Abstract
Habitat degradation resulting from anthropogenic activities poses immediate and prolonged threats to biodiversity, particularly among declining amphibians. Many studies infer amphibian response to habitat degradation by correlating patterns in species occupancy or abundance with environmental effects, often without regard to the demographic processes underlying these patterns. We evaluated how retention of vertical green trees (CANOPY) and coarse woody debris (CWD) influenced terrestrial salamander abundance and apparent survival in recently clearcut forests. Estimated abundance of unmarked salamanders was positively related to CANOPY ( Canopy = 0.21 (0.02–1.19; 95% CI), but not CWD ( CWD = 0.11 (−0.13–0.35) within 3,600 m2 sites, whereas estimated abundance of unmarked salamanders was not related to CANOPY ( Canopy = −0.01 (−0.21–0.18) or CWD ( CWD = −0.02 (−0.23–0.19) for 9 m2 enclosures. In contrast, apparent survival of marked salamanders within our enclosures over 1 month was positively influenced by both CANOPY and CWD retention ( Canopy = 0.73 (0.27–1.19; 95% CI) and CWD = 1.01 (0.53–1.50). Our results indicate that environmental correlates to abundance are scale dependent reflecting habitat selection processes and organism movements after a habitat disturbance event. Our study also provides a cautionary example of how scientific inference is conditional on the response variable(s), and scale(s) of measure chosen by the investigator, which can have important implications for species conservation and management. Our research highlights the need for joint evaluation of population state variables, such as abundance, and population-level process, such as survival, when assessing anthropogenic impacts on forest biodiversity.
Highlights
Anthropogenic habitat degradation is a primary threat to global biodiversity [1,2]
Greater than 30% of amphibian species worldwide are at risk of extinction from different forms of environmental degradation, with anthropogenic habitat degradation often cited as a leading cause of population declines [3,4,5]
For this study we focused on quantity of green-trees and coarse woody debris (CWD), as opposed to characteristics of individual pieces because quantity is directly linked to the Michigan Department of Natural Resources (MDNR) structural retention guidelines [29]
Summary
Anthropogenic habitat degradation is a primary threat to global biodiversity [1,2]. For example, greater than 30% of amphibian species worldwide are at risk of extinction from different forms of environmental degradation, with anthropogenic habitat degradation often cited as a leading cause of population declines [3,4,5]. Most observational and experimental studies on amphibians and forestry use indices like species richness (counts of the number of species), relative abundance (counts of individuals within a species), or occurrence (counts of occupied sites) as response variables [14,15]. These state variables are useful for inferring broad-scale impacts of environmental perturbations [16,17], they have been criticized for failing to elucidate mechanisms of demographic change[13,14,18]. Population patterns (counts) and processes (demography) should be jointly evaluated to better understand wildlife response to habitat degradation
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