COS 49-3 - Humans elicit community change via consumptive and non-consumptive impacts on keystone species

Background/Question/Methods

Worm and Paine (TREE 2016) proposed that humans are hyperkeystone species - agents that commonly impact other keystone species and thus ecological communities. Here, we test one major element of the hyperkeystone hypothesis: that humans impose community changes via their influence on keystone species not only via direct consumptive effects but also via non-consumptive processes like widespread and significant changes to atmospheric, terrestrial, and aquatic systems. To comprehensively address this hypothesis, we first conducted a systematic literature search to create an evidence-informed list of keystone species. We then quantified various community responses (e.g. changes in geochemical cycling rates, biodiversity, and landscape cover, etc) to human-caused declines or removals of keystone species using a log risk ratio to standardize the magnitude of diverse community responses.

Results/Conclusions

We found evidence for 128 keystones, which occurred on every continent except Antarctica and in every major biome. Although ranging from 2 to 190,000 kilograms, median body mass was modest (3,278 g). Many keystone species (n = 22; 16%) are rodents, most of which (n = 21; 95%) act as key bioturbators in their communities. Fewer known keystones (n = 13, 10%) are carnivores – an Order commonly associated with keystone processes. We also found that keystone reductions or extirpations resulting from non-consumptive effects (which were common, occurring in 40 of 128 contexts) produced a similar magnitude of community response (x = 0.74, n = 40, 95% CI [0.43, 1.05]) as consumptive effects (x = 1.19, n = 28, 95% CI [0.71, 1.67]). Collectively, these patterns showing the prominence of small-bodied and lower-trophic level taxa suggest a reconsideration of what species and processes are involved in keystone interactions, as well as highlight the myriad ways in which humans impact ecological communities via their influence on keystone species.