How does extreme predation risk impact antipredator behavior in birds?
Variation in predation risk can drive plastic and evolved behaviors and physiology. This can impact predator-prey dynamics, population persistence, and evolutionary trajectories. However, little is known about how predator-driven natural selection in recently-diverged populations acts along ecological gradients, despite such an approach’s potential for illuminating the impacts of predation.
The Behavioral Complexity Lab is continuing work on predator-driven behavior of tropical understory birds. After a short hiatus to focus on the Hawaii VINE Project, we are jump-starting work that takes advantage of (1) a “natural” experiment created during the creation of the Panama Canal when Barro Colorado Island (BCI) was isolated from the mainland, and (2) a set of 21 forest plots across the Isthmus of Panama. Our foundational work using meta-analysis spanning 80 years of data has detected divergent age-specific selection between island and mainland sites, with high adult and low nest survival on BCI compared to the mainland. Further work examined parental responses to age-specific mortality risk along the gradient by presenting models of adult/offspring predators at nests and found evidence of suppression of antipredator behavior, suggesting how low sensitivity of parents to predators may positively impact population persistence in predator-high environments. The Behavioral Complexity Lab will be conducting additional, short experiments to examine how parents assess proximate predation risk in different environments. We are also continuing work on hormonal stress in response to proximate predation risk, an avenue of research that is sorely neededif we are to understand the mechanistic basis of antipredator responses in organisms with differing life-histories.
What is the impact of behavior on patterns of predator-driven natural selection?
Because current phenotypic variation is often already constrained by natural selection, it is difficult to understand how natural selection acts on phenotypes that may fall outside of the current trait distribution. This prevents understanding as to how selection may act on novel trait values. In unpiiblished work, we explored how selection operates on avian nest phenotypes in Panama. We manipulated (outside of existing phenotypic space) two traits along a nest predation-risk gradient in Panama: egg color and nest decoration (moss added by the parents) and discovered evidence of correlational selection–or selection acting on combinations of traits–acting on these traits. Selection on both decorative moss and egg maculation was similar at high and low nest predation sites. However, at the high predation site, natural nests were positioned at an adaptive optimum, despite their reduced apparent survival ( in preparation for Evolution), suggesting that parents are behaviorally responding to–and mitigating–strong selection by nest predators by adding moss to nests.
Currently, with collaborators, we are using two long-term data sets (10+ years) of tropical birds to investigate the shape of natural selection acting on nests (with Emily DuVal, in preparation; and with Corey Tarwater, in preparation). These studies will elucidate how the temporal dynamics of natural selection impact plastic responses by breeding individuals.