Do people really just use geographic maps instead of habitat to a) find in
the wild and b) plan for conservation of threatened species? I know I
always check what a species' required or usual habitat is.
> On 12/12/2007, L&L Knight <> wrote:
> > http://ucsdnews.ucsd.edu/newsrel/science/12-07ThreatenedBirds.asp
> > Threatened Birds May Be Rarer than Geographic Range Maps Suggest
> > December 10, 2007
> > By Kim McDonald
> > Geographic range maps that allow conservationists to estimate the
> > distribution of birds may vastly overestimate the actual population
> > size of threatened species and those with specific habitats, according
> > to a study published online this week in the journal Conservation
> > Biology.
> > "Our study found that species ranges in general tend to get
> > overestimated, but that this trend is particularly pronounced for birds
> > that are threatened, rely on specialized diets or have small
> > habitats," said Walter Jetz, an assistant professor of biological
> > sciences at UC San Diego and the lead author of the study, which will
> > appear in the February issue of the printed journal. "This suggests
> > that many threatened species of birds may be even rarer than we
> > believe and are in greater danger of going extinct."
> > "Our findings indicate that the ranges of most vulnerable bird species
> > are experiencing the highest overestimation, thereby painting a rosier
> > picture of their distributions than is actually the case," said Cagan
> > Sekercioglu, a senior research scientist at Stanford University and a
> > co-author of the study. "This suggests that the conservation status of
> > many narrow-ranging, specialized and threatened bird species may be
> > worse than we think."
> > Jetz, Sekercioglu and James E.M. Watson of Britain's Oxford
> > University evaluated geographic range overestimation and its potential
> > ecological causes for 1,158 bird species across 4,040 well-studied
> > survey locations in Australia, North America and Southern Africa.
> > Comparing the range maps with actual bird surveys, such as those
> > conducted by the Audubon Society, the scientists found that most
> > species actually occur in only 40 to 70 percent of the range suggested
> > by their range maps. In other words, these birds are not actually
> > found in 30 to 60 percent of their supposed range.
> > The scientists also found range overestimation increases for species
> > with smaller ranges and with more specialized dietary and habitat
> > requirements. Range maps most strongly overestimate the distribution
> > of narrow-ranging species and ecological specialists. As a
> > consequence, species threatened or near threatened with extinction are
> > also subject to particularly high range overestimation, on average 62
> > percent overestimation compared to 37 percent overestimation in
> > non-threatened species.
> > 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 ounderstimating <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 we're starting with a range estimate for a population that is much
> > larger than it truly is, then we have started with the wrong parameter
> > for our future projections of climate change," he said. "If you've
> > already started with an overestimate of the range, then there's a real
> > danger in understimating the risks of extinction in future projections
> > of climate change."
> > www.birding-aus.org
> > birding-aus.blogspot.com
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> John Leonard
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