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School of Environment and Natural Resources


Lauren Hostert's Graduate Defense Seminar

Aug 1, 2014, 9:00am - 10:00am

A Graduate Defense Seminar will be presented by Lauren Hostert, an MS student in Fisheries and Wildlife Sciences, on Friday, August 1 at 9:00 a.m. in 382 Kottman Hall. She will present The role of individual variation in the in the consumption of non-native prey: implications for the evolution of diet specialization and biological invasions.

Abundant non-native species frequently cause changes in natural environments by altering the composition and abundances of native species. One explanation for why non-native species are able to reach higher densities outside of their native range is because they escape their natural enemies (i.e. enemy release hypothesis). Although the release of non-native species from their natural enemies may be due to lower densities or diversity of predators, parasites or pathogens, there are many alternative mechanisms that can reduce the predation pressure that a non-native species may experience following introduction into a new environment. In this study, I examined how individual variation in diet, morphology, competitive ability (i.e. aggression) of a native predator (common mudcrab, Panopeus herbstii), along with the relative energetic value of alternative prey  contributes to the consumption of a recently introduced, non-native prey species (green porcelain crab, Petrolisthes armatus). Specifically, in this study I: 1) quantified within-population variation in diet breadth and competitive ability of native P. herbstii predators, 2) evaluated the influence of competitive ability on within-population variation in diet and the consumption of non-native prey, P. armatus , and 3) compared the relative caloric content of the native prey species of P. herbstii (G. demissa, C. virginica, and E. depressus) with that of the non-native prey P. armatus . AIC model comparisons indicated that predator sex, aggression, and competitor presence were the most important factors influencing diet specialization of P. herbstii predators, wherein predators that exhibited specialist diets were female and more aggressive. Individual P. herbstii predators also tended to display specialist diets in the presence of a competitor. Individuals that specifically specialized on P. armatus were also female, but less aggressive individuals. Individual P. herbstii predators displayed more specialized diets on P. armatus in the absence of a competitor.  The total number of P. armatus consumed was best explained by sex and size, whereby females and larger individuals consumed greater numbers of P. armatus. Also, in the presence of no alternative prey, females and smaller individuals consumed great quantities of P. armatus. Results from the oxygen bomb calorimetry analysis indicated that non-native P. armatus and native ribbed mussels Geukensia demissa have similar specific energies that are significantly greater than native eastern oysters Crassostrea virginica and depressed mud crabs Eurypanopeus depressus (which are not statistically different from one another). Overall, these results demonstrate that there is considerable individual variation in diet (i.e. some individuals are specialists, some generalists) and the consumption of P. armatus among the tested population of P. herbstii predators. P. armatus  is a considerably profitable prey type compared to native prey yet only a sub-set of the population including females consumes P. armatus in large proportions. This gives some insight as to why P. armatus has been able to establish and maintain high population densities in this area but it produces more questions regarding why some individuals continue to not consume this abundant, profitable prey item.