Disturbance and dispersal as drivers of beta-diversity: A synthesis of experiments
The effects of disturbance on site-to-site variation in species composition (beta-diversity) appear to be highly contingent. Disturbance is often observed to decrease beta-diversity through convergent selection of disturbance-tolerant species, resulting in homogenization of community composition. In contrast, disturbance can increase beta-diversity through two alternative processes: divergent selection of species across environmental gradients, or through stochastic effects on species richness in local communities. In addition, the effect of disturbance on beta-diversity may depend on the rate of dispersal among communities. We tested these hypotheses by synthesizing results from 23 factorial-field experiments that manipulated local disturbance and dispersal in plant communities distributed broadly across North America and Europe. Using a null-model approach, we tested the extent to which disturbance and dispersal interactively create non-random patterns of beta-diversity after controlling for observed changes in local species richness. We then conducted a meta-analysis using a random-effects model to assess general patterns across experimental studies.
Disturbance and dispersal had opposing effects on beta-diversity. In some studies disturbance increased beta-diversity more than expected by chance, with overall trends suggesting divergent selection. Only one study showed evidence of convergent selection. In contrast, dispersal decreased observed beta-diversity, especially in disturbed communities. However, the effects of dispersal disappeared after controlling for observed changes in local richness. Our results suggest that disturbance can increase landscape level biodiversity through non-random processes, but acts synergistically with dispersal to homogenize species composition across a landscape. This study lends insights into how community assembly may be altered by changes in disturbance and dispersal – two processes heavily influenced by human-driven environmental change and relevant for habitat restoration.