Interaction strengths

Efforts to characterize and estimate the functional forms and strengths of species interactions in species-rich communities are hampered by the multitude of direct and indirect interactions such systems exhibit. Empirical insights have also been constrained by an assumption that the feeding behaviors of specialist predators are representative of the behaviors exhibited by generalist predators, which are far more common in nature. This is largely because logistical and statistical constraints have limited almost all studies to species-poor systems of single predator species interacting with only one primary prey species. Even inherently generalist predators have thereby been reduced to effective specialists, whether in manipulative experiments or in time-series analyses. New ways to quantify species interaction strengths are needed to identify keystone species, inform the development of mathematical models, and further our understanding of the processes that regulate community structure and dynamics.

Much of our work to date has sought to develop an observational approach with which to overcome many of the aforementioned limitations. The approach relies on (1) predator feeding surveys for estimating the proportions of predator indivdiuals who are caught in the act of feeding on different prey categories (i.e. species), and (2) estimates of prey detection times, typically derived from laboratory experiments, that determine the probability of observing a feeding event when conducting a feeding survey. These data allow us to estimate a predator population’s (or predator indivdiual’s) prey-specific feeding rates which, in conjuction with (3) estimates of prey and predator abundances, allow us characterize the functional forms of their interactions. We have applied the approach in both stream and intertidal communities.