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Temporal Changes in Insular Populations of the Pika (Ochotona Princeps)

Smith, Andrew T.
Ecology 1980 v.61 no.1 pp. 8-13
Ochotona, extinction, habitats, islands, mammals, population size, temporal variation, California
Temporal change in size of populations of a small alpine mammal, the pika (Ochotona princeps), at Bodie, California, USA, was analyzed by comparing a 1972 census of the observed spacing of pikas on discrete islands of habitat to a similar 1977 census. The islands of habitat varied in size and distance from one another. Overall results from each census were strikingly similar. Not all of the islands were occupied and most seemed to contain fewer individuals than they could hold. The populations apparently represent dynamic equilibria between extinction (which was inversely related to island size), and recolonization (which was inversely related to inter—island distance). In spite of these similarities, the population size of individual islands changed dramatically. Eight previously unoccupied islands were colonized and 11 island populations became extinct. Fifty—three percent of 77 islands compared changed their degree of saturation within the 5—yr period. Changes in percent saturation of available habitat on islands varied among island sizes and degrees of isolation. All cases of turnover (extinction or recolonization) occurred on small or medium—sized islands. Within these island size categories, turnover increased with isolation. Extinction of populations on islands close to a source of potential colonists was apparently minimized by recurrent colonization, a verification of the rescue effect.