text: For freshwater organisms, landscapes are divided naturally into discrete drainage basins by watersheds, episodically isolated and reunited by erosional processes. In regions like the Amazon Basin (or more generally Greater Amazonia, the Amazon basin, Orinoco basin, and Guianas) with an exceptionally low (flat) topographic relief, the many waterways have had a highly reticulated history over geological time. In such a context, stream capture is an important factor affecting the evolution and distribution of freshwater organisms. Stream capture occurs when an upstream portion of one river drainage is diverted to the downstream portion of an adjacent basin. This can happen as a result of tectonic uplift (or subsidence), natural damming created by a landslide, or headward or lateral erosion of the watershed between adjacent basins.
  Concepts and fields
  Biogeography is a synthetic science, related to geography, biology, soil science, geology, climatology, ecology and evolution.
  Some fundamental concepts in biogeography include:
  allopatric speciation – the splitting of a species by evolution of geographically isolated populations
  evolution – change in genetic composition of a population
  extinction – disappearance of a species
  dispersal – movement of populations away from their point of origin, related to migration
  endemic areas
  geodispersal – the erosion of barriers to biotic dispersal and gene flow, that permit range expansion and the merging of previously isolated biotas
  range and distribution
  vicariance – the formation of barriers to biotic dispersal and gene flow, that tend to subdivide species and biotas, leading to speciation and extinction; vicariance biogeography is the field that studies these patterns