The researchers study was limited to mostly temperate areas with relatively high-quality data on bird distributions. They said they expect that in the tropics, where the majority of bird species reside, but where research and data on bird distributions are more limited, that the problem of overestimating bird species ranges may be even more extensive than the scientists found for Australia, North America and South Africa.
People have been treating tropical and temperate data on bird distributions as if they are of equal quality, said Walter Jetz. But the overestimation is especially large for tropical species, which have much smaller geographic ranges, smaller population sizes, are more specialized, and are in greater danger of extinction than those in temperate areas.
Jetz and Allen Hurlbert of the National Center for Ecological Analysis and Synthesis in Santa Barbara published a related study in the August 14 issue of the Proceedings of the National Academy of Sciences, that found that range maps of birds less than 200 kilometers in area also overestimate the area of occupancy of individual species and mischaracterize spatial patterns of species richness.
Jetz added that range maps are becoming especially important for ecologists making projections of the impact of climate change on the health of specific populations and that these two studies demonstrate that conservationists need to be especially careful when making predictions about future risks to species during rapid climate change.
If were starting with a range estimate for a population that is much larger than it truly is, t
|Contact: Kim McDonald|
University of California - San Diego