Abstract
Size-based dominance hierarchies influence fitness, group size and population dynamics and link dominance structure to evolutionary and ecological outcomes. While larger individuals often gain dominance, social status may influence growth and size in return, resulting in feedbacks among status, growth and size. Here, we present two models evaluating how these feedbacks influence the emergence of size structure in a dominance hierarchy. In the first, size influences competition for food and investment in suppressing growth of groupmates. Stable size differences emerged when suppression was greatest for similarly sized individuals and size had little effect on competition for food. The model predicted size divergence when size strongly affected competition for food. In the second model, we used a dynamic game to solve for optimal investment in growth suppression as a function of size structure. Investment in growth suppression was favoured only when dominants and subordinates were similar in size, generating size ratios different than those expected by chance. Variation in the feedbacks among growth, size and status can explain variation in emergent size structure of dominance hierarchies and its consequences for conflict within groups.This article is part of the theme issue ‘The centennial of the pecking order: current state and future prospects for the study of dominance hierarchies’.
Highlights
Dominance is strongly correlated with relative body size, with larger individuals dominant to smaller ones (e.g. [1,2,3])
This size structure can influence conflict within groups (e.g. [4]), the maximum sizes of groups [5,6] and the population dynamics of organisms that live in size-structured hierarchies [5,7,8]
Dominance results from repeated agonistic interactions among individuals [9] and, as size can determine resource holding potential [10,11], large size may allow individuals to gain and maintain status through such interactions
Summary
Dominance is strongly correlated with relative body size, with larger individuals dominant to smaller ones (e.g. [1,2,3]). Relative size influences success at size-based competition for food and ability to suppress partner growth. Because optimal strategies could change given absolute and relative size and temporal proximity to reproductive events, as well as depend on the expected strategies of partners, we used a discrete stochastic dynamic game (Model 2) to predict the size ratios at which dominant and subordinate individuals attempt to suppress partner growth and the consequences of these policies on size ratios at the evolutionary stable strategy (ESS). The values of the parameters that influence the opportunity and ability to suppress partner growth ( y, h, u, q, z and C ) must be sufficiently large that rÃu exists. To focus on growth suppression, we assume for Model 2 that k = 0, so that there is no size-based competition for food and θ = 1 for both individuals. In equation (2.9), ε is the length of the discrete time step. 5 G is a continuous time growth function that depends on the events occurring in a given time step: Ambs À Dms
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