long-term small mammal population dynamics at the hj andrews experimental forest
This project has been ongoing since 2011 and was the basis of Matt Weldy's MS thesis. The overarching goal of this study is to better understand spatial and temporal dynamics of small mammal populations in an undisturbed old-growth forest, and how changes in those populations are linked to the spatiotemporal dynamics of predator populations such as northern spotted owls and mammalian carnivores.
In the first chapter of Matt's thesis he estimated the abundances, autocorrelations, and spatiotemporal associations of 4 small mammal species: Humboldt’s flying squirrels (Glaucomys oregonensis), Townsend's chipmunks (Neotamias townsendii), western red-backed voles (Myodes californicus), and deer mice (Peromyscus maniculatus). The analysis was conducted with data from 2011–2016 using live-trapping mark-recapture methods on 9 sites across elevation and canopy openness gradients of a late-successional forest in HJ Andrews Experimental Forest. Species-specific adult sex ratios, juvenile to adult ratios, and adult body masses were not widely variable among grids (i.e., little spatial variation). Abundance estimates, on the other hand, varied by as much as 4-fold among years and 6-fold among sites. Published paper coming soon!
In Matt's second chapter he estimated grid-specific apparent annual survival, population growth rate, and recruitment of Humboldt’s flying squirrels and Townsend's chipmunks at the same site with same years of mark-recapture data. We found that temporal variation of vital rates strongly exceeded spatial variation in most cases. Apparent annual survival was nearly constant temporally and spatial for Humboldt’s flying squirrels, but was consistently lower and more variable among years for Townsend’s chipmunks. Recruitment was variable among years for both species. Apparent annual survival contributed more than recruitment to the population growth rate of Humboldt’s flying squirrels, but for Townsend’s chipmunks recruitment consistently contributed more than apparent annual survival to the population growth rate. These findings suggest differing life history strategies for these co-occurring species. This study demonstrated significant temporal variation, suggesting that inferences based on short time series or solely on abundance could lead to misunderstanding of population status and associations with different forest types. Published paper coming soon!