Assessment of hypotheses about dispersal in a long-lived seabird using multistate capture-recapture models
Résumé
1. Dispersal contributes to spatio-temporal variation in population size and is a key process in studies of life history evolution and studies with conservation implications. However, dispersal is still one of the major gaps in our knowledge of ecological dynamics. The very large literature on metapopulation dynamics lacks empirical bases on dispersal and relevant behavioural parameters. We used multistate capture-recapture models (data from 1988 to 2001) to address hypotheses about movement probability and habitat selection within a system of two breeding colonies in Audouin's gulls (Larus audouinii), an endemic species breeding in the Mediterranean and considered as threatened. 2. Movement probability varied over time, and differed greatly between the colonies. 3. We did not find evidence of an influence of colony size or density of predators on movement probability. 4. In dispersers, our results did not support the hypotheses that movement probability between year t and t + 1 was influenced by mean breeding success in the colony of origin (i.e. an indicator of habitat quality) or the destination colony in year t or t + 1, or by the ratio of breeding success in these colonies in year t or t + 1 (i.e. quality gradient). 5. Overall, movement probability was higher from the smaller colony to the larger, and from the colony with lower breeding success in year t to the more productive one. This provides slight support for two nonexclusive hypotheses about habitat selection (con-specific attraction and conspecific success attraction). 6. Movement probability from the smaller, less productive colony was very high in some years, suggesting that the dynamics of both colonies were strongly influenced by adult dispersal. However, in absolute numbers, more individuals moved from the larger, more productive colony to the smaller one. This suggests that the system may function as a source-sink system. 7. Use of multistate models to reassess local survival showed that survival was lower in the less productive colony with higher emigration probability. This may reflect genuine differences in mortality between colonies, or more probably differences in permanent emigration from the study area.