Parasites are unloved and unlamented creatures and the very mention of them sends a shiver down many a spine. Creatures like lice, bedbugs and ringworms can cause great harm, lots of nuisance and plenty of suffering to their human hosts upon whom they depend for their survival.
Yet most parasites are harmless to people as only 4% of them pose any threats to us. Not only that but parasitic creatures, from plants to animals, serve vital ecological functions, which is why they should feature in global conservation plans, argue a team of scientists in the United States.
“Parasites are an incredibly diverse group of species, but as a society, we do not recognize this biological diversity as valuable,” explains Chelsea Wood, who researches the ecology of parasites at the University of Washington and is the author of a paper in the journal Biological Conservation on the need to save parasites globally from extinction. “[W]e are losing parasites and the functions they serve without even recognizing it.”
Many of us might think of parasitic animals as unworthy of protection, yet they are among the most diverse, ecologically important animals on Earth, the scientists note. Being as diverse as they are, parasites range from parasitic plants like mistletoes to less loveable creatures like water-dwelling isopods that feed on the tongues of fish so they occupy a very wide spectrum of ecological niches.
Yet they are among the least protected species that rarely if ever feature in wildlife or ecosystem conservation efforts.
“For decades, ecologists have been calling for research to understand parasites’ important ecological role, and increasingly, to protect as many species from extinction as possible. However, most conservationists still work within priority systems for funding and effort that exclude or ignore parasites, or treat parasites as an obstacle to be overcome,” write the researchers, whose work is supported by the National Science Foundation in the US.
The scientists have laid out 12 targets to advance the cause of parasite biodiversity conservation, including more research and better conservation management. Importantly, they argue that half of the world’s parasites should be taxonomically described and named within the next decade so that these creatures and their ecological roles could be better understood.
“If species don’t have a name, we can’t save them,” observes Colin Carlson, an assistant professor at Georgetown University. “We’ve accepted that for decades about most animals and plants, but scientists have only discovered a fraction of a percentage of all the parasites on the planet. Those are the last frontiers: the deep sea, deep space, and the world that’s living inside every species on Earth.”
However, the scientists stress that their conservation scheme does not extend to parasites that infect humans and domesticated animals because these should be controlled. Nor is it a given, they stress, that parasites in nature are universally at a risk of extinction. “We [should] not take for granted that every parasite is dwindling toward extinction or about to cause a major outbreak,” Wood emphasizes.
Many parasites are highly complex, she explains. Some of them require several hosts throughout their lives, which may mean that first they infect fish or amphibians but end up getting transmitted to birds to reproduce. To do this, they may manipulate the behavior or even anatomy of their first fish or amphibian host to ensure they become more susceptible to being eaten by birds so that the parasite can end up in its required new host.
Wood and her colleagues designed an experiment around 16 ponds in the East Bay region of central California to see how local parasites responded to changes in their environment. In eight of the ponds the scientists installed such structures as bird houses, floating perches and mallard decoys so as to attract more birds to the sites. In the remaining eight ponds they made no changes.
After a period of two years the researchers analyzed parasite biodiversity in each of the 16 ponds. What they found was that some parasites declined in number when there were more birds around while other parasites increased in tandem. In other words, different species of parasites will respond differently to changes in their environment, which should come as no surprise.
Whether a drastically changed climate and environment in coming decades will lead to an explosion of parasites or an extinction of them will depend on several variables, but “we need to anticipate both trajectories,” Wood stresses. “The trick now is to figure out what traits will predict which parasites will decline and which will increase in response to biodiversity loss.”
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