Biotic and Abiotic Predictors of Larval Salamander Size and Density
Both abiotic and biotic factors influence population and community structure. However, the simultaneous assessment of the relative importance of both types of factors is rarely performed for multiple traits of a population, such as body size and abundance. Comparisons among different demographic rates are necessary for teasing apart the importance of species interactions and/or environmental conditions on both population and community structure. We tested whether biotic (e.g., larval competition) or abiotic factors influenced larval salamander density and body size in natural populations of two known salamander competitors, Ambystoma talpoideum and A. maculatum. Over six years, we surveyed 33 ponds where these species co-occur in western Kentucky, USA. We found that larval densities between species were positively correlated, and that habitat features had contrasting, species-specific effects. Larval sizes for each species showed negative intra- and interspecific relationships with larval densities of each species, but larval A. maculatum generally exerted the stronger relative interspecific effect. Overall, our study highlights that different characteristics of a population (i.e., body size or abundance) may be differentially affected by abiotic and biotic factors, even for ecologically similar, sympatric species. Understanding which traits are regulated by each component will advance our knowledge on how populations and communities are structured.

Study area in Land Between the Lakes National Recreation Area (LBL), Kentucky, USA. The Trace is the primary paved road through LBL. Water to the west of the study area is Kentucky Lake and water to the east is Lake Barkley. The county boundary line separates Trigg (south) and Lyon (north) counties.

Predicted relationships for significant covariates of larval abundance of A. maculatum and A. talpoideum (panel H) in Period 1 (P1) and Period 2 (P2). Gray circles are naïve estimates of larval abundance. Solid lines are predicted estimates of abundance and dashed lines are 95% credible intervals. Note the difference in scales in y-axes between P1 and P2.

Predicted relationships for significant covariates of larval size of A. maculatum in Period 1 (P1) and Period 2 (P2). Solid lines are predicted relationships of abundance and dashed lines are 95% credible intervals. Gray circles are raw values of SVL. Note the difference in scales in y-axes between P1 and P2. See Figure 4 for A. talpoideum.

Predicted relationships for significant covariates of larval size of A. talpoideum in Period 1 (P1) and Period 2 (P2). Solid lines are predicted relationships of abundance and dashed lines are 95% credible intervals. Gray circles are raw values of SVL.

Relationship of head width (HW) to snout–vent length (SVL) for larval A. maculatum (black triangles and line) and A. talpoideum (gray circles and line). Symbols show raw data values, and lines show predicted relationships.
Contributor Notes
Associate Editor: J. Kerby.