In October 1996, Hurricane Lili was a killer in Central America. In Cuba, itdestroyed homes and cane crops. But at its final landfall, among the smallislands of the central Bahamas, the great storm was a stroke of extraordinaryfortune for three American scientists -- a catastrophe that created in hours thenatural conditions they had speculated about for 20 years.
The resulting information may answer long-standing questions about catastrophicimpacts on ecosystems, and could help conservationists plan better ways topreserve natural habitat.
"This was the experience, not of one lifetime, but of several lifetimes," saidone of the three scientists, UC Davis ecologist Thomas Schoener, who is stillamazed by the story two years later.
"I think it's unique in science," Schoener continued. "You have here a verydestructive event that strikes any given site very infrequently, theexperimental site was very well studied for a number of years, and theinvestigators not only were there during and after the hurricane, but also hadcompleted their annual population censuses just hours before the storm arrived. It won't happen again in scientific research."
A description of the adventure from UC Davis ecologist David Spiller, WashingtonUniversity evolutionary biologist Jonathan Losos, and Schoener appears in thisFriday's issue of the journal Science.
On Oct. 18, 1996, Spiller and Losos had just returned to Great Exuma Island fromsurveying the spider and lizard populations on 19 smaller islands nearby. Thework was part of a long-term study of the islands' food web.
On Great Exuma, the researchers found faxed weather bulletins from Schoener, whowas in Davis, that warned of Hurricane Lili's approach. In darkness, as thewinds rose to gale force, they helped their Bahamian friends board up buildings,then collected their irreplaceable notebooks and headed for a sturdy house onhigher ground.
Soon, the researchers write in the Science article, "The highly improbablehappened. ... Hurricane Lili, the first major hurricane to strike anywhere inthe Exumas since 1932, passed directly over our study site with sustained windsof 90 knots [about 110 miles per hour] and a storm surge of nearly 5 meters[about 15 feet]."
They emerged after the storm, Spiller said, to find roofs missing, sailboatscapsized and their 15-foot research boat resting atop a clump of trees.
The boat was recovered and, the Science article continues, "The next day, assoon as the storm subsided, and for 3 days thereafter, we recensused populationson all the islands."
Then, and in repeated observations during the next year, the researchers foundevidence for a hypothesis advanced by Schoener in 1983: When Anolis lizards aremissing from small Caribbean islands with lizard-friendly habitat, hurricanesare to blame.
Their unprecedented before-and-after data, the authors write, also helped themevaluate other, more general hypotheses about the ecological impact of a naturalcatastrophe. They concluded:
- Larger organisms were more resistant than small ones to the immediate impactof a moderate disturbance, but the more prolific organisms recovered faster. Onislands that were partly protected, and hence only moderately disturbed, 34percent of lizards were washed away by the storm, compared with 79 percent ofspiders. Yet after a year the numbers of lizards had not changed, while thenumber of spiders had returned to pre-hurricane levels.
- Local extinction risk was related to population size when the disturbance wasmoderate, but not when it was catastrophic. On partly protected islands nolizard population was wiped out, even though some islands previously had fewerthan five lizards. Nine of 22 spider populations were eliminated. On exposed,hence catastrophically disturbed, islands all lizards and spiders becameextinct, even though some populations previously had 140-190 individuals.
- After a catastrophic disturbance, the organisms that could disperse the mostreadily recovered the fastest. In one year, spider numbers on the exposedislands reached about one-third of their pre-hurricane levels, but there were nolizards. Spiller said in an interview that the spiders were probably blown ontothe depopulated islands and thrived in the absence of the predatory lizards.
Understanding such effects is more than academically interesting, Spiller said. It could help shape programs for preserving natural communities.
"For instance, if you have an endangered species in a floodplain, these resultsshould be of great concern. Areas that are physically protected may be worth alot more in the conservation scheme than exposed areas," Spiller said. "Thatfactor usually isn't taken into consideration."
Spiller and Losos will return to Great Exuma this October, in the last weeks ofthe 1998 hurricane season, to continue following the recovery of the biota onthe devastated islands.
The above story is based on materials provided by University Of California, Davis. Note: Materials may be edited for content and length.
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