Arctic spiders spinning new food web as climate warms — and that's a good thing

Facing warmer temperatures, wolf spiders are changing up what’s for dinner, and in doing so, lessening the effects of climate change in their ecosystem.
Wolf spiders are top predators in the tundra. Their activity has cascading effects on below-ground food webs, decomposition rates, and soil nutrients, but these effects are different under warmer-than-usual temperatures. (Kiki Contreras)
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In the Arctic, the wolf spider is a carnivorous beast. With climate change, biologists have discovered the spiders surprisingly shift their tastes, and in doing so, could have a cooling effect in their ecosystem. 

Pound for pound, the wolf spider is the most abundant predator in the Arctic. It eats more creatures than polar bears or wolves. If you rounded up all the wolf spiders, they'd outweigh all the wolves in the Arctic 80 times over.

Top predator status

Their role as a top predator means they can tell scientists like Amanda Koltz quite a bit about how climate change is affecting the North. She spent years working with these wolf spiders in the Arctic, and discovered that as the climate warms, these spiders are not only changing what they eat, but they could also reduce the effects of climate change around them.

Experimental plots were used to test the effects of altered wolf spider densities and warming on organisms below ground, decomposition, and soil nutrient availability. (Courtesy Nell Kemp/PolarTREC 2013/Arctic Research Consortium of the United States)

It's a perfect example of the unexpected chain reactions that can happen in the food web as the climate warms.

In the Arctic, the wolf spiders main prey are these small, wingless arthropods called detritivores, or springtails. The springtails eat fungus. The fungus decomposes the soil.

But in the Arctic, the permafrost soil contains huge stores of locked-in carbon. As the permafrost warms up and starts to thaw, it is becoming available to be decomposed by this fungus. As it gets decomposed, it releases more carbon, which increases the rate of climate change. 

More prey with more predators?

In Koltz's study they assumed that more wolf spiders meant fewer springtails, which meant more fungus, and more decomposition. But they actually found the opposite.

"What we actually found is that under warmer temperatures when we had high densities of wolf spiders in the plots we saw more springtail prey, and that was surprising because, why would you see more prey when you have more predators?"

Arctic wolf spiders are larger in years with earlier snowmelt, suggesting that there could be more arctic wolf spiders as the climate warms. Shown here is a female wolf spider with her juvenile offspring, which she carries on her abdomen. Adult arctic wolf spiders are less than half an inch long. (Amanda Koltz)

"What we think is that maybe under warmer temperatures when you have higher densities of wolf spiders they are more active and more competitive with one another and they could end up killing each other or being more competitive with other small spiders in those enclosures."

Follow the food web fully

The wolf spiders may be changing their diet because competition is higher and they need to kill and eat their competitors, so less of their regular prey will get eaten, which means less decomposition, and less carbon going into the air. 

"It was really neat because we found that wolf spiders can influence rates of decomposition on the tundra. That's really cool. And that effect changes under warming. And so that really highlights that we need to look at these food web level interactions under warming and look at the higher trophic levels."