Understanding species' roles and dynamic importance in empirical food webs

Background/Question/Methods

In the past decades, community ecology has come to recognize not just the importance of the species in a community but also the interactions between them. For example, the organization of predator-prey interactions is known to mediate a community's ability to respond to threats such as extinctions or invasive species. It is likewise understood that individual species are not interchangeable within a community. One especially well-known example of this phenomenon corresponds to the idea of “keystone species” whose removal from the community leads to an atypically large disturbance. Despite the importance to ecology and conservation, however, the link between these two ideas---the structure of the food web and the dynamic importance of species within their community---remains unclear.

In this presentation, we will introduce a novel means with which to determine individual species' roles within their community based upon how they and their interactions “fit into” their community's food web. Importantly, we demonstrate that this structural feature has a direct dynamic analog with which we can quantify the relative importance of species within their community in terms of their contribution to food-web robustness. Therefore, instead of focusing on one to a few keystone species, we can characterize the roles of all species in a community---from the smallest insect to the largest predator.

Results/Conclusions

We analyze the set of species' roles for the species that make up a variety of empirical food webs from across the globe. There is considerable variation across the data; some species do indeed appear to be keystone species of critical importance to their community while others would appear to contribute rather little. Upon further examination, we find significant phylogenetic signal on species' importance within their community, that is, phylogenetically-related species tend to be of similar importance. Intriguingly, this pattern appears to transcend the specifics of the individual food webs: related species from different communities tend to be of similar relative importance to their local communities. Our study provides a solid framework from which to quantify the importance of different species across the tree of life and to assess the community-wide consequences of their extirpation.