Effects of food supplementation and helminth removal on space use and spatial overlap in wild bank vole populations

Animal space use and spatial overlap can have important consequences for population-level processes such as social interactions and pathogen transmission. Identifying how environmental variability and inter-individual variation affect spatial patterns and in turn influence interactions in animal populations is a priority for the study of animal behavior and disease ecology. Environmental food availability and macroparasite infection are common drivers of variation, but there are few experimental studies investigating how they affect spatial patterns of wildlife. Bank voles (Clethrionomys glareolus) are a tractable study system to investigate spatial patterns of wildlife and are amenable to experimental manipulations. We conducted a replicated, factorial field experiment in which we provided supplementary food and removed helminths in vole populations in natural forest habitats and monitored vole space use and spatial overlap using capture-mark-recapture methods. Using network analysis, we quantified vole space use and spatial overlap. We compared the effects of food supplementation and helminth removal and investigated the impact of season, sex, and reproductive status on space use and spatial overlap. We found that food supplementation decreased vole space use while helminth removal increased space use. Space use also varied by sex, reproductive status, and season. Spatial overlap was similar between treatments despite up to three-fold differences in population size. By quantifying the spatial effects of food availability and macroparasite infection on wildlife populations, we demonstrate the potential for space use and population density to trade off and maintain consistent spatial overlap in wildlife populations. This has important implications for spatial processes in wildlife including pathogen transmission.

Methods
These data were collected during field sampling of wild bank voles at our experimental study sites. Voles were longitudinally monitored using capture-mark-recapture methods on standardized trapping grids over 48 hours (traps checked 4x in 48 hours) once a month from June to October 2021. Sites were randomly assigned to one of four treatment pairings (food supplementation only, helminth removal only, both food supplementation and helminth removal, no manipulation). Captured voles were marked with a unique passive integrated transponder (PIT tag) for identification. The capture location (trap number) was recorded for each vole at each capture. The sex and reproductive status of captured voles were assessed once per month. Data was collected in the field by hand, digitized, and cleaned for quality control. The capture data here represents all captures in 2021 where sex and reproductive status data were recorded. These data were then used in social network analyses in program R to estimate space use of bank voles and spatial overlap between individuals in each population.