Date of Award

12-15-2014

Document Type

Open Access Dissertation

Department

Biological Sciences

First Advisor

Brian Helmuth

Second Advisor

David S. Wethey

Abstract

Untangling natural systems’ complexity requires understanding the mechanisms responsible for organisms’ responses to environmental change. Recently, significant advances have been made by recognizing the relevance of direct and indirect effects, which take place when multiple biotic and abiotic factors influence each other. I examined potential direct effects of environmental variables on a predator-prey interaction, as well as potential indirect effects of these variables on the interaction itself. I placed emphasis on behavioral and physiological adaptations, which would potentially contribute/modify these effects. My study system was comprised of a rocky intertidal keystone predator, the sea star Pisaster ochraceus, and its main prey the mussel Mytilus californianus. While previous work had explored the influence of both seawater and aerial temperature on their interaction, few studies had explicitly considered the physiological basis of such responses. Given the direct links between Pisaster body temperature and physiological performance, in Chapter 1 I asked, where exactly is Pisaster located? And, what physiological consequences it might bring? Pisaster exhibited a size-dependent distribution, with small animals found higher on the shore. Also, most individuals were found in refugia at low tide, reflecting Pisaster risk-avoiding strategy, despite generally mild conditions. We suggest that the strategy may help prevent exposures to extreme (although rare) events.

Chapter 2 provided an opportunity to compare thermal performance between the predator Pisaster and prey Mytilus. Within an environmental stress model framework, I asked: which species would be more negatively impacted by thermal stress? To avoid influencing individuals’ response, I tested this idea indirectly via thermal performance curves (TPC). I described TPCs for both species, which first allowed comparing them based on their intrinsic thermal sensitivities. Second, these curves were used to calculate thermal performance using field body temperature data. I collected data on body mass indices and heat-shock protein 70kDa to evaluate both species general physiological condition and levels of extreme thermal stress. Thermal sensitivity varied between species and site of origin. Contrary to previous findings, I observed that Mytilus performance resulted more negatively affected by temperatures than Pisaster, and no effects of movement behavior were detected. Chapter 4 describes a Dynamic Energy Budget (DEB) model for Pisaster. I discussed the models’ ability to simulate growth throughout ontogeny, shrinkage when food is scarce, and the combined effects of changes in body temperature and food availability. This model should prove useful in predicting Pisaster physiological responses to environmental change.

Included in

Biology Commons

Share

COinS