1. Environmental heterogeneity influences biodiversity patterns such as species richness and
community composition, but we do not know how it shapes community structure in terms of the
number of rare and abundant species. This question is particularly relevant to modified landscapes
such as agro-ecosystems, where intensive management creates highly homogeneous landscapes,
which often lead to loss of rare taxa and dominance by a few aggressive species.
2. It can be difficult to evaluate the effects of management on communities in different localities
due to regional differences in species richness and composition. Because species abundance distributions
(SADs) express assemblage structure in comparable units, they can be used to characterize
communities irrespective of species composition, and for this reason provide a novel means of
assessing the effects of management.
3. We analysed the SADs of weed communities across a gradient of environmental heterogeneity
generated by different management treatments. We tested the hypothesis that environmental
heterogeneity promotes multimodality in SADs by comparing observed patterns with those
predicted for simulated random samples from homogeneous communities.
4. Observed SADs from a homogeneous environment did not deviate from predictions. By contrast,
SADs from increasingly heterogeneous environments were progressively and consistently
multimodal.
5. These results demonstrate that environmental heterogeneity, resulting from variation in
management treatments, leaves a signature on the SAD.
6. Synthesis and applications.
Our study shows that Species Abundance Distributions are informative
indicators of environmental heterogeneity in modified landscapes. Weed communities include
both rare species, which are often of conservation interest and pose little threat to crops, and
abundant species, which can be problematic. Our analysis suggests that creating environmental
heterogeneity by varying management treatments across the landscape can be an effective way of
promoting biodiversity and decreasing the abundance of problematic species.