Abstract
Climate-driven sympatry may lead to competition for food resources between species. Rapid warming in the West Antarctic Peninsula (WAP) is coincident with increasing gentoo penguin and decreasing Adélie penguin populations, suggesting that competition for food may exacerbate the Adélie penguin decline. On fine scales, we tested for foraging competition between these species during the chick-rearing period by comparing their foraging behaviors with the distribution of their prey, Antarctic krill. We detected krill aggregations within the horizontal and vertical foraging ranges of Adélie and gentoo penguins, and found that krill selected for habitats that balance the need to consume food and avoid predation. In overlapping Adélie and gentoo penguin foraging areas, four gentoo penguins switched foraging behavior by foraging at deeper depths, a strategy which limits competition with Adélie penguins. This suggests that climate-driven sympatry does not necessarily result in competitive exclusion of Adélie penguins by gentoo penguins. Contrary to a recent theory, which suggests that increased competition for krill is one of the major drivers of Adélie penguin population declines, we suggest that declines in Adélie penguins along the WAP are more likely due to direct and indirect climate impacts on their life histories.
Highlights
Climate-driven sympatry may lead to competition for food resources between species
The competitive exclusion principle suggests that Adélie penguins could be displaced if they compete with gentoo penguins for the same food resources[8]
A recent hypothesis suggested that the decrease in Adélie penguin abundance in the West Antarctic Peninsula (WAP) is due to increased competition between krill predators and a long-term decline in Antarctic krill (Euphausia superba), the penguins’ main prey[9]
Summary
Climate-driven sympatry may lead to competition for food resources between species. Rapid warming in the West Antarctic Peninsula (WAP) is coincident with increasing gentoo penguin and decreasing Adélie penguin populations, suggesting that competition for food may exacerbate the Adélie penguin decline. In long-established colonies, previous studies demonstrate that penguin species avoid competition by using different foraging habitats horizontally[12], vertically[13], and temporally[14] It is not clear if habitat partitioning occurs for newly established sympatric interactions due to recent climate changes. Autonomous underwater vehicles (AUVs), travelling at similar speeds, depth ranges and endurance as a foraging penguin, can sample the dynamic marine environment as experienced by a penguin[20,21] These AUV’s navigate in nearshore coastal environments, and can simultaneously measure multiple trophic levels and physical properties of the water column. We deployed an AUV informed by real-time positions of foraging penguins outfitted with satellite transmitters to measure the prey field and ocean properties Using these innovative methods, we investigate the existence of competitive exclusion between sympatrically breeding Adélie and gentoo penguins
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