Density-dependent foraging and colony growth in a pelagic seabird species under varying environmental conditions

Davies, Rachel D.; Wanless, Sarah; Lewis, Sue; Hamer, Keith C.. 2013 Density-dependent foraging and colony growth in a pelagic seabird species under varying environmental conditions. Marine Ecology Progress Series, 485. 287-294.

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Intra-specific competition for food resources affects both foraging behaviour and population growth rates in many species, highlighting a need to better understand how changing environmental conditions affect individuals in populations of different sizes. Using chick-rearing northern gannets as a model, we examined the influence of colony size on per capita population growth rates over 2 time periods (1994-2000 and 2000-2009) and on foraging trip durations in each of 2 years (2000 and 2009) at 10 colonies in 2 separate regions of the UK and Ireland (the North Sea and the Celtic/Irish Sea). The slope of the relationship between population size and foraging trip duration in 2009 was less than one quarter of that in 2000, suggesting a much weaker influence of population size in 2009, presumably due to less intense intra-specific competition for prey resources at sea. There was also regional variation, with colonies in the Celtic/Irish Sea growing substantially slower for their size over the period between 2000 and 2009 than did colonies bordering the North Sea, whilst observed trip durations in 2009 were on average 13% shorter than predicted from population size at colonies bordering the North Sea, but 32% longer than predicted at colonies in the Celtic and Irish Seas. These data suggest less favourable conditions for gannets in the latter region in recent years, and that annual variation in trip durations will be particularly marked at large colonies, making them especially vulnerable to adverse effects of low prey availability at sea.

Item Type: Publication - Article
Digital Object Identifier (DOI):
Programmes: CEH Topics & Objectives 2009 - 2012 > Biodiversity > BD Topic 1 - Observations, Patterns, and Predictions for Biodiversity > BD - 1.4 - Quantify and model interactions to determine impacts ...
CEH Sections/Science Areas: Watt
ISSN: 0171-8630
Additional Keywords: competition, climate change, northern gannets, Morus bassanus, North Sea, populations
NORA Subject Terms: Ecology and Environment
Date made live: 12 Jul 2013 14:49 +0 (UTC)

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