Size at Metamorphosis and Water Loss in a Desert Anuran (Scaphiopus couchii)

We measured net water flux and tolerance to dehydration as a function of size at metamorphosis in the desert anuran Scaphiopus couchii (Anura: Pelobatidae). Experimental conditions were based on extensive sampling in the field of environmental conditions available to and encountered by recently metamorphosed toadlets. Size had little effect on dehydration tolerance. Nevertheless, because larger toadlets lost water at a lower mass-specific rate, they had an advantage in the time available before reaching a critical level of dehydration. Field studies also provide a context for interpreting physiological differences in water loss. In the desert, moist soil has a patchy distribution in space and time. Larger metamorphs, because they can survive longer in the intervening dry areas, may have more time to locate suitable microhabitats.