Competition indexes to compare environmental conditions for secondary consumers between different faunal assemblages

Abstract

The availability of resources and the competition with secondary consumer have been proposed as key limiting factor for the European human dispersals during Early and Middle Pleistocene. However, to determine the actual influence of these factors on the distribution of human populations it is necessary to quantify them and compare the values among different sites or environmental conditions. A standard method to measure competition intensity and resource availability in different assemblages is thus required. The ratio primary consumer biomass to secondary consumer biomass is commonly used to describe trophic conditions of a mammal community. However, this ratio is an oversimplification, since the feed habits and limitations of the sencondary consumers are not taken into account. We present different indexes to measure the intensity of competition between secondary consumers in faunal assemblages with a standard approach using a mathematical model based on Leslie Matrices. In this way, competition intensity may be compared between different faunal assemblages. The mathematical model provides sustainable densities for each secondary consumer species in an assemblage, taking into account the available prey and the competitors, while expected densities are estimated from allometric equations. We apply several indexes to these results relating estimated and expected densities, number of individuals and biomass for secondary consumers. The different indexes provide different information helpful to analyze competition intensity between secondary consumers. Comparing several faunal samples with these indexes would be a first step to get a standardized tool. Several methods to estimate the intensity of competition between secondary consumer in faunal assemblages are presented. These methods are based on the estimated densities obtained from a mathematical model, which standardizes the estimations of competition intensity allowing comparisons between different assemblages to be carried out. However, the faunal assemblages included in the comparison should be complete enough, i.e. representative of the living community, in order to make these estimations reliable.