Geographic variation in reproduction and survival of kelp gulls Larus dominicanus vetula in southern Africa

Abstract

Different populations of a species tend to vary in survival and reproduction, but the extent and scale of such spatial variation are poorly known. We estimated survival and clutch size of kelp gulls Larus dominicanus vetula across their entire African range. At this large geographic scale, we found no evidence for spatial variation in survival, and there was no variation in clutch size. However, there was considerable variation in clutch size among colonies within regions. Over the whole study, mean annual survival of juvenile and adult birds was 0.44 and 0.84, and mean clutch size was 2.2 eggs. A matrix population model showed that population growth was least sensitive to variation in clutch size, and the observed variation in clutch size could not fully account for the observed variation in population growth among colonies and regions. Our results thus suggest that dispersal and/or variation in survival (including egg/nestling survival) at a small spatial scale are also important for the spatial pattern of kelp gull population dynamics. These results are consistent with a metapopulation approach to spatial population dynamics.