The consequences of adult foraging success on the components of lifetime fitness in a semelparous,sit and wait predator

Summary We evaluated the role of adult foraging success in the lifetime fitness of female crab spidersMisumena vatia. Misumena are semelparous, sit and wait predators that hunt for insect prey on flowers, in this study primarily on inflorescences (umbels) of milkweedAsclepias syriaca. We used path analysis to integrate previously performed experimental and observational studies, thereby establishing the magnitude, correlations and causal relationships of key foraging and life history variables and their roles in lifetime fitness. A path proceeding from maternal hunting patch choice through maternal mass, clutch mass and number of dispersal-age young was the dominant element and explained a large part of the variation. Other paths that incorporated parasitism of the egg mass and predation of young leaving the nests made only small impacts on variation. No trade-offs were found, primarily because a single factor, maternal mass (a maternal effect) resulting from foraging success, provided major benefits for successive life history stages. Since differences in the numbers of eggs, egg loss and mortality at dispersal resulted almost entirely from differences in maternal mass, they are controlled by the maternal generation and, thus, are appropriately attributed to the lifetime fitnesses of the mothers, rather than to those of their offspring.     

Climate mediates the success of migration strategies in a marine predator

Individual behavioural specialisation has far‐reaching effects on fitness and population persistence. Theory predicts that unconditional site fidelity, that is fidelity to a site independent of past outcome, provides a fitness advantage in unpredictable environments. However, the benefits of alternative site fidelity strategies driving intraspecific variation remain poorly understood and have not been evaluated in different environmental contexts. We show that contrary to expectation, strong and weak site fidelity strategies in migratory northern elephant seals performed similarly over 10 years, but the success of each strategy varied interannually and was strongly mediated by climate conditions. Strong fidelity facilitated stable energetic rewards and low risk, while weak fidelity facilitated high rewards and high risk. Weak fidelity outperformed strong fidelity in anomalous climate conditions, suggesting that the evolutionary benefits of site fidelity may be upended by increasing environmental variability. We highlight how individual behavioural specialisation may modulate the adaptive capacity of species to climate change.     

r‐ and K‐selection in fluctuating populations is determined by the evolutionary trade‐off between two fitness measures: Growth rate and lifetime reproductive success

In a stable environment, evolution maximizes growth rates in populations that are not density regulated and the carrying capacity in the case of density regulation. In a fluctuating environment, evolution maximizes a function of growth rate, carrying capacity and environmental variance, tending to r‐selection and K‐selection under large and small environmental noise, respectively. Here we analyze a model in which birth and death rates depend on density through the same function but with independent strength of density dependence. As a special case, both functions may be linear, corresponding to logistic dynamics. It is shown that evolution maximizes a function of the deterministic growth rate r₀ and the lifetime reproductive success (LRS) R₀, both defined at small densities, as well as the environmental variance. Under large noise this function is dominated by r₀ and average lifetimes are small, whereas R₀ dominates and lifetimes are larger under small noise. Thus, K‐selection is closely linked to selection for large R₀ so that evolution tends to maximize LRS in a stable environment. Consequently, different quantities (r₀ and R₀) tend to be maximized at low and high densities, respectively, favoring density‐dependent changes in the optimal life history.