Altruism and the evolution of resource generalism and specialism

The evolution of resource specialism and generalism has attracted widespread interest. Evolutionary drivers affecting niche differentiation and resource specialization have focused on the role of trade-offs. Here, however, we explore how the role of cooperation, mediated through altruistic behaviors, and classic resource–consumer dynamics can influence the evolution of resource utilization. Using an evolutionary invasion approach, we investigate how critical thresholds in levels of altruism are needed for resource specialization to arise and be maintained. Differences between complementary (essential) and substitutable resources affect the evolution of resource generalists. The strength of resource preferences coupled with the levels of altruism are predicted to influence the evolution of generalism. Coupling appropriate evolutionary game and ecological dynamics lead to novel expectations in the feedbacks between social behaviors and population dynamics for understanding classic ecological problems.

the adaptive dynamic approach, this invasion approach considers evolutionary conditions when mutations are finite and only sometimes small (Bonsall and Mangel 2009). Our analysis begins by defining an ecological model and thus creating the background in which the evolution of can resource utilisation occur. We establish using the evolutionary game and the ecological dynamics (eqn 1-8). Next an appropriate measure of fitness is defined. When strategies are rare and ecological processes such as density dependence operate, this measure of fitness is the per capita population-level growth rate (e.g., 1 N dN dt ). Finally, changes in fitness with respect to specific life-history traits allow both the origin and maintenance of resource utilisation strategies to be explored.

A Evolution of Resource Specialization
The dynamics of the resource utilisation are dependent on both the proportion of cooperators in a population given by the replicator equation (equation 2) and the dynamics of the ecological interaction between specialist consumers and a resource (described by equations 4-5). Under linear resource consumption rate (f (β i , x) = β i x i ) (equation 7), the population-level growth (fitness) of a novel rare consumer strategy (x i , M i ) can be found linearizing the equations (eqn 2, 4-5) around the equilibirum resource density (N * ), finding the partial derivatives for the novel invading strategy and then taking the determinant of the resulting Jacobian matrix (Pielou 1977): where λ is the measure of fitness and N * is the equilibrium abundance of the resource in the absence of the novel consumer (M i ) strategy. The entries in this matrix are the partial derivatives associated with the way in which the novel consumer strategy utilises the resource and the dynamics of the cooperators within this novel strategy. The fitness measure (λ) is obtained by solving the characteristic equation of A which is given by: If the difference between mutant and resident strategy is small such that selection is weak then λ is sufficient small and terms involving λ 2 are negligible so fitness is then: .

(A.4)
Contours of fitness associated with resource specialization based on equation (A.4) are illustrated in Figure 1.

B Evolution of Resource Generalism
The evolution of resource generalism proceeds in a similar way by defining both the ecological dynamics and the measure of fitness and then evaluating the changes in fitness.

a) Substitutable Resources
On substitutable resources, the dynamics of the consumers are determined by equation (9) where a preference for particular resources leads to linear increases or decreases in resource utilisation.
Resources are then entirely substitutable. As before the dynamics of cooperation is determined by the replicator equation (eqn 2). Analysis proceeds by modifying the appropriate terms in the matrix (equation A.1). In particular, (when there are two substitutable resources) the partial derivatives associated with the ecological dynamics are now: where q j is the preference for the j th resource. Again taking the determinant of this matrix (B.1) (under linear consumption -equation 7) provides a measure of the fitness of the generalist strategy on substitutable resource. Applying the weak selection limit yields: . (B.2) Figure 3 illustrates the fitness contours associated with the evolution of resource utilization on substitutable resources.

b) Complementary Resources
On complementary (essential) resources the consumer dynamics are specified by equation (10).
Modifying the terms in the invasion matrix (equation A.1) leads to the following set of partial derivatives: Solving the characteristic equation from the determinant of equation B.3 under the weak selection limit gives the fitness of a generalist strategy on two complementary resources. This yields: .
(B.4) Figure 4 illustates the fitness contours associated with this expression.