June 22, 2005 MANHATTAN -- It's too late for the dinosaurs; the dodo as well.
But research by a Kansas State University biology professor on how chronic habitat loss increases the extinction risk of migratory songbirds may provide some insight about how other animals might respond to a similar loss of habitat. The research, sponsored by the Environmental Protection Agency's Wildlife Risk Assessment Program, is chronicled in a recent issue of the journal, Ecological Applications.
Kimberly With, an associate professor in K-State's Division of Biology, along with two colleagues, developed a landscape-based population model to evaluate extinction risk for several types of migratory songbirds that breed in the temperate forests and grasslands of the United States. After breeding there, the birds then migrate south to spend the winter months in Central and South America.
With's research objective was to assess how chronic habitat loss can impact extinction risk for migratory songbirds. With said habitat loss and fragmentation are considered to be the greatest threats to biodiversity worldwide.
"This is an issue that affects many different types of systems, not just here in the United States, but globally as well," With said. "Migratory songbirds are a group of particular concern, especially in North America."
With said a majority of songbirds in the United States are in reality "neotropical migrants," ones that spend only four or five months in this country. The majority of their life is spent in Central or South America. Because the birds breed in habitats throughout North America, however, it is important to understand how the widespread destruction, degradation and fragmentation of that habitat -- which involves not just losing habitat, but isolating the remaining habitat fragments -- affects the breeding success of these species.
The researchers used computer-generated songbirds that possessed characteristics similar to the types of species that might be found in nature.
"We then generated different scenarios of dynamic landscape change," With said, "using neutral landscape models in which breeding habitat was systematically destroyed at various rates."
According to With, one concern was that the rate at which habitat was being destroyed might be just as important, if not more so, than the amount of habitat lost or how fragmented that habitat had become.
"The assessment of a species' extinction risk may depend not only upon the current state of the landscape and its projected trajectory of change, but also on its past disturbance history," With said. "The extinction risk was assessed relative to the vulnerability threshold, the point where the change in population growth rate scaled to the rate of habitat loss falls below 21 percent.
The researchers discovered that the rate at which habitat was being destroyed or fragmented was quite important, but in rather counterintuitive ways.
"Our model predicts that songbirds are likely to exhibit lagged responses to habitat loss in landscapes undergoing rapid change," With said. "In such scenarios, the landscape changed more rapidly than the demographic response time of the population, such that population growth rates never exceeded the vulnerability threshold, even though these species inevitably went extinct. "
Thus, songbirds in landscapes undergoing rapid change might not be assessed as ''at risk'' until the population has been seriously eroded, which would obviously compromise the success of management actions aimed at recovering the population.
With said the model illustrates how assessment of a species' extinction risk may vary widely among landscapes of similar structure, depending upon how quickly the landscape achieved its current state. Thus, information on the current landscape state (e.g., amount of habitat or degree of fragmentation) may not be sufficient for assessing long-term population viability and extinction risk in the absence of information on the history of landscape disturbance.
"To some degree we can use these migratory songbirds as indicators of how other animal species might respond to habitat loss and fragmentation," With said.
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