Recent changes in the earth’s climate have been linked with changes in distribution, size and performance of many animal populations. Understanding these changes is critical for environmental scientists if we are to predict what will happen to animal populations under climate change. Many studies of bird populations have documented changes in phenology, or timing, with changing climate, such as earlier breeding seasons, but far fewer examples exist from mammal populations.
In 2011, the project published a paper in Global Change Biology, led by Dr Kelly Moyes. This study documented dramatic changes in the timing of events in the deer population over a 28 year period. Birth dates advanced by almost twelve days. The timing of the rut became earlier, with females coming into oestrus around seven days earlier, and males starting and ending their rutting activities six and eleven days earlier respectively. This also means the rutting season has got longer over time. Finally, the date on which males cast the previous year’s antlers was around six days earlier over the 28 years, and cleaning dates (when males remove the velvet from their antlers, signalling the end of antler growth) advanced by seven days. At the same time, the study found that a measure of climate associated with plant growth- ‘growing degree days’ also increased over time, and could explain a lot of the changes observed.
So how is this affecting the deer population? The study found no change in calf birth weight or survival, and no change in male breeding success over the study period. Although the timing of the deer year was clearly changing over time, it was still unclear why and how it might affect the population in the long term.
Towards the end of 2011, Loeske Kruuk and colleagues won a Natural Environment Research Council grant to fund further research into the effects of climate change on the Rum Red Deer population. In the first part of the grant, we aim to investigate the links between climate, vegetation and deer: has the vegetation changed over time? Is that linked with changes in climate? And how do changes in vegetation affect the timing of deer life history events?
However, if we are to understand how the population might respond to climate change in the future, we need to know not just how traits are changing, but why. This link between the observed changes, and the mechanisms underlying them in animal populations, is poorly understood. The long term nature of the Rum Red Deer Project, and the breadth of information we record about the deer, gives us a fantastic opportunity to address this question.
Broadly, we are seeking to understand whether the changes we observe are due to i) changes in the population structure (for example more young animals breeding); ii) ‘phenotypic plasticity’, individuals adjusting the timing of their breeding to environmental conditions; or iii) evolutionary change: the population evolving to breed earlier as a response to selection driven by climate change.
We will then use this understanding, along with future climate change scenarios, to explore the likely impact of continued climate change on the future of this deer population; and hopefully shed light on what climate change will mean for deer populations across Scotland.