The world's richest tadpole communities show functional redundancy and low functional diversity: ecological data on Madagascar's stream-dwelling amphibian larvae.
BACKGROUND
Functional 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.


RESULTS
Species 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.


CONCLUSIONS
We 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.
Strauss
Axel
A
Zoological Institute, Technical University of Braunschweig, Braunschweig, Germany. a.strauss@tu-bs.de
Reeve
Erik
E
Randrianiaina
Roger-Daniel
RD
Vences
Miguel
M
Glos
Julian
J
D000663:Amphibians; D000818:Animals; D044822:Biodiversity; D017753:Ecosystem; D007814:Larva; D008270:Madagascar; D025341:Principal Component Analysis; D012044:Regression Analysis; D045483:Rivers
Proc Natl Acad Sci U S A. 2009 May 19;106(20):8267-72
19416818
Science. 2001 Oct 26;294(5543):843-5
11679667
J Anim Ecol. 2007 Sep;76(5):977-85
17714276
Front Zool. 2005 Mar 16;2(1):5
15771783
Appl Environ Microbiol. 2000 Oct;66(10):4361-5
11010883
Proc Biol Sci. 2002 Aug 22;269(1501):1721-7
12204134
Ecol Lett. 2009 Jan;12(1):22-33
19087109
Ecol Lett. 2006 Jun;9(6):741-58
16706917
Curr Biol. 2008 Jan 8;18(1):1-8
18164201
Nature. 2000 Feb 24;403(6772):853-8
10706275
J Anim Ecol. 2009 Mar;78(2):305-14
18671805