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The density, weight and the biomass, weight distribution can be generated by the species, weight distribution together with density fluctuations : evidence from model species distributions in the Hymenoptera

Ulrich W.

Polish Journal of Ecology

1999

Vol. 47, no 1

87-101

This paper tests the hypothesis that the density - weight distribution of species assemblages may be generated alone by underlying weight dependent density fluctuations by constructing several model species - weight and density - weight distributions. The simulations revealed that indeed even a slight dependence of density fluctuation on body weight generated typical density - weight distributions with upper density boundaries and triangular shapes. Other ecological explanations, such as metabolic constrants or arguments based on fractal geometry, may therefore not be necessary to explain the pattern. In a second step of analysis the density - weight relationship was combined with various species - weight distributions (computed over log[2] weight classe) to show that in nearly all parameter settings steadily rising biomass distributions with a decline only towards the largest weight classes result. The generality of the equal biomass hypothesis is therefore rejected. A general model is developed to explain several of the patterns in density - weight and species - weight plots assuming only underlying weight dependent speciation and extinction rates and weight dependent density fluctuations.