The role of ecological filtering, dispersal limitation and species traits in determining food web structure and function

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Why don't all species occur everywhere? And how does the fact that species are limited in their occurrence affect how food webs function? My proposed research with invertebrate food webs in Canada, Costa Rica and Brazil will answer both of these questions. Species may not occur everywhere because they have not had enough time or opportunity to colonize (dispersal limitation), because the habitat is not suitable (habitat filtering), because other species restrict them from occurring (biotic filtering) or because a series of chance events has led to the species going locally extinct (ecological drift). I will distinguish between these options using observations and transplants. I predict that the relative importance of these mechanisms will differ between small and large organisms, and between predators and their prey. Species that differ in these types of traits are also likely to play a very different functional role in food webs, and we predict that manipulations of dispersal limitation or habitat filtering will therefore also the rate at which energy and nutrients flow through the food web. Finally, functional trait differences between species may have a strong evolutionary signal, such that closely related species have similar traits. If so, the net relatedness of species in a community ("phylogenetic diversity") may be a strong correlate of ecosystem function.