophyte symbiosis provided a net benefit to its host by increasing population growth. Indeed, we saw costs to host survival that were outweighed by boosts to growth and reproduction.

Yule_field

More surprisingly, we saw some patterns that we did not expect given previous theory. Early life history stages, like germination and seedling establishment, were critically important for determining the locations of transmission rate thresholds below which these beneficial symbionts go extinct.  For example, if seedlings are able to survive to adulthood 2% of the time, endophytes will not be able to persist if endophyte symbiotic adults produce endophyte symbiotic seeds, as opposed to endophtye-free seeds, less than 50% of the time. However, if seedlings establish 3% of the time, endophyte persistence requires a transmission rate of more than about 75%.  This complex interaction between early life history and vertical transmission arises because higher seedling establishment leads to a greater proportion of the population being made up with seedlings, which will be dominated by endophyte-free plants at low transmission rates. This result also highlights the need for a greater understanding of the mechanisms behind variation in endophyte transmission.

We believe that the modeling approach we developed will be broadly applicable to understanding how species interactions, especially those involving vertically transmitted symbionts, influence populations.  For myself, this research, which I began as an undergraduate, is influencing my thoughts on species interactions as I start my graduate career at the University of Arizona.  In the future, I hope to continue integrating models with empirical data. I believe that doing so is a  particularly powerful way to improve our understanding of relationships in nature that so often slide on the continuum between mutualism and parasitism.

Posted by: oikosasa | February 12, 2013

To join the party or not…?

Did you believe that hermite crabs were always seeking lonelyness? Oh, now, partytime might attract the hermits as well! Read more in the new Early View paper “Eavesdropping foragers use level of collective commotion as public information to target high quality patches” by Mark Laidre. Here is Mark’s own short verison of the paper:

Aggregation

Many people like a party that’s pumping and jostling at just the right amount. Too little commotion and it’s just not attractive. The same seems to hold for terrestrial hermit crabs, which are highly social animals that frequently join aggregations of conspecifics to acquire valuable resources like food or shells. We conducted an experiment to determine what level of commotion from an aggregation would be most attractive to crabs that were eavesdropping outside the aggregation and deciding whether or not to join. The experiment involved creating the equivalent of a puppet show for hermit crabs, with several plugged shells being jiggled at the end of fishing line to simulate different levels of jostling by an aggregation. The jostling of these sham aggregations represented the sort of wild commotion and fighting that goes on when hermit crabs are competing with one another naturally. Indeed, when hermit crabs are contesting highly-quality food resources or when they are in the process of evicting another individual from its shell, their aggregations exhibit especially high levels of natural jostling. In our experiment, we found that eavesdropping hermit crabs were most attracted to the sham aggregations that were jostled at higher rather than lower levels, suggesting that the crabs were using the raucous public commotion as a reliable cue to the presence of valuable resources that were worth competing over. Our experiments provide the first evidence that animals use the behavioral by-products of collectives as a way to increase their own personal foraging efficiency.

Posted by: oikosasa | February 7, 2013

Environmental pollution goes theoretical ecology

Pollution issues meet complex food-web modelling and theoretical ecology in the Early View paper “The more polluted the environment, the more important biodiversity is for food web stability”, by Leslie Garay-Narvaez, Matias Arim, José D. Flores and Rodrigo Ramos-Jiliberto.

RodrigoHere’s the background story to the study, written by Rodrigo Ramos-Jiliberto:

I was the advisor (together with M. Arim) of Leslie Garay-Narváez, who recently obtained her PhD degree at the University of Chile. This article is the first chapter of her PhD dissertation. When we began to think about possible alternatives for her thesis work, Leslie decided to combine a theoretical approach for studying the dynamics of food webs, with questions related to the effect of human disturbances, particularly pollution. Our desire was to connect very abstract work, based on mathematical modeling and complex networks, with practical needs of social interest. Thus, we decided to go in the direction of revising or perhaps reformulating some key issues of ecological theory, which had been building (explicitly or implicitly) with a pristine world in mind, but considering a polluted world. We envisioned developing some sort of “applied theoretical ecology of polluted complex systems”. In this article we show how the complexity-stability relationship is affected by pollution. Two other papers are in the pipeline.

LeslieAs a result of Leslie’s work, our institution, the National Center for Environment (CENMA), appreciated the importance of theoretical ecology, and many members of our academic community agreed in that applied questions are affordable from a sound, theoretical perspective. After that, three months ago, Leslie became a happy mother of a baby and obtained a 3-year postdoc fellowship at the University of Chile. Indeed in developing countries like ours, science is a fine form of living, and theoretical ecology even better !

Posted by: oikosasa | February 4, 2013

Pasture – red kangaroo – dingo interactions

Read David Choquenot’s and David M. Forsyth’s new Early View paper “Exploitation ecosystems and trophic cascades in non-equilibrium systems: pasture – red kangaroo – dingo interactions in arid Australia” to learn more!

Here’s Dave’s background story to the study:

Fig1_Dave Forsyth at Kinchega National Park

This article had a long gestation. The seeds were sown in 2000, when two influential articles were published in The American Naturalist on the inter-related topics of trophic cascades (Schmitz et al. 2000 Am. Nat. 155, 141) and the Exploitation Ecosystems Hypothesis (EEH; Oksanen and Oksanen 2000 Am. Nat. 155, 703). After reading these articles we discussed the idea of adding the dingo (the top-order predator in mainland Australia) to Graeme Caughley’s two-link rainfall – pasture – red kangaroo model (Caughley & Gunn 1993 Oikos 67, 47), to test whether an empirically derived model could recreate EEH predictions and generate trophic cascades. In Caughley’s system, which was based on data collected in Kinchega National Park (western NSW; Image 1), prevailing productivity is tightly linked to rainfall through its effect on pasture growth and dieback. However, rainfall in this ecosystem is highly stochastic between seasons and years. Over the subsequent ten years we worked sporadically to test whether this system could produce dynamics consistent with the EEH and trophic cascades.

The model did reproduce the three zones predicted by the EEH, but a surprising outcome was the discovery of an additional zone at productivities above which the maximum densities of the dingo was achieved. The additional zone, in which kangaroo densities increased and pasture biomass declined due to the re-engagement of the kangaroo-pasture feedback loop, occurred because dingo densities are believed to be socially regulated (via dominant female infanticide): if dingo densities are instead constrained wholly by the availability of kangaroos then that zone disappears, kangaroos become less abundant and pasture biomass more abundant.

Kangaroo

Increasing stochasticity in seasonal rainfall had sometimes counter-intuitive effects on model outcomes. High levels of stochasticty led to more frequent extinction of dingoes from the system, resulting in the re-engagement of the kangaroo-pasture feedback loops. Hence, increasing stochasticity led to increased attenuation in this system.

Roger Pech (Landcare Research, New Zealand) thoughtfully suggested that we use the normalized difference (rather than the absolute difference) of the log-response ratios to evaluate attenuation in this system. Roger’s suggestion will be appropriate to other studies assessing attenuation in trophic cascades.

Several journal reviewers also suggested that we assess the effects of potential diet switching by dingoes from kangaroos to reptiles, as has been observed in some areas of arid Australia. We found that prey switching by dingoes to reptiles weakened trophic cascades.

The role of the dingo as a trophic regulator has been the subject of much recent debate, with some scientists calling for culling to cease and reintroductions to be made in areas where it has been extirpated. The rationale for returning dingoes to previous densities in parts of their range focuses primarily on their potential to reduce the abundance of introduced red foxes and feral cats. However, our study suggests that additional benefits may occur through regulation of large kangaroo abundance, and the associated release of vegetation from grazing pressure. Depending on the degree to which the diversity of each trophic level is maintained by consumption-mediated co-existence, these changes may have flow on implications for amongst herbivores and vegetation biodiversity in these ecosystems.

Our study has generated testable predictions about interactions between top-order carnivores, their prey, and vegetation across productivity gradients. These predictions are obviously highly testable in Australia where dingo management is widespread. However, the generality of the predictions could also be tested in entirely different predator-driven ecosystems.

Posted by: oikosasa | February 1, 2013

The elephant in the room

Nunez1

What makes invasive species invasive? Find some of the answers in Rafael Zennis and Martin Nunez paper “The elephant in the room: the role of failed invasions in understanding invasion biology”  now on Early View.

Here, Martin Nunez gives a short background:

Invasive species grow bigger, reproduce earlier and more often, and spread faster than other species, right? Well, sometimes yes, but not always. Many known invasive species have populations introduced in areas where they do not naturalize or invade after arrival. As it turns out, only invasive populations exist in nature. In this study, we reviewed the literature on invasions and found that failures are the most numerous and often ignored part of the biological invasion process. We learned that very few people are interested in introduced populations that do not thrive in the new environment. There are many anecdotal reports on failures, but really few studies on why these populations fail. We also found that different mechanisms may be causing failures vs. successes, but more research is needed to shed light on this. Based on these findings, we show and discuss research areas where it may be key to incorporate more info on failures to avoid an important bias.

Nunez2

Maritine pines (Pinus pinaster) are invasive in many parts of the southern hemisphere, but in Rio Negro, Brazil, experimental plantations died out 18 years after planting leaving no trace of its past presence in the area, now colonized by exotic eucalyptus and native araucaria pines.

We focused our study on reviewing cases of species that are invasive somewhere, but that fail to invade in other areas, habitats or time periods. We did this because these situations can provide useful information on the particular mechanism of invasion (e.g., what is different between areas where the species invade and where the species does not invade?). We avoided studying species that never invaded, which might provide little information about other invasive species.  Finally, we put caution in the use of the term “invasive” to indicate an intrinsic species-level trait because even some of the most aggressive invaders are reportedly unable to colonize some area. This does not change, however, the fact that when introduced organisms do invade, they may cause considerable changes in community and ecosystem dynamics.

Posted by: oikosasa | January 31, 2013

Waste to hurry

Do animals spend too much energy on just being? Read Bas Kooijman’s new Early View paper “Waste to hurry: dynamic energy budgets explain the need of wasting to fully exploit blooming resources” to find out! Here, Bas gives you the background to the study:

Many years ago, I did a very simple experiment, which results puzzled me for a long time. Take 6 beakers, fill them with water, add 5 daphnids each, and feed them with algae daily. The beakers got 6, 12, 30, 60, 120 and 240 million cells per day, respectively, for 24 days. Except for the highest feeding level, all daphnid populations settled to constant numbers per beaker in this period and the numbers are directly proportional to the feeding levels. To convince myself that it really is the feeding level that controls the numbers, I gave all beakers 30 million cells per day after 24 days and indeed all numbers converged to that level. From this we learn that a 2.8 mm daphnid needs 6 algal cells per second at 20°C and they cannot grow or reproduce with this intake and all need it for maintenance only. With plenty of food they can become over 4 mm and produce some 20 young per day. It turns out that they have a specific maintenance cost that is two orders of magnitude bigger than is typical for animals. My problem was to understand why.

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Some two years ago, I started the add_my_pet collection of data on animal energetics, and fitted the standard Dynamic Energy Budget model to each species. These data and the model cover all aspects of energy and mass balances during the full life cycle of individuals, including the embryo stage. The collection has representative of most larger animal phyla, ranging from 2.4e-8 g hairy-backs to  1.6e8 g blue whales. I developed this model to separate overhead costs of assimilation, growth and reproduction from maintenance. Because of the presence of reserve as quantifier for metabolic memory, this task is less easy than is generally recognized. In fact, it requires a whole new view on the relationships between respiration, metabolic rate and maintenance. With help of many enthousiastic people, the add_my_pet collection grew till 165 species at present.

By comparing extremes in specific maintenance costs I found the explanation for the very high maintenance costs of daphnids and for why it took me that long to see it. It is namely completely counter-intuitive: animals need to waste resources to boost their growth and reproduction. Within the context of the Dynamic Energy Budget theory, it is completely logical and easy to understand, the only problem is to recognise it. It has been sitting right before me for 30 years and I didn’t see it. Intuition is not always a good advisor.

Posted by: oikosasa | January 30, 2013

Editor’s choice Febuary

DriesEditor in Chief Prof. Dries Bonte introduces the two Editor’s choice papers in the February Issue: (Note that Editor’s choice papers are Open Access)

For the February issue of Oikos, we decided to highlight Sorte’s forum paper on the importance of flow direction and limitation to redistribution for the persistence of species in the light of climate change, and the contribution of Stier et al., demonstrating the use of model-based approaches to study functional predator-prey responses within a community context. These contributions were chosen according to our motto of synthesising ecology.

Sorte (2013) emphases the role of directional flows of wind or water currents as an important factor limiting species’ distributions, especially when equilibrium conditions become disrupted by human interference. There is a consensus that adaptation or tolerance may not be sufficient for many species to persist under conditions of climate change, and that dispersal is essential to keep track with the shifting climate window. In cases of actively moving organisms, such movements can be expected to be informed and at least partly in the direction of the shifting window. Passively dispersing organisms, being either wind dispersed plants, rafting arthropods or planktonic stages of many marine vertebrates and invertebrates are expected to face constrained movements due to their dependency on flow directions. Such asymmetric air and water flows need to be considered when assessing the vulnerability of populations and species to climate change. Cascade Sorte provides a synthesis on how the interplay between directional flows and life histories may limit species’ distributions and their persistence under climate change. The review comes up with clear predictions that may help ecologists to detect the set of passively dispersing species at risk, but equally provides clear considerations for future research.

Adrian Stier and colleagues provide a novel analytical tool for analysing predator foraging behaviour and offer insight into the processes driving the dynamics of coral reef fish. While group benefits are well documented from a single-species point of view, we lack insights on how such group benefits change according to the community context. In their study, the authors use a shoaling coral reef fish as a model species to test how prey group benefits change according to group size, the presence of competing predators and alternative prey. They use an original approach by quantifying mortality rates as perceived from the predator’s perspective, so by quantifying changes in the predator’s functional response. Their sets of experiments confirm group size advantages by reduced predation risks, but these benefits decrease in the presence of alternative prey species. While there is already quite some literature demonstrating such a community context of predator-prey interactions, the applied model-based approach allowed for testing several alternative hypotheses of mechanisms leading to variation in functional responses.

Posted by: oikosasa | January 29, 2013

Surf and Turf 2: Snorkeling with wildebeest

We have now come to the second Surf and turf paper in Oikos february issue. I let Deron Burkepile introduce you to his study “Comparing aquatic and terrestrial grazing ecosystems: is the grass really greener?”

Burkepile_snorkeling_bison

At a big ecology meeting, you can often tell what people study by how they dress – the marine ecologists (Hawaiian shirts, flip flops), the terrestrial ecologists (Chacos or Tevas, Carharts). As an ecologist, the communities and ecosystems you study often define you – forest ecologist, intertidal ecologist, benthic ecologist. Like our current series of reviews and commentaries in Oikos trying to bridge the gaps among terrestrial, marine, and freshwater ecology, we often compare and contrast the different patterns and process in our different ecosystems via reviews and our meta-analyses. We search for common patterns and themes and build testable hypotheses, even theories. Yet, many of us don’t have research experience outside of a couple of closely related ecosystems. For many of us, branching out to a new ecosystem means including tropical forests into our research program on temperate forests. But, I would argue that we could all be better ecologists, if we truly had diverse research experiences on our ecological resumes, and the field would be better for it.

Having had a diversity of research experience, I feel like I am one of the lucky ones. I’ve spent more than a decade studying coral reefs, even lived underwater for a total of twenty days in the Aquarius, an undersea research station off of Key Largo, Florida to study herbivorous fishes (parrotfishes and surgeonfishes) and their importance to reef ecosystems. But, I also got to spend two years living in a tent in Kruger National Park in South Africa (periodically having to put my computer in the refrigerator to keep it from overheating in the 40°C+ heat). Instead of parrotfish and surgeonfish, I was studying elephants, wildebeest, and impala and how these different herbivores structured savanna ecosystems. While the beasts were different, the ecological processes were not. I like to think I’m the only ecologist who has gotten to live and work both in the bush in Africa and also underwater (if you know otherwise, please don’t burst my bubble).

How did I get from coral reefs to African savannas and back? It all started with reading broadly. While studying for my qualifying exams as a graduate student in coral reef ecology, I came across the classic papers on the Serengeti by Sam McNaughton and the book Serengeti: Dynamics of an Ecosystem by Sinclair and Norton-Griffiths. I was enthralled reading about wildebeest migrations, the dynamics of multiple large predators, and the overwhelming impact of herbivores on the landscape. As I was devouring the coral reef ecology literature, I couldn’t help thinking how similar coral reefs and African savannas actually were. Instead of herds of wildebeest there were schools of parrotfish. Instead of roving impala, there were marauding urchins. Regardless of whether the system was wet or dry, big, diverse groups of herbivores ran the show. I was fixated on how cool it would be to test similar hypotheses about how diverse groups of herbivores impact community structure and ecosystem function in two structurally different, but functionally similar ecosystems.

After convincing my future post-doc advisor, terrestrial ecologist Melinda Smith, that it would be a good idea to let a marine ecologist who had never even been to the African continent to go live in a tent in South Africa and study ungulates, it was mostly downhill from there. Of course I had to learn a brand new ecosystem (dry vs. wet), a new set of taxonomy (grasses vs. seaweeds), a new set of dangers (lions vs. sharks), get used to new field methods (see picture as exhibit A), and learn a new set of literature (fun, and probably the most challenging part). There are clearly concepts that don’t cross these ecosystem boundaries. The effects of drought and water stress are extremely important at our sites in the savanna – on a coral reef, not so much of a problem. But after six years of working in both African and North American savannas while also continuing my work in reef systems (yes I have a lot of frequent flyer miles), I’ve been able to build a much more nuanced and thorough understanding of how herbivores shape ecosystems and of the drivers that determine herbivory.

So I encourage ecologists at all levels (especially ones early in their careers) not just to read broadly but to research broadly. Start a collaboration with someone in a very different ecosystem than your primary research. If you work in forests, go talk to someone about kelps. It will push your intellectual boundaries and stimulate more ideas to tackle in your primary research area. Every aspect of your career will likely benefit, from your lectures to your journal reviews to your grants.

I remember in my first few months in South Africa walking through an area of savanna where an African buffalo herd had been the day before. The soils were churned, the small shrubs mangled, the grasses gnawed. But what I remember most was the amount of dung. Buffalo flops everywhere. I distinctly remember thinking how important these big herds must be for moving nutrients around the landscape and impacting primary production. That same scene came to mind a couple of years ago while diving on a coral reef watching big schools of fish congregate around corals. That same thought then popped into my head – how important these fish must be for moving nutrients around within this landscape. So, now one of my lab’s main areas of research is the impact of fish-derived nutrients on coral reef community structure and ecosystem function. My blended heritage of marine and terrestrial ecology will, hopefully, continue to help me unravel the connections and common themes between wet and dry ecosystems. Even now, when I am following a parrotfish around the reef documenting its feeding behavior, I can’t help but think “What would a rhino be doing?”

Posted by: chrislortie | January 25, 2013

The future of publishing for ecology & evolutionary biology

An NCEAS working group examining the future of publishing in ecology and evolutionary biology (http://www.nceas.ucsb.edu/projects/12651) would like to solicit your input. Our goal is to establish a baseline of your opinions on the current state of scholarly communication for our field so as to highlight potential gaps and improvements. The survey includes the opportunity to provide feedback on the value of Twitter, blogging, social networking, and other online outlets as it relates to publications.

The survey will take approximately 7-10 minutes.

http://bit.ly/eebpublishing

Posted by: oikosasa | January 25, 2013

Surf and Turf 1

Yesterday, Randi Rotjan and Josh Idjadi introduced us to the Surf and Turf concept. Today, Howard V. Cornell gives a short background to his and Susan P. Harrison’s Surf and Turf paper “Regional effects as important determinants of local diversity in both marine and terrestrial systems”:

When Josh Idjadi and Randi Rotjan organized the Surf and Turf Symposium at the 2009 meeting of the Ecological Society of America, it was immediately clear that they had identified an important problem. Marine and terrestrial ecologists do not always follow each others’ work, and as a result, there is not enough cross-fertilization of ideas derived from the study of these two realms. When Josh and Randi invited Susan Harrison and me to participate in the symposium, it forced us to think hard about how large-scale biogeographic  and evolutionary processes affect the species diversity in marine vs. terrestrial communities. Because of differences in dispersal between atmospheric and aquatic media, the ease of identifying marine vs. terrestrial species pools, and the historical development of marine and terrestrial community ecology, marine ecologists have placed more emphasis on the importance of large-scale effects on community structure than terrestrial ecologists. Nevertheless, it became clear to us upon reflection that large-scale processes are important in both realms but such processes are studied in different ways. We were grateful for the opportunity afforded by the symposium to look at this issue more deeply and as a result, have come to a clearer understanding of the general importance of examining different spatial scales when trying to understand ecological patterns. Below is a short summary of our paper.

s&t1bs&t1Terry Hughes

One apparent difference between marine and terrestrial ecology is that the influence of regional processes on local populations and communities is better established in the marine literature. We examine three potential explanations: 1) influential early studies emphasized local interactions in terrestrial communities and regional dispersal in marine communities. 2) regional-scale processes are actually more important in marine than in terrestrial communities. 3) recruitment from a regional species pool is easier to study in marine than terrestrial communities. We conclude that these are interrelated, but that the second and especially the third explanations are more important than the first. We also conclude that in both marine and terrestrial systems, there are ways to improve our understanding of regional influences on local community diversity. In particular, we advocate examining local vs. regional diversity relationships at localities within environmentally similar regions that differ in their diversity either because of their sizes or their varying degrees of isolation from a species source.

s&t1

Figure: Scenarios for propagule supply in marine and terrestrial systems. (a) In marine systems, habitats are immersed in a homogeneous surrounding medium containing propagules of many species with few dispersal barriers, many of which pass through the fitness filter and are able to recruit to the habitat. (b) In terrestrial systems, topography and environmental heterogeneity erect larger dispersal and fitness barriers to arriving propagules and ‘seed banks’, confound arriving propagules with those already present in the habitat.

Posted by: oikosasa | January 24, 2013

Surf and Turf in Oikos Feb 2013

Check out the Surf & Turf papers in the February Issue! For an introduction to the concept, I leave the word to our Surf and Turf editors Josh Idjadi and Randi Rotjan. Their introductory paper in the February Issue is found here. Presentations of the actual papers are to come on this blog the following days!

CP.RotjanD

It is an interesting time to be a scientist. We have access to more research tools and information than ever before, including literature access. With that access comes great opportunity: data mining, meta-analysis, global comparisons and insights, and cross-disciplinary and cross-system inspiration. However, this tremendous level of access also opens up the conversation about responsibility: are we responsible for reading that huge literature? The answer is, by necessity, “of course not”.  But like everything in science and in life, this is not a black and white issue. Among the many shades of gray are whether or not you have the responsibility to read everything in your field (traditionally, “yes”), but defining ‘your field’ is ever-harder. Is your field defined by the organism you work on? By the ecosystem you work in? By the methodology you use? By the types of questions you try to answer? The answer is “all of the above, depending on the situation”. Practically, however, it would be impossible to read and absorb information on all of these levels, in real time, all of the time. Not only do we have more access to information, but there is more information! More scientists, more journals, more articles, and more communication mediums (including blogs, like this one). In reality, we all simply do the best we can, all-the-while recognizing the importance of deep and wide reading to good scholarship.

Recently, in a rare moment of quiet and clarity, we realized that our worlds had become very “marine”. Though we both graduated from more traditional and cross-system biology departments and considered ourselves ecologists, in reality, we were working in marine systems, attending marine conferences, and immersed in marine literature. We missed being part of the general biological scene, and we wanted to engage in the scholarly exercise of thinking about some of our research questions from the perspective of a different field.  “Surf and Turf” emerged as a concept – not to wholly solve the problem – but as one part of the solution to service cross-systems cravings in a way that would be relatively short, with a reasonable time investment, and would engage collaborators in a meaningful discourse without diluting point-of-view by trying to reach consensus in a single document. We thought an effective format for this concept might be a main piece on a topic by a system-specific author, with short responses written by other system-specific authors. In this multi-paper-per-topic dialogue, the goal was to achieve breadth without compromising depth in a format that didn’t swamp an individual author by forcing an all-systems literature review, and in a way that didn’t swamp the already overwhelmed reader who is forever trying to keep up with their own field (however it may be defined).

Our authors found both agreement and debate in the 2 topics highlighted by Oikos (regional determinants of diversity, and grazing ecology), and we hope this virtual issue showcases these 2 topics as proof-of-concept examples for future Surf and Turf endeavors. In the process of putting this virtual issue together, we engaged with a number of other authors who are pursuing other venues for several additional topics. Oikos was a wonderful place to launch this concept – and we are now hoping that other journals and authors will embrace it. Still immersed in our system-specific questions, we both value and recognize the importance of cross-systems ecology as one of the key drivers of synthesis. This will not be our last attempt at cross-systems thinking, and we encourage you to do the same.  And at the least, and in this cluttered world of fast-flowing literature: thank you for reading.

-Randi Rotjan & Josh Idjadi

Posted by: oikosasa | January 23, 2013

Is competition less common i harsh environments?

What do animals actually do in poor environments? Compete more or facilitate for each other? Isabel Barrio and her co-workers studied this in herbivores in the harsh alpine tundra, resulting in teh new Early View paper: Extending the stress-gradient hypothesis – is competition among animals less common in harsh environments? Here’s Isabel’s own background story to the study:

marmot1

Many summers in the alpine tundra have inspired our study.  Alpine environments are strongly seasonal and are characterized by harsh environmental conditions, but they can host a surprisingly large numbers of herbivores.  Annual net primary productivity in alpine ecosystems is generally low, so negative interactions (i.e. competition for resources) are usually expected to dominate among herbivores.  However, the stress gradient hypothesis (SGH) developed by plant ecologists leads to the opposite prediction; namely, that in stressful environments, positive interactions (i.e. facilitation) would be the most common type of interaction.  But, are plants and animals so different in this respect?  Although facilitation among animals has been described in some highly productive ecosystems, such as tropical savannas, no theoretical framework exists that relates the balance between positive and negative interactions along environmental gradients.  In our paper “Extending the stress-gradient hypothesis – is competition among animals less common in harsh environments?” we evaluate how the stress-gradient hypothesis might apply to terrestrial herbivores.  

squirrel

We considered  alpine herbivores for developing our framework, because most examples of the SGH come from alpine plant communities.  According to the SGH, and given that stress for herbivorous animals in these environments can be equated to inverse productivity gradients, we wondered if positive interactions would prevail in alpine environments because of their low productivity.  We reviewed the available examples on interactions among alpine herbivores and found very few experimental studies on this topic.  Interestingly, they were biased towards reporting on significant competitive interactions.  Despite this bias, we found no evidence of competition being the dominant interaction type in low productivity alpine environments, which directly challenges the dominant view among animal ecologists.  Although we did not find strong support for the SGH either, we argue that specifically designed experiments can help investigate the applicability of this framework to terrestrial vertebrates.  Extending the SGH through clear predictions can provide a solid starting point for understanding the role of positive and negative interactions in structuring terrestrial animal communities.

sheep marmot

Posted by: oikosasa | January 21, 2013

Editor’s choice January

From January 2013 our Editor’s in Chief select two papers in each issue as Editor’s Choice. Those papers are Open Access, and the complete January Issue is OA! Here, Dries Bonte explains why they chose the following for the January issue. Read more here about News in Oikos 2013.

DriesThe following papers Pattern Detection in Null Model Analysis’ (Werner Ulrich and Nicholas J. Gotelli) and How does the invasive/native nature of species influence tadpoles’ plastic responses to predators’ (Eudald Pujol-Buxó, Olatz San Sebastián, Núria Garriga and Gustavo A. Llorente)were selected as the first editor’s choice papers for 2013.

We selected these papers for two different reasons, thereby demonstrating the different pathways by which ecologists can create synthesis in their own field of expertise. The work by Pujol-Buxó considered the importance of phenotypic plasticity in both functional morphology and behaviour in a set of invasive and native prey and predators. The work brings synthesis by merging concepts of behavioural ecology, developmental plasticity and invasion ecology and provides a mechanistic understanding of invasions in a well selected set of species (interactions).  It is true that the ecological impacts of invasions are becoming well understood, often in the sense of impact on population and species dynamics of native species. However, since all changes in ecology should ultimately result in altered selection pressures and back, more effort is needed to understand eco-evolutionary dynamics of species invasions, both in the invasive and native species. This field becomes nowadays overwhelmed with theory and empirical work is clearly lagging behind, so contributions like this are essential as critical tests of the developed theory.

The second contributions Ulrich and Gotelli emphasises on the proper use of different metrics to identify distinctive patterns in species x site presence-absence matrices. These approaches are important for understanding metacommunity organisation. Because the behaviour of different metrics is often correlated, it proved to be difficult to distinguish different patterns. Therefore, Ulrich & Gotelli created synthesis by testing the performance of a suite of null models and metrics that have been proposed to measure patterns of segregation, aggregation, nestedness, coherence, and species turnover. While there is no need to provide more detail here, they concluded that sources of non-randomness are best assessed by using different combinations of metrics. As such the paper is a natural and logic continuation of their previously published and highly valued consumer’s guide to nestedness analysis. We are sure that this contribution will receive the same attention and use in future community ecology.

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Posted by: oikosasa | January 18, 2013

Friday!

It’s always fun to read all submitted manuscripts. Especially when explanations are like this:

bakerypostdocI’m very happy that it doesn’t happen too often!

This one was actually copied from  #overlyhonestmethods

Have a great weekend everyone!

Posted by: oikosasa | January 17, 2013

Understanding wood decomposition

How do wood decomposition relate to other traits in the tree? Answered by Benjamin G. Jackson and co-workers in the Early View paper “Are functional traits and litter decomposability coordinated across leaves, twigs, and wood? A test using temperate rainforest tree species”. Here’s Benjamin’s short summary and his pedagogic figure showing the results:

Dead wood represents an important pool of carbon and nutrients entering the decomposer subsystem in forested ecosystems. However, our understanding the factors regulating wood decomposition remain poorly characterized. In our study we ask two main questions:

  1. Do tree species with leaves that decompose rapidly also have wood that decomposes rapidly?
  2. Do the same functional traits that control leaf litter decomposition control the decomposition of wood?

We addressed these questions by comparing how traits and litter decomposition vary across 27 co-occurring tree species from temperate rain forests in New Zealand. For each tree species, we quantified the functional traits of their green leaves and leaf, twig and wood litter and then decomposed the three litter types under controlled conditions. Below we show how the main findings of our study fit into the broader picture emerging from recent research into plant functional traits and litter decomposition.

Fig1. Oikos Blog entry for Jackson et al 2012

Posted by: oikosasa | January 15, 2013

Oikos in 2013: advancing synthesis in Ecology

Oikos’ Editor in Chief, Prof. Dries Bonte, presents some interesting news and wishes you all a wonderful 2013:

DriesA survey among readers revealed that Oikos is considered as a solid, high quality journal publishing broad ecological topics, often controversial papers and synthesising papers.  Synthesis in Ecology is already for long time our branding, but it is not always clear for readers and authors what is actually meant by that. For us, bringing synthesis is the only way to make serious advance in ecology. This can be achieved by merging different methodological, disciplinary, taxonomical or geographical aspects of ecology to create novel insights that move beyond providing the n-th case study on a certain ecological topic. While this rather confirmative research is intrinsically highly valuable, and inevitable to eventually create synthesis, Oikos will continue to prioritise the publication of the most novel, synthesising contributions. In a world flooded by scientific journals, such initiatives are essential to remain updated with the newest advances and insights in the field.

One new direction Oikos is heading for is the publication of meta-analyses as a separate section. Chris Lortie, our senior expert editor will be in charge of these incoming papers, evaluate proposals and invite original contributions. Dustin Marshall remains responsible for handling incoming Forum papers.

Authors publishing manuscripts that create synthesis –either meta-analyses, forum or regular papers- in Oikos will receive from 2013 onwards a real incentive, by providing fast publication, highlights of their work in the issue and social media, and open access. These papers will be highlighted as editor’s choice, and a box on the synthesis will be provided on each of these papers. In the near future, we will ask all authors to provide such a synthesis box at submission. When feasible, virtual issues centred on these synthesising contributions will be published.  In the near future, you can expect for instance such a guest-edited issue on Surf and Turf papers, and some more other exciting proposals have been received. More news on these will follow on our Facebook-page and on the Oikos-blog of course. On the other hand, Oikos will refrain from publishing rebuttal papers, but instead welcome balanced commentary papers that progress the field as a forum.

Oikos will further invest in the blog to show what Oikos is, communicate with readers, to serve authors with promotion of their papers. The base will be posts about papers in Early View that are provided by the authors. It could be photos, a background story to the study, a popular summary.  Essentially we seek for the blog answers on the following questions:  how did you get the idea, how long have you spent working on the project, any mistakes, why that species/system/field site etc.

As you can read, we do continue our investments to bring Oikos at the front in publishing the most exciting work in the field of ecology. We received about 1000 manuscripts in 2012 (of which we can print approximately 220 to keep the backlog rather limited). The editorial work is consequently only possible by having an extremely dynamics and motivated team, starting with the senior editors and 50+ handling editors that take fast and well-considered decisions on the incoming manuscripts, technical and managing editors processing all incoming and accepted papers, and of course, all our readers and authors that are engaged in the publication process by providing peer review of the highest quality. I truly thank you all for your work to support Oikos as a leading journal in ecology. My best wishes for 2013!!

Isn’t it just amazing how well adapted the tiny parasitic wasps are? Parasitoids want to lay their eggs in good, yummy caterpillars. Yummy caterpillars are those feeding on high quality plants. Quality of plants is partly determined by if their roots have been eaten by below ground herbivores. Plants smell differently above ground, depending on if their roots have been eaten or not. These odour variations are learned by the parasitic wasps when identifying the high quality hosts.

These results are presented in the new Early View paper “Effect of belowground herbivory on parasitoid associative learning of plant odours” by Marjolein Kruidhof and her co-workers. Here’s Marjolein’s own summary:

Only experienced parasitic wasps adapt their preference for plant odours in the presence of root feeders

Parasitic wasp laying eggs into a caterpillar

Although hidden in the soil, insects that feed on plant roots often do not go unnoticed by insects living aboveground. Upon root feeding, the odour the plant emits into the air changes. Tiny parasitic wasps, which lay their eggs inside the body of host caterpillars that feed on the plant leaves, use these plant odours to locate their hosts. Researchers from the Netherlands Institute of Ecology (NIOO-KNAW) in the Netherlands tested whether two closely-related parasitic wasp species, Cotesia glomerata and C. rubecula, expressed a preference for plants with or without Delia radicum root feeders. As inexperienced wasps of both species did not respond to the presence of root feeders, they continued to investigate whether the parasitic wasps could develop a preference after gaining experience when parasitizing caterpillars on root-infested or root-uninfested plants. Indeed, both wasp species adapted their preference for plant odours to the presence of root feeders, but did so in an opposite direction.  While C. glomerata learned to prefer the odour of plants with intact roots, C. rubecula learned to prefer the odour of root-infested plants. These findings stress the importance of not only assessing the influence of root herbivores on the responses of inexperienced parasitic wasps, but of also taking learned responses into account. In a publication that will soon appear in Oikos the authors discuss the possible reasons why these two parasitic wasp species respond so differently towards the presence of root feeders.

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What are the chances that the reefs recover? And how likely is it that they just turn into seeweed-dominated ecosystems instead?  Important issues that Peter Mumby and his colleagues have studied and modelled in the new Early View paper “Evidence for and against the existence of alternate attractors on coral reefs”.

Here’s Peter’s summary of the study:

Coral reefs have been heavily stressed by local anthropogenic disturbances, like fishing and pollution, as well as global events such as ENSO which can cause coral bleaching and wreak devastation on living coral. Ideally, corals would recover after some kind of disturbance but a number of studies have documented a lack of recovery and even continued decline of corals rather than return to a coral-rich ‘attractor’. This raises the question, ‘do coral reefs exhibit multiple attractors?’. If they do, then it is possible for negative feedbacks to emerge that not only prevent reef recovery but reinforce themselves and trap reefs within an undesirable state, often dominated by seaweed. If reefs do become trapped in an undesirable state it might prove extemely difficult for management to reverse the decline and facilitate the return of a healthy ecosystem. 
 
Ecological models of coral reefs have studied the effects of various disturbances including the fishing of herbivores such as parrotfishes. Theory predicts that Caribbean coral reefs do indeed exhibit alternate attractors particularly in their somewhat degraded states today. However, empirical studies have claimed to find no evidence to support this theory. There is, therefore, a controversy over whether reefs can become trapped in seaweed-dominated systems. In this paper we argue first that the empirical studies were incapable of testing for multiple attractors. We then provide new comparisons between theoretical predictions and field observations, both of which are consistent with multiple attractors. However, it is also possible to fit a simpler model to empirical data that does not exhibit multiple attractors. When we take a careful look at this model we find that it makes several troubling ecological assumptions, which lead us to doubt its veracity.
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Proving the existence of multiple attractors is extremely challenging and there is, as yet, no definitive proof either way. However, the weight of theory and field observation appears to support the notion for Caribbean coral reefs. Given this, and it’s important conservation implications, we feel that management should proceed on the conservative – and more likely – assumption that reefs can become stuck in seaweed states if stringent steps are not taken to increase their resilience.
Posted by: oikosasa | December 18, 2012

Playing dead – when not needed to

The Ecology of Playing Dead – when not needed to…something that Xinqiang Xi, John N. Griffin and Shucun Sun have diged deeper into in their new Early View paper “Grasshoppers amensalistically suppress caterpillar performance and enhance plant biomass in an alpine meadow”.

Read Shucun Sun’s story about Playing dead behaviour in grasshoppers:

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As a child, I would often wake in the middle of the night thinking I could hear a burglar in the kitchen downstairs (in reality, my family cat coming through the cat flap). I would lay there, alert in bed, not daring to move in case I would be heard. By mistaking sounds of the cat for those of a burglar, I had inappropriately employed a danger avoidance strategy, costing myself much-needed sleep. We know that, in nature, prey are often highly-tuned to the signals of their predators and take action to avoid predation, like growing defensive body armor, shifting habitats, or even playing dead. Prey take these energetically demanding measures because being eaten tends to be rather more costly to one’s fitness! However, just like my childhood anecdote, prey species can get it wrong and misidentify a friend for a foe, reacting to cues from animals within their trophic level (competitors) that pose no predation threat. This sort of interaction could be common in nature and may not only incur a cost for the ‘victim’ but also have knock-on effects to other species that interact with them.

In our paper, we describe and explore the direct and indirect consequences of interactions between two common grazing insects in alpine meadows of the Tibetan Plateau in northwestern China. We ran a season-long field experiment in which we manipulated the presence and absence of the caterpillar, Gynaephora alpherakii, and grasshopper, Chorthippus fallax, in enclosures, and measured responses of both grazer species and their plant resources. After two months we discovered a strong negative one-way interaction between these species – the seldom considered form of interaction known as amensalism. While caterpillars showed reduced growth, survival, egg production, and delayed metamorphosis in the presence of grasshoppers, there was no reciprocal negative affect of caterpillars on grasshoppers. Because caterpillars are voracious grazers, changes in their activity and survival caused by the presence and absence of grasshoppers propagated to influence the composition and biomass of plants.

We put the amensalistic interaction down to a case of mistaken identity. We observed that by whacking into – and landing heavily upon – grass stems as they move about the meadows, grasshoppers trigger a death-feigning response in caterpillars whereby caterpillars, upon perceiving risk, drop to the ground from the grass stems and leaves where they forage, cease movement, and curl up for about 20 minutes before resuming foraging. Repeated disturbances from the seasonally abundant grasshoppers could have significant effects on feeding time and energy uptake. Indeed, caterpillars in the same enclosures as grasshoppers were observed actively foraging significantly less frequently than when they were alone – evidence of the cost of mistakenly playing dead and helping to explain grasshopper effects on caterpillar growth, timing of metamorphosis, and grazing impact on plants.

Our study provides a rare example of amensalism in a natural ecosystem and shows that it can result from a previously unappreciated mechanism – mistaken identity. Furthermore, this work highlights that such interactions can have significant consequences for the functioning of ecosystems, as revealed by marked shifts in the relative abundances of plant functional groups and overall biomass. Strong amensalistic interactions, if common, could have consequences for our understanding of key issues, such as the evolution of risk-reducing behaviors and traits and the link between consumer biodiversity and ecosystem functioning.

Posted by: oikosasa | December 14, 2012

The Arctic tundra as a natural laboratory

In the new Early View paper “Predator-mediated interactions between preferred, alternative and incidental prey in the arctic tundra”, Laura McKinnon and her colleagues used the Arctic Tundra in Canada as a natural laboratory to study predator-prey interactions.

20708cHere is Laura’s short version of the paper:

Predators can have direct impacts on prey populations by decreasing survival and fecundity, and in turn, prey populations can also drive predator densities.  These interactions between predator and prey can often lead to coupled cycles in population abundance, many studies of which have become classic textbook examples in ecology.  More recently, these models have been expanded to incorporate multiple prey species and even multiple trophic levels in order to have a better understanding of the causes and consequences of predator prey interactions in more complex realistic environments.  However, testing these models in complex ecosystems can become rather cumbersome due the sheer number of interactions between species.  Luckily, there are some terrestrial ecosystems, such as the Arctic tundra which provide less complex natural laboratories in which to study trophic interactions between predators and multiple prey items.   In our recent study, we took advantage of this natural laboratory to study indirect interactions between preferred, alternative and incidental prey.

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In the arctic tundra, numerical and functional responses of predators to preferred prey (lemmings) affect the predation pressure on alternative prey (goose eggs) and predators aggregate in areas of high alternative prey density.  Therefore, we hypothesized that predation risk on incidental prey (shorebird eggs) would increase in patches of high goose nest density when lemmings were scarce.  By measuring predation risk on artificial shorebird nests in quadrats varying in goose nest density on Bylot Island (Nunavut, Canada) across 3 summers with variable lemming abundance, and monitoring quadrats for predator activity, we provide evidence that the abundance of preferred prey influences the indirect relationship between alternative and incidental prey.  Predation risk on artificial shorebird nests increased in the presence of increasing goose nest densities, especially at low lemming abundance, as predicted.  In addition to supporting our incidental prey hypothesis which suggests that when preferred prey decrease in abundance, short-term apparent competition via aggregative response can occur between alternative and incidental prey, these results also provoke interesting applied questions regarding the potential effects of increasing goose densities on incidental prey such as shorebirds.

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Posted by: oikosasa | December 13, 2012

Opossums’ seed dispersing job

Seed diseprsal by animals is an important ecological service. How selective or general the animals are in their choice of fruits to eat might have a huge effect on dispersal of the plants. Read more in the new Early View paper “Individual variation in resource use by opossums leading to nested fruit consumption” by Mauricio Cantor et al.

Here is the authors’ own summary of the paper:

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Seed dispersal by fruit-eating vertebrates is an important ecological service that has consequences for the plant community and regeneration process. Despite recent findings on the ecological relevance of within population diet variation far less attention has been devoted to the role diet variation for ecological services, such as seed dispersal. In this paper we unravel fruit consumption patterns by the white-eared opossum (Didelphis albiventris), a South American didelphid, which is regarded as an important seed disperser commonly found in disturbed environments, where vegetal regeneration is especially required.

opossum4_SetzWe detected fruit consumption patterns suggesting these opossums may differ in their degree of fruit selectivity what may result in heterogeneity in seed dispersal efficiency within the population. In this sense, the actual result of the seed dispersal provided by these animals probably differs from what one would expect from the average behavior of the population. The result of such heterogeneity would probably be dependent on the proportion of opportunistic and selective individuals in the population. This frequency-dependent seed dispersal may have implications to both plant individuals and species, affecting plant performance and the local plant community composition.

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Posted by: oikosasa | December 12, 2012

Will your photo be on Oikos cover 2013?

249518_413427882044243_950633876_nOikos is changing it’s cover style in 2013. Replacing the quote, there will now be a photo. We therefore, as an annual competition, call for photos illustrating the Oikos’ goal of Synthesising Ecology. We seek a photo also demonstrating ecology in action (e.g. processes or interactions), not only a single organism or a landscape.

Please send your photos together with the oikos-photo-competition-form2 to oikos@oikosoffice.lu.se, with Photo competetion as subject, before January 31st 2013. The winner will be awarded a book price from Amazon for a value of 100 Euro. The winning photo will be at the cover of all issues of Oikos from April 2013-December 2013. A selection of contributions will be exhibited at the Oikos meeting in Linköping, Sweden Feb 4-6.

Competition Rules:

Entries must be digital images, submitted electronically, in jpg or tiff-format. Images must be available in 300 ppi.

Digital enhancements must be kept to a minimum and must be declared. Both the original and the enhanced image must be submitted.

File names must include appplicant’s surname.

Photos must be accompanied by an entry form that describes illustrated species and scene. Download the oikos-photo-competition-form2

A prize committee consisting of Managing Editor, Editor in Chief, deputy editors, Technical Editor of Oikos and the Director of the Oikos Editorial Office, will judge which photo that best suits our requests. The decision by the committee is final.

All submissions will be entered under a Creative Commons License and will be displayed on Oikos webpage and social media and may be used  for commercial purposes. Download Creative Commons License here.

Oikos takes no responsibility for submitted images being lost, damaged or dealyed.

Posted by: oikosasa | December 10, 2012

Winners in a changing world

Invasive species may actually increase resistance to climate changes. Celia Olabarria and co-workers studies this interaction in marine macroalgal assemblages.  Now on early View: Response of macroalgal assemblages from rockpools to climate change: effects of persistent increase in temperature and CO2

Here is a short summary by the authors:

Climate change is one of the greatest threat  that marine systems are facing. Changes in ocean temperature, biogeochemistry, sea level, UV radiation, and circulation patterns have been identified over the last few decades. Specifically, warmer and more acidic oceanic water (due to the increase of CO2 in the atmosphere and oceans) are of great concern to marine biologists. Non-indigenous species are also impacting marine communities around the world at an unprecedented rate. These species are often ecosystem engineers (e.g. brown canopy algae) that can replace native species and their functional role in the ecosystem, or modify habitat characteristics and food sources for consumers. We do not have information about how invaded communities will respond to climate change compared to non-invaded communities.

Marine macroalgae that dominate the rocky intertidal in most oceans, and in temperate and Polar regions cover rock surfaces in the shallow subtidal, make a substantial contribution to marine primary production (10%) and describe important ecological functions. They may be also actively involved in lowering global warming and climate change. Research about effects of different climate change scenarios on macroalgae has found quite variable and species-specific responses. Until now, most research has focused on the effects of climate change on single macroalgae species, rather than on whole communities. While this approach is useful for understanding species-specific mechanisms behind the effects of environmental changes, it ignores species interactions which may buffer or amplify individual responses thereby altering predicted assemblage-level responses.

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Macroalgal assemblages from rock pools are interesting model systems to study climate-driven changes because they are composed of different morpho-functional groups of varying diversity and identity of species. Despite coping with daily and seasonal variations in pH and temperature, their response to more persistent changes are unknown. We were able to manipulate temperature and CO2 concentration in mesocosms to evaluate how these to climate-change factors affected several ecosystem functioning variables at both individual and assemblage level. For that, we used synthetic macroalgal assemblages of varying diversity and identity of species resembling those characteristic of rock pools.

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Results revealed that the increase in temperature and CO2 concentration may interact and affect the functioning of coastal macroalgal assemblages, with effects largely dependent on species composition of assemblages. Although the effects of assemblage richness were mostly negligible, significant differences were found between the response of native and invaded assemblages. Data suggested that  invaded assemblages might be more resistant in the predicted future scenario of climate change. This paper emphasises the importance of using multiple stressors-study approaches at community level to get better predictions of climate change impacts on ecosystem functioning.

Photo: F. Arenas and M. Matias

Posted by: oikosasa | December 7, 2012

High-fat food makes females unattractive

Protein or fat in food – which is best? Well, if you’re a female preying mantid, you should definitely go for the high-protein diet! Females on high-lipid diet attract much fewer males than females on high-protein diet. These results are presented in the new Early View paper “Macronutrient intake affects reproduction of a predatory insect” by Katherine L. Barry and Shawn M. Wilder.

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Here is a short summary by Katherine:

164bWe tested how diet affected the reproductive success of female praying mantids by feeding them live locusts that were injected with solutions of lipid or protein.  Not too surprisingly, females fed high-lipid locusts gained more fat and produced about half as many eggs as females fed high-protein locusts. 

We also tested female attractiveness by placing females in small mesh cages (that excluded visual cues) within large enclosures, and allowing males to choose between females from the different feeding treatments.  Usually females with more eggs are more attractive than females with less eggs and, in our study, the high-protein females attracted more males (56 males) than the high-lipid females (1 male).  However, the effect was much more extreme than we predicted.  In previous studies, females were fed a standard diet of crickets, and individuals with as few as one egg were able to attract up to three males.  But in our study, females on the high-lipid diet had over 20 eggs on average but only one female attracted one male.  Hence, diet quality seems to have a large effect on the quantity or quality of pheromone produced by females.  It would be interesting to test how diet mediates pheromone production in praying mantids and if similar effects occur in other species of arthropods.

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Posted by: oikosasa | December 6, 2012

Are you a helper?

Do you have any “helper” around you? Maybe are you one yourself? “Helpers” are those researchers who regularly provide valuable feedback to their colleagues’ manuscripts and to scientific discussions.  Who regard this feedback as part of the research, and a part of their working tasks. However, their input is awarded as best with their names in the acknowledgement of the publication, and not that often in the author field.

Alexander Oettl, a professor in Immunology at Georgia Institute of Technology, Atlanta, USA, studied the effect of “helpers” by comparing their colleagues’ impact of papers (IF of journals, n publications and citations) before and after the “helpers” involvement.  What he found was a clear positive effect of the involvement of the “helpers” for their colleague’s publications.

The question is – how are these helpers awarded? In evaluations of applications for academic positions and research grants, factors as large numbers of highly cited papers get higher rates than increasing over all scientific quality in the group or at the department. Perhaps it’s time for a new metric to take into account – average acknowledgements per year?

Read Oettl’s paper in Nature here  (Figures from Oettl’s paper)

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