The effect of competition on shared food resources in carnivore guilds

Abstract

The study aims to develop a model for quantifying competitive relations within carnivore guilds. Previous methods were able to calculate competition or niche overlap, but were not applicable to the entire guild. They only permit a pairwise view among the guild members and neither the amount of the resource nor the role of the resource in the diet of each guild member is considered.The model we introduce is based on the theory of competition-free carrying capacity (CFCC). This CFCC value represents the maximum population size under the assumption that the guild member would exploit its essential resources alone in the absence of competitors. Because the actual population size is known, the percentage to which the guild member exploits its CFCC can be calculated. The loss of CFCC to other guild members is called competition effect. The effects can be calculated by a set of equations and the characterization of each guild member by its actual population size, prey mass spectrum, and daily meat intake.The model is applied to the large carnivore guilds in the Serengeti (Tanzania) and the Kruger National Park (South Africa) to show how a guild of large carnivores is structured. The guild structures of the Serengeti and the Kruger National Park are different with respect to the roles the guild members play. The spotted hyena (Crocuta crocuta) plays the dominant role by exploiting most of its CFCC and having strongest competition effects to the other guild members in the Serengeti. In the Kruger guild, this position is occupied by the lion (Panthera leo).