Factors influencing Ambystoma spp. breeding pond selection and larval persistence in ephemeral ponds

Background/Question/Methods

Ambystomid salamanders utilize ephemeral ponds for breeding and larval habitat. My focal species are the spotted (Ambystoma maculatum) and the blue-spotted complex (Ambystoma laterale and Ambystoma laterale-jeffersonianum) salamanders.  In an initial study in June 2012, I found two ponds, one with only Ambystoma maculatum, and the other only with A. laterale-jeffersonianum larvae. The two hypotheses I am testing are (1) abiotic factors caused these species to breed in one pond over another, or (2) the difference was due to competition. In April 2013, I surveyed 9 ephemeral ponds near Farwell, MI for salamander egg masses.  Egg masses were identified to species and their locations within the pond were noted.  Within each pond, I haphazardly chose several locations to measure the abiotic variables of pH, temperature, dissolved oxygen (D.O.), conductance, turbidity, and depth. The number of locations chosen was in relation to the size of the pond in order to include representative microhabitats. 

Results/Conclusions

Preliminary results suggest that ponds with Ambystoma maculatum egg masses differ from other ponds with egg masses in temperature (n₁=6, n₂=30, U=172.5, p<0.001) and in D.O. (n₁=4, n₂=30, U=120.0, p<0.001).  Ponds with egg masses and ponds without egg masses had no significant differences among any of the abiotic variables measured. Our results suggest that while the ponds with and without eggs may not be significantly different, Ambystoma maculatum appear to be choosing to lay eggs in ponds with higher temperatures and lower D.O. than other species. This is unusual considering A. maculatum require higher D.O. levels for their eggs than other Ambystoma species.  This would suggest abiotic variables are affecting the choice of the salamanders, but does not answer the question of competition.