Effects of shell size on behavioural consistency and flexibility in hermit crabs

Animal personalities are assumed to be present when there are consistent between-individual differences in behaviour, whereas behavioural flexibility occurs when individual responses are continuously adjusted. Where both possibilities have been tested for, individuals may show both behavioural consistency and flexibility. Therefore, to gauge the importance of consistent individual differences in behaviour, it is useful to compare the strength of consistency with that of plasticity in behaviour. Here we investigate startle responses in hermit crabs (Pagurus bernhardus (L., 1758)) in high- and low-risk situations. We vary the level of risk between situations by manipulating the quality of empty gastropod shells available to the crabs. Comparison of statistical effect size estimates for tests of concordance and difference between situations reveals a strong pattern of consistent between-individual differences in behaviour in comparison to a statistically significant but reactively weak pattern of behavioural flexibility. Although the startle duration varied, on average, in crabs from different sites, this was mainly due to different responses during an in situ phase of the experiment.