Interspecific differences in temperature preference and use of temperature as a predation refuge in tadpoles

Background/Question/Methods Three species of spadefoot toads breed in ephemeral pools of the Sonoran desert.  These pools have a strong temperature gradient (up to 10 C) and shallow areas often exceed the critical thermal maximum (CTM) for these species.  Using microcosm and gradients in gutters we show how temperature preference for each species correlates with its CTM and habitat use within natural pools.  In addition, we show how temperature preference and habitat use change in the presence of carnivore morphs of Spea bombifrons, the primary predator in this system. 

Results/Conclusions

Scaphiopus couchi has the highest of both and is usually found in the shallowest areas.  Spea multiplicata (omnivore morphs) has a lower preference and CTM and uses all areas of pools similarly.  In the presence of predators (carnivore morphs), S. couchi shows no change in either preference or habitat use but S. multiplicata shift to warmer and shallower habitats, often entering areas that exceed its CTM.  Temperature near the CTM seems to be used as a deterrent to predators with S. couchi not responding because it is already found in such areas, but with S. multiplicata increasing its use of shallows but also risking an increase in ‘overheating’.  Shifts in temperature preference influence both survival rates and life-history traits in S. multiplicata.