Abstract

The timing of reproduction in plant and animal species is a strong determinant of offspring viability and reproductive success. The large changes in climate reported the last decades could therefore have unprecedented consequences on population dynamics. The breeding time of many species have changed over the past two to three decades in response to climate change, and a developing trophic mismatch between the peak of energy demands by reproducing animals and the peak of forage availability has caused many species’ reproductive success to decrease. The main aim of this thesis was to determine how reproductive phenology of reindeer (Rangifer tarandus) responds to the changes in its environment and whether there could be resulting fitness consequences. Using long-term datasets of 45 years of birth dates, 13 years of mating behaviors and 14 years of copulation dates of a semi-domesticated reindeer population in Kaamanen, northern Finland, I showed that both the reindeer timing of mating and timing of calving have occurred earlier over time, in response to climate. Climatic variables at four key periods in the reproductive cycle of reindeer were identified as driving the changes in reindeer breeding phenology: winter, late winter/early spring, summer and autumn. Those phenological changes allowed reindeer to keep track of its changing environment, leading to an improvement in females’ reproductive success. I also found a “head-start” benefit with some females always doing better than others do. However, a later vegetative senescence in autumn negatively affected females’ physical condition in winter and the subsequent calf’s birth weight and calf’s first-summer survival. If climatic changes were to exacerbate, the population dynamics of several ungulate species will certainly be affected.