Influence of field technique, density, and sex on home range and overlap of the southern red-backed vole (Myodes gapperi)

Home range is shaped by an individual’s interactions with the environment and conspecifics, and both size and placement may vary in response to population fluctuations. The method used to collect locational data may also affect home-range estimates. We examined the effect of density, sex, and field method on home range of southern red-backed voles (Myodes gapperi (Vigors, 1830)) inhabiting eastern hemlock (Tsuga canadensis (L.) Carrière) forests. Twelve mark–recapture grids were used to census M. gapperi from 2014 to 2017. In 2017, individuals were radio-collared. Home-range size, core-area size, and shared space were calculated using kernel density estimators from both mark–recapture and radiotelemetry data. Density effects on home range and core area were analyzed and differences between sex and field method were compared. We found (i) density did not affect home-range size, (ii) male home range was larger than female home range, (iii) females shared space more frequently and to a greater extent with males than other females, and (iv) home-range estimates were not significantly different between mark–recapture and radiotelemetry. Male home range, however, was larger under radiotelemetry and may reflect a truncation effect when mark–recapture grid size is smaller than male home range.

Response of a Small Mammal Population Postremediation for an In Situ Oil Pipeline Blowout on the Athabasca Oil Sands

Two releases from steam assisted gravity drainage (SAGD) wellheads occurred 3 yr apart. To track recovery of the affected areas, red-backed voles were studied 1 and 4 yr later, using population estimates, hepatic detoxification effort, body condition, and tissue metal levels as bioindicators of site recovery. From years 1 to 4, higher ethoxyresorufin-O-deethylase induction was no longer evident, capture rate was lower, and body lead residues were no longer (inversely) correlated with body condition. Environ Toxicol Chem 2019;38:1542-1548. © 2019 SETAC.

Ecological processes determining the distribution dynamics of vole populations during forest succession

The size and distribution of animal populations may vary drastically over time following a disturbance event. While both competition and predation can control the size of animal populations, changes in the relative importance of these two density-dependent processes remain poorly documented during ecological succession. Here, we combined habitat selection and optimal foraging theory to identify the processes that can explain the increase in red-backed voles (Myodes gapperi) during post-logging forest succession in boreal ecosystems. Specifically, we assessed the extent to which changes in intra- and interspecific competition and in predation risk can explain variation in abundance and distribution of voles during post-harvest forest succession. We estimated the abundances of the red-backed vole and of its main competitor, the deer mouse (Peromyscus maniculatus), in adjacent pairs of logged (5-66 years old) forest stands and uncut stands (> 120 years old). We found that voles increased their preference for uncut stands with increasing conspecific density. Foraging experiments revealed that in early-seral forest stands, voles increased their feeding effort in the presence of deer mice, particularly in safer food patches. This behaviour is expected from foraging theory when interspecific competitors increase predation risk. Apparent competition would thus limit the density of red-backed voles, and changes in the relative strength of this process during forest succession would control patterns of distribution and abundance of the species.

Weather-driven change in primary productivity explains variation in the amplitude of two herbivore population cycles in a boreal system

Vertebrate populations throughout the circumpolar north often exhibit cyclic dynamics, and predation is generally considered to be a primary driver of these cycles in a variety of herbivore species. However, weather and climate play a role in entraining cycles over broad landscapes and may alter cyclic dynamics, although the mechanism by which these processes operate is uncertain. Experimental and observational work has suggested that weather influences primary productivity over multi-year time periods, suggesting a pathway through which weather and climate may influence cyclic herbivore dynamics. Using long-term monitoring data, we investigated the relationships among multi-year weather conditions, measures of primary productivity, and the abundance of two cyclic herbivore species: snowshoe hare and northern red-backed vole. We found that precipitation (rain and snow) and growing season temperatures were strongly associated with variation in primary productivity over multi-year time horizons. In turn, fourfold variation in the amplitude of both the hare and vole cycles observed in our study area corresponded to long-term changes in primary productivity. The congruence of our results for these two species suggests a general mechanism by which weather and climate might influence cyclic herbivore population dynamics. Our findings also suggested that the association between climate warming and the disappearance of cycles might be initiated by changes in primary productivity. This work provides an explanation for observed influences of weather and climate on primary productivity and population cycles and will help our collective understanding of how future climate warming may influence these ecological phenomena in the future.