PARENT SESSION
Contributed Oral Session 116: Predator - Prey Ecology: Modeling
Thursday, August 11, 8:00 AM - 11:30 AM, Meeting Room 518 C, Level 5, Palais des congrès de Montréal

How predators and prey distribute themselves across space: comparing empirical data to alternative models of movement rules.

Luttbeg, Barney¹, Hammond, John¹, Sih, Andrew¹, ¹ University of California, Davis, Davis, CA

ABSTRACT- While many studies have examined how prey distribute themselves in response to predators or how predators distribute themselves in response to prey, surprisingly few theoretical or empirical studies have examined how the two interact. How predators and prey distribute themselves is potentially shaped by the distributions of their 1) own species and 2) the other species, and 3) the distribution of resources and shelter across space. We present an examination of how these three factors affect the movement rules of prey (Pacific tree frog tadpoles, Hyla regilia) and predators (dragonfly nymphs, Aeshna palmata) in an experimental arena with two food patches that differ in the amount of prey's resource. Predator and prey distributions between the two patches were recorded at regular intervals over 3 hours and the minimum rates of movements between the patches were calculated. These data were compared to alternative models of how the probability of a prey or predator's switching patches depends on combinations of the proportion of prey, the proportion of predators, and the level of resources in the patch prior to individuals moving or not moving between patches. The relative evidence from the data for each of the alternative models were quantified using a model comparison approach utilizing Akaike Information Criteria. We find that prey movement between patches is primarily a positive function of the proportion of predators and prey in their current patch; i.e., that prey avoid both predators and competitors, but pay less attention to resources per se. For predators, their probability of movement decreased as the level of the prey's resource increases. That is, the predators appear to be basing their movement more on the distribution of the prey's resource than the distribution of prey and other predators. This surprising result matches a theoretical prediction that in a predator-prey race, predators should match the distribution of the prey's resource while prey should distribute themselves uniformly across patches. We compare these results to other metrics of how predators and prey are distributed, such as spatial overlap and coincidence.

Key words: movement rules, spatial distributions, predator and prey, Akaike information criteria