Effects of large-scale disturbance on metacommunity structure of terrestrial gastropods: temporal trends in nestedness

Distributions of species often exhibit nested structure, such that assemblages at species-poor sites are proper subsets of taxa at more species-rich sites. Traditionally, this has been viewed as a large-scale biogeographic pattern and treated implicitly as static from a temporal perspective. Nonetheless, recent work suggests that nestedness may arise at multiple spatio-temporal scales. A 13-year data set encompassing the effects of two large-scale natural disturbances (hurricanes Hugo and Georges) on terrestrial gastropod assemblages was used to test the hypothesis that changes in species composition resulting from disturbance alter the degree of nestedness exhibited over time at two spatial scales. Gastropod assemblages were least nested immediately following disturbance, and nestedness increased thereafter. Although land-use history influenced the degree of nestedness, trajectories of nestedness following disturbance were similar irrespective of disturbance history or hurricane identity. The effects of hurricanes with respect to nestedness of terrestrial gastropods may be general and predictable, even though species respond to hurricanes in disparate fashions. By damaging some localities within the forest more severely than others, a hurricane dismantles extant patterns of species composition and severs connections among sites, as inhospitable microclimatic conditions limit dispersal of gastropods. As time passes and the forest canopy regenerates, conditions ameliorate, and movement among sites becomes more frequent. Thus, a conclusion based on a single time period may not characterize the study system in general. Consequently, explanations for nested structure that incorporate variability in ecological as well as evolutionary time will improve the applicability and comparability of nested subsets analysis across study systems.