Patterns of the Abundance of Species: A Comparison of Two Hierarchical Models

Abstract

We compare two hierarchical, predictive models that explain the log-series pattern of distribution of species abundances. The Sequential Breakage Model (SBM) is based on the appropriation of fragments from the community niche volume, while the Habitat-Based Model (HBM) assumes a contemporary use of environmental volume by species acting in different scales. A detailed analysis of assumptions of the SBM indicates that its predictions rely on the establishment of a link between the niche overlap and abundance of species. We show that this link is inadequate and may be incorrect. The agreement between the abundances predicted by the SBM and the abundances observed in assemblages composed of three species cannot be thus considered as validation of this model. We conclude, however, that such an agreement supports the Habitat-Based Model. The predictions of the HBM are generated from a realistic combination of commonly observed ecological phenomena (habitat heterogeneity and patchiness), species properties (differentiated degrees of specialization), and the assumed relation between them. The latter model is sensitive to habitat heterogeneity. This difference may be used in testing both models under different ecological conditions and at various scales.