When studying for a doctoral degree (PhD), candidates submit a thesis that provides a critical review of the current state of knowledge of the thesis subject as well as the student’s own contributions to the subject. The distinguishing criterion of doctoral graduate research is a significant and original contribution to knowledge.
Once accepted, the candidate presents the thesis orally. This oral exam is open to the public.
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 three key periods in the reproductive cycle of reindeer were identified as driving the changes in reindeer breeding phenology: winter, late winter/early spring, 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, “too long” vegetative growing seasons negatively affected females’ physical condition in autumn and the subsequent calf recruitment. If climatic changes were to become exacerbate, the population dynamics of several ungulate species will certainly be affected.