DOI: 10.5061/dryad.j2qv8
title: Data from: Disturbance alters beta-diversity but not the relative importance of community assembly mechanisms

description: 1.Ecological disturbances are often hypothesized to alter community
 assembly processes that influence variation in community composition
 (β-diversity). Disturbance can cause convergence in community composition
 (low β-diversity) by increasing niche selection of disturbance-tolerant
 species. Alternatively, disturbance can cause divergence in community
 composition (high β-diversity) by increasing habitat filtering across
 environmental gradients. However, because disturbance may also influence
 β-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 β-diversity alone cannot be
 used to unambiguously discern the relative importance of community
 assembly mechanisms. 2.We compared β-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 β-diversity
 after controlling for differences in local community size and regional
 species abundances between unburned and burned landscapes. 3.Observed
 β-diversity was higher in burned landscapes. However, this pattern
 disappeared or reversed after controlling for smaller community size in
 burned landscapes. 4.β-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 β-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 fire-induced 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.
description: Species Composition
 DataAbundances of 43 woody
 plant species recorded in 93 0.05-ha (10 x 50 m) unburned and burned
 forest plots in the Missouri Ozarks, USA (N = 46 unburned plots, N = 47
 burned plots). The plots were located in two state parks: Ha Ha Tonka
 State Park and Lake of the Ozarks State Park. Abundance was measured as
 the number of individual stems greater than or equal to 2 cm at diameter
 breast height (1.3 m). Each row represents the abundance of a species in a
 plot.SpeciesCompositionData_DRYAD.csvPlot Environmental DataSoil and topographic variables measured in 93 0.05-ha (10 x 50 m) unburned and burned forest plots in the Missouri Ozarks, USA, from May-June 2012 (N = 46 unburned plots, N = 47 burned plots). The plots were located in two state parks: Ha Ha Tonka State Park and Lake of the Ozarks State Park. Soil variables include calcium, cation exchange capacity, exchangeable acidity, magnesium, neutralizeable acidity, organic material, particle size (clay, sand, and silt), nitrogen (ammonium and nitrate), pH, phosphorus, potassium, and texture. Topographic variables include aspect, elevation, and slope. Each row represents a plot.PlotEnvironmentalData_DRYAD.csv