Spatial variation in life-history trade-offs results in an ideal free distribution in Black Brant Geese

Ideal free distribution theory predicts that individuals distribute themselves so fitness is equal among patches. In this paper we evaluate all components of adult fitness to assess the hypothesis that individuals distribute themselves among seven brood-rearing areas so that trade-offs among different life history traits result in equal mean fitness among individuals using different areas. We used estimates of vital rates (clutch size, nest survival, pre-fledging survival, post-fledging survival, juvenile survival, and breeding probability) to estimate brood-rearing-area-specific per capita recruitment rates and survival for adult females. We summed brood-rearing-area-specific per capita recruitment and adult survival to calculate brood-rearing-area-specific estimates of lambda. We found little variation in lambda among brood-rearing areas and lifetime fitness implications of changing brood-rearing area were negligible (< 1% brood-rearing area mean fitness). We conclude that adult female Black Brant distribute themselves in an ideal free manner, resulting in equal fitness among females using these areas.