Using rarefaction to isolate the effects of patch size and sampling effort on beta diversity
Beta diversity describes how species composition varies across space and through time. Current estimators of beta diversity typically ignore the effects of within-patch sample size, determined jointly by local abundance and sampling effort. Many ecological processes such as immigration, predation, or nutrient limitation affect abundance and asymptotic beta diversity concurrently; thus, existing metrics may confound changes in asymptotic beta diversity with changes that result from differences in abundance or sampling. Results from a stochastic simulation model illustrate how decreasing within-patch sample size may either increase or decrease observed beta diversity, depending on the type of metric, sample size, and community properties; these changes are easy to understand, and predict, by considering the effects of sampling on variance. A modified, patch-level form of rarefaction controls for variation in within-patch sample size; two case studies illustrate the utility of this approach. Studies seeking a mechanistic link between ecological process and beta diversity will continue to benefit from explicit consideration of sampling effects.
This paper was authored by Adrian C. Stier (me), Benjamin M. Bolker, Craig W. Osenberg. You can find a copy of the manuscript here, or contact me directly for a PDF.