PARENT SESSION
Oral Session #55: Predator - Prey Interactions.
Presiding: R. Dueser
Wednesday, August 7. 8:00 AM to 11:30 AM. Cochise Meeting Room, TCC.
Mechanisms of resource polymorphism: Responses to differences in predation risk among habitats.
Eklov, Peter*,1, Svanback, Richard1, 1 Uppsala University, 752 36, Uppsala, Sweden, Sweden
ABSTRACT- Interspecific resource competition has long been regarded as a major cause of phenotypic differentiation and a first step of adaptive radiation. However, competition may not always be the proximate factor since predators may affect phenotypic differentiation by indirectly changing competitive interactions among individuals. This can be done either by that predators reduce the number of competitors or change the behavior (activity or habitat use) of competitors. We conducted a pond experiment to test whether behavioral responses of juvenile perch, Perca fluviatilis, to predatory perch were related to predator density in different habitats (open water and vegetation). We further tested if habitat shifts due to the presence of predators could explain divergence in phenotypic patterns among juvenile perch. The results showed that the prey stayed mainly in the open water in the absence of predators whereas in the presence of predators, prey chose to stay in the habitat with the lowest number of predators. Measurements of the preys′ phenotype at the end of the experiment demonstrated a divergence where the prey that mainly stayed in the vegetation had a deeper body than those that mainly stayed in the open water. The pattern was not due to selection by predators because survival of the prey did not differ from the control. Furthermore, there was a strong positive correlation between a deeper body and proportion of littoral fauna in the diet of the prey. There was also a strong correlation between diet breadth and phenotypic variation supporting the conclusion that the variation in morphology depends on differences in diet of the prey. The results suggest that differences in predation risk affect diet of prey that in turn, have consequences for the preys′ phenotype which could be an initial step in resource polymorphism leading to phenotypic divergence in perch.
KEY WORDS: polymorphism, predator-prey, habitat, fish