Climate change is a pervasive and compelling situation affecting natural populations. Despite confirmation that climate change is occurring, its effects on ecological communities is less understood. A model system to address these effects is small mammal communities, especially those including deer mice (genus Peromyscus) which are wide-ranging and ecologically dominant in many ecosystems. Previous models and data suggest P. leucopus (white-footed deer mouse) is extending its range northward, due to milder winters, and displacing P. maniculatus gracilis (woodland deer mouse). The goal of this research was to determine species-specific responses to climate change using long-term data on these species from a forested site on the Upper Peninsula of Michigan. Although non-manipulative, these data can identify long-term trends in mouse populations. Trapping data on these populations was collected at permanent grids from 2011 through 2018, in addition to body mass and length measures, allowing estimation of body condition using the scaled mass index (SMI). Abundances and SMI were compared between Peromyscus species and year to determine annual population changes.
Results/Conclusions
Peromyscus maniculatus were more abundant than P. leucopus in every trapping grid in every year of trapping. Moreover, the annual rate of increase was more variable for P. leucopus, presumably because of lower population sizes. P. leucopus had higher SMI scores than P. maniculatus, except in 2015, when scores for P. maniculatus were higher. A particularly severe winter (based on indices derived from air temperature and snowfall) characterized this year. Finally, overwinter survival was essentially nonexistent for P. leucopus, but has been increasing for P. maniculatus since 2015. Thus, data reported here do not support the idea that P. leucopus are displacing P. maniculatus in this northern forest. Although body condition was higher for P. leucopus, overwinter survival was still low for the southern species. Effects of climate change for deer mice is more complex than milder winters: reduction of snow cover during the winter removes the insulating layer that helps protect communal nests during drastic decreases in air temperature. It is more likely that P. leucopus, being a habitat generalist, is more likely to thrive in areas with more disturbance.