Why aren't all species everywhere?

A project undertaken at the Australian Institute of Marine Science (AIMS), and supervised by M J Caley

No one species is found everywhere.  While it is easy to understand why this is true for some species, such as those whose distributions end where the land meets the sea, the distributions of many others are not so obviously restricted by features of their physical environment.  These species’ ranges appear to end for no particular reason.  Why this is so is an intriguing problem?  Natural selection should work to adapt species to conditions beyond the edges of their current geographic range.  This process, in turn, should cause the continual expansion of species’ ranges.  Some theory about why natural selection fails to increase species’ ranges has now been developed.  There have been, however, almost no tests of this theory in nature.  Consequently, the evolution of geographic borders, a fundamental trait of all species, and one which has very important consequences for conservation and management, is one of the most poorly understood topics in modern evolutionary biology.  We are testing why species’ borders form using comparative analyses of life histories of reef fishes on the Great Barrier Reef.  This study represents only the first necessary step in understanding the evolution of species’ borders.  It is part of a large multidisciplinary study that will ultimately incorporate the development of species’ borders theory and quantitative and molecular genetic studies of the evolution of species’ ranges.