Robustness of temperate versus tropical food webs: comparing species trait-based sequential deletions

Abstract

Loss of species can unleash a cascade of secondary extinctions that cause dramatic changes in the structure and dynamics of food webs. The consequences for the food web depend on the traits of the species that are lost; thus, it is crucial to identify species’ traits associated with secondary extinction risk. Another important issue is to determine where the most vulnerable ecosystems are located. In this study, we aimed to compare the robustness of temperate versus tropical ecosystems to species loss. A total of 34 intertidal rock pools were analysed from a temperate and a tropical region (17 pools in each). Binary food web networks were assembled for each pool depicting who eats whom. Eighteen topological network properties were estimated to compare temperate and tropical webs. Robustness, a measure of network tolerance to species extinction, was assessed. Species loss was simulated in silico using sequential deletion protocols aimed at species that were (1) most connected, (2) least connected, (3) most abundant, and had the largest (4) body mass (mean weight) and (5) size (mean length). Tropical food webs exhibited higher robustness than temperate food webs. Both temperate and tropical food webs were less robust when the removal was directed at the most-connected species, confirming that highly connected species are particularly important in food webs. This study revealed, for the first time, that the positive relationship previously found between robustness and connectance is only confirmed for temperate webs, highlighting the need for more tropical case-studies in general data sets.