Mixed-species social aggregations in Madagascan tadpoles - determinants and species composition

The frequency, species composition, and determinants of mixed-species tadpole aggregations were analysed under natural conditions in a dry forest of western Madagascar. Most aggregations ( 73%) were formed by more than one species, with up to four species per individual aggregation. Dyscophus insularis (Microhylidae) and Aglyptodactylus securifer (Mantellidae) were the most abundant species in these aggregations. Using a logistic regression model we analysed to what extent the presence and absence of aggregations in a pond can be predicted by its biotic and abiotic habitat variables. Aggregations are more likely in deep, clear ponds with little leaf litter cover on the bottom, while the overall density of invertebrate predators in the pond seems to play a minor role. Our observations suggest that the formation of mixed-species aggregations in tadpoles of the Kirindy Forest in our system is primarily a reaction to vertebrate predators. Therefore, aggregation behaviour may play a key role in the ability of several anuran species to utilize these spawning waters that are unpredictable in regard to the presence of fish and other vertebrates.