Wolf spiders change their diets when it warms, leading to ecosystem shifts that could buffer against further warming.
Stephen Dalton/Minden Pictures
By Michael Price
The 4-centimeter-long wolf spider may be having an outsize effect on the Arctic climate. When temperatures rise, the aggressive, ambushing arachnids switch up their diets, eating each other instead of an insect that keeps a greenhouse gas–belching fungus in check, researchers report. As a result, the spiders may be indirectly reducing greenhouse gases over the Arctic and keeping the region cooler than it would be otherwise.
“What this paper illustrates so well is how hard it is to predict the effects of warming temperatures on any particular community,” says Sarah Gilman, a biologist at Claremont McKenna College in California who studies the ecological effects of climate change. But until researchers know why the wolf spider’s diet is shifting, it will be hard to project the results of a small experiment to the entire region.
The wolf spider (of the Lycosidae family) is one of the most abundant and dominant Arctic predators. Kilogram for kilogram, they have about 80 times more biomass than gray wolves in some parts of Alaska. Their chief prey is the 0.6-centimeter-long springtail, which they stalk and ambush. The antennae-sporting insect, in turn, eats soil-dwelling fungi, which release potent greenhouse gases such as carbon dioxide and methane when they feed on decomposing plants and animals.
To see how the spiders might be affecting the climate, Amanda Koltz, a biologist at Washington University in St. Louis, Missouri, and colleagues set up camp in Toolik, Alaska, at the foothills of the glacier-filled Brooks Range mountains. Marching over squishy mounds of moss, dodging giant mosquitoes, and working in the Alaskan summer’s 24-hour daylight schedule, “It reminded me of The Land Before Time,” she says.
Over the next several weeks, the researchers collected hundreds of wolf spiders from under rocks and logs and placed them in 30 1.5-meter experimental ring enclosures. In half of these outdoor plots, they installed a warming chamber that raised the temperature by about 2°C, mimicking the effects of a warming climate. Different plots also had different numbers of spiders. The team let nature play out for 14 months, then returned to see what became of these experimental ecosystems.
Koltz hypothesized that more spiders would mean fewer springtails—and that held true for the normal-temperature enclosures. But within the artificially warmed rings with higher-than-average wolf spider numbers, there were also higher-than-average numbers of springtails. And that translated into less fungus, less decomposed plant matter, and, theoretically, less greenhouse gas escaping, the team reports today in the Proceedings of the National Academy of Sciences.
Koltz suspects that when large numbers of these territorial spiders are around—as happens when temperatures rise—they more often compete, fight with, and eat each other, as well as other spiders that prey on springtails. All this infighting may free up the springtails so they can munch away on soil fungus, preventing the gas-releasing breakdown of organic material.
Although it’s unclear exactly how much gas is sequestered this way, Koltz says the sheer number of wolf spiders and springtails suggests this shifting predator-prey relationship, and its impact on soil decomposition, could act as a buffer against warming in the Arctic. Figuring out exactly how big that buffer is will require a lot more research. “Everyone loves to hate spiders,” she says, but “they have an important role to play in ecology.”
Source: Science Mag