Biogeography

Abstract

Abstract Biogeography focuses on the distribution of life forms over the world. Tiger beetles are not evenly distributed across the United States and Canada (fig. 8.1). Range maps for tiger beetles in the United States and Canada show that no two species have exactly the same geographical distribution. On the contrary, each species has a distinctive range, whether measured in total area, shape of the boundaries, or latitudes and altitudes. As with almost all other groups of animals and plants, more species of tiger beetles occur in some parts of the continent than in others. Why should this be? One answer involves historical movements of tiger beetle populations. The evidence for long-range movements of tiger beetles in North America is limited to a few anecdotal examples. Adults in more or less continuous habitats like rivers and ocean beaches have obvious routes of dispersal. However, movements of other species over discontinuous habitats are known. Strong favorable winds are likely involved with the dispersal of species like the S-banded Tiger Beetle, which lives on the muddy tidal flats of the Gulf of Mexico and the west and east coasts of North America. Specimens of this species have been found as far inland as Kansas and on offshore oil platforms in the Gulf of Mexico, 160 kilometers from the nearest land. However, this species has not established a population anywhere in inland North America, but these long-range movements may explain why it occurs on virtually every island in the Caribbean.