University of British Columbia Vancouver, British Columbia, Canada
Background/Question/Methods
Species interactions play important roles in many ecological processes, including energy transfer, pollination, dispersal, and other symbioses. The maintenance of biodiversity in ecosystems may depend on these interactions. In some cases, loss of a species from an ecosystem results in the extinction of other species, an event known as co-extinction. This can occur directly due to the loss of an obligate symbiotic relationship or indirectly through the loss of regulation of the population of another species. The susceptibility of organisms to co-extinction may be determined by the structure of the ecological network to which they belong. For example, a large-seeded plant will lose its dispersal capabilities if its only disperser goes extinct, threatening its long-term persistence. When interactions are determined by traits with phylogenetic signal, the structure of an interaction network will also be shaped by the phylogenetic structure of the community of interacting species. Here, I examine the relationship between phylogenetic structure and network structure, providing novel insight into how independent evolutionary history contributes to patterns of ecological interaction. I collected published bipartite networks describing interactions between plants and birds. I then explored how phylogenetic properties, especially the evolutionary distinctiveness of species, relates to the properties of interaction networks.
Results/Conclusions
I found that evolutionary distinctiveness is associated with fewer redundant interactions, and in a large bird-pollinator network, I show that nonrandom extinction of birds based on evolutionary distinctiveness resulted in earlier isolation (loss of all interactions) of plants when compared to extinction at random. My results suggest that organisms with high evolutionary distinctiveness play outsized roles in the maintenance of fringe species that have few interactions, and that the consequences of their extinction tend to be high in terms of cascading biodiversity loss. In contrast, organisms with low evolutionary distinctiveness are more likely to provide redundant interactions that buffer against network isolation; the consequence of a single extinction of such species is less severe.
