COS 207-1 - Diets of coastal and inland western fence lizard populations in Washington State

Background/Question/Methods

The Western Fence Lizard (WFL, Sceloporus occidentalis) is widely distributed in western North America, with population-level morphological and behavioral variation that can be influenced by local climate and habitat, as well as by diet. Our study examines WFL populations at inland, coastal forest, and beach habitats in Washington State, and investigates: 1) the role of marine resources in the diets of beach versus coastal forest and inland populations, and 2) dietary differences among beach populations in relation to beach topography and habitat structure. Lizards were collected from five beaches along Puget Sound, a coastal forest site ~1000m from the shoreline, and an inland site at ~2,000’ elevation east of the Cascade Range. We collected lizard tail clippings and diet samples at each site for carbon and nitrogen stable isotope analysis.

Results/Conclusions

Beach lizard δ¹³C and δ¹⁵N values were distributed along a mixing line defined by marine and terrestrial diet sources. Variability among individual lizards within a population indicated some lizards consume more marine prey than others. Coastal forest lizards did not rely on marine prey despite their proximity to Puget Sound. A difference in the δ¹³C values of coastal forest and inland lizards may reflect the influence of hydroclimate at each site (1,000 vs 200 mm/yr precipitation). Variation in the average proportion of marine diet among beach populations may relate to shoreline topography adjacent to driftwood habitat. Steep bluffs and densely forested hillslopes could impede terrestrial foraging, while open fields could provide ample terrestrial prey. Our study documents a unique spatial subsidy in which marine nutrients and energy from the Puget Sound ecosystem enter the terrestrial food web via beach dwelling WFL. Variation among lizards within beach populations raises interesting questions about the ecological importance of individual foraging behaviors.