Salamander growth rates increase along an experimental stream phosphorus gradient

Area of Science:

• Ecology
• Aquatic Ecology
• Ecosystem Dynamics

Background:

• Nutrient loading effects often diminish with trophic distance, leaving higher consumer responses unclear.
• Few studies examine nutrient enrichment propagation through food webs or the relative importance of nitrogen (N) vs. phosphorus (P).

Purpose of the Study:

• To investigate how nitrogen and phosphorus enrichment affect vertebrate predators in detritus-based headwater streams.
• To determine if nutrient effects on predators differ based on N vs. P and N:P ratios.

Main Methods:

• Conducted two-year whole-stream N and P additions in five streams, creating nutrient concentration and N:P ratio gradients.
• Monitored growth rates of caged and free-roaming larval salamanders (Desmognathus quadramaculatus).
• Assessed average body size of larval Eurycea wilderae.

Main Results:

• Salamander growth rates and body size increased significantly with phosphorus concentration (up to 40% and 60%, respectively).
• Effects were consistent across species, methodologies (caged vs. free-roaming), and temporal scales (3 months vs. 2 years).
• Nitrogen concentration did not show a significant relationship with salamander growth or body size.

Conclusions:

• Salamander growth is primarily influenced by the alleviation of ecosystem-level phosphorus limitation.
• Moderate phosphorus enrichment can substantially impact vertebrate predators in detritus-based food webs.
• Findings emphasize the critical role of phosphorus in supporting higher trophic levels in these ecosystems.