Use of functional diversity to assess determinant assembly processes of testate amoebae community

Functional diversity is among the main components of biodiversity, by quantifying the characteristics of organisms and by investigating which assembly processes prevail in the organisation of communities. The objective of this study was to assess the functional diversity of testate amoebae in floodplains, verifying whether the determinant assembly process of the community is related to environmental filters or the limiting similarity. We tested the hypothesis that the functional diversity of the testate amoebae would be lower than randomly expected in the hydrological periods, influenced by environmental filters. In addition, the functional diversity of the testate amoebae was expected to be strongly influenced by variables related to the productivity of the environments, since the food resources are the most important environmental factors in the assembly of testate amoeba communities. Sampling was carried out quarterly between 2002 and 2011 on the surface of the pelagic zone in six floodplain environments. Results showed that the values were lower than randomly expected according to the functional diversity indices. In addition, the functional diversity was predicted by the environmental variables related to the productivity of the environments according to multiple regression analyses. Our results highlight that functional diversity was mainly influenced by the environmental filters. The limiting similarity and neutral processes could not be totally discarded, and the three mechanisms of community assembly can occur. The environmental filters were linked to productivity and consequently to food resources, which are determinant in the assembly of the testate amoebae community, corroborating our predicted hypothesis.