Running around the clock: competition, aggression and temporal partitioning of running wheel use in male mice

The strategies that animals use to obtain valuable resources are affected by resource quality and availability (e.g. spatial distribution), population dynamics (e.g. competitor-to-resource ratio) and individual characteristics (e.g. competitive ability). Theoretical papers and field observations suggest that aggressive resource competition, particularly by individuals with high competitive ability, increases as the competitor-to-resource ratio increases. On the other hand, individuals with low competitive ability should adopt a scramble competitive strategy, for example by expanding their home range or utilizing resources at suboptimal times. We tested these theoretical predictions in male house mice, Mus musculus domesticus, by experimentally manipulating the distribution of a desirable resource, a running wheel. Four male mice were exposed to three treatments (zero, one or four running wheels present) using a repeated measures design. We found that aggression increased as the competitor-to-resource ratio increased. In addition, mice with high competitive ability had species-typical nocturnally biased activity and running wheel use patterns, while mice with low competitive ability had more diurnally biased activity and running wheel use patterns. Our results show that aggression encourages less competitive mice to adopt a scramble competitive strategy through temporal partitioning and provides empirical evidence for the predictions of resource defence theory.