Ecosystem Vulnerability to Species Loss: a Broad Study of Real-World Food Webs

The world is facing widespread species extinctions. Seeking to understand their indirect effects on ecosystems, we analyse over 200 weighted food webs from around the whole Earth. Combining a large survey of empirical networks with an assessment of multiple measures of their vulnerability, we bring the first such data-based evidence into the ecological complexity-stability debate.
Assuming donor-controlled flow dynamics, we simulate the effects of removal of a single node from the studied food webs. We find that small and highly connected food webs are more vulnerable to indirect impacts of species extinctions. The average change of biomass of a group of species (node) in a food web appears to be roughly inversely proportional to the number of nodes in the network. Several factors mitigate against biomass loss and secondary extinctions, including the redundancy of pathways and heterogeneity of flows. Moreover, an abundance of cycles promotes the biomass increases that might follow an extinction.