How Species Heterogeneity and Trophic Structure impact the Diversity-Stability Debate

The diversity-stability debate in ecology — whether increasing the number of interacting species promotes or hinders the robustness of an ecosystem to perturbations — has not yet been fully resolved. This question is especially important in the face of accelerating biodiversity loss. To gain insight, we employ a community assembly model in which species are sequentially added and removed, considering the dynamics of an ecosystem. We incorporate two facets of ecosystems (species heterogeneity and the presence of intrinsically unstable species) that have been under-explored in theoretical models. We do this by separating species into intrinsically stable producers and intrinsically unstable consumers. We assign biologically relevant interaction types within and between these groups and find that consumers can be stabilized solely through interactions with stable producers. We show that having more predation interactions within consumers results in a trophic structure that increases the robustness of the entire ecosystem to perturbations and supports greater species diversity. Artificially removing consumer species causes larger extinction cascades than removing producers. These findings highlight how intrinsically unstable consumers have a disproportionate influence on ecosystem stability and emphasize the important role apex predators play in stabilizing complex ecological networks.