Intraspecific competition in a social spider

Authored by K Ulbrich, JR Henschel

Date Published: 1999

DOI: 10.1016/s0304-3800(98)00180-x

Sponsors: No sponsors listed

Platforms: C++

Model Documentation: Other Narrative Mathematical description

Model Code URLs: Model code not found

Abstract

An individual-based model was developed to investigate the population dynamics of a permanently-social spider, Stegodyphus dumicola (Eresidae), in relation to intraspecific competition for food. This further develops our initial model that demonstrated that individual variability in body mass causes contest competition and is based on it. This confirmed field observations. In the present study, we examined whether intraspecific contest competition for food could be a mechanism for density regulation in S. dumicola. We investigated the consequences of contest competition on the individual variability in body mass as well as on the individual fitness of female spiders. Results demonstrate that colony size stabilises above a threshold of food level. At low food levels the risk of colony extinction is high because only few individuals survive and reproduce. Contest competition for food leads to high variance in body mass under conditions of food scarcity. Those variances tend to decrease with increasing food resources and a threshold of food level separates ranges of high and low variances. Model results indicate that individual females differ significantly by their fitness. An optimum of fitness was found at intermediate food levels. Results suggest that contest competition is a mechanism of density regulation in spider societies which stabilises colony size as well as variability in body mass and fitness. (C) 1999 Elsevier Science B.V. All rights reserved.

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differentiation