Reconstructed Dynamics of Rapid Extinctions of Chaparral‐Requiring Birds in Urban Habitat Islands

Reconstructed Dynamics of Rapid Extinctions of Chaparral‐Requiring Birds in Urban Habitat Islands The distribution of native, chaparral‐requiring bird species was determined for 37 isolated fragments of canyon habitat ranging in size from 0.4 to 104 hectares in coastal, urban San Diego County, California The area of chaparral habitat and canyon age (time since isolation of the habitat fragment) explains most of the variation in the number of chaparral‐requiring bird species. In addition, the distribution of native predators may influence species number. There is statistical evidence that coyotes control the populations of smaller predators such as foxes and domestic cats. The absence of coyotes may lead to higher levels of predation by a process of mesopredator release. The distance of canyons from other patches of chaparral habitat does not add significantly to the explained variance in chaparral‐requiring species number–probably because of the virtual inability of most chaparral‐requiring species to disperse through developed areas and nonscrub habitats. These results and other lines of evidence suggest that chaparral‐requiring birds in isolated canyons have very high rates of extinction, in part because of their low vagility. The best predictors of vulnerability of the individual species are their abundances (densities) in undisturbed habitat and their body sizes; together these two variables account for 95 percent of the variation in canyon occupancy. A hypothesis is proposed to account for the similarity between the steep slopes of species‐area curves for chaparral‐requiring birds and the slopes for some forest birds on small islands or in habitat fragments. The provision of corridors appears to be the most effective design and planning feature for preventing the elimination of chaparral‐requiring species in a fragmented landscape. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Conservation Biology Wiley

Reconstructed Dynamics of Rapid Extinctions of Chaparral‐Requiring Birds in Urban Habitat Islands

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Publisher
Wiley
Copyright
"Copyright © 1988 Wiley Subscription Services, Inc., A Wiley Company"
ISSN
0888-8892
eISSN
1523-1739
DOI
10.1111/j.1523-1739.1988.tb00337.x
Publisher site
See Article on Publisher Site

Abstract

The distribution of native, chaparral‐requiring bird species was determined for 37 isolated fragments of canyon habitat ranging in size from 0.4 to 104 hectares in coastal, urban San Diego County, California The area of chaparral habitat and canyon age (time since isolation of the habitat fragment) explains most of the variation in the number of chaparral‐requiring bird species. In addition, the distribution of native predators may influence species number. There is statistical evidence that coyotes control the populations of smaller predators such as foxes and domestic cats. The absence of coyotes may lead to higher levels of predation by a process of mesopredator release. The distance of canyons from other patches of chaparral habitat does not add significantly to the explained variance in chaparral‐requiring species number–probably because of the virtual inability of most chaparral‐requiring species to disperse through developed areas and nonscrub habitats. These results and other lines of evidence suggest that chaparral‐requiring birds in isolated canyons have very high rates of extinction, in part because of their low vagility. The best predictors of vulnerability of the individual species are their abundances (densities) in undisturbed habitat and their body sizes; together these two variables account for 95 percent of the variation in canyon occupancy. A hypothesis is proposed to account for the similarity between the steep slopes of species‐area curves for chaparral‐requiring birds and the slopes for some forest birds on small islands or in habitat fragments. The provision of corridors appears to be the most effective design and planning feature for preventing the elimination of chaparral‐requiring species in a fragmented landscape.

Journal

Conservation BiologyWiley

Published: Mar 1, 1988

References

  • Mediterranean Type Ecosystems: Origin and Structure
    Cody, M. L.
  • The island dilemma: lessons of modern biogeographic studies for the design of natural reserves
    Diamond, J. M.
  • Bird survival in an isolated Javan woodland: island or mirror
    Diamond, J. M.; Bishop, K. D.; Balen, S.
  • The carnivores
    Ewer, R. F.
  • Explorations in bird‐land geometry
    Goldstein, E. L.; Gross, M.; DeGraaf, R. M.
  • The fragmented forest: island biogeography theory and the preservation of biotic diversity
    Harris, L. D.
  • Population variability and extinction in the avifauna of a tropical land bridge island
    Karr, J. R.

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