An appraisal of the fitness consequences of forest disturbance for wildlife using habitat selection theory

Abstract

Isodar theory can help to unveil the fitness consequences of habitat disturbance for wildlife through an evaluation of adaptive habitat selection using patterns of animal abundance in adjacent habitats. By incorporating measures of disturbance intensity or variations in resource availability into fitness-density functions, we can evaluate the functional form of isodars expected under different disturbance-fitness relationships. Using this framework, we investigated how a gradient of forest harvesting disturbance and differences in resource availability influenced habitat quality for snowshoe hares (Lepus americanus) and red-backed voles (Myodes gapperi) using pairs of logged and uncut boreal forest. Isodars for both species had positive intercepts, indicating reductions to maximum potential fitness in logged stands. Habitat selection by hares depended on both conspecific density and differences in canopy cover between harvested and uncut stands. Fitness-density curves for hares in logged stands were predicted to shift from diverging to converging with those in uncut forest across a gradient of high to low disturbance intensity. Selection for uncut forests thus became less pronounced with increasing population size at low levels of logging disturbance. Voles responded to differences in moss cover between habitats which reflected moisture availability. Lower moss cover in harvested stands either reduced maximum potential fitness or increased the relative rate of decline in fitness with density. Differences in vole densities between harvested and uncut stands were predicted, however, to diminish as populations increased. Our findings underscore the importance of accounting for density-dependent behaviors when evaluating how changing habitat conditions influence animal distribution.

Partial cutting in old-growth boreal stands: An integrated experiment

“…Habitat preference of voles also varied as a function of their density, with uncut stands being selected over any of the four silvicultural treatments when vole abundance was low. The preference for uncut stands against selection cut stands disappeared, however, at high vole densities (Hodson et al 2010). It remains that, while our observations support Vanderwel et al ' s (2009) assertion that retention levels ≥50% mitigate the impact of forest harvesting, vole populations are still impacted by such rather high retention levels.…”

“…The Red-backed Vole is generally associated with habitats that provide protective cover from predators and that satisfy their high demands for water (Vanderwel et al 2009). In our study, red-backed voles were most abundant in stands with high moss coverage, high vertical cover, and high conifer basal area, which are typical of high retention levels (Hodson et al 2010, i.e., uncut stands and selection cuts. Habitat preference of voles also varied as a function of their density, with uncut stands being selected over any of the four silvicultural treatments when vole abundance was low.…”

“…As hare density increased, the preference for uncut stands over SCt and SCp essentially vanished, whereas CPRS and CPPTM were strongly avoided, regardless of hare density (Hodson et al 2010). Further, silvicultural treatment effects seemed to be more closely linked to local increases in predation risk than to decreases in browse availability (Hodson et al 2010). Clearcut stands tend to remain poor-quality hare habitats for at least four years following harvest (Ferron et al 1998).…”

“…The effects of our silvicultural treatments on wildlife were assessed during the first three years after cutting by monitoring beetles, birds, small mammals, and Snowshoe Hare (Lepus americanus Erxleben) populations (Hodson et al 2010, Hodson 2011, Légaré et al 2011. Because these animals were studied in the main units without prior marking of trees to harvest, the results are informative about what could be expected in an operational context.…”

The Effects of Wildfire on Mortality and Resources for an Arboreal Marsupial: Resilience to Fire Events but Susceptibility to Fire Regime Change

“…Behavioural responses can mediate the impacts of disturbance on animal populations [19], [20]. Potential responses to post-fire resource decline include range-shifting to track the remaining resources [21]; reduced individual resource use; increased sharing of the remaining resources [22]; or flexibility in resource selection [20].…”