Evolutionary Ecology

, Volume 11, Issue 2, pp 195–204

The relationship between geographic area and the latitudinal gradient in species richness in New World birds

  • TIM M. Blackburn
  • KEVIN J. Gaston

DOI: 10.1023/A:1018451916734

Cite this article as:
Blackburn, T.M. & Gaston, K.J. Evolutionary Ecology (1997) 11: 195. doi:10.1023/A:1018451916734


One hypothesis for the latitudinal gradient in species richness observed in most animal taxa is that the richness of a region is determined by its geographic area. However, the relationship between geographic area and species richness across regions is generally weak. It has been suggested that this is because species from the tropics spill out of this region of high richness, artificially inflating the richness of other regions. This generates the interesting prediction that the area and richness of extra-tropical regions should be more strongly correlated if tropical species are excluded. We test this prediction using the avifauna of the New World. We find that there is indeed a relationship between the land area and species richness of a region once tropical species are excluded. This relationship is independent of the latitude and productivity of regions. Both latitude and productivity can explain variance in richness unexplained by land area. There is no relationship between land area and species richness if tropical species are not excluded from the analysis, suggesting that tropical species do indeed mask the relationship between richness and area. We conclude that our results generally support the geographic area hypothesis, although tests of its other predictions and on other land masses are required.

extra-tropical geographic area latitudinal gradient New World birds species richness tropical 

Copyright information

© Chapman and Hall 1997

Authors and Affiliations

  • TIM M. Blackburn
    • 1
  • KEVIN J. Gaston
    • 2
  1. 1.NERC Centre for Population BiologyImperial CollegeAscot, BerkshireUK
  2. 2.Department of Animal and Plant SciencesUniversity of SheffieldSheffieldUK

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