Evol Ecol Res 11: 253-263 (2009)     Full PDF if your library subscribes.

Spite, egotism, population stability, and resource conservation

William L. Vickery1 and Joel S. Brown2

1Département des Sciences biologiques et Groupe de recherche en écologie comportementale et animale, Université du Québec à Montréal, Montréal, Québec, Canada and 2Department of Biological Sciences, University of Illinois at Chicago, Chicago, Illinois, USA

Correspondence: W.L. Vickery, Département des Sciences biologiques et Groupe de recherche en écologie comportementale et animale, Université du Québec à Montréal, C.P. 8888, Succ. ‘Centre-Ville’, Montréal, Québec H3C 3P8, Canada.
e-mail: vickery.william@uqam.ca


Questions: What effects does the presence of spiteful behaviour (a behaviour that risks harm to the actor in order to harm others) within a population have on population dynamics? Can these population-level effects influence interactions with prey? Do changes in prey abundance have feedback effects on the frequency of spiteful behaviour? Does altruism (a behaviour that helps others at the risk of harming the actor) also have population-level effects?

Mathematical methods: A game theory model of the evolution of spite within a population is combined with a model of predator–prey dynamics.

Key assumptions: Our analysis applies to cases where spite reduces individual fitness without destroying resources (prey). Predators, which may be spiteful, consume prey with a type II functional response. Prey experience logistic growth. Predator growth depends on prey consumption.

Predictions: If spite can invade a population, the resulting conflict within the population reduces its consumption of prey and thus lowers prey mortality. This results in an apparent conservation of resources. This reduction in prey consumption can increase the stability of the predator–prey interaction. Surprisingly, the addition of spite to a predator population may increase its equilibrium density at the predator–prey equilibrium. Through its effect on population dynamics, spite can lead to an interaction between evolutionary and ecological dynamics resulting in an evolutionarily stable equilibrium with a mixture of spiteful and non-spiteful strategies. Behaviours whose harm to others exceeds their benefits to the actor can also stabilize predator–prey interactions. Altruism (a behaviour that risks harm to the actor in order to benefit others) can have the opposite effect of spite at the population level.

Keywords: altruism, egotism, natural selection, population size, population stability, resource conservation, spite.

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