Comparing Population Patterns to Processes: Abundance and Survival of a Forest Salamander following Habitat Degradation

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.

Tamm review: Terrestrial vertebrate biodiversity and intensive forest management in the U.S.

“…Generally, salamander richness and abundance were positively correlated with stand age (North Carolina, Petranka et al 1994; Oregon and Washington, Kroll et al 2008). When mature forest was clearcut, salamander populations were dramatically reduced, or emigrated into the soil profile or out of the harvest area where they were not detectable (Petranka et al 1994, Semlitsch et al 2008, Otto et al 2014). After the effects of the initial disturbance, populations slowly increased over time (Petranka et al 1994).…”

“…For downed wood and canopy cover, effect sizes of the relationships tended to be imprecise (Otto et al 2013), suggesting that other factors affect salamanders. Although few studies have evaluated relationships between amphibian vital rates and structural retention, terrestrial salamander survival was positively related to canopy and downed wood retention in Michigan (Otto et al 2014). Similarly, abundances of ensantina (Ensatina eschscholtzii) and clouded salamanders (Aneides ferreus)…”

“…However, additional study of biodiversity relationships with forest road systems is warranted. We also suggest more research on effects of intensive forest management practices on vertebrate vital rates, as abundance can provide misleading inference on population performance (e,g., Abele et al 2013, Otto et al 2014. More research is needed on effects of IFM within a landscape context (Tscharntke et al 2012), especially if it is (1) the predominate forest system in a given landscape; (2) is imbedded or interspersed with other forest management systems (e.g.…”

Slow Lives in the Fast Landscape: Conservation and Management of Plethodontid Salamanders in Production Forests of the United States

“…Thus, without close examination of relationships between these groups, one could have interpreted erroneously that a pattern existed in salamander responses to a broader context, including herbaceous plants. Finally, despite their abundance, terrestrial salamanders often have low or variable detection and recapture rates, as well as small body sizes, factors that complicate tracking individuals and quantifying population responses accurately [79,[92][93][94][95]. …”

Does forest extent affect salamander survival? Evidence from a long‐term demographic study of a tropical newt

“…Annual survival of P. hongkongensis increased with greater extent of forest cover around breeding pools, suggesting that this factor was a strong indicator of the quality of core terrestrial habitat. Previous studies have demonstrated impacts of forest clearance on survivorship of amphibians (Connette & Semlitsch, ; Otto, Roloff, & Thames, ; Rittenhouse, Harper, Rehard, & Semlitsch, ; Rothermel & Semlitsch, ; Todd & Rothermel, ) and consequential increases in risk of population extinction where forest cover has been reduced substantially (Harper, Rittenhouse, & Semlitsch, ), as well as life stage‐specific responses to different timber management practices (Semlitsch et al., ). As population dynamics in longer‐lived amphibians, such as P. hongkongensis , are mediated largely by the survival of adults (Berven, ; Gill, ; Wilbur, ), protection of undisturbed forests around breeding sites is essential for population viability.…”