Abstract
Changes in land use, such as mountaintop removal mining with valley fills (MTR-VF), often results in headwater streams with elevated specific conductivity (SC). Stream salamanders appear to be particularly sensitive to elevated SC, as previous studies have shown occupancy and abundance decline consistently among all species and life stages as SC increases. Yet, the proximate mechanism responsible for the population declines in streams with elevated SC have eluded researchers. We sampled salamander assemblages across a continuous SC gradient (30–1966 μS/cm) in southeastern Kentucky and examined the diet of larval and adult salamanders to determine if the ratio of aquatic to terrestrial prey (autochthony), total prey volume, aquatic prey importance (Ix), and body condition are influenced by SC. Further, we asked if threshold points for each diet component were present along a gradient of SC. Larval salamanders experienced a 12–fold decline in autochthony at 153 μS/cm, a 4.2–fold decline in total prey volume at 100 μS/cm, a 2.2-fold decline in aquatic Ix at 135 μS/cm, and a rapid decline in body condition as SC increased. Adult salamanders experienced a 3–fold decline in autochthony at 382 μS/cm, no change in prey volumes, a 2-fold decline in aquatic Ix at 163 μS/cm, and a decline in body condition as SC increased. Our results indicate that SC indirectly affects stream salamander populations by changing the composition of diet, which suggests that food availability is a proximate mechanism that leads to reduced population occupancy, abundance, and persistence in streams with elevated SC.
Highlights
In the central Appalachians of the United States, land-use disturbances have resulted in an environmental gradient of water chemistry; surface waters that vary in specific conductance (SC) in relation to land-use (Hartman et al, 2005; Fritz et al, 2010; Bernhardt and Palmer, 2011; Lindberg et al, 2011; Griffith et al, 2012)
Our results indicate that specific conductivity (SC) indirectly affects stream salamander populations by changing the composition of diet, which suggests that food availability is a proximate mechanism that leads to reduced population occupancy, abundance, and persistence in streams with elevated SC
Elevated SC from MTR-VF has been shown to be negatively correlated with stream salamander occupancy and abundances in Central Appalachia (Muncy et al, 2014; Price et al, 2016, 2018; Hutton et al, 2020)
Summary
In the central Appalachians of the United States, land-use disturbances have resulted in an environmental gradient of water chemistry; surface waters that vary in specific conductance (SC) in relation to land-use (Hartman et al, 2005; Fritz et al, 2010; Bernhardt and Palmer, 2011; Lindberg et al, 2011; Griffith et al, 2012). Ap palachian streams with elevated SC from MTR-VF often have reduced aquatic macroinvertebrate abundance, biomass, and diversity (Chambers and Messinger, 2001; Kennedy et al, 2003; Hartman et al, 2005; Pond et al, 2008; Fritz et al, 2010; Pond, 2010, 2012; Merriam et al, 2011; Cormier et al, 2013; Boehme et al, 2016; Voss and Bernhardt, 2017). The reduction in aquatic macroinvertebrate abundance and diversity in streams with elevated SC may be a proximate mechanism explaining the consistent declines in the occupancy and abundance of salamanders along the SC gradient
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