BRAZIL NUT FRUIT CAPSULES AS PHYTOTELMATA - INTERACTIONS AMONG ANURAN AND INSECT LARVAE

Under experimental conditions, body size, and thus indirectly priority effects, determines the outcome of predator-prey interactions among the aquatic larvae of a small assemblage of anuran and insect species using a patchily distributed microcosm. This assemblage occurs naturally in fallen fruit capsules of the Brazil nut tree, Bertholletia excelsa (family Lecythidaceae), in lowland tropical forest in Amazonian Brazil. Three of the species (the tadpole of a poison frog and the larvae of a giant damselfly and a culicid mosquito) are predators in the system and form a guild in which all are capable of feeding mutually on smaller individuals of the other two species. The larvae of the two insects are also cannibalistic, although the tadpole is not. Predator-prey experiments among certain pairs of these three species revealed size-related intra-guild predation. The results of these experiments and observations on naturally occurring capsules indicate that only one individual of any species per fruit capsule will survive to adulthood. Field-sampled capsules revealed low densities of guild members, with few co-occurrences among them. Whether this is due to the timing of the study in the early part of the rainy season or some other factor limiting accessibility to the fruit capsules is unknown. Although priority effects are well known among assemblages of competitors, this study reveals that potentially they can significantly affect predator-structured systems. The larva of a fourth species in the assemblage, a small bufonid toad, is detritivorous and palatable to the three predaceous species. In the presence of one of the three predaceous species, survival of the bufonid larvae depends on a rapid time to metamorphosis and on saturation of the microcosm with enough individuals in a clutch that some will survive to metamorphosis.