Effects of compositional heterogeneity and spatial autocorrelation on richness and diversity in simulated landscapes

Landscape structure plays a key role in mediating a variety of ecological
processes affecting biodiversity patterns, however, its precise effects
and the mechanisms underpinning them remain unclear. While the effects of
landscape structure have been extensively investigated both empirically,
and theoretically from a metapopulation perspective, the effects of
spatial structure at the landscape scale remain poorly explored from a
metacommunity perspective. Here, we attempt to address this gap using a
spatially explicit, individual-based metacommunity model to explore the
effects of landscape compositional heterogeneity and per se spatial
configuration on diversity at the landscape and patch level via their
influence on long-term community assembly processes. Our model simulates
communities composed of lineages of annual, asexual organisms living,
reproducing, dispersing, and competing within grid-based, fractal
landscapes which vary in their magnitude of spatial environmental
heterogeneity and their degree of spatial environmental autocorrelation.
Communities are additionally subject to temporal environmental fluctuation
and external immigration, allowing for turnover in community composition.
We found that compositional heterogeneity and spatial autocorrelation had
differing effects on richness and diversity and the landscape and patch
scales. We also note a slight negative effect of compositional
heterogeneity on the median total landscape population size.
Landscape-level diversity was driven by community dissimilarity at the
patch level and increased with greater heterogeneity, while landscape
richness was largely the result of the short-term accumulation of
immigrants and decreased with greater compositional heterogeneity. Both
richness and diversity decreased in variance with greater compositional
heterogeneity, indicating a reduction in community turnover over time.
Patch-level richness and diversity patterns appeared to be driven by
overall landscape richness and local mass effects, resulting in maximum
patch-level richness and diversity at moderate levels of compositional
heterogeneity and high spatial autocorrelation.