Professor Columbia University New York, NY, United States
Abstract: Recent theoretical studies have shown that intraspecific trait variability (ITV) can foster or hinder coexistence. Most of these studies have focused on the effects of ITV on niche differences and competitive exclusion while neglecting an ecological factor that shapes trait variation: environmental heterogeneity. Spatial and temporal environmental heterogeneity are ubiquitous and lead to diversifying selection, a force that generates and maintains intraspecific variation. ITV can come from genetic variation, plasticity (the correlation within a genotype of phenotype with environment), or bet- hedging (intra-genotypic trait variation that is stochastic with respect to the environment). Although there has been much theoretical attention to plasticity in the ecology literature, few studies have examined the evolution of plasticity through ecological mechanisms: the impact of competition or environmental favorability. We seek to bridge this gap by modeling the ecological conditions under which plasticity evolves and answer: 1) What factors limit the evolution of plasticity? 2) What limits the degree of plasticity? and 3) Under what conditions do we see multiple optimum strategies of ITV versus a single strategy? We follow the modeling structure of Botero et al. (2015), which present three strategies for coping with environmental heterogeneity and favorability in a multi-generational model: bet-hedging, adaptation, or plasticity. This model used simulation over various rates of environmental variation over time. We advance this framework by using analytical methods to incorporate spatial and temporal heterogeneity. First, we find that plasticity is favored over both bet-hedging and no plasticity under almost any structure of spatial heterogeneity. This compares to the temporal case (as explored by Botero et al., 2015), where plasticity evolves only when temporal variation is slow. However, the degree of optimal plasticity (slope of the reaction norm) is narrowly constrained by the degree of environmental heterogeneity. Even with no inherent costs to plasticity, it does not benefit individuals to be infinitely plastic. We have not yet found indications of multiple optima in the case of purely spatial heterogeneity but are now implementing a spatial and temporal model to see if there are multiple optimal strategies that could lead to coexistence.
