When closely related species overlap, the competition for scarce food resources can be fierce. Addi ho is a Ph.D. student at the British Antarctic Survey, is linked to the University of Exeter (World Wide Fund for Nature) and Addi ho . Her research focuses on how climate change affects interactions between sympatric Antarctic penguin species, and how to predict their response to future climate scenarios.

Because of its influence on population size and distribution, competition is an important factor in ecology. It also helps to understand how species react to climate change. It can be between species (intraspecific), and within species. It is especially intense in communities where closely related species are able to breed at high density and share few food resources. Niche partitioning reduces the potential negative effects of competition, most often diet, foraging areas and staggered reproduction (isochrony).

A paper published in the Journal of Animal Ecology examined how Adelie (Pygoscelis.adeliae), and the chinstrap. Staggered breeding is an alternative to breeding penguins on Signy Island, South Orkney Islands. It reduces competition between Adelie (Pygoscelis adeliae) and chinstrap (P. Both species are closely related and both eat the same prey. They are also experiencing large population declines. They are subject to high levels of interspecific rivalry. Signy Island is situated in one of the fastest warming regions on Earth. We wanted to find out if the population declines are due to climate change.

We created a 3D model of their foraging behavior during the breeding cycle using GPS and time-depth recorder tag tags that measure pressure. Their breeding cycle takes approximately 4 months. It consists of three stages: incubation (brood-guard), creche, and brood. Logistical constraints made it impossible to tag all the individuals within the population. We therefore created a virtual colony using the tagging data. This allowed us compare the foraging areas between the two populations at each stage of their breeding cycle and to determine their overlap. These two species are similar in size and can reach similar depths to catch prey. This makes it likely that they will be competing for food in overlapped areas. Future climate change impacts were examined by artificially removing the 28-day breeding offset and watching how species overlapped in these conditions.

Both species used similar foraging areas within their breeding stages, but they differed between the breeding stages. (See figure below – A=incubation; B=broodguard; C=creche, red=chinstrap, Blue=Adelie). Combining this with the 28-day offset in their breeding, they leapfrogged each other throughout the breeding year, which meant that they were foraging at different places on the same day. The species were able to share their foraging niches, reducing overlap and competition by 54% throughout the entire breeding season. If the breeding offset were to decrease by just one day, the overall breeding season would see an increase of 2.1%.

Utilisation distribution kernels of peripheral (95%) (thin line) and core (50%) foraging areas (shaded area with thick line) using raw GPS data of foraging trips during incubation (a) guard (b) and crèche (c) stage for Adélies (blue) and chinstraps (red) overlaid on bathymetry (metres) shown in greyscale shading.

Both species are advancing their breeding due to climate change, but they are doing it at the same time, maintaining the niche partitioning, 28-day offset, and keeping the niche partitioning intact. It is therefore resilient to climate change, and is not causing the population declines observed across the Western Antarctic Peninsula.

This paper quantifies the competition reduction provided by staggered breeding and provides a better understanding of the mechanisms that climate change impacts on these species. The leapfrogging behavior described here may also occur in other seabird species, and could alter their responses to environmental change or new species.