Diet composition: A proximate mechanism explaining stream salamander declines in surface waters with elevated specific conductivity

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 mu S/ 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 mu S/cm, a 4.2-fold decline in total prey volume at 100 mu S/cm, a 2.2 fold decline in aquatic Ix at 135 mu S/cm, and a rapid decline in body condition as SC increased. Adult salamanders experienced a 3-fold decline in autochthony at 382 mu S/cm, no change in prey volumes, a 2-fold decline in aquatic Ix at 163 mu S/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.

Automated summary

Changes in land use, such as mountaintop removal mining with valley fills, often lead to headwater streams with elevated specific conductivity (SC), which affects stream salamanders. Increased SC indirectly impacts stream salamander populations by altering the composition of their diet, reducing food availability and ultimately leading to reduced population occupancy and abundance.