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BackgroundFunctional diversity illustrates the range of ecological functions in a community. It allows revealing the appearance of functional redundancy in communities and processes of community assembly. Functional redundancy illustrates the overlap in ecological functions of community members which may be an indicator of community resilience. We evaluated patterns of species richness, functional diversity and functional redundancy on tadpole communities in rainforest streams in Madagascar. This habitat harbours the world's most species-rich stream tadpole communities which are due to their occurrence in primary habitat of particular interest for functional diversity studies.ResultsSpecies richness of tadpole communities is largely determined by characteristics of the larval habitat (stream structure), not by adult habitat (forest structure). Species richness is positively correlated with a size-velocity gradient of the streams, i.e. communities follow a classical species-area relationship. While widely observed for other taxa, this is an unusual pattern for anuran larvae which usually is expected to be hump-shaped. Along the species richness gradient, we quantified functional diversity of all communities considering the similarity and dissimilarity of species in 18 traits related to habitat use and foraging. Especially species-rich communities were characterised by an overlap of species function, i.e. by functional redundancy. By comparing the functional diversity of the observed communities with functional diversity of random assemblages, we found no differences at low species richness level, whereas observed species-rich communities have lower functional diversity than respective random assemblages.ConclusionsWe found functional redundancy being a feature of communities also in primary habitat, what has not been shown before using such a continuous measure. The observed species richness dependent pattern of low functional diversity indicates that communities with low species richness accumulate functional traits randomly, whereas species in species-rich communities are more similar to each other than predicted by random assemblages and therefore exhibit an accumulation of stream-specific functional traits. Beyond a certain species richness level, therefore, stream-specific environmental filters exert influence whereas interspecific competition between species does not influence trait assemblage at any species richness level.

We provide detailed morphological descriptions of the tadpoles of Malagasy river bank frogs of the subgenera Ochthomantis and Maitsomantis (genus Mantidactylus, family Mantellidae), and data on relative abundance and habitat preferences of Ochthomantis species from Ranomafana National Park in southeastern Madagascar. Our study includes the tadpoles of six described and four undescribed candidate species. Eight of these larvae were previously unknown. Tadpoles were identified by DNA barcoding. Due to the very rudimentary taxonomic knowledge on Ochthomantis, we followed a ‘reverse taxonomy’ approach in which adult classification was to a great part determined on the basis of larval differences. By this procedure we even identified one candidate species whose adults remain still unknown. The majority of tadpoles in Ochthomantis and Maitsomantis have a rather similar body shape and they usually have similar habitat requirements. However, on the basis of the structure of their oral disk we identified three distinct groups: the first includes the femoralis-like tadpoles of Mantidactylus femoralis, M. ambreensis, M. zolitschka, M. argenteus, and of the candidate species named M. sp. 42, M. sp. 43 and M. sp. 47. They all have a reduced oral disk with poorly keratinized jaw sheaths and labial teeth. The mocquardi-like tadpoles of M. mocquardi and M. sp. 64 are placed in the second group and are characterized by a further reduction of oral disk structures, i.e. a complete lack of labial teeth. The third group includes only M. majori and is characterized by the transformation of the upper jaw sheath into three thorn-shaped projections. Based on a preliminary molecular phylogenetic analysis the reduction of keratinized oral structures in M. majori may have occurred convergently to that in M. mocquardi. The ecological data indicate that the tadpoles of the three most abundant species in Ranomafana (M. femoralis, M. majori and M. sp. 47) do not obviously differ in their choice of microhabitat although the differences in their oral structures indicate that they might use different food resources. They all show a preference for the stream areas with slow current and leaf litter substrate.