Breeding habitat selection across spatial scales: is grass always greener on the other side?
Résumé
Habitat selection theory predicts that natural selection should favor mechanisms allowing individuals to choose habitats associated with the highest fitness prospects. However, identifying sources of information on habitat quality that individuals use to choose their breeding habitat has proved to be difficult. It has also proven difficult to identify dispersal costs that prevent individuals from joining the highest-quality sites. A synthesis that integrates dispersal costs and habitat selection mechanisms across space has remained elusive. Because costs of dispersal are generally distance-dependent, we suggest that a habitat selection strategy of sequential proximity search (SPS) can be favored by natural selection. This strategy requires that animals make decisions at multiple scales: whether to stay or leave the previous breeding site, depending on reproductive success; then, if dispersal is chosen, use information on neighborhood habitat quality to decide whether to stay in the neighborhood or leave, expanding the search area until the nearest suitable site is chosen. SPS minimizes distance-dependent dispersal costs while maximizing benefits of gaining a better habitat. We found evidence of breeding dispersal behavior consistent with this strategy in a kittiwake population stratified into a spatial hierarchy from colonies to nest sites. We used a mixed sequential regression model to study dispersal decisions, indexed by breeding dispersal movement, of 2,558 individuals over 32yr. Scale-dependent dispersal propensities of kittiwakes varied according to breeding status, breeding experience, sex and individual identity. We suggest that distance-dependent dispersal costs result from strong competition among kittiwakes for nest sites. Individual decisions regarding dispersal (whether to leave or not, and where to go) depend on nesting habitat quality as well as the competitive ability required to keep territory ownership in a previous site, or to acquire a new site; this ability varies according to distance between sites and individual characteristics. Additional studies are needed to establish the generality of SPS in habitat selection.