State-dependent capital and income breeding: a novel approach to evaluating individual strategies with stable isotopes
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RESEARCH
Open Access
State-dependent capital and income breeding: a novel approach to evaluating individual strategies with stable isotopes Kim Jaatinen1*, Markus Öst1,2 and Keith A. Hobson3,4
Abstract Background: Species-specific strategies for financing the costs of reproduction are well understood, forming a continuum ranging from high to low reliance on stored nutrients. Animals relying mostly on stored reserves are termed ‘capital breeders’, whereas ‘income breeders’ rely mostly on concurrent intake when financing the costs of reproduction. The role and adaptive value of individual variation in these strategies remain elusive. Life-history theory posits that capital breeding should be favoured when offspring reproductive value peaks, typically occurring early in the season, and that current income should increasingly be used with progressing season. Because resource limitation may hamper flexible resource allocation, a corollary prediction is that only good-condition individuals may show the expected seasonal shift in resource use. To test this prediction, we examined stable isotopes (δ13C and δ15N) in blood and lipid-free egg yolk of breeding eider females (Somateria mollissima) from the Baltic Sea to assess the role of individual variation in the use of proteins from local diet vs. stored reserves. Results: We show for the first time that individuals from a single population differ in their utilization of stored reserves and concurrent intake to finance the costs of reproduction. Consistent with our prediction, heavy females predominantly used stored reserves for producing egg yolks early in the season, increasingly relying on local feeding with later onset of breeding, whereas light females showed no seasonal change in allocation strategy. Conclusions: Stable isotope profiling at the individual level is a powerful tool for monitoring relative changes in investment strategies through time, showing promise as an early warning indicator of ecological change in food webs. Keywords: Resource allocation, Reproductive allocation, Stable isotopes, Capital vs. income, Climate change, Somateria mollissima
Background The varying degree to which animals rely on stored reserves and on concurrent intake when financing the costs of reproduction led Drent and Daan [1] to classify bird species as either capital or income breeders based on the cues that determine egg-laying and clutch-size decisions. Later, this dichotomy was extended to a host of animals and plants; reliance on stored resources characterizes capital breeding whereas utilization of concurrent food intake is termed income breeding [2]. The more recent realization that these strategies only * Correspondence: [email protected] 1 Novia University of Applied Sciences, Coastal Zone Research Team, Raseborgsvägen 9, FI-10600 Ekenäs, Finland Full list of author information is available at the end of the article
represent endpoints of a continuum [3] spurred interest in examining the degree to which species are capital or income breeders and the adaptive val
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