Study shows urban sprawl threatens genetic diversity

By Mike Lee,  San Diego News

September 22, 2010

– U.S. Geological Survey

This map of the area near Thousand Oaks shows the degree of genetic isolation being experienced by a small songbird called the wrentit (Chamaea fasciata). Biologists from the U.S. Geological Survey and the National Park Service said that as urban development fragmented the Santa Monica Mountains into isolated “habitat islands”, wildlife populations have become genetically isolated. They said animals are unable cross urban barriers to breed with neighboring members of their own species.

Urban sprawl in Southern California is limiting the genetic diversity of animal populations and possibly making them more prone to extinction, according to new research by federal biologists.

Their study, released this week, was billed as one of the first concrete pieces of evidence that show significant genetic changes in populations caused by habitat fragmentation.

Researchers assessed four species — three lizards and a bird — in the Santa Monica Mountains near Thousand Oaks. Co-author Robert Fisher at the U.S. Geological Survey in San Diego said a similar study recently was started in San Diego County to see what has happened to genetic diversity in a region where habitat “connectivity” and conservation planning goes back several years.

His work in the Santa Monica Mountains suggests “habitat islands” are forming where animals are unlikely to be related to the same species in neighboring areas. In addition, animals within smaller and more-isolated habitat patches are closely related to one another.

Research showed that when animals are unable to cross roads and other urban barriers they begin to inbreed and lose their genetic diversity. Decreased genetic diversity may increase a species’ chances of extinction because it limits their ability to adapt to environmental changes.

“We’re starting to see the same genetic isolation across multiple species in the same region, from invertebrates to vertebrates.” said Fisher. “These are really significant findings that will help us understand to what extent urban barriers impact wildlife populations.”

The studied species were chosen to represent different ecological niches and a range of mobility within the coastal scrubland ecosystem. Western skinks tend to be secretive debris-dwellers, while Western fence lizards are relatively fast and mobile.

“What’s interesting is that these four species are abundant and widespread in Southern California,” said Katy Delaney, the lead author of the study at the National Park Service. “But if even these species are being negatively impacted by urban barriers, then what’s happening to the rarer, more specialized species in this region?”

Mike Lee: (619)293-2034; Follow on Twitter @sdenvirobeat.