Effects Of Temporal Variation In Predation Risk On Predator Prey Interactions

Author : Jason Scott Sadowski
Publisher :
ISBN 13 : 9781392884539
Total Pages : pages
Book Rating : 4.8/5 (845 download)

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Download or read book Non-consumptive Effects at the Intersection of Climate Change, Invasive Species, and Temporal Variation written by Jason Scott Sadowski and published by . This book was released on 2019 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Predators have large effects on their prey and in turn the ecosystems that they inhabit. The very act of hunting and consuming prey changes prey densities and the interaction rates of prey with other species. But, predators are also known to have strong fear effects on their prey caused by the predator’s presence in the environment. There can be a few different mechanisms for these fear effects such as the expression of antipredator behavior (e.g., hiding) or the growth of antipredator defenses (e.g., spines). These mechanisms in turn influence prey growth and reproduction leading to further effects through the community at large. While the chapters of my dissertation look at different questions and use different methods, they are all united in their attempt to understand the factors that could modify these fear effects. Specifically, my dissertation examines how fear effects are modified by climate change, invasive species, and temporal variation. The first chapter examines how climate change could interact with introduced predator species to create novel fear effects. The presence of native nonlethal predators is known to change prey behavior, but introduced predators may not be recognized by native prey. In theory, prey may not have coevolved with the chemical cues or behavior of an introduced predator. At the same time, prey are also constrained in their behavior by the environment. Climate change induced increases in air and water temperature may affect prey metabolism and thus the abilities of prey to respond to predators, especially in marine ectotherms. I measured how the growth rates of an intertidal snail (Acanthinucella spirata) changes in the presence of nonlethal native (Romaleon antennarium) or non-native (Carcinus maenas) crabs under elevated temperatures in both field and lab experiments. Across my experiments introduced crabs induce as great or greater reductions in snail growth than native crabs under ambient conditions; but, under warmer conditions these patterns switch such that native crabs induce greater reductions in snail growth than introduced crabs. I then linked these patterns to how effectively each predator can attack small or large snails. In this case, native crabs can attack snails of all sizes, whereas the introduced crabs are more effective at the smaller size classes. Taken together, this chapter indicates that native snails are more likely to grow into larger size classes when the introduced crab is present at warmer temperatures, and may consider the introduced crab to be less of a threat at those temperatures. The second chapter links a specific mechanism of fear effect, antipredator behavior, to qualities of the predator. I developed a food chain model where predators eat prey and prey in turn eat a resource. Both predators and prey consumed their food at a rate dependent on how fast they move through the environment such that faster consumers encounter food items at a faster rate. Prey respond to increases in predator abundance by hiding and thereby slowing their average movement rates. This behavior creates a tradeoff between hiding and foraging because slowing reduces the prey’s rate of finding and consuming resources. I modeled two different types of communities, one with fast-moving “mobile” predators and the other with slow-moving “sit-and-wait” predators. Antipredator behavior was ineffective against mobile predators, but was highly effective against sit-and-wait predators. Antipredator responses to sit-and-wait predators allowed prey to increase in abundance as resources increased, whereas antipredator responses to mobile predators had no effect. Antipredator responses to sit-and-wait predators eliminated population cycles in the community, while antipredator behavior to mobile predators again had no effect. Overall, how predators forage is an important, previously unexamined aspect for both predator-prey cycles and prey abundance. In the third chapter, I examined how changing the temporal pattern of predation risk influences the prey’s foraging rate. Previous research on temporal variation in risk indicates that when prey are exposed to longer risk periods, they reduce their foraging rates. However, whether the distribution of these risk periods has an effect independent of total exposure time is unexamined. For example, multiple short risk periods may have a greater effect than one long risk period even if the total amount of time is equivalent. I developed a model of prey growth and prey foraging that incorporates a temporally variable predator and tested this model using a laboratory experiment. The experiment measured how a marine snail’s (Nucella ostrina) growth and foraging rate on barnacles (Balanus glandula) changes in response to crab predators (Cancer productus). Over 8 weeks, snails were exposed to predators for 100% of the time, 50% of the time or 0% of the time. I used two 50% treatments and exposed snails to crabs either every other week (high frequency), or for 4 weeks in a row (low frequency). Both my model and my experiment indicated that prey reduce their growth and foraging under high frequencies of risk. Moreover, when snails were exposed to high frequencies of risk, they ate less during both safe and risky periods, suggesting that this risk regime shifted the snail’s perception of background risk. Therefore, the effects of high frequency risk are intrinsically different from low frequency risk even when the total amount of exposure time is the same. The prey’s capacity to remember previous risk periods is likely an important component for further understanding the effects of temporally variable predators.