Effects of temperature on anti-predator behaviour in the guppy, Poecilia reticulata

Warmer environmental temperatures are likely to increase the frequency of predator-prey interactions in ectothermic animals, and therefore might be expected to influence anti-predator behaviour. In a first experiment, groups of recently fed guppies, placed in a novel environment, schooled significantly more closely at 26°than at 22°C. Changes in two of three measures of schooling tendency over time indicated that aggregation increased during the trial periods, probably as a result of increased familiarity within the experimental groups. In a second experiment, pairs of female guppies were tested at 22°and 26°C, with and without predation threat from a confined cichlid. From multifactor analysis of 18 behaviour types, temperature was shown to affect behavioural time budgets profoundly, particularly in the presence of the predator. At the higher temperature, a shift occurred from inactive anti-predator behaviours and minimal foraging activity towards active predator inspection-related behaviours and a much higher level of feeding. Guppies in the warmer water might have been physically able to school more closely as a result of faster swimming ability, or might have used temperature as a cue indicating higher potential predation risk, and aggregated accordingly. The use of temperature as a source of information about the biotic environment is discussed.