Abstracts Biological Sciences

Habitat segregation of two ambystomatids in mountain ponds, Mount Rainier National Park

by Brendan J. Brokes

Ambystoma macrodactylum (long-toed salamander) and A. gracile (northwestern salamander) are two common salamander species occupying key trophic positions in mountain ponds of Mount Rainier National Park. The objective of this research was to document and evaluate the distributions and abundances of the two species, relative to habitat characteristics of ponds in the park. Amphibian distributions and abundances were assessed in 20 ponds from June through September 1993 to 1996. Nutrient concentrations (total nitrogen, Kjeldahl-N, total phosphorus, and orthophosphate-P), habitat characteristics (surface area, depth, elevation, substratum organic content lost on ignition, amount of coarse woody debris, aquatic vegetation, and bottom firmness), and water quality (temperature, dissolved oxygen, alkalinity, conductivity, and pH) were measured. Distinct habitat associations were found for each Ambystoma species. Ponds with one species only were different in surface area, maximum depth, substratum organic content, and elevation. Ponds with A. macrodactylum were small, shallow, high in elevation, and had firm sediments low in organic matter relative to A. gracile ponds. Ambystoma macrodactylum ponds typically contained little coarse woody debris relative to the amount of aquatic vegetation. Ambystoma gracile ponds were large, deep, low in elevation, had flocculent sediment high in organic content, abundant coarse woody debris, and little aquatic vegetation relative to A. macrodactylum ponds. Two ponds supported reproducing populations of both species and exhibited habitat characteristics intermediate to the allopatric pond types. These findings suggest that habitat complexity plays an important role in the segregation of A. macrodactylum and A. gracile.