Human Influence on Species Richness and Community Structure in Mediterranean Biome Freshwater River Basins

Explaining patterns of species richness is a central theme in community ecology and conservation.  Ecologists have focused on local (within a site), regional (among sites in a given region), or geographical (among regions) explanations of diversity patterns.  In the case of freshwater fish, studies illustrate that biological factors (competition and predation) and physical factors (habitat diversity, water chemistry, flow regime, temperature and channel morphology) interact to influence species richness within and among communities and operate within a range of spatial scales. 

This study identified global patterns of species richness and trophic diversity in twelve Mediterranean biome freshwater fish communities located on six continents.  Differences were found in both species richness and trophic diversity between continental river basins.

Trophic diversity differed greatly among the continental locations in both number of trophic levels present and the type of tropic levels represented.  This finding helps to further explain and define some long held theories on the biogeographical evolutionary histories of these locations.  Additionally, the resulting differences illustrate the effects humans have had on community structure by introducing invasive species.

This study also examined energetic, ecological, and historical factors that may explain freshwater fish species richness and trophic diversity among Mediterranean biome river basins.  The energetic factor, average annual discharge, was found to explain species richness; and that none of the seven factors measured explained trophic diversity. This result is contrary to studies that have shown net primary productivity as explaining species richness in global freshwater fish communities.  The difference presented in this study states that all basin studies were focused on one habitat type, the Mediterranean biome, whereas other studies examined several varying habitat types. 

The resulting information illustrates the heavy influence that human changes to natural river flow regimes, mainly dams, have on freshwater fish species richness and bio diversity.  The resulting specific knowledge can help conserve species richness and manage river basins altered by human activity.