PARENT SESSION
Contributed Oral Session 104: Predator - Prey Ecology: Communities; Defenses
Wednesday, August 10, 1:30 PM - 5:00 PM, Meeting Room 521 A, Level 5, Palais des congrès de Montréal

The influence of size-specific interactions in predator-prey systems.

Rudolf, Volker¹, ¹ University of Virginia, Charlottesville, VA, USA

ABSTRACT- Many predators undergo sever size changes during their ontogeny. Within populations, size differences between cohorts can lead to asymmetric competition or cannibalism, such that individuals respond differently towards similar sized conspecifics than to larger or smaller conspecifics. Such trait-mediated indirect interactions within predator populations might influence the predator's impact on the population dynamics of its prey. Different sized predators will likely present different risks for the prey such that prey behavioural responses may differ according to predator size. Few studies have analyzed how changes in the relative abundance of size classes within a predator affect predator-prey interactions. This study examined trait mediated indirect interactions between different size classes of a cannibalistic predator and how the relative abundance of different size classes within a predator population affects prey survival and behaviour. I tested for these effects using larvae of the stream salamanders, Eurycea cirrigera and Gyrinophilus porphyriticus, by altering the densities and combinations of predator size classes in experimental streams in a 2 x 2 factorial design. Results showed that the presence of large individuals can significantly alter the impact of a density increase in small conspecifics on prey survival through non-lethal means. With large conspecifics present, increasing the relative frequency of small G. porphyriticus resulted in a significant lower mortality of E. cirrigera than expected from trials without large G. porphyriticus present. Small individuals changed their behaviour and habitat use in the presence of larger conspecifics, most likely to avoid cannibalism. E cirrigera responded differently in activity and habitat use to each predator size class. These results demonstrate that the impact of a predator can be significantly altered by trait-mediated indirect interactions between different sized cohorts and between different cohorts and prey. This suggests that we need to account for the size structure within predator populations to make reliable predictions on how changes in predator abundance affect prey populations.

Key words: Size-structure, Trait-mediated indirect interactions, population dynamics, community ecology