Workpackage 04

Member of the

Freshwater Information Platform

Workpackage 04

Contemporary and Past Patterns in Freshwater Biodiversity

Responsible Institute: Institut de Recherche pour le Développement (IRD)

Key research questions:

  • Which factors best explain the variation in freshwater species biodiversity patterns? Are these factors recurrent among a wide variety of groups of organisms?
  • What is the relative role of each of the three hypotheses in explaining biodiversity gradients, and more particularly what is the true role of history?
  • How do the roles change at varying spatial scales? Is the relative role of each of the three hypotheses recurrent among organisms?
  • What are the consequences of human activities on these natural biodiversity patterns?
  • Can palaeoecological micro- and macrofossil records in lake sediments be used to identify changes in freshwater biodiversity?

Understanding historic and contemporary patterns of freshwater biodiversity is an important pre-requisite to predict the future distribution patterns and population trends driven by socio-economic pressures and climate change. The factors responsible for the past and present biodiversity patterns have long been studied by ecologists, bio-geographers and palaeontologists. Of the dozens of hypotheses put forward, three have consistently emerged as explanations of variation: species-area, species-energy, and history.

The species-area hypothesis refers to the existence of a positive relationship between the number of species present in a given area and the size of that area, explained by a combination of size-dependent extinction and speciation rates as well as the influence of the diversity of the habitat. For the first, the probability of extinction for a given species increases with a reduction in population size, which is assumed to be a function of the size of the area in which it lives. The second explanation suggests a positive effect of area on speciation rate by exposing species to greater ecological heterogeneity and more geographical barriers. The third explanation suggests that larger areas have more habitat types, thus allowing more ecological niches and consequently favouring the coexistence of more species.

The species-energy hypothesis, predicts a positive correlation between species richness and the energy available within the system, either as the factor determining available resources (e.g. primary production) or as the upper and lower physiological limits of species. In the former, one would expect an ecosystem variable such as net primary production to be an important predictor of species richness, whereas in the latter, autecological variables such as temperature tolerance would predominate. Historical hypotheses attempt to explain patterns in species richness as a function of recolonisation of systems and thus by the degree of maturity achieved since the last major climate change (e.g. retreat of Pleistocene glaciers ca. 10,000 years ago).

An important aspect of our research will be to quantify the ability of these overarching hypotheses to predict biodiversity changes across taxonomic groups and at increasingly smaller scales. The inclusion of factors related to the degree of fragmentation of water bodies, eutrophication processes and temperature regime changes will further allow us to evaluate the potential effects of these types of stressors on contemporary freshwater biodiversity patterns. A key contribution to our understanding of biodiversity trends will come from the integration of historical data sets (lake sediments, repeated plankton sampling over multiple decades) to determine the temporal scales on which patterns change.