Predator-driven Selection Shapes Behaviors And Life-history Of A Neotropical Rainforest Bird

Spatial variation in predation risk may drive changes in prey traits such that prey populations are phenotypically divergent from one another, which can influence life-history strategies, patterns of speciation, and even adaptive radiations. This dissertation explores how selection shapes behaviors and the life-history of a Neotropical rainforest bird (Western slaty antshrike, Thamnophilus atrinucha). We examined populations at two sites in central Panama (island and mainland), first quantifying the extent of divergent predator-driven selection pressure at both sites (Chapter 1). Using meta-analysis of published nest and adult survival estimates for multiple bird species, we determined that understory birds on the island experience reduced nest survival and increased adult survival. By linking nest survival of replicate plots across island and mainland to extensive surveys of nest predators, we determined that monkeys and snakes are likely the primary agents of selection against nests. We then demonstrate (Chapter 2) how age-specific mortality influences age structure. We employed a correlation between antshrike territorial songs and chronological age, a relationship that enables estimation of demographic parameters. We report that populations under increased nest predation risk are indeed older. In (Chapter 3), we examined how predator-driven selection acts on nests and eggs. Using manipulations of nest appearance (moss on nest) and egg maculation, we found evidence that correlational selection is acting on both traits. Naturally built antshrike nests and eggs on the island were closer to their adaptive optimum than mainland nests, suggesting that BCI parents may be responding to increased nest predation risk. Because BCI parents experience higher adult and lower nest survival than mainland parents, we used predator models to explore how reproductive value of parents influences response to adult and offspring predators (Chapter 4). Contrary to that predicted, we found that parents on BCI show reduced risk-aversion to adult risk. We discuss potential reasons for such antipredator suppression. We found that decreased nest survival was associated with more time spent incubating, a pattern that suggests that parental behaviors are driven by predation risk. These results suggest that predator-driven divergent selection may have marked influences on behavioral plasticity and demographic change.