Adaptation to the temporal environment: evolutionary ecology of mammalian phenologies

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Energy acquired from the environment must exceed that which is expended in its acquisition. Any trait that yields a greater energy surplus will permit greater allocation to survival and/or reproduction and, hence, represent an adaptation. In this way, phenologies (i.e., timing of annual life history events) can be viewed as adaptations to the temporal environment. Achieving proper synchrony between energetically expensive events (e.g., reproduction) and periods of resource abundance is especially consequential for birds and mammals. Endothermy has enabled these taxa to colonize some of the coldest areas on the globe, but it entails substantial energetic costs. Slight asynchrony will thus have severe energetic (and thus, fitness) consequences. While avian phenologies have attracted scientific and public interest for centuries, our understanding of mammalian phenologies is comparatively poor. I propose to investigate phenological variation in three powerful wild mammal study systems. Red squirrels (Tamiasciurus hudsonicus) and Columbian ground squirrels (Urocitellus columbianus) are similar in size, phylogenetically related and have overlapping ranges in western Canada. However, whereas red squirrels are active year-round, Columbian ground squirrels hibernate for 8-9 months. Fully censused and pedigreed populations have been studied in the southwest Yukon since the late 1980's (red squirrels) and in southwest Alberta since the early 1990's (Columbian ground squirrels). Complete life history data (including phenological records) have subsequently been obtained from thousands of individuals. Black-tailed prairie dogs (Cynomys ludovicianus) present the opportunity to study a similar degree of variation within one species as seen across the above two. While populations throughout most of their range are active year-round, they hibernate at the northern edge in southern Saskatchewan. I propose to study populations across the transition from hibernating to winter-active. With these three systems, I will meet three core objectives over the next five years. First, phenological investigations typically focus on single traits during the initiation of reproduction. Ecological and physiological associations (e.g., carry-over effects and circannual clocks, respectively) and genetic correlations, however, will directly influence both the current expression of phenological traits and their future evolutionary trajectories. I will thus investigate the causes (genetic and environmental) and consequences (for individual fitness and population viability) of (co)variation in the full sequence of phenological traits. Second, optimal allocation of energy involves appropriate distribution both across competing demands (maintenance, growth and reproduction) and time (within a year and over a lifetime). I will take advantage of the complete life history datasets to investigate how variation in phenological traits correlates with variation in other life history traits. Lastly, phenological shifts are the most commonly reported ecological response to climate change. The relative influences of phenotypic plasticity and microevolution in producing these shifts will influence both their rate and ability to be sustained. I will use a combination of quantitative genetic inference and experimentation (reciprocal translocation) to disentangle the relative roles played by these two processes. This series of complementary objectives, employed within three exceptionally powerful study systems, will enable me to make great strides in meeting my long-term objectives - to gain a better appreciation of phenology as a fundamental axis of life history variation and an improved ability to predict how climate change will affect wild populations.