Associations of the Van Dyke's Salamander (Plethodon vandykei) with Geomorphic Conditions in Headwall Seeps of the Cascade Range, Washington State

We explored the association between Van Dyke's Salamander (Plethodon vandykei) and hydrologic condition, geomorphology, and vegetation structure in headwall seeps in the Cascade Range of Washington State. After conducting salamander surveys and measuring habitat characteristics at 40 seep sites from July to August of 2002, we modeled occurrence of P. vandykei at three site scales: between seeps, within seeps, and between microhabitat sites. We ranked a priori models using Bayesian Information Criterion (BIC). Using logistic regression, with presence and absence as the response, we found best approximating models for the occurrence of P. vandykei at the three site scales is predicted by hydrological and geological habitat characteristics. Between seeps, the probability of the occurrence of P. vandykei increased with increasing proportions of seep face having both dry and sheeting hydrology, and increasing proportions of seep face > 5 m high. Within seeps, the probability of the occurrence of P. vandykei was negatively associated with seeps where total overhead cover was > 25%. Between microhabitat sites, the probability of the occurrence of P. vandykei was positively associated with increases in the percent cover of small cobble, small gravel, and bedrock. P. vandykei appears to be associated with habitats that maintain cool thermal and hydric conditions favorable for a species that is sensitive to heat and desiccation due to physiological constraints.