Posted by: oikosasa | October 17, 2012

Fruit-frugivore interactions not that simple after all…

Now online: Perea et al. “Context-dependent fruit-frugivore interactions: partner identities and spatio-temporal variations”

Here Ramon Perea summarizes the study:

Plants are able to use animals as vectors for the dispersal of their seeds. Many fleshy fruits constitute a food attractive for different vertebrate species, that usually ingest jointly the edible pulp and the seeds, which are later defecated or brought up in suitable conditions for germination. Studies on this kind of plant-animal mutualism, called endozoochory, are numerous, but usually refer to only one pair of mutualists, or are made during one fruiting season or at only one place.

Does seed dispersal by mammals depend on the spatio-temporal context in which the interaction takes place? For instance, species abundances, specific seed crops, availability of alternative foods or vegetation structure usually change from year to year or from one habitat to another at the same locality. Many of these changing factors might affect important attributes of the plant-animal interaction. In our particular case of seed dispersal, the environmental context might modify, for example, the quantity of seeds dispersed (interaction strength) or the quality of dispersal (seed treatment, deposition on suitable sites for germination and survival, etc.), which could eventually alter the so-called sign of the interaction (from a highly successful dispersal –mutualism- to a highly unsuccessful dispersal –antagonism).

Our field work was performed in the Doñana National Park (SW Spain), under Mediterranean conditions, where we collected about 1600 faeces of a whole assemblage of fruit-eating mammals (frugivores: red fox, badger, red deer, wildboar and rabbit).  About 300,000 seeds of fruit-bearing plants were recovered of these faeces, measuring frequency of seed occurrence, plant species and seed damage for three different habitats.

For each particular fruit-frugivore pair, the interaction strength largely varied with the spatio-temporal context (year and habitat) at our local scale, leading to a low specificity across the seed-frugivore network. Frugivory and potential endozoochory should not be simply considered a mutualism leading to successful seed dispersal, but a rather variable relationship along the mutualism-antagonism continuum, depending on the ecological context.

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