Posted by: Jeremy Fox | November 15, 2011

Free idea for a provocative review paper: comparing ‘selection’ in evolution vs. ecology

Selection isn’t just something that happens in evolution. Selection occurs whenever one type of organism, by virtue of its properties, leaves more descendants than another type of organism (actually, ‘selection’ isn’t even limited to organisms, or to ancestor-descendant relationships; see Price 1995). One species outcompeting another is not fundamentally different from one asexual genotype outcompeting another, even though the former is the sort of thing ecologists study while the latter is the sort of thing evolutionary biologists study. My fellow Oikos editor Mark Vellend has written about this.

These close analogies immediately suggest all sorts of possibilities for theoretical and empirical work (e.g., Fox et al. 2010). The application of neutral theory, originally developed in evolutionary biology, to community ecology is one ‘hot’ example, but it’s far from the only one. Here’s another one, which some enterprising reader should turn into a review paper: compare the strengths and effects of selection in ecology vs. evolution. What I have in mind is a review paper that would pull together data from ecology and evolution to address questions like the following:

How strong is selection in ecology vs. evolution? Recent reviews have already compiled data on the strength of selection in evolution (Kingsolver et al. 2001). Analogous data in ecology would compare the fitnesses (per-capita growth rates), or fitness components, of competing species with different phenotypic traits, using standard Lande-Arnold methods. Is selection among species typically stronger or weaker than selection among different phenotypes within species?

How strong is local adaptation in ecology vs. evolution? Local adaptation is an expected outcome of evolution by natural selection whenever there are sufficiently-strong trade-offs in fitness across environments. Local adaptation has a couple of distinct senses, but basically it just means that organisms are fitter where they’re found (their ‘home’ site) than elsewhere. You test for it by growing different types of organism (different genotypes, or different species) in the same environment (a common garden experiment), and ideally you repeat the experiment in different environments so that every type gets tested in both its home environment and in various other environments (a reciprocal transplant experiment). In evolution, experiments that look for local adaptation generally find it, although it’s often fairly weak (Hereford 2009). But in some subfields of ecology, especially invasion ecology, it’s often suggested that organisms should be fitter where they’re not ordinarily found–think of a non-native species that has left behind its natural enemies. It’s unclear whether such “anti-local adaptation” is actually common, though, or whether ecologists merely pay a lot of attention to the rare examples. Note that, when local environments are extremely differentiated, it’s totally obvious that there’s ecological local adaptation. Palm trees can grow on tropical islands and fir trees can’t, while the reverse is true in boreal forests. Cows can’t grow in the water, and sea cows can’t grow on land.  The interesting question is about what happens in less-extreme cases.

How strong is negative frequency dependence in ecology vs. evolution? Negative frequency dependent selection, which means that relative fitness of a given type increases as its relative abundance declines, is a necessary condition for stable coexistence of different types of organism. It’s known in both ecology and evolution, although mostly in laboratory or semi-natural settings. The most straightforward way to test for it is to manipulate the relative abundance of different types of organism (ideally while holding total abundance constant), and then measure their relative fitnesses. Ecologists have often performed this sort of experiment, especially with plants, where the basic experimental design has its own name (DeWitt replacement series). So probably the relevant ecological data have been well-reviewed somewhere, but I doubt they’ve been quantitatively compared to evolutionary data.

I’m not aware of much theory that predicts the answers to these questions–this review would be more about pulling together the available data in order to give theory a target to shoot at.

Advertisements

Responses

  1. […] the Oikos blog, such as my “free idea for a provocative review paper” posts (see here, here, and here), are mostly those which I’m happy for others to pick up and run with, because […]


Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

Categories

%d bloggers like this: