Resource availability and predation risk influence fighting behavior and the maintenance of dominance hierarchies in crayfish (#390)
Dominance hierarchies, resulting from repeated agonistic interactions, reduce fighting and alter an individual's access to resources. Although the effect of size difference on the formation of hierarchies has drawn ample attention, few studies have investigated factors that may impair hierarchy maintenance. In the wild, major ecological factors, such as food availability and predation pressure, often vary substantially both spatially and temporally. However, little is known how cues from these ecological factors influence decision making of animals in contest situations, especially with regard to hierarchy maintenance.
To examine the effects of resource availability and predation risk, we conducted repeated fight contests (three contests without manipulation, two with food and one with predation manipulation) between pairs of noble crayfish males, Astacus astacus. To be able to focus on the effects of ecological factors, we size-matched the opponents, since larger crayfish usually dominate smaller ones.
We found that individuals achieving dominant status in non-resource contests had priority access to a limited, defendable food resource in a future contest. However, in the presence of a food resource subdominants decreased their submissive and avoidance behaviors but increased their percentage of winning, which may indicate an increase in their fighting motivation. In line with the asset-protection principle, individuals that had been dominant in a preceding non-predation risk contest increased their submissive and avoidance behaviors in the presence of a predation threat. This gave subdominants the chance to win a larger percentage of interactions in the predation risk contest than in the non-predation risk one.
Generally, our results indicate that reversals in the dominance status can occur when contestants have similar fighting ability and that changing ecological factors may further contribute to hierarchy dynamics. Overall, our results suggest that ecological factors have to be taken into account to better understand the causes and consequences of dominance in nature.