Speciation, the process of creating new species, plays a big role in species diversity. In emydid turtles, regions where they have been around longer have more species. Eastern North America has the most species because it's where emydids started out. In the southeast, there are more species because turtles have smaller ranges, not because there are more species in each community. Glaciation and speciation in different areas over time have led to these patterns. Speciation can make ranges smaller and increase regional diversity without adding more species locally. The time it takes for speciation to happen affects species richness in various ways.