Spatial scale influences the outcome of the predator–prey space race between tadpoles and predatory dragonflies


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1. How predators and prey distribute themselves across space can have large population and community-level consequences by affecting the frequency and potential strength of interactions between and within trophic levels. The general pattern that emerges from numerous studies is that predators seek areas with higher prey densities and prey avoid areas with higher predation risk. However, little is known about the behavioural mechanisms underlying the emergent spatial patterns between freely interacting predators and prey.

2. We examined the behaviour and space use of groups of Pseudacris regilla (Pacific treefrog) tadpole prey and larval Rhionaeschna multicolor (blue-eyed darner) odonate predators in arenas consisting of four patches of the prey’s resources divided into two spatial scales over two observation periods a day apart. Distributions were assayed both alone and together. We predicted scale should inherently affect the resulting spatial patterns because factors such as selection, competition, interference, movement ability and prey responses to predators all have potentially similar effects as scale become larger or smaller. These factors predict that prey should be more able to dictate the spatial pattern at smaller scales and predators at larger scales.

3. Results generally match these predictions with measures of joint space being consistent with the predators dictating the joint space use more than expected at the larger scale. Moreover, at the smaller scale, either the predator and prey responses offset or reverse to favour the prey. We used a model selection approach to look at the underlying behavioural rules shaping these spatial patterns. Prey were more likely to leave patches with lower resources across both scales. However, their response to predators and competitors differed between the scales, with prey appearing to become trapped with predators only at the larger scale and only avoiding other prey at the small scale.

4. These results highlight the importance of investigating freely interacting predators and prey and the factors that are likely to affect the predator’s or prey’s ability to dictate spatial patterns. An ability to predict predator–prey spatial outcomes should be a great benefit with habitat fragmentation and shifting population densities, distributions and community compositions.