Mechanisms for development and maintenance of biodiversity in neotropical floodplains.

Floodplains are ecosystems, which oscillate between terrestrial and aquatic phases. Therefore, their biodiversity corresponds to the sum of species living in the aquatic-terrestrial transition zone and permanent aquatic and terrestrial habitats within the floodplain, e.g., permanent water bodies and tree canopies. Major factors determining total biodiversity are number of species and their abundance in the connected permanent aquatic and terrestrial ecosystems, the habitat diversity inside the floodplain, the physico-chemical conditions of soils and water, the type of flood pulse driving the system, the actual climate and the paleoclimatic conditions. Biodiversity in different plant and animal groups in floodplain ecosystems varies strongly because of differences in their genetic variability resulting in different levels and ranges of adaptations to the flood pulse. Diversity depends in part on speciation in the headwaters, where populations are separated from each other because gene flow up and down river hinders speciation in the floodplains along the main channels. Also lateral migration of terrestrial organisms into the floodplain and adaptation of life cycle and reproductive strategies to the flood pulse seem to be important mechanisms for speciation. In the Neotropics, more than two million square kilometers are covered by various types of floodplains. Examples of the impact of the different factors on species diversity of selected plant and animal groups are given and the importance of floodplain ecosystems for total species diversity and speciation in the Neotropics is discussed