The effect of species extinctions on island biogeographic patterns

The study of island systems has provided the basis of much of what we understand about a number of biogeographic patterns. However, islands have also suffered numerous extinctions as a result of human activities. The extent to which these extinctions have influenced the many different patterns we study as island biogeographers, and thus what we consider to be ‘natural’, is largely unknown. Here, we use a simulation approach to illustrate the impacts of anthropogenic extinctions on various macroecological and biogeographical patterns on islands. We simulated an archipelago consisting of five islands and filled these islands with a realistic set of species, each possessing four functional traits. Using this dataset, we then calculated a number of biogeographic patterns, including the slope of the island species–area relationship, functional richness and beta-diversity (taxonomic and functional). The next stage of the simulation modelled the colonization of the archipelago by humans, represented by a 50% reduction in the carrying capacity of the archipelago and by an associated wave of species extinctions. When the extinction simulation process was finished, the various metrics were re-calculated. The results illustrate that all the analyzed patterns are affected to some degree by the human-induced loss of species. Overall, our results highlight how the extinction of species as a consequence of human actions on islands can influence our interpretation of ‘natural’ island biogeography patterns.