Amphibian diversity and phenolic concentration across a canopy cover gradient

Background/Question/Methods

Amphibians commonly breed in vernal ponds, where their eggs hatch, and their larvae live until metamorphosis. Amphibian species are commonly separated into two groups: those that breed in ponds without canopy cover, and those that breed in ponds with canopy cover. Research has shown that the larvae of open canopy species perform poorly in closed canopy ponds, while the inverse relationship is not observed. Closed canopy ponds typically have substrates composed entirely of decaying leaf matter, which contain high concentrations of phenolic compounds, which can be toxic in high concentrations. With this study we sought to determine which factors affect the concentration of phenolic compounds within a pond, and whether or not the phenolic concentration of a pond affects which species can effectively utilize it for breeding.

                Ten ponds were identified on the Edwin S. George Reserve, five of which had a closed canopy, and five of which had an open canopy. Water samples were collected from each pond and analyzed for the total dissolved organic carbon, and the total phenolic concentration. An amphibian survey was conducted at each pond and used to estimate the population sizes of amphibians using these ponds.

Results/Conclusions

There was not a significant difference in the phenolic concentration between closed and open canopy ponds. The two highest phenolic concentrations observed were both in closed canopy ponds. A high level of variation was found in the concentration of phenolic compounds found in different tree species leaf litter, with Red Maple having the highest concentration, and Red Oak having the lowest concentration. There was an increase in the average concentration of phenolic compounds in the ten sample ponds between spring and summer. There was a negative correlation between amphibian species richness and the concentration of phenolic compounds within a pond.

                These results indicate that the amount of canopy cover may not be as important as the type of canopy cover in determining the phenolic concentration within a pond. The negative correlation between amphibian species richness and phenolic concentration has important implications for amphibian conservation, as there may be direct effects of forest composition on amphibian species richness, and species specific interactions between the canopy and amphibians. Forest community may be an important factor when planning amphibian re-introductions, or conservation efforts.