BIODIVERSITY may have a downside: parasites are likely to become a problem as the number of species in a protected area increases. If this is true, maximising the biodiversity of wildlife reserves may not always be the best option.
Over the past few years, conservationists have tried to minimise the transfer of disease-causing microbes and protozoans between species. These pathogens can ruin attempts to move members of threatened species to game reserves. But larger parasites such as roundworms and tapeworms, which tend not to be lethal, have received much less notice.
That may turn out to be a glaring oversight. Vanessa Ezenwa, an ecologist now with the US Geological Survey in Reston, Virginia, estimated parasite loads in impala on five fenced game reserves in Kenya by counting eggs in faecal samples. In a forthcoming issue of Biological Conservation, Ezenwa reports that reserves containing higher numbers of bovid species 鈥� buffalo and antelopes, in other words 鈥� had significantly higher parasite diversity (DOI: 1016/j.biocon.2003.09.016).
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This means that those game reserves that support a higher bovid diversity than nearby natural habitats have also become parasite reserves. That鈥檚 because some parasites can infect a large range of related species. 鈥淓ach species you add potentially brings new parasites. By adding host diversity, you鈥檙e adding parasite diversity automatically,鈥� Ezenwa says.
Until now, conservation biologists have paid little heed to the possibility that their efforts may increase parasite diversity. 鈥淚t has never occurred to me as something that one worries about in a natural ecosystem,鈥� says Richard Estes, a biologist in Peterborough, New Hampshire, who heads the Antelope Specialist Group of the World Conservation Union (IUCN).
Ezenwa does not recommend that conservationists should avoid creating highly diverse reserves, or decimate existing ones. Before any changes in conservation policy, her results would need to be confirmed by a much larger study over a wider geographic range. Moreover, Ezenwa saw no sign that these parasites harmed their animal hosts significantly. But she suggests reserve managers may want to begin monitoring parasites in case they rise to more damaging levels.