Evolution of Helping and Harming in Viscous Populations When Group Size Varies

Abstract

JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.. Online enhancement: appendix.abstract: Recent years have seen huge interest in understanding how demographic factors mediate the evolution of social behavior in viscous populations. Here we study the impact of variation in group size on the evolution of helping and harming behavior. Although variation in group size influences the degree of relatedness and the degree of competition between groupmates, we find that these effects often exactly cancel, so as to give no net impact of variation in group size on the evolution of helping and harming. Specifically, (1) obligate helping and harming are never mediated by variation in group size, (2) facultative helping and harming are not mediated by variation in group size when this variation is spatial only, (3) facultative helping and harming are mediated by variation in group size only when this variation is temporal or both spatial and temporal, and (4) when there is an effect of variation in group size, facultative helping is favored in big groups and facultative harming is favored in little groups. Moreover, we find that spatial and temporal heterogeneity in individual fecundity may interact with patch-size heterogeneity to change these predictions, promoting the evolution of harming in big patches and of helping in little patches.

Evolution of Helping and Harming in Heterogeneous Groups

“…Setting the left-hand side (LHS) of inequality (3) equal to 0, we find the condition where the actor is indifferent with regards to helping/harming slightly more versus slightly less. This condition can be re-arranged into the form C/B = A, where A defines the potential for helping (Rodrigues and Gardner 2012;cf. Gardner 2010) and −A defines the potential for harming (Rodrigues and Gardner 2012).…”

“…This condition can be re-arranged into the form C/B = A, where A defines the potential for helping (Rodrigues and Gardner 2012;cf. Gardner 2010) and −A defines the potential for harming (Rodrigues and Gardner 2012). Assuming that the life-for-life relatedness of a secondary recipient is less than that of the actor (ρ S < 1), then A = (ρ P − ρ S )/(1 − ρ S ).…”

“…Most of this literature has assumed that populations are homogeneous in individual quality, other than differences relating to sex (but see Frank , , ; Johnstone ; Rodrigues and Gardner , ). However, within‐group heterogeneities are likely to be important for the evolution of social behavior, especially in determining which individuals enact which behaviors (Hamilton ; Alexander ; Michener and Brothers ; West‐Eberhard ; Milinski ; Rubenstein ; Craig ; Alexander et al ; Pamilo ; Crozier and Pamilo ; West‐Eberhard ; Bourke ; West et al ).…”

Ecological and demographic correlates of cooperation from individual to budding dispersal

“…For example, we might consider populations in which group size varies (e.g. Rodrigues & Gardner, 2013a) or cases in which group members differ in their quality (e.g. Rodrigues & Gardner, 2013b).…”

Demography, life history and the evolution of age‐dependent social behaviour

“…Therefore, I hold the costs ( C 's) and benefits ( B 's) constant across the different social interactions. To investigate the direction and intensity of kin selection acting on the expression of age‐dependent social behaviour, I focus on the potential for helping, which gives the highest cost‐to‐benefit ratio that still allows for the evolution of the social behaviour (Rodrigues & Gardner, ). We find the potential for helping by setting the LHS of Hamilton's rule to zero, and rearranging, to obtain A ij = C ij / B ij , where A ij is the potential for helping.…”