Resource partitioning and niche hyper‐volume overlap in free‐living Pygoscelid penguins

Summary 1. Species potentially competing for the same resource are considered to be able to co‐exist if they occupy different niches. In an apparent example of this, Adélie, Chinstrap and Gentoo penguins all feed predominantly on krill Euphausea superba at certain sites of sympatry in Antarctica and are proposed to exploit different niche hyper‐volumes via differential area and depth utilization. 2. Patterns of foraging for 49 of these penguins breeding in sympatry were assessed using dead‐reckoning loggers to examine foraging niche overlap. 3. Area use overlaps were 0·29 for Adélie ∩ Chinstrap, 0·44 for Adélie ∩ Gentoo, and 0·40 for Chinstrap ∩ Adélie and depth use overlaps were 0·69 for Adélie ∩ Chinstrap, 0·48 for Adélie ∩ Gentoo, and 0·52 for Chinstrap ∩ Gentoo Penguins. 4. Foraging efficiency was greatest for Adélie Penguins diving near surface waters (0–15 m) while Chinstraps were most efficient at medium depths (15–60 m) and Gentoo Penguins most efficient at deeper depths (> 60 m). There appear to be physiological reasons for this. Penguins primarily exploited those depths where they were most efficient. 5. The overlap for foraging periods was 0·47 for Adélie ∩ Chinstrap, 0·26 for Adélie ∩ Gentoo, and 0·40 for Chinstrap ∩ Gentoo Penguins. Chinstraps foraged primarily at night, Gentoos during the morning and Adélies in the afternoon. Temporal differences in foraging may result in the three species exploiting krill at those depths where it is best adapted to pursue it, this being mediated by the diel vertical migration of krill. 6. Integration of all measured parameters together gives minimal overlap between species with total overlaps of 0·09 for Adélie ∩ Chinstrap, 0·05 for Adélie ∩ Gentoo, and 0·08 for Chinstrap ∩ Gentoo Penguins so it appears that these penguins conform to conventional theory in avoiding competition in areas of sympatry. However, a model incorporating prey movement between hyper‐volumes indicates that penguins may still compete, even in the virtual absence of hyper‐volume overlap. 7. This study shows that Pygoscelid penguin do indeed exploit different hypervolumes in areas of sympatry but that such exploitation of different niches by sympatric species feeding on a common resource does not necessarily result in reduced competition if the mobility of prey is high.