Explaining responses to climate change in a wild vertebrate population

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Recent changes in the earth's climate have been associated with numerous changes in animal and plant populations: for example, as temperatures have risen, the average timing of key events such as breeding has shifted substantially earlier in many species. However, we still have only limited knowledge of the actual mechanisms driving such responses to climate change. Importantly, we need to understand reasons for the changes that are occurring in the specific characteristics or traits (such as timing, growth or fecundity) that determine individuals' fitness and hence that shape a population's overall rate of growth or decline. Changes in a population's characteristics over time could be driven by one, or more, of three different processes:(i) population-level demographic changes in the representation of different age groups, each of which may display different trait values; (ii) individual-level phenotypic plasticity, whereby an individual expresses a different value of a trait dependent on the environmental conditions it experiences; (iii) genetic-level evolutionary change, whereby the genetic composition of the population changes in response to climate change favouring different genes under novel environmental conditions;These contrasting mechanisms can all generate a trend in the average value of a trait over time, but they have different implications for continued responses to a changing environment, and for whether or not a population can 'keep up' with climate change. Dissecting their relative contributions requires detailed, long-term data-sets. Partly because of this, this analysis of the relative contributions from each mechanism to observed responses to climate change have not yet, to our knowledge, been quantified for any wild animal population. We propose to address this gap using a study of a wild population of red deer (Cervus elaphus) on the Isle of Rum, NW Scotland.This project will enable an analysis of nearly four decades of data on more than 4000 individually-monitored deer. We will first explore the direct and indirect effects of climatic and/or vegetation variation on deer traits; this will require extensive assessments of changes in vegetation properties, for which we will use long-term ground-level and remote sensing data. Our primary aim is then to quantify the relative contributions of the three processes listed above to these trends. Finally, we will use insights from these analyses to create models of the dynamics of the population and of individual traits, and hence to generate predictions for future rates of population growth or decline.The Rum red deer project is arguably the best data resource anywhere for this analysis. The new data collection we propose will provide detailed indications of changes in vegetation properties over the study period, as well as sufficient numbers of records of the morphology, reproductive success, survival, timing characteristics and behaviour of individuals across different decades to test the mechanisms outlined above. Our multi-generation, genetically-validated pedigree will enable us to estimate the extent to which individual characteristics are under genetic control, whether climate change has altered patterns of natural selection on these characteristics, and whether the population has shown an evolutionary response to this selection. We also have extensive experience of the complex statistical and modelling techniques required for the analysis. Our ambition is to provide the most comprehensive analysis to date of how a wild animal population is responding to climate change and whether there are limits to its natural capacity to change. Our study will be the first of its kind. Given the importance of large herbivores to the way ecosystems function, our results will have implications for future management policy as well as offering fundamental insights into the mechanisms by which climate change affects wild populations.