High energy expenditure at the core of a seabird’s winter range:
metabolic mechanisms for range limits
Abstract
Understanding how geographic range limits are shaped is a central and
challenging question in ecology that has become particularly critical in
the context of global environmental changes. A central hypothesis in
several theories for range limitations is that the density, fitness and
performance of individuals decrease towards the edge of the range as
organisms become maladapted when approaching the limit of their
environmental tolerance (‘Abundant-centre Hypothesis’). Energy is a
critical resource, especially in winter when environmental conditions
deteriorate, and this hypothesis predicts that high energy expenditure
(low performance) at the range limit would lead to rapidly dwindling
body mass and reduced fitness. We investigated this hypothesis in an
Arctic breeding seabird wintering in the North-Atlantic, the
black-legged kittiwake (Rissa tridactyla). From 2008 to 2019, we tracked
118 adult kittiwakes (n= 178 tracks) with geolocation devices and
saltwater immersion sensors to estimate the time-activity budget and
energy expenditure of individuals during winter, and estimated their
reproductive success after their return to the colony during summer.
Density was indeed higher towards the center of the range. However,
contrary to the predictions, the energy expenditure of individuals was
higher at the centre of the range and decreased towards the edge. In
contrast, there were no spatial differences in the reproductive success
of individuals wintering at the centre versus at the edge of their
range. We conclude that performance and fitness did not increase towards
the centre of the range, implying that although resource acquisition was
likely higher at the abundant centre, energy expenditure was also
higher, so that individual fitness was constant across the range.