Data from: Disturbance alters beta-diversity but not the relative importance of community assembly mechanisms

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.