Investigating the effects of forest structure on the small mammal community in frequent-fire coniferous forests using capture-recapture models for stratified populations

Abstract

Small mammals comprise an important component of forest vertebrate communities. Our understanding of how small mammals use forested habitat has relied heavily on studies in forest systems not naturally prone to frequent disturbances. Small mammal populations that evolved in frequent-fire forests, however, may be less restricted to specific habitat conditions due to the instability of these resources in time and space. We investigate how canopy cover and the volume of coarse woody debris (CWD), covariates that are considered important for small mammals, impact abundance and body mass of eight small mammal species. Based on live-trapping data collected across 23 sites over three years in a frequent fire forest in the Sierra Nevada we apply capture-recapture models for stratified populations, a statistically rigorous, rarely used framework that allows joint modeling of detection, abundance and its response to covariates. Canopy cover had a strong negative association with the abundance of yellow-pine chipmunks and California ground squirrels, and a strong positive association with deer mice. CWD had a strong negative association with the abundance of golden-mantled ground squirrels, yellow-pine and long-eared chipmunks, and a strong positive association with deer mice. Whereas canopy cover influenced abundance and body mass similarly, CWD had a positive association with body mass and a negative association with abundance in some species. These patterns could arise if suitable habitat is monopolized by socially dominant individuals. Despite these habitat associations, the small mammal community in our study was dynamic and diverse, with spatial and temporal variation in dominant species suggesting that species were flexible in their use of habitat. This study suggests that it is important to understand the disturbance regimes when investigating habitat requirements, coexistence and evolutionary ecology of small mammal species.