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Climate Change Makes Spiders Bigger—And That’s a Good Thing

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Theresa Machemer, National Geographic

High temperatures make arctic wolf spiders ditch their favorite food, indirectly helping the environment.

 

Amanda Koltz, an Arctic ecologist at Washington University in St. Louis, studies not only how a warming climate affects predator-prey relations, but also how changes in those relationships influence the broader ecosystem. “I really felt like the animal element was potentially missing from this story,” she says.

Scientists have known for almost a decade that climate change would impact spider populations. A 2009 study showed that a warmer Arctic with earlier springs and longer summers could make wolf spiders both larger and—because larger spiders can produce more offspring—more abundant. (Read expert advice on what to do if you find a spider in your home.)

Wolf spiders will eat most insects and spiders smaller than themselves, and they also dabble in cannibalism; if their populations get too dense, they’ll eat each other. But one of their favorite foods is a fungus-eating arthropod called the springtail. If wolf spiders eat more or fewer springtails, how will the amount of Arctic fungus—and the resulting rate of fungal decomposition—vary?

With all this in mind, Koltz set up some five-foot-wide experimental ecosystems in the Alaskan Arctic. For two summers, she and her team monitored how temperature and the number of spiders changed the mix of organisms within these hemmed-off patches of permafrost.

In higher temperatures, decomposition occurs more quickly and wolf spiders are more active, so Koltz expected that when her mini-ecosystems got warmer, their wolf spiders would drastically reduce the springtail population. But Koltz found just the opposite.

In plots with more spiders, the spiders actually ate fewer springtails. These larger springtail populations then ate more fungus, which lowered the rate of decomposition. Among the hotter plots, the one with more spiders decomposed less than plots with almost no spiders. In a way, the spiders are helping to fight climate change in the arctic tundra.

 

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