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Insular Biogeography in Continental Regions. I. The Northern Andes of South America

Francois Vuilleumier
The American Naturalist
Vol. 104, No. 938 (Jul. - Aug., 1970), pp. 373-388
Stable URL: http://www.jstor.org/stable/2459123
Page Count: 16
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Insular Biogeography in Continental Regions. I. The Northern Andes of South America
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Abstract

In order to test whether the theory of insular biogeography also applies to a continental situation, species diversity and endemism were studied among the birds living in islands of paramo vegetation above timberline in the northern Andes of South America. Stepwise regression analyses were performed, assuming that measures of environmental diversity (especially area) and of isolation (interisland distances) permit prediction of species numbers and numbers of endemics in a continental situation, as they do in archipelagos. With seven independent variables included in the equations, prediction of species diversity and endemism was extremely good. From 92% to 97% of the variance in species numbers can be accounted for by regression, the best fit (97%) being obtained with a linear model. From 87% to 93% of the variance in number of endemics can be predicted by regression, a semilog model providing the best fit (93 % ). The Andean islands conform to archipelagos in two ways: first, because the species-area curve offers a reasonable prediction, as a first approximation, of species numbers; and second, because the numbers of endemics can best be predicted by some measure of interisland distance. The paramo islands differ from oceanic islands, however, because the distance effect curve is more linear than exponential, and because there is no statistically significant correlation between endemism and area of islands. These differences can be explained if isolation between islands is less absolute, so that the probability distribution of dispersal away from a source area is uniform, instead of exponential or normal.

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