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Since residents of Monteverde began to informally monitor the golden toads’ (Bufo periglenes) activity in 1972, these toads have emerged en masse from their underground retreats every year in April and May. During 1988, however, something was definitely wrong. I found only one golden toad in the Monteverde Cloud Forest Reserve in northwestern Costa Rica; in the previous year I had seen over 1,500 individuals. During the following month, I could not find harlequin frogs (Atelopus varius) at my study site along the Río Lagarto near Monteverde—on a single day just the year before, I had found over 700 individuals . In the literally hundreds of times I had censused the stream in recent years, harlequin frogs were always abundant, no matter the time of year, no matter the weather conditions. Observations It has now been more than fifteen years since golden toads last congregated at rain pools in the elfin forest and harlequin frogs sat on moss covered boulders at the Río Lagarto. One-half of the 50 known species of anurans from the vicinity of Monteverde disappeared in the late 1980s (Pounds et al., 1997). A likely culprit was a prolonged drought caused by a severe El Niño weather pattern in 1986–1987. Still, other species persisted . Why did certain species disappear while others remain seemingly unaffected? During the past fifteen years, reports of declines and disappearances of amphibians around the world have revealed a similar pattern: within a given area, only certain species have been strongly affected. If we could identify particular traits of the affected species, perhaps we could better protect those species identified as being the most vulnerable. By examining studies of declines within anuran assemblages from fairly protected areas around the world in Brazil, Costa Rica, Australia, and California, we can rule out habitat destruction, modification, or degradation as a cause of observed declines. Within these assemblages, some recognizable patterns emerge with regard to which species have declined. Severe frost likely caused local declines and extinctions of frogs at Boracéia in southeastern Brazil (Heyer et al., 1988). Four of the five species that disappeared have terrestrial modes of reproduction involving either complete independence of water or terrestrial eggs that hatch into tadpoles and then wriggle their way into water. The fifth species has aquatic eggs and tadpoles requiring an extremely long developmental time. Severe population declines occurred in other species with terrestrial eggs that undergo direct development, as well as still other species that lay their eggs on leaves above water and have aquatic larvae. In contrast, most of the species that lay their eggs in ponds and have aquatic tadpoles were still common during the census periods. A similar pattern emerges from an assemblage of frogs that breed in mountain streams around Santa Teresa in southeastern Brazil (Weygoldt, 1989). Of 13 species, eight have declined or disappeared. Weygoldt speculated that a likely cause for the declines was extremely dry winter weather. Of the eight species that were strongly affected, four were thought to be particularly susceptible to drought because of long developmental periods of aquatic larvae. The other four species all laid a small number of large eggs and exhibited specialized modes of reproduction that involve at least the egg stage out of water. The five species believed to be holding their own are all treefrogs that have aquatic eggs and larvae. Of the 25 species of anurans that had disappeared from the vicinity of Monteverde by 1990, only five of these reappeared during 1991–1994. Interestingly, although Pounds et al. (1997) found no significant association between the presence/absence of species and the mode of reproduction, an association between the presence/absence of species and habitat selection was established. Contrary to the pattern found in the assemblages in Brazil, the Costa Rican species completely independent of water were less likely to be affected than those associated with aquatic habitats. In a recent paper, Williams and Hero (1998) examined patterns of ecological characteristics of various rainforest frogs that are either declining or not declining from the wet tropics of Australia. They identified the combination of low fecundity, high habitat specificity, and stream breeding as characteristics of the declining species. Just as relevant, they found no difference between the declining and nondeclining species in their temporal activity period (diurnal or nocturnal), body size, or use of microhabitat. High specificity to breeding sites (particularly stream breeding ) was likewise associated with anuran declines in the Yosemite area of the California Sierra...

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