Ecological Constraints Influence the Emergence of Cooperative Breeding When Population Dynamics Determine the Fitness of Helpers

Abstract

Cooperative breeding is a system in which certain individuals facilitate the production of offspring by others. The ecological constraints hypothesis states that ecological conditions deter individuals from breeding independently, and so individuals breed cooperatively to make the best of a bad situation. Current theoretical support for the ecological constraints hypothesis is lacking. We formulate a mathematical model that emphasizes the underlying ecology of cooperative breeders. Our goal is to derive theoretical support for the ecological constraints hypothesis using an ecological model of population dynamics. We consider a population composed of two kinds of individuals, nonbreeders (auxiliaries) and breeders. We suppose that help provided by an auxiliary increases breeder fecundity, but reduces the probability with which the auxiliary becomes a breeder. Our main result is a condition that guarantees success of auxiliary help. We predict that increasing the cost of dispersal promotes helping, in agreement with verbal theory. We also predict that increasing breeder mortality can either hinder helping (at high population densities), or promote it (at low population densities). We conclude that ecological constraints can exert influence over the evolution of auxiliary help when population dynamics are considered; moreover, that influence need not coincide with direct fitness benefits as previously found. K E Y W O R D S :Alloparental care, helpers-at-the-nest, inclusive fitness, kin selection, mathematical model, sociality.In many cooperatively breeding species, nonbreeding individuals (i.e., auxiliary individuals) postpone or forgo their own reproduction to increase the fecundity of others. Cooperative breeders include a taxonomically broad set of species that occur in a wide range of environments (Jennions and MacDonald 1994;Cockburn 1998;Leadbeater et al. 2011; Wong and Balshine 2011). Thus, the help provided by nonbreeding auxiliaries represents one of the most diverse forms of cooperation in nature.The adaptive significance of auxiliary help is often explained in terms of its direct and indirect fitness benefits (Wiley and Rabenold 1984;Brown 1987;Heinsohn and Legge 1999; CluttonBrock 2002;Griffin and West 2002). Direct benefits of help accrue through the production of descendant offspring. These are realized, for example, when a helpful auxiliary gains valuable parenting experience (Skutch 1961), or when a helpful auxiliary contributes to the formation of a larger, more productive group that it will inherit at some later date (Wiley and Rabenold 1984;Kokko et al. 2001; Clutton-Brock 2002). Indirect benefits of help accrue through increased production of related, nondescendant offspring. For indirect benefits to play a role in the emergence and maintenance of auxiliary help, helpers must be able to associate with breeding kin (Griffin and West 2002). While both direct and indirect fitness benefits likely promote the evolution of helpful behavior in cooperatively breeding species (Clutton-Brock 2009), we ch...

Modelling effects of nonbreeders on population growth estimates

“…In contrast to the negative frequency-dependent effects of nonbreeders in our models, helpers have positive effects on breeding. Cooperative breeding and helping behaviour is often closely linked with family structure and kinship, prompting different types of models and questions than ours (Hatchwell 2009;McLeod & Wild 2013).…”

Evolution of delayed dispersal and subsequent emergence of helping, with implications for cooperative breeding

“…Should that same individual not compete successfully, it may still survive to compete as a disperser in the next time period. In this way, an individual who delays dispersal is no worse off than one who did not (the absence of opportunity cost is common in models of cooperative breeding in stable habitats (McLeod and Wild, 2013)). In fact, delaying dispersal naturally affords individuals the opportunity to compete for vacancies twice: on its natal territory the first time, and elsewhere the second time.…”

“…Models of the evolution of cooperative breeding often assume an individual's tendency to delay dispersal is linked to its tendency to help (Motro, 1993;Pen and Weissing, 2000;Leggett et al, 2012;McLeod and Wild, 2013;Wild and Koykka, 2014). Those that have sought to separate the link between staying and helping have either treated relatedness as a fixed parameter (Kokko and Johnstone, 1999;, have neglected the possibility that relatedness builds within social groups while placing severe limits on subordinate numbers (Koykka and Wild, 2015), or have focused on modelling delayed dispersal only (Kokko and Lundberg, 2001;Kokko and Ekman, 2002).…”

“…Evidence also suggests that the evolution of delayed dispersal preceded the emergence of helping in certain eusocial insects (Thorne, 1997). Our approach, therefore, is to separate an individual's dispersal decision from its decision to help, in contrast to many previous models (Motro, 1993;Pen and Weissing, 2000;Leggett et al, 2012;McLeod and Wild, 2013;Wild and Koykka, 2014). We implement this approach by constructing and analysing a model for the evolution of delayed dispersal (Model I).…”

Inclusive-fitness logic of cooperative breeding with benefits of natal philopatry

“…It should be noted, however, that linking dispersal and helping, as we have done here, is known to underestimate the importance of ecological conditions (e.g. limited available habitat) in the emergence of help [30]. …”