Ecological communities are vulnerable to realistic extinction sequences

• Loss of species will directly change the structure of ecological communities, which in turn may cause additional species loss (secondary extinctions) due to indirect effects (e.g. loss of resources or altered population dynamics). The vulnerability of food webs to repeated species loss is expected to be affected by food web topology, species interactions and the order in which species go extinct. Species traits such as body size, abundance and connectivity probably determine the vulnerability to extinction of species and, thus, the order in which species go primarily extinct. However, how different sequences of primary extinctions affect the vulnerability of food webs to secondary extinctions, when species abundances are allowed to respond dynamically, is not well understood. So far, only one study has incorporated species dynamics when assessing the effect of different extinction sequences on community structure, and only a limited number of extinction sequences have been evaluated. Here, using complex model food webs and including population dynamics, we analyze the effect of 33 extinction sequences on community structure using R50 (the proportion of primarily removed species needed to cause a 50% reduction in species richness) as a measure of community robustness to secondary extinctions. As expected, we find community structure to be highly vulnerable to removal of primary producers. More surprisingly, removing species based on traits that are strongly linked to the trophic position of species (such as large-bodied species, rare species, species with a high net effect, species with a high trophic position) are found to be as destructive as removing only primary producers. Such top-down oriented removal of species are often considered to correspond to realistic primary extinctions of species, but earlier studies, based on topological approaches, have not found such realistic extinction sequences to have any drastic effect on the remaining community. Thus, our result suggests that ecological communities could be more vulnerable to realistic extinction sequences than previously believed.

Nyckelord

Community structure

extinction sequence

food webs

species loss

community robustness

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