Behaviour as part of ecological adaptation
- H. W. Fricke1
© Biologischen Anstalt Helgoland 1973
1. An animal's behaviour represents part of its ecological adaptation to the environment (inanimate surroundings, food, enemies, conspecifics and animals of other species).
2. In the case of feeding, plankton filter feeders are referred to which exhibit identical activity periods, the same choice of habitats and comparable types of movement during feeding; this parallelism is interpreted as adaptation to the mode of nourishment. Similarity in feeding behaviour is indicative of convergent development. In ophiurids, water-current filtration appears to be an ancient physlogenetic characteristic. It is present in numerous species, indicating that this type of behaviour is homologous. Garden eels (Heterocongridae) are also plankton feeders. Their mode of feeding reveals analogies to that of marine benthonic invertebrates. Fishes which feed on sea urchins exemplify adaptations to prey capture and enemy avoidance. Sea urchins have developed adaptive protections against being preyed upon; these tend to result in escaping potential predators or preventing contact with them. Nocturnal activity appears to be an adaptation leading to enemy avoidance. Behaviour patterns of predators are described and compared. Preying on sea urchins appears to be a convergent development based on pre-adaptations in behaviour patterns and morphological structures. Particular adaptations are always based on characteristics already present.
3. Social behaviour is also part of the ecological adaptation of an animal to its environment. The social behaviour of the Pomacentridae is cited as example. Studies on the monogamous anemone fishAmphiprion bicinctus showed that its well-developed aggressive behaviour to both conspecifics and non-conspecifics can be easily released.A. bicinctus drives away all large fishes from its territory, including predators of the anemone. Well-developed intraspecific aggression necessitates effective aggression inhibition with respect to the sexual partner. The potential aggression of one member of the pair must be continually neutralised by submissive behaviour on the part of its mate. Members of a pair recognise each other individually. In situ experiments showed that they recognise the partner mainly through visual characteristics. Comparison of social behaviour inA. bicinctus with that of other pomacentrids should reveal adaptations to life in the narrow confines of the sea anemone.
4. Butterfly fishes (Chaetodontidae), which live in coral reefs, are monogamous. Their social structure and conspicuous coloration are considered as adaptations to extremely high species densities (up to 14 sympatric species), which are ecologically specialised in various ways. Continual monogamy and conspicuous coloration enable sympatric species to live in the same environment. The difference in coloration between the juveniles and adults is considered species camouflage, a mechanism enabling the juveniles to survive and reach maturity within the home range of the adults.