Turnover importance: Operationalizing beta diversity to quantify the generalism continuum

Abstract

Abstract Generalization is difficult to quantify, and many classifications exist. A beta diversity framework can be used to establish a numeric measure of generalist tendencies that jointly describes many important features of species interactions, namely spatiotemporal heterogeneity. This framework is promising for studying generalized symbiotic relationships of any form. We formulated a novel index, turnover importance (T). T describes spatiotemporal heterogeneity in interactor assemblages, an inherent feature of generalist relationships that is not captured by available metrics. We simulated the behaviour of T relative to other available metrics, calculated T for native North American orchid‐insect relationships, and tested correlations between T and eco‐geographic variables. We performed case studies to demonstrate applications of T for conservation and eco‐evolutionary studies. T behaves predictably across simulations, and dynamically interacts with site number, gamma diversity, and species range sizes. T is moderately sensitive to sampling depth. Orchids with higher T scores occupy larger ranges and broader climatic niches. Alternative interactor‐specific measures of generalism are best employed for local‐level community networks over short timespans. While these interactor metrics can assess use versus availability in local communities, T can be used to measure spatiotemporal patterns of variation in interactor assemblages across a focal species' range. This study provides a roadmap for future work focused on better understanding the patterns and consequences of generalized relationships.