THE EFFECTS OF DROUGHT ON POPULATION-STRUCTURE, ACTIVITY, AND ORIENTATION OF TOADS (BUFO-QUERCICUS AND B-TERRESTRIS) AT A TEMPORARY POND

From 1985 through 1990, I monitored the populations of two species of toads, Bufo quercicus and B. terrestris, at a temporary pond in the xe ric uplands of north-central Florida. A drift fence with pitfall traps completely encircled the pond basin; the fence was monitored 5 days p er week throughout the year. The 5-year study coincided with a severe regional drought that resulted in generally short hydroperiods at unpr edictable times of the year More than 800 toads were captured. Success ful metamorphosis never occurred at the pond although toads continued to visit it throughout the study. The sex ratio was male biased in B. quercicus but not in B. terrestris, although significant variation was observed from one gear to the next. Likewise, the size-class structur e and length-weight patterns varied among species, sexes, and years. A lthough fewer toads entered the pond basin as the study progressed, to ads may have gone elsewhere to breed or they may have remained in refu gia. Thus, decreased capture does not necessarily indicate that a drou ght-related population decline occurred. Drought may have disrupted no rmal arrival patterns and length of slay within the pond basin. Drough t also could be responsible for variation in annual size-class structu re of captured toads. The uncertainty of the hydroperiod both spatiall y and temporally in adjacent breeding sites, the ability of toads to m ove long distances with the potential for migration between breeding s ites, and the lack of specificity in the choice of breeding sites (i.e . permanent versus different types of temporary wetlands) may lead to the formation of metapopulations in the xeric upland habitats of north -central Florida. Long-term monitoring under a variety of climatic con ditions is needed to assess the effects of drought and other types of environmental stresses on toad populations.