When animals are observed on multiple occasions, consistent between-individual differences in
behaviour, often referred to as animal personality, may be observed. However, this does not mean that
the behaviour of a given individual is readily predictable. While some individuals show low levels of
variation around their behavioural mean, others show high levels of variation, and there may be significant
between-individual differences in this intraindividual variation (‘IIV’) in behaviour. While it has
been suggested that IIV might reduce susceptibility to predators, little is known about the functions or
causation of IIV. We investigated the effects of temperature on the startle response duration of hermit
crabs, Pagurus bernhardus. For poikilothermic animals, temperature has a direct and multiplicative influence
on metabolic rate, which in turn is expected to influence behaviour because of its effect on
energy requirements. At the level of mean startle response durations, the effect of temperature was
dependent on treatment order; within treatment orders, individuals showed different reaction norms. In
contrast, at the level of IIV, while the presence of significant between-individual differences was
dependent on treatment order, there was a clear unidirectional effect in both treatment orders for individuals
to be less predictable at higher temperature. Thus, predictability in behaviour appears to vary
with a key environmental variable that is known to influence energy requirements and potentially the
level of risk that individuals are willing to accept.
When animals are observed on multiple occasions, consistent between-individual differences inbehaviour, often referred to as animal personality, may be observed. However, this does not mean thatthe behaviour of a given individual is readily predictable. While some individuals show low levels ofvariation around their behavioural mean, others show high levels of variation, and there may be significantbetween-individual differences in this intraindividual variation (‘IIV’) in behaviour. While it hasbeen suggested that IIV might reduce susceptibility to predators, little is known about the functions orcausation of IIV. We investigated the effects of temperature on the startle response duration of hermitcrabs, Pagurus bernhardus. For poikilothermic animals, temperature has a direct and multiplicative influenceon metabolic rate, which in turn is expected to influence behaviour because of its effect onenergy requirements. At the level of mean startle response durations, the effect of temperature wasdependent on treatment order; within treatment orders, individuals showed different reaction norms. Incontrast, at the level of IIV, while the presence of significant between-individual differences wasdependent on treatment order, there was a clear unidirectional effect in both treatment orders for individualsto be less predictable at higher temperature. Thus, predictability in behaviour appears to varywith a key environmental variable that is known to influence energy requirements and potentially thelevel of risk that individuals are willing to accept.
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