Monday, August 2, 2010

PS 11-93: Relative abundance and habitat use of two larval salamanders in western Kentucky

Thomas L. Anderson, Murray State University and Howard Whiteman, Murray State University.


Temporary pond ecosystems are model study systems for examining community interactions such as interspecific competition.  Many experimental studies have been conducted on larval pond salamanders in the laboratory and mesocosm setting.  Fewer studies have examined interactions in natural populations, which can also provide great insight into community dynamics.  Spotted (Ambystoma maculatum) and mole (Ambystoma talpoideum) salamanders occur syntopically throughout much of their distribution, but coexistence in breeding ponds is infrequent.  Furthermore, the two species’ competitive dynamic is well-known from laboratory experiments, but information from natural ponds is limited.  The study objective was to determine relative densities of larval A. maculatum and A. talpoideum, assess their habitat use within pond communities and examine competitive interactions.  Sampling of thirty woodland ponds (size range of 90m²- 900m²) was conducted in Land Between the Lakes National Recreation Area, Kentucky in June 2009.  Larval salamander density was estimated for each pond using a dropbox, and individual size measurements (e.g. snout-to-vent length) were taken for each salamander.


Of the ponds sampled, seventeen contained A. maculatum only; eleven contained both focal species and two ponds held only A. talpoideumNotophthalmus viridescens (red-spotted newt) was also found in fourteen ponds.  When coexistence occurred, A. maculatum outnumbered A. talpoideum by approximately 14:1 (range of 3:1 to 38:1).  However, A. talpoideum was, on average, larger in SVL than A. maculatum, providing a potential size advantage in competitive interactions.  Size ratios could be influenced by the presence of paedomorphic adult A. talpoideum, which can act as both a predator and competitor. Density and SVL did not differ for either species when comparing single-species ponds versus mixed-species ponds.  Thus, the competitive interaction between these two species may be, in part, driven by the combination of larval density and body size.  Density data collected will be used to design mesocosm competition experiments using the proportions observed in natural ponds.