The importance of habitat heterogeneity, biotic interactions and dispersal in abundance–occupancy relationships

Summary1 In simple microcosm systems, the form of interspecific abundance–occupancy relationships has been found to be dependent on biotic interactions. However, in more complex systems such effects may be obscured by those of habitat heterogeneity. Here we test this proposal using laboratory microcosms of protists and bacteria. 2 The independent effects of species interactions and heterogeneity were tested by comparison of the abundance–occupancy relationship formed in multiple habitat patch systems containing all species together, with that relationship formed by combining data from equivalent systems containing each protist species alone and between homogeneous and heterogeneous environments. 3 There was more residual variation about positive interspecific abundance–occupancy relationships formed in heterogeneous environments in interacting and non‐interacting communities as the majority of species were more restricted in the number of patches they could occupy compared to homogeneous landscapes. 4 Abundance–occupancy relationships in interacting communities were better defined than those in non‐interacting communities. The inclusion of interspecific interactions caused a reduction in the abundance and occupancy of the majority of species and changed the position of species within the relationship. 5 Our results show that biotic interactions influence the abundance–occupancy relationships even with imposed environmental heterogeneity. However, in heterogeneous environments, for some species these processes occurred in fewer patches, causing increased residual variation about positive interspecific abundance–occupancy relationships compared to homogeneous environments.