Community evenness and sample size affect estimates of predation intensity and prey selection: A model-based validation.

Abstract

Predation estimates inferred from the preserved records of predation traces are essential in evaluating the evolutionary effect of ecological interactions. It is, however, crucial to establish how sampling intensity and community composition of an assemblage influence the reliability of these measures. Using a resampling technique, we evaluated the effect of sampling intensity and a communitys evenness on the inferred predation estimates. We theoretically simulated model communities representing different levels of evenness, predation intensity, and predatory behavior (selective, non-selective). We calculated the total predation intensity and the number of prey species for each community. We then resampled each community without replacement and noted variations in the inferred measure from the accurate estimate as the sampling intensity increased. Our results demonstrate that the evenness of a community does not influence the inferred predation intensity for non-selective predation. However, communities with highly selective predation are sensitive to evenness and sampling intensity; inferred predation intensity of these assemblages can substantially differ from the actual value. The inferred number of prey species is also influenced by the communitys original evenness, predation selectivity, and predation intensity. When predation is selective, sampling intensity heavily influences communities with low evenness and low predation intensity; inferred predation intensity is underrepresented in smaller sample sizes. For communities of low evenness and predation intensity where rare species are attacked preferentially, the inferred prey richness differs significantly at a small sample size. We proposed a post-facto standardization method for comparing predation estimates of discrete communities that differ in the sample size. We validated its utility using the published predation data of the Plio-Pleistocene molluscan fossil assemblage. The present approach attempts to provide critical insight into the reliability of predation estimates and may help in comparing predation patterns across time and space. Several factors, including preservation bias, might impact the final predation signature of an assemblage. It warrants a future research direction to develop a comprehensive framework of post-hoc standardization of assemblages with differing predation styles and preservation history.