Present address: National Environmental Research Institute, Department of Arctic Environment, University of Aarhus, Frederiksborgvej 399, DK-4000 Roskilde, Denmark.
The demographic impact of extreme events: stochastic weather drives survival and population dynamics in a long-lived seabird
Article first published online: 28 JUN 2008
© 2008 The Authors. Journal compilation © 2008 British Ecological Society
Journal of Animal Ecology
Volume 77, Issue 5, pages 1020–1029, September 2008
How to Cite
Frederiksen, M., Daunt, F., Harris, M. P. and Wanless, S. (2008), The demographic impact of extreme events: stochastic weather drives survival and population dynamics in a long-lived seabird. Journal of Animal Ecology, 77: 1020–1029. doi: 10.1111/j.1365-2656.2008.01422.x
- Issue published online: 13 AUG 2008
- Article first published online: 28 JUN 2008
- Received 16 August 2007; accepted 2 April 2008; Handling Editor: Henri Weimerskirsch
- modelling climate impacts;
- random-effect models;
- stochastic population dynamics
- 1Most scenarios for future climate change predict increased variability and thus increased frequency of extreme weather events. To predict impacts of climate change on wild populations, we need to understand whether this translates into increased variability in demographic parameters, which would lead to reduced population growth rates even without a change in mean parameter values. This requires robust estimates of temporal process variance, for example in survival, and identification of weather covariates linked to interannual variability.
- 2The European shag Phalacrocorax aristotelis (L.) shows unusually large variability in population size, and large-scale mortality events have been linked to winter gales. We estimated first-year, second-year and adult survival based on 43 years of ringing and dead recovery data from the Isle of May, Scotland, using recent methods to quantify temporal process variance and identify aspects of winter weather linked to survival.
- 3Survival was highly variable for all age groups, and for second-year and adult birds process variance declined strongly when the most extreme year was excluded. Survival in these age groups was low in winters with strong onshore winds and high rainfall. Variation in first-year survival was not related to winter weather, and process variance, although high, was less affected by extreme years. A stochastic population model showed that increasing process variance in survival would lead to reduced population growth rate and increasing probability of extinction.
- 4As in other cormorants, shag plumage is only partially waterproof, presumably an adaptation to highly efficient underwater foraging. We speculate that this adaptation may make individuals vulnerable to rough winter weather, leading to boom-and-bust dynamics, where rapid population growth under favourable conditions allows recovery from periodic large-scale weather-related mortality.
- 5Given that extreme weather events are predicted to become more frequent, species such as shags that are vulnerable to such events are likely to exhibit stronger reductions in population growth than would be expected from changes in mean climate. Vulnerability to extreme events thus needs to be accounted for when predicting the ecological impacts of climate change.