Active research projects

These projects are all either a part of my dissertation or ones that I am the primary researcher.

1. The effects of climate change and invasive species on non-consumptive effects in marine systems

Predators are known to influence prey populations via both direct consumption of individuals, and also through non-consumptive processes.  Chemical and other cues from predators can change prey behavior and potentially reduce foraging rates, however, novel introduced predators may not be recognized by native prey. Response to predator cues may be influenced by climate driven changes in air or water temperature affecting consumer metabolism and foraging rates. To examine these forces, we measured how the foraging rate of an intertidal whelk (Acanthinucella spirata) on Asian date mussels (Musculista senhousia) changes in the presence of native crabs (Romaleon antennarium) or non-native crabs (Carcinus maenas) in Tomales Bay, CA.  We conducted follow-up in the laboratory to make sure that temperature was causing the patterns observed in the field. In general, we found that whelks exposed to native crabs had much lower growth rates than those exposed to non-native crabs. However, snail responses were variable to non-native crabs, which mean that either not all snails recognize non-native crabs, or that the consumption of native snails has not selected for an optimal degree of response in this population.

2. Predator foraging mode controls the effect of antipredator behavior in a tritrophic model

Antipredator behavior is known to have a strong effect on prey population dynamics. While there have been many studies of antipredator behavior in population dynamic models, none have examined how antipredator behavior interacts with predator foraging mode. To examine this process, we incorporated predator and prey velocities into a simple tritrophic food chain.  In this model, antipredator behavior allows prey to respond to predators by slowing their velocity in response to predator density.  Prey can slow their velocity to hide from predators, but this in turn reduces their ability to consume resources, creating a tradeoff between hiding and foraging. We examined the effects of both fast-moving predators “mobile” predators and slow-moving “sit-and-wait” predators on equilibrium prey density and the amplitude of predator-prey cycles.  We found that antipredator behavior was ineffective against mobile predators, but it was very effective against sit-and-wait predators. Antipredator responses to sit-and-wait predators reduced top-down control and allowed prey density to increase with increased carrying capacity. Furthermore, antipredator responses to sit-and-wait predators eliminated population cycles within the community, whereas antipredator behavior had no effect on population cycles within mobile predator communities. Therefore, our model demonstrates predator foraging mode must be taken into account when examining predator-prey cycles. We discuss the potential implications of this model for invasive species and for trophic cascades.

3. The cascading effects of temporal variation in risk

There is a large body of research that focuses on the effect of predation risk on a prey’s foraging behavior. There is a separate branch of research that investigates how patterns of risk through time influence prey behavior in general. Few studies have asked whether different patterns of risk through time will impact how much foraging a prey will undertake. This project is a joint modeling and experimental project that asks if more frequent predator exposures will lead to reduced prey foraging activity relative to less frequent exposures even though the total amount of time remains the same. I developed a theoretical model of prey state that allows prey to incorporate both predation risk and hunger level into their decisions for optimal amount of time foraging. I am currently following up on this model with an 8 week laboratory experiment that examines how Nucella ostrina respond to different patterns of Cancer productus risk. The patterns are either constant risk, no risk, risk every other weeks, or risk for four weeks in a row only. Each week we measure the number of Balanus glandula consumed, and at the end of the experiment we will measure the change in N. ostrina mass.

4. Incorporating subsurface data into models of top predator behavior

To understand the ecology of many mobile predators, researchers rely on satellite tags. Typically for air-breathing oceanic mammals, an animals track can be separated into periods of dives and period of transit.  However, for these tags require the animal to surface in order for an accurate GPS location, which makes them impractical for many gilled animals that only surface infrequently. Using a track of GPS position along may not be an accurate estimate of their behavioral state. Therefore, I have been working on incorporating subsurface data along with the GPS points of a gilled top predator the blue shark (Prionace glauca) in order to determine if the subsurface data will change our inferences of top predator behavior.

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