Biodiversity for a state is determined by species diversity, levels of rarity and risk, endemism, and number of species lost to extinction. California, Hawaii, Texas, and Alabama have the highest biodiversity levels in the US. Alabama is ranked #1 for fish diversity and #1 among eastern states for species diversity. Alabama has 43% of snails species, 63% of mussels species, 23% of crayfishes species, 38% of fishes species, and 52% of turtles species of the total US and Canada species richness. This richness is partly due to climate, geology, hydrology, and drainage evolution. Climate is a key factor because our climate is relatively constant year round (it may not seem like it since we live here, but compared to other places it is). The lack of direct physical impact from habitat destroying glaciers has also played a role in our biodiversity. Alabama has a great degree of physiographic diversity. Alabama has six regions of physiographic diversity.
This picture labels five of the regions and the sixth is the line, called the Fall Line, that separates the East Gulf Coastal Plain from all the others. Continuing drain evolution, which separates species from their natural habitat and puts different species in the same environment which sometimes creates new species, is a big player in the biodiversity of Alabama.
All of these things lead to the extremely high levels of biodiversity in the state of Alabama.
Picture taken from Dr. Huryn’s Freshwater Studies class from Fall 2013.