Causes And Consequences Of Behavioral Trait Variation In Marine Consumer Assemblages

Consumer behavioral traits related to feeding and defense directly and indirectly influence population dynamics, community properties, and ecosystem processes. A rich literature describes how these traits vary across species, and a growing body of work also describes consistent and significant individual variation in feeding preference, habitat use, and escape behavior within populations and species. However, few studies have assessed how behavioral trait variation is distributed across various levels (ie. individual, population, species) within consumer assemblages. Moreover, consumer behavior is rapidly changing due to widespread and intensifying human activities, and yet we know little about how managing these activities may restore consumer behavior and function within impacted ecosystems. Consequently, feeding and anti-predator defense traits are a promising but largely overlooked measure of consumer function and of consumer responses to ecosystem management. Here, focusing on invertebrate herbivores and predatory fishes on California rocky reefs, I ask: how do the behaviors of individuals and species contribute to the ecological function of consumer assemblages in a dynamic world?;First, I teased apart the sources of variation in diet choice within an ecologically important herbivore guild on rocky shores. Repeated laboratory feeding assays of individual grazers across eight species suggest that species differences in feeding preference largely underlie broader patterns of herbivory on rocky shores (Chapter 1). Nevertheless, some species exhibit individual specialization, and all species exhibit broad within-individual variation, such that predictable variation in preference both among and within individuals also contributes to herbivore resource use and function. Next, I shifted my focus to a heavily exploited predator assemblage in kelp forests, to assess the effects of human extraction and recreation on predator behavior and function. Through field surveys of flight initiation distance across marine protected areas, I ascertained that different predatory fishes occupy distinct microhabitats within the kelp forest, yet these species reduce escape behavior similarly in response to long-term protection from fishing and the presence of divers (Chapter 2). Finally, evaluating predation rates by these same predatory fishes through field deployments of artificial prey, I discover that enhanced escape behavior and reduced per capita foraging rates across fishes at newer protected areas is linked to delayed foraging and lower overall predation rates in these areas (Chapter 3). These findings suggest that the behavior of exploited consumers remains altered by fishing, contributing mechanistically to delayed recovery of predator ecological functioning at newly protected areas.