Experimentally fragmented communities are more aggregated

Summary

• 1
  I investigated the effect of habitat fragmentation on species richness, aggregation and community dominance and composition for predators and non-predators at two spatial scales. Two independent experiments were considered, both using a microecosystem of microarthropods inhabiting moss patches.
• 2
  In the study at a larger spatial scale, species richness was lower in the more fragmented habitats, due possibly to the lack of a metapopulation ‘rescue effect’. In the smaller-scale study, species richness was again lower in the fragmented habitats, but did not depend on whether a connecting moss ‘corridor’ was complete or broken. Fragmentation affected predators more than non-predators in both studies.
• 3
  The degree of aggregation both within and among habitat patches was greater in the fragmented species-poor communities, especially for predators. Theory suggests that lower migration in the fragmented communities may either (a) lead to greater aggregation and lower species richness simultaneously, or (b) greater aggregation, leading to increased dominance and hence lower species richness.
• 4
  There was no clear association between community dominance and species richness.
• 5
  Community composition was affected by fragmentation in both studies, but knowledge of trophic level and mite developmental stage was insufficient to predict these effects.