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|  Steven Morgan, Ph.D.
Ecology and Evolution of Marine Life Histories Phenotypic plasticity in response to multiple predators-
NSF-funded research is being conducted in my laboratory to investigate induced morphological defenses and survivorship of foundation species of the intertidal community (three species of mussels) in response to the presence of three types of predators with different feeding modes (seastar, crab, whelk). In the laboratory, growth rates were slowed in the presence of one of these predators or a combination of predators, indicating that mussels are paying the maximum costs to defend against single or multiple predators. Larger adductor muscles were induced in mussels by seastars, which pry valves apart to insert their stomachs, and shell thickness by whelks, which drill through the shell. Native Mytilus californianus were eaten less readily by all three types of predators due to their thick shells, large adductor muscle and reduced soft tissue mass; whereas the other native species M. trossulus was the easiest to consume and the invasive M. galloprovincialis was intermediate.
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The goal of ecological studies has been to understand the processes that control population density and community structure. However, equally important ecological questions are why do organisms within a population look different, and what are the population and community consequences of these differences? Surprisingly few ecologists have begun to address both of these questions. Currently, our understanding of phenotypic plasticity comes from studies that focus on how an organism responds to a single environmental condition. As a result, we do not understand how an organism will respond in nature when there is more than one environmental condition that can induce changes. Furthermore, we have a poor understanding of how plasticity in an organism affects other members of its community. The importance of phenotypic plasticity in the context of a community in which multiple predators (seastar, crab, whelk) may induce defenses of a foundation species of prey (mussel) is being determined by addressing three specific questions. 
A complementary three-year predator removal experiment was conducted in intertidal boulder fields, and multiple measurements of over 1200 mussels revealed that phenotypic plasticity is determined by the interaction of multiple environmental factors and cannot be extrapolated from simple laboratory experiments. Lastly, feeding preferences of the three predator types for the three species of mussels relative to prey traits were investigated in the laboratory and field. Many previous studies on the induction of morphological plasticity have confounded differences in mean conditions and differences in variation, and our work on morphological responses to the amount of environmental variation is an important new line of research. 
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