MEPS 375:289-304 (2009)  -  DOI: https://doi.org/10.3354/meps07743

ABSTRACT: Habitat selection by top predators that are largely free from predation pressures is a function of prey availability and interspecific competition. Such competition can be minimized through niche dimensions: mechanism of resource partitioning based on prey choice and foraging tactic. This study compared habitat use patterns of 5 top predators (bottlenose dolphins, double-crested cormorants, osprey, brown pelicans and terns) within Florida Bay with respect to each other, their prey and habitat variability. Foraging dolphins, osprey and pelicans exhibited similar habitat use patterns in shallow, turbid, productive waters with high proportions of mud and mudbank bottom types. These same habitat characteristics also described the distribution of their major prey items: mullet and catfish. Competition between these 3 predators is likely diluted by foraging tactic variation. Conversely, the habitat use patterns of cormorants showed strongest association with deeper water, with low chlorophyll a and turbidity levels, less mud and mudbank habitat, and greater proportions of hardbottom and seagrass bottoms. Those prey items of cormorants with less competition from other predators examined displayed the same habitat associations. Cormorants in Florida Bay may concentrate their foraging efforts on less competitive prey, occurring more frequently in habitats where these prey items dominate. Despite Florida Bay’s limited bathymetric relief, habitat use patterns of top predators are significantly influenced by depth, and subsequently bottom type. Sighting rates of all predators, except non-foraging dolphins, peaked in shallow mudbank habitats. This pattern of strong habitat overlap among predators implies currently adequate resource availability and/or niche dimensions among interspecific competitors.

KEY WORDS: Habitat use · Competition · Foraging tactics · Seabirds · Bottlenose dolphin · Habitat structure · Niche overlap · Nonmetric multidimensional scaling