Evol Ecol Res 13: 253-267 (2011)     Full PDF if your library subscribes.

Scarce resources, risk sensitivity, and egalitarian resource sharing

Emanuel A. Fronhofer1, Henrik Pasurka1, Oliver Mitesser2 and Hans Joachim Poethke1

1Field Station Fabrikschleichach, University of Würzburg, Rauhenebrach, Germany and 2Universitäts- und Landesbibliothek, Technische Universität Darmstadt, Darmstadt, Germany

Correspondence: E.A. Fronhofer, Field Station Fabrikschleichach, University of Würzburg, Glashüttenstr. 5, D-96181 Rauhenebrach, Germany.
e-mail: fronhofer@biozentrum.uni-wuerzburg.de


Background: Some recent findings in social spiders appear to be at odds with risk-sensitive foraging theory.

Question: Can egalitarian resource sharing be explained by a simple risk-sensitive foraging model that includes density dependence?

Mathematical method: A dynamic model of a population of individually foraging animals that breed in groups and share food for survival and reproduction. To derive conditions for egalitarian group formation, the model minimizes the amount of resources needed per capita at population-dynamic equilibrium. It combines density-dependent population growth with evolutionary dynamics, so extending classical models of risk-sensitive foraging.

Key assumptions: Fitness is a non-linear function of an animal’s energy state. Egalitarian resource sharing reduces variance in foraging success. Population growth is density dependent. The model is designed to be general enough to apply to a wide range of organisms, from insects and arachnids to birds and mammals.

Predictions: Our model predicts optimal group sizes – which minimize the amount of resources needed per capita at population equilibrium – and yields a more complex evolutionary pattern than the simple dichotomy of risk-prone or risk-averse behaviour. Even in saturated environments with severe competition – and, consequently, low food availability – high variance in foraging success will favour group formation.

Keywords: egalitarian groups, resource sharing, risk-sensitive foraging, social spiders.

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