Prey and predator space use: the effects of predator identity and multiple predators

Background/Question/Methods

Predator and prey are often faced with a situation where each is capable of altering their spatial distribution in response to the other. It has been shown with models and experiments that predator and prey spatial distributions are best understood as the product of a game within and between species with the outcome depending on the risk that the predator imposes on the prey and information that prey have about the locations of predators. No previous study has looked at how predator and prey spatial games differ with predator identity or with multiple predator species present. We tested how tadpoles of Pacific treefrogs (Pseudacris regilla) use space in the absence and presence of two their predators, blue-eyed darners (Rhionaeschna multicolor) and tiger salamanders (Ambystoma tigrinum) larvae. Predators, prey, or both were placed into an arena with 4 patches that differed in the amount of the prey's food present. We videotaped the trials and recorded the locations of individuals every 20 minutes for 4 hours. We expected the salamanders to be more voracious predators than the odonate larvae, but to also cause less release of alarm cues because they consume the tadpoles whole and thus release less alarm cue.

Results/Conclusions

Salamander larvae caused higher predation rates on the tadpoles than the dragonfly larvae both when the two predators were in separate arenas and when in the same arena. Presence of the predators caused a shift in the prey's space use. When alone in an arena, tadpoles were significantly more often in the patch with the highest resource level than in the other three patches. Dragonfly larvae when alone also tended to favor occupying the higher resource patches, but the salamander larvae did not. The presence of either predator or both predators caused a significant shift of prey patch use towards the lower resource patches. Dragonfly larvae caused a larger shift in prey patch use than did the salamanders. The presence of the other predator significantly affected the spatial overlap of each of the predators with prey. With the other predator not present, dragonfly and salamander larvae had a high and low spatial overlap with the tadpoles respectively. However, when the three species were together the salamander overlap with the tadpoles was significantly increased and the dragonfly overlap with the tadpoles was decreased. Our results suggest that this shift in overlap was due to changes in the factors affecting tadpole movement.