Geographic structuring of Antarctic penguin populations

Aim We hypothesized that regional spatial organization of Antarctic penguin breeding populations was affected by social factors, that is, proximity and size of adjacent colonies, and by physical factors, that is, availability of breeding habitat and proximity of polynyas and submarine canyons where prey is abundant. The hypothesis of Furness and Birkhead (1984), that forage competition and density-dependence affect geographic structure of seabird populations, was tested previously for Antarctic penguins when biologging to quantify colony foraging areas was less common and when assessments of colony size reflected a compendium of historical counts. These data on foraging areas and colony size are now available following 20 years of frequent biologging and real-time satellite data on colony locations and sizes. Location Antarctica. Major taxa studied Penguin species. Time period Present day. Methods We prepared a literature summary on the basis of biologging studies to improve assessment of foraging ranges. We collated colony sizes from recent sources and integrated them with data on submarine canyon systems and polynyas. We used geospatial models to assess the relationships of the latter features to colony size, clustering, and distribution around Antarctica. Results The equal spacing of emperor penguin colonies was constant, with spacing a function of foraging range. In contrast, colonies of other penguin species were clustered, with small colonies adjacent to one another and within the outer edge of the foraging area of large colonies. Colonies and especially clusters occurred near polynyas and canyons around Antarctica. Main conclusions Density-dependent processes and geography explained penguin colony distribution. We conclude that inter- and intraspecific trophic competition affects the geographic structuring of colony distribution and size, although not necessarily in the same way among species. Results are relevant to assessing effects of climate, ecosystem dynamics, fisheries and other factors on penguin population trends at regional scales. We suggest that considering penguin colony distribution and abundance at the regional or cluster level is necessary to understand changes in these attributes.