MOVEMENT ECOLOGY OF PREDATORS

 

A goal of my research program is to better understand how the movement of highly mobile species structures marine ecosystems and our ability to study them. Focusing on the role of movement is particularly interesting for sharks, many species of which are physiologically required to never stop swimming. My research currently addresses three major questions: 

(1) How does the movement and distribution of predators affect our ability to study and assess their populations?

I use field surveys and spatially explicit modeling approaches that directly account for the ways in which animal movement may impact and bias population assessments. These efforts have been used to reassess a shark population at a near pristine coral reef to better understand what these ecosystems may have looked like before human impacts became pervasive. By accounting for animal movement, we were able to provide insight into the structure of healthy coral reef ecosystems, and show that inverted biomass pyramids do not represent the trophic structure of pristine reefs at island-wide scales.

(2) What is the role of competition in shaping coral reef ecosystems with healthy predator populations?

Competition between species plays a fundamental role in structuring marine ecosystems. Using acoustic telemetry, I am interested in understanding how competition structures space use in a variety of marine species. In sharks, we have shown that competitive advantages may vary across different habitat types within a coral reef ecosystem. In herbivorous reef fishes, we found that territory size and space use was primarily driven by exploitative competition with the surrounding herbivore community, not predation risk, as has been previously cited.

(3) What role do predators play in the transfer of energy throughout coral reef ecosystems?

I am interested in trying to understand how mobile marine predators can act as nutrient vectors and what impacts this has on the ecosystems in which they reside. In coral reef ecosystems, reef sharks play an important role connecting the pelagic ecosystem with the nearshore reef. Some reef sharks forage primarily in the offshore environment, yet reside on reefs, where they maintain relatively small activity spaces. For the grey reef shark, we found that consumption of pelagic prey and subsequent egestion on the nearshore reef leads to a high level of nitrogen deposition (94.5 kg/day) around Palmyra atoll.