Experimental Evidence of a Risk-Sensitive Reproductive Allocation in a Long-Lived Mammal

• Published in: Ecology (Durham) 2008-03, Vol.89 (3), p.829-837
• Main Authors: Bårdsen, Bård-Jørgen, Fauchald, Per, Tveraa, Torkild, Langeland, Knut, Yoccoz, Nigel Gilles, Ims, Rolf Anker
• Format: Article
• Language: English
• Subjects: Adaptation, Physiological; Adipose Tissue - metabolism; Animal and plant ecology; Animal physiology; Animal reproduction; Animal, plant and microbial ecology; Animals; Animals, Newborn - growth & development; Biological and medical sciences; Calves; Climate; Concepts & Synthesis: Emphasizing New Ideas to Stimulate Research in Ecology; cost of reproduction; Ecological life histories; Ecology; environmental stochasticity; Experiments; Female; Female animals; Food Supply; Forage; Fundamental and applied biological sciences. Psychology; General aspects; Herds; Hypotheses; life history; Mammalia; Natural grasslands; phenotypic plasticity; Pregnancy; prudent parent; Rangifer tarandus; Reindeer; Reindeer - metabolism; Reindeer - physiology; Reproduction - physiology; Seasons; Stochastic Processes; Summer; Vertebrates: general zoology, morphology, phylogeny, systematics, cytogenetics, geographical distribution; Winter
• ISSN: 0012-9658; 1939-9170
• DOI: 10.1890/07-0414.1

When reproduction competes with the amount of resources available for survival during an unpredictable nonbreeding season, individuals should adopt a risk-sensitive regulation of their reproductive allocation. We tested this hypothesis on female reindeer (Rangifer tarandus), which face a trade-off between reproduction and acquisition of body reserves during spring and summer, with autumn body mass functioning as insurance against stochastic winter climatic severity. The study was conducted in a population consisting of two herds: one that received supplementary winter feeding for four years while the other utilized natural pastures. The females receiving additional forage allocated more to their calves. Experimental translocation of females between the herds was conducted to simulate two contrasting rapid alterations of winter conditions. When females receiving supplementary feeding were moved to natural pastures, they promptly reduced their reproductive allocation the following summer. However, when winter conditions were improved, females were reluctant to increase their reproductive allocation. This asymmetric response to improved vs. reduced winter conditions is consistent with a risk-averse adjustment in reproductive allocation. The ability of individuals to track their environment and the concordant risk-sensitive adjustment of reproductive allocation may render subarctic reindeer more resilient to climate change than previously supposed.