Population Genetics and the Spatial Scale of Conservation of Colonial Waterbirds

Depending on levels of historical and contemporary gene flow, the spatial scale of populations of colonial waterbirds may range from individual colonies to entire species. Understanding the spatial scale of populations is important for conservation for several reasons: (1) for estimating levels of gene flow and thus the capacity for natural recolonization; (2) for conserving genetic resources both within individuals and within species; (3) for assessing the scale of impact of natural and anthropogenic mortality; (4) for identifying appropriate sites for population monitoring and restoration; (5) for determining a colony's uniqueness; (6) for identifying source and sink populations; and (7) for estimating effective population sizes. The geographic scales of populations may be estimated from direct observations of demographics and/or from a variety of molecular techniques; the most powerful studies combine 2 or more methods. Recent studies of murres and murrelets indicate the importance of understanding the spatial scale of populations for conservation. Although few investigations have been done on colonial waterbirds, preliminary analyses of published studies suggest that the geographic scales of populations tend to be greater in species with an "island" type population structure or an offshore foraging mode than in those with a "stepping-stone" type of population structure or an inshore foraging mode. In some cases, the spatial scale of a population may be smaller than the colony.