Ontogenetic changes in the association between antipredator responses and growth variables

Abstract.  1. An organism's growth parameters are expected to depend on environmental constraints, such as predation risk and food supply. However, antipredator responses, food intake, and thus growth of an animal may be mediated by behavioural traits, which are likely to differ among developmental stages. In this study, it was investigated how the relationship between growth and behavioural antipredator responses changes during ontogeny in the time-constrained dragonfly species Libellula depressa , and which factors influenced specific behavioural decisions at different points in ontogeny.
2. The results revealed that behavioural strategies differed between larval developmental sages, depending on associations between larval growth, food supply, and predation risk. Early in ontogeny, faster development was correlated with high larval activity and high food supply. This resulted in high activity levels under high food conditions irrespectively of predator presence, and under low food supply in predator absence only. In the intermediate stage of development, all larvae displayed a high activity level, which was correlated in general with fast development. However, growth later in ontogeny was not only influenced by the activity level, but also by predator presence and food supply, with larvae reared under high food supply and/or in presence of predators attaining a higher final mass. Thus, not only the way in which larval growth parameters and behaviour are related changed during development, but also whether the factors influenced larval growth and behaviour. Once the larvae reached the ultimate stage of development, in which they overwinter, behavioural patterns observed were consistent with model predictions.
3. It is advocated that behavioural plasticity of prey organisms in different developmental stages should be analysed in the context of associated growth variables.