| Abstract: | This paper proposes that not only do species arise and subsequently become extinct but may behave in fundamentally similar fashions between their times of origin and extinction. Four major steps in the species' life cycle are recognized, based on the relative success of the organism as reflected in such traits as relative abundance, extent of subspeciation, and characteristics of geographic distribution. The first stage, or neospecies, is characterized by increasing abundance and expanding range; representatives are found in many introduced forms, including the English sparrow and European starling. The second stage, or mesospecies, has stable range boundaries, a relatively great abundance, and extensive subspeciation, as illustrated by the song sparrow, gray wolf, house rat, and many others. In the third stage, or euspecies, the level of abundance is generally high and the range boundaries stable, but subspeciation is scant or absent. The final stage, or telospecies, is marked by reduction in range, absence of subspeciation, and a low level of abundance and is exemplified by the whooping crane and other forms nearing extinction. |