Caviar in the rain forest: monkeys as frog-spawn predators in Taï National Park, Ivory Coast

Extract

The high predation pressure in aquatic environments is generally assumed to be the ultimate cause of terrestrial breeding in anurans (Downie 1993, Magnusson & Hero 1991, Poynton 1964, Yorke 1983). It has evolved multiple times and is presently found in most anuran families (Bogart 1981, Duellman 1992). It is often associated with higher humidity and thus lower desiccation risk in tropical forests (Duellman & Trueb 1986). Most clutches that are oviposited terrestrially are either hidden in subterranean refuges or attached more or less exposed to vegetation (Duellman & Trueb 1986, Lamotte & Lescure 1977). Exposed clutches however, face the risk of desiccation, even in rain-forest environments (Rödel pers. obs.) and are still vulnerable to predation. Such disparate groups as various arthropods (Villa 1977, 1980; Villa & Townsend 1983, Vonesh 2000), frogs (Crump 1974), snakes (Roberts 1994, Scott & Starrett 1974, Warkentin 1995) and birds (Brosset 1967), have been reported to feed on these clutches. The foam nests,which occur in at least six tropical anuran families, seem to provide better protection. Their drying surface and their more or less liquid interior offers the tadpoles an aquatic environment that is well protected against desiccation and predation (Duellman & Trueb 1986, Seymour & Loveridge 1994). In addition the bubbles of the foam facilitate oxygen diffusion within the nest and may even provide a capacious oxygen store for eggs and hatched tadpoles (Seymour & Loveridge 1994). Few predators have been reported to feed on foam nests, one of which,paradoxically, is a frog (Drewes & Altig 1996). In the Taï National Park, Ivory Coast, we discovered a quite unexpected group of predators preying on foam nests and frog clutches exposed on leaves: monkeys.