A new study has found that 1 in 3 of the world’s parasite species could go extinct over the next century, as a result of climate change. The research found that rising temperatures could cause many species, along with some of their hosts, to lose the territory where they survive.

“Parasites are obviously a hard sell,” admitted the study’s lead author, UC Berkeley graduate student Colin J. Carlson. Yet, despite many people’s reflexive disgust at parasites, such a widespread extinction of parasite species could have far-reaching effects on the world’s ecosystems.

Wolves were also once considered pests, and when they began to disappear, ecosystems went out of balance. Wolves were essential to keeping the populations of their herbivore pre y in check, allowing plants to survive and thrive.

Scientists are only beginning to study the roles that parasites play in their ecosystems. In some, parasites account for most of the biomass in a given ecosystem. For the most part, researchers in the past have ignored the roles that parasites play in food webs, concentrating on the links between predators and prey. Since then, they have found that up to 80 percent of relationships in a given food web involve parasites.

Much like wolves, parasites keep their host’s populations in check, by either killing them, limiting their ability to reproduce, or even making them more vulnerable to predators.

Rising temperatures now threaten these parasite species along with their hosts. Carlson’s team sought a broad perspective on threatened parasites, by studying the current range of each species to understand what climates they can survive in, and how they might be affected by rising temperatures. The team spent five years building a database of this information.

They found some species, such as fleas and tapeworms, would have low tolerance for changing temperatures. Other species were found to be vulnerable since their hosts were themselves threatened by climate change. They concluded that about 30 percent of the species could disappear entirely. Others, such as the deer tick, which causes Lyme disease, could enjoy an expanded range.

Parasites such as deer ticks would arrive in territory where other parasite species are dying off, potentially allowing them to do even more damage in an ecosystem with less competition. Many diseases that affect humans come from parasites or pathogens that have moved from an animal species to human hosts.

According to Carlson:

“If parasites are keeping disease down in wildlife, they might also be indirectly keeping them down in humans. And we might lose that.”

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