for National Geographic News
Eight-legged, wriggly, and potentially menacingtarantulas don't figure in many people's top ten favorite furry animals, though Memphis Zoo, Tennessee biologist and curator Steve Reichling might disagree. In fact, his longtime passion for the largest of spiders has led to their enlistment in a unique experiment.
Reichling has embarked on a novel, decades-long project: to map and quantify Belizean forest degradation with the assistance of 50 or more tarantulas surgically implanted with radio transponders.
Like much of Central and South America, Belize's rainforests have been altered by successive human cultures beginning with the Maya. For most of human history this has involved sustainable methods of land use such as small-scale slash-and-burn farming. However, modern large-scale agriculture is destroying rainforest at an unprecedented rate.
Reichling and his veterinarian colleague Chris Tabaka are collecting information about the success of tarantula populations in rainforest sites, and using it as a measure of the degree of damage to these habitats. The project, which began in March 2000, is expected to continue for at least 20 years, to follow what happens as the current tarantula residents die out and are replaced.
Tarantulas are particularly suitable bio-indicators to map environmental change, because they can live for 20 years and remain in one burrow for life, making them easy to relocate year after year, says Reichling.
So-called bio-indicator species are those that scientists monitor to help understand how environmental change is affecting their habitat as a whole. Bio-indicators have included mammals, plants, and other species. For example, lichens, some of which need pristine air to flourish, have been used to indicate levels of atmospheric pollution in cities.
Though there are many suitable long-lived plant and vertebrate species to monitor tropical ecosystems, most invertebrates have relatively short lifespans, said Stuart Longhorn, who works on tarantula conservation genetics at The Natural History Museum in London. "Tarantula spiders are one of a few exceptions, and can provide a totally different viewpoint [from] studies of vertebrates and plants alone," said Longhorn.
In order to quantify the impact of agriculture on natural habitat over the next 20 years or more, Reichling is following the fortunes of tarantula communities at three different sites in and around Belize's Lamanai Archeological Reserve. Each site consists of mature old-growth forest, long-barren open pastures, traditionally managed forest, and sites newly cleared for farming.
The researchers have already radio-tagged 50 individuals of two common Belizean species of tarantula: the cinnamon tarantula, Crassicrus lamanai, which usually inhabits sun-baked clearings, and the redrump tarantula, Brachypelma vagans, which much prefers dense forest. Changing proportions of the two species at forested sites should offer a quantitative measure of when deforestation has progressed to such a degree that the plot is no longer suitable for its original assemblage of species.
"We are especially interested in documenting an expected shift on the recently cleared areas [from a redrump-dominated site] to a cinnamon-tarantula-biased site," said Reichling. As old redrumps die out, if the habitat is no longer suitable, they won't be replaced, he said.
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