Disturbance alters beta‐diversity but not the relative importance of community assembly mechanisms

Abstract

Summary1. Ecological disturbances are often hypothesized to alter community assembly processes that influence variation in community composition (b-diversity). Disturbance can cause convergence in community composition (low b-diversity) by increasing niche selection of disturbance-tolerant species. Alternatively, disturbance can cause divergence in community composition (high b-diversity) by increasing habitat filtering across environmental gradients. However, because disturbance may also influence b-diversity through random sampling effects owing to changes in the number of individuals in local communities (community size) or abundances in the regional species pool, observed patterns of b-diversity alone cannot be used to unambiguously discern the relative importance of community assembly mechanisms. 2. We compared b-diversity of woody plants and inferred assembly mechanisms among unburned forests and forests managed with prescribed fires in the Missouri Ozarks, USA. Using a null-model approach, we compared how environmental gradients influenced b-diversity after controlling for differences in local community size and regional species abundances between unburned and burned landscapes. 3. Observed b-diversity was higher in burned landscapes. However, this pattern disappeared or reversed after controlling for smaller community size in burned landscapes. 4. b-diversity was higher than expected by chance in both landscapes, indicating an important role for processes that create clumped species distributions. Moreover, fire appeared to decrease clumping of species at broader spatial scales, suggesting homogenization of community composition through niche selection of disturbance-tolerant species. Environmental variables, however, explained similar amounts of variation in b-diversity in both landscapes, suggesting that disturbance did not alter the relative importance of habitat filtering. 5. Our results indicate that contingent responses of communities to fire reflect a combination of fireinduced changes in local community size and scale-dependent effects of fire on species clumping across landscapes. 6. Synthesis. Although niche-based mechanisms of community assembly are often invoked to explain changes in community composition following disturbance, our results suggest that these changes also arise through random sampling effects owing to the influence of disturbance on community size. Comparative studies of these processes across disturbed ecosystems will provide important insights into the ecological conditions that determine when disturbance alters the interplay of deterministic and stochastic processes in natural and human-modified landscapes.

Does functional homogenization accompany taxonomic homogenization of British birds and how do biotic factors and climate affect these processes?

“…The observed relationships of changes in taxonomic and functional turnover with climatic variance, year‐to‐year predictability, long‐term trends, and extreme events measures at various scales show that more negative changes in turnover, that is, homogenization, occur in unstable environments, while a stable environment maintains spatial turnover and promotes more positive changes. This contrasts with the findings of Martin and Ferrer (2015), who showed that for Mediterranean birds, mammals, amphibians, and reptiles, temporally variable environments maintained higher spatial turnover; however, it supports the suggestion that environmental disturbances contribute to community homogenization through niche selection of disturbance‐tolerant species (Myers, Chase, Crandall & Jiménez, 2015). Environmental stability–spatial turnover relationships appear to be sparse within the literature, and the results found in the present paper open up a potential area of future research to further investigate this relationship.…”

Herbivory and presence of a dominant competitor interactively affect salt marsh plant diversity

“…However, we also found that RC metric was higher than expected at random when S. densiflora was removed, indicating an increased importance of processes that drive community divergence far from the null model expectation (see Myers et al. ). In this context, in a recent work, Guo et al.…”

Disturbance differentially affects alpha and beta diversity of ants in tallgrass prairies

“…In short, the observed b diversity values (b obs ) were compared to b diversity values generated from null models (b null ) and standardized differences between b obs and b null were used as independent estimates of b diversity (b dev ). To determine whether b obs diversity and b dev -diversity differed between the harvest and control treatments, we performed non-parametric analysis of variance based on distance to centroid values (i.e., homogeneity of multivariate dispersion tests) with the betadisper function in R (Anderson et al 2011, Myers et al 2015. First, we created an abundance-based (Bray-Curtis) dissimilarly matrix between all possible paired sites.…”

“…While the removal of biomass was conducted similarly across all experimental sites, repeated harvesting may have altered environmental conditions in ways that allowed for differential rates of mortality, colonization, and varied strength of competition for newly open space, resulting in large differences in community composition among harvested sites (Myers et al 2015). Dissimilarity in ant community composition was largely driven by rare species (e.g., B. depilis, F. incerta, and M. americana) and small-sized nesters (e.g., M. fracticornis and F. vinculans).…”