Environmental variability and phenology evolution: impacts of climate change and spring onset on reproductive timing in a small mammal

The phenology, or timing of life history events, of organisms affects both ecological and evolutionary dynamics. Recent work has illustrated the effects of climate change on the phenology for many species. Changing selective pressures on phenology can have consequences for species if the reliability of phenological cues decreases or if climate change affects interacting species differentially. There are now numerous examples, in which earlier mean timing of spring has selected for earlier phenology of organisms. However, much less is known about how changes in the variability of spring — and consequently the reliability of cues — might affect species. We built a general model of animal population dynamics to study both the ecology and evolution of phenological events under climate change. We parameterized this model for a population of the collared pika (Ochotona collaris) found in the Yukon, Canada. In line with past work, we show that an earlier timing of spring snowmelt will select for an earlier timing of reproduction. In addition, we show that variability in the onset of spring also selects for earlier reproduction. However, evolution or plasticity in juvenile mortality, due to late snowmelt, can lead to later reproduction. These results highlight the importance of looking at the variability, and not only the mean, in spring onset. The specific relationship between the mean and variability of spring onset coupled with the ability of a population to be plastic or adaptable will determine the long-term effects of climate change on the phenology of species.