July 4, 2012
Social Bats More Likely To Pay Higher Price From White-nose Syndrome
redOrbit Staff & Wire Reports - Your Universe Online
New studies conducted by biologists at University of California, Santa Cruz (UCSC) show that the effects of white-nose syndrome, a deadly bat disease, may be worse in bat colonies who are increasingly social during hibernation. The study found that bat species that tend to cluster together during hibernation, even with declining populations, would continue to spread white-nose syndrome.
In 2006, white-nose syndrome made a dramatic appearance in the state of New York, and it continues to move into the United States and Canada, destroying entire bat populations. Bats will hibernate in abandoned mines and caves, in varying numbers of individuals. The disease spreads across the bodies of the bats, disturbing their hibernation patterns and causing strange behavior and death.
Biologists from UCSC focused on six different bat species in the study, finding that some populations show a trend towards extinction, while others stabilize after reaching low numbers. “All six species were impacted by white-nose syndrome, but we have evidence that the populations of some species are beginning to stabilize, which is really good news,” stated Kate Langwig, lead author of the paper and UCSC graduate. “This study gives us an indication of which species face the highest likelihood of extinction, so we can focus management efforts and resources on protecting those species.”
The National Science Foundation (NSF), the National Institutes of Health (NIH), and Ecology and Evolution of Infectious Diseases (EEID) funded the study. The study, published on July 3, 2012, focused on population trends affected by white-nose syndrome in the six bat species between the years of 1979 and 2010.
“Managing disease outbreaks appears to be a daunting task, given the complexity of most ecosystems,” stated the EEID program director at the NSF, Sam Scheiner. “This study, however, shows that in fact we can identify the key factors needed for adequate management.”
Langwig and the co-authors of the paper examined the population trends of the six bat species, and how severely they decreased after white-nose syndrome appeared in their colonies. They also looked at the effects of the disease on large and small colonies.
“We found that in the highly social species that prefer to hibernate in large, tightly packed groups, the declines were equally severe in colonies that varied from 50 bats to 200,000 bats,” stated Marm Kilpatrick of UCSC, a co-author of the paper. “That suggests that colonies of those species will continue to decline even when they reach small population sizes.”
These predictions have support from declining population trends in different bat species since white-nose syndrome first appeared. The colonies that are not highly social tend to stabilize at lower numbers, while sociable bat species show a tendency to decline rapidly. One species, however, is pushing through that trend, even though they are highly social.
One of the most common bat species throughout the northeast, known as the little brown bat, is displaying behavioral changes in hibernation. Once preferring to roost in clusters, the little brown bat individuals are now roosting separately from one another.
"Our analysis suggests that the little brown bats are probably not going to go extinct because they are changing their social behavior in a way that will result in their persisting at smaller populations," stated Kilpatrick.
The Indiana bat, another highly sociable species, has not shown the same behavior, and as a result will most likely decline to near extinction. “Since the appearance of white-nose syndrome, both species have become more solitary, but the change is much more dramatic in the little brown bats,” stated Langwig.
She also stated, “We now see up to 75 percent of them roosting singly. For Indiana bats, only 8 to 9 percent are roosting alone, which does not appear to be enough to reduce transmission rates.”
Unfortunately, these stabilizing numbers may not be enough to save bat species like the northern long-eared bat from extinction. While the number of individuals with white-nose syndrome decreased as the populations decreased, fourteen local populations of the northern long-eared bat went extinct only two years after the discovery of the disease within their colonies. After five years, none of the populations in the studied area endured.
“Northern long-eared bats may be particularly susceptible to the disease, so they continue to get hit pretty hard even after transmission rates are reduced,” stated Langwig.
Another solitary type of bat, the tri-colored bat, has shown dissimilar yet slightly hopeful trends during the three to four year period after the disease appeared in their species. Their levels stabilized, although their populations did decrease.
The two least affected species, the eastern small-footed bats and the big brown bats, are primarily solitary hibernators, although they sometimes roost in small bunches. Langwig stated, “It's not clear why they have been less affected by the disease than other species.”
According to co-author Kilpatrick, one potential reason for this trend in the two species, is that they roost in areas where the disease is not as likely to occur. The biologists studied different microclimates and hibernation roosts within them, finding that arid or cool climates were less likely to be favorable to white-nose syndrome. Kilpatrick stated, “It appears that the driest and coolest caves may serve as partial refuges from the disease.”
Much of the data gathered on bat populations was collected from surveys conducted by state agencies in the past forty years. The U.S. Fish and Wildlife Service and Bat Conservation International also funded the research.
Co-authors besides Langwig and Kilpatrick include Jason Bried of Oklahoma State University, Alan Hicks of the New York State Department of Environmental Conservation, Thomas Kunz of Boston University, and Winifred Frick of UCSC.