Analysis of species abundance patterns in assemblages with relatively large number of species has been an important issue in community ecology for several decades. Following Preston's pioneering work, Sugihara proposed a rondel to account for such patterns in a diverse range of communities, which has been given further support from analyses of recent data that are considered to be of particularly high quality. This paper re-examines Sugihara's approach and points out that there has been confusion and misunderstanding among workers as to the exact nature of his widely- publicised hypothesis. In particular, the 'fixed ratio' division cannot be considered as an expected (average) pattern of the triangular assumption; they represent fundamentally different entities. Further, Tokeshi's Random fraction model should not be treated as synonymous with Sugihara's fixed division model. The RF model has its own identity as a niche apportionment model and can account for patterns in some species-rich assemblages. With this background, this paper proposes a new niche apportionment model to explain relative abundance patterns in ecological communities, termed the Power fraction model. The PF model envisages that the probability (p) of selection for a subsequent division is positively but weakly related to niche sizes/abundances (x) of species as a power function (pαx(k) where 0 ≤ k ≤ 1.0; i.e. niche division/invasion is more likely in species with high abundance/large niche) and that division occurs with any ratio (i.e. a barrier to split a species' population may occur anywhere in the species' range), with the RF model representing an extreme case on the spectrum of the PF model. The Power fraction model with k ~ 0.05 or k ~ 0-0.2 demonstrates a good fit to a miscellany of data from species-rich assemblages. The PF model is not restrictire in terms of division ratios, and can be framed as either a community-specific or a global explanation of patterns. Thus, the new model is more flexible and realistic from ecological and evolutionary points of view and offers a possibility of cross-community comparisons within a uniform, integrative framework.
All Science Journal Classification (ASJC) codes
- Ecology, Evolution, Behavior and Systematics