Antipredator Behavior and the Ontogenetic Shift

For immature animals, prior to reproductive success, it is crucial that individuals continually assess the ambient predation risk in their environment and respond in ways that reduce their chances of death. Such antipredator behavior is often traded-off with other advantageous behaviors; e.g. foraging less to avoid predatory encounters. They eat less and grow more slowly but live to reproduce. In species with complex life-histories, sharply increased predation risk occurs during ontogenetic shifts as small, vulnerable individuals move into habitats with different suites of predators (new species, larger size and increased/decreased prevalence). The movements mediating the shift often create increased exposure to predators and these changes in the predator milieu during ontogenetic shifts may act as behavioral "bottlenecks," where only the individuals that can assess local predators and respond with appropriate antipredator behavior survive. Although many animals make pre-reproductive ontogenetic shifts, little is known about the role that antipredator behavior plays during these crucial periods. How does an animal's behavior reduce its chances of predation in species that make ontogenetic shifts to different predator milieus during immature stages?

To address this question requires determining the predator milieu in a particular area for a focal prey species. This includes 1) the prevalence of predators, 2) their hunting tactics, 3) the relative size of the predator, 4) the degree of exposure of the prey, and 5) the physical characteristics of the environment (e.g. shelter availability, water clarity, topography). In this context, the question can be addressed on two levels: mechanisms of predator assessment and the effectiveness of antipredator behavior for survival. In other words, how do animals determine what a predator is and how does their behavior keep them from being eaten?

Although this question can be addressed either on purely theoretical or empirical grounds, given the lack of information from natural systems pertaining to this particular subject, it is appropriate to first consider an empirical study system. An appropriate system should focus on an animal which makes ontogenetic shifts in predator milieus, has a well-described life-history, allows for comparisons with other species which do not make ontogenetic shifts and is practical to work with. In my research, I am working with the Caribbean spiny lobster Panulirus argus, a marine crustacean which has multiple, pre-reproductive ontogenetic shifts and has been subject to intensive ecological and behavioral study for the last 30 years. Additionally, a closely related, sympatric species which does not make ontogenetic shifts, Panulirus guttatus, allows for comparison with the behavior of P. argus.