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15 August 2018 Effects of climate change and environmental variability on the carrying capacity of Alaskan seabird populations
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Marine birds in Alaska, USA, have been monitored systematically for more than 4 decades, and yet it remains unclear why some populations have increased while others have declined. We analyzed the population dynamics of 5 seabird species—Black-legged (Rissa tridactyla) and Red-legged kittiwakes (R. brevirostris), Common (Uria aalge) and Thick-billed murres (U. lomvia), and Tufted Puffins (Fratercula cirrhata)—across 4 decades in Alaska. We tested hypotheses that each species' carrying capacity varied continuously through time with climate cycles and/or in response to habitat covariates. Using an information-theoretic approach, we evaluated competing candidate stochastic growth models of each species' annual rate of change, incorporating various environmental covariates. The North Pacific Index and Pacific Decadal Oscillation were the most important climatic covariates across the whole of Alaska, where the former generally was negatively related to rates of population change, and the latter positively related. Across the 40-yr time series, we found slight decreases in zooplankton (i.e. krill) concentrations across the Gulf of Alaska, and significant increases in sea surface temperature across the Aleutian Islands. Kittiwakes showed the greatest level of sensitivity to these 2 environmental changes. Our results provide evidence that deteriorating secondary productivity (i.e. euphausiids) has contributed to declines of Black-legged Kittiwakes in the Gulf of Alaska. In contrast, the carrying capacity of murres has increased across the state, even in regions affected by warming waters and reduced productivity. These results suggest that kittiwakes act as indicators of detrimental impacts of climatic variability, whereas murres demonstrate resilience to such environmental change. Identifying the ecological factors that explain seabird population dynamics is necessary to understand the implications of climate and environmental change for long-term marine ecosystem dynamics.

© 2018 American Ornithological Society.
Holly F. Goyert, Edward O. Garton, and Aaron J. Poe "Effects of climate change and environmental variability on the carrying capacity of Alaskan seabird populations," The Auk 135(4), 975-991, (15 August 2018).
Received: 8 March 2018; Accepted: 6 June 2018; Published: 15 August 2018

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