Amy Forsythe (Queen’s University)
Ecological and evolutionary consequences of individual heterogeneity
April 1st 12:30-1:30pm ET
Among-individual variation in vital rates, such as mortality and birth rates, exists in nearly all populations. While traditional life-history theory predicts that such individual heterogeneity will manifest as trade-offs between individual vital rates, accumulating empirical evidence reveals that positive covariances among vital rates are also prevalent across a wide variety of taxa. Research further suggests that individual heterogeneity scales up to influence population dynamics, however little is known about the effects of different kinds of individual heterogeneity on ecological and evolutionary processes. Here, we synthesize the existing literature into a single and comparatively straightforward framework with explicit terminology and definitions. We then apply this conceptual framework to develop age-structured models that compare the ecological and evolutionary consequences of individual heterogeneity in which intrinsic vital rates are permanent throughout an individual’s life (“fixed condition”) or can change at any time (“dynamic condition”). We find that heterogeneity can affect mean fitness in ways that depend on the sign of the covariance among intrinsic survival probabilities and birth rates, where a positive covariance leads to greater mean fitness in populations with individual heterogeneity structured as fixed condition, while a negative covariance (trade-off) favours populations with dynamic condition. These results emphasize the importance of not only considering among-individual variation in vital rates, but also the structure of that variation (positive or negative covariance, fixed or dynamic condition), when making predictions about the ecological and evolutionary dynamics of populations.