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As the northern latitudes continue to warm, increasing temperatures are changing the physiological shape and behavior of one of the Arctic’s most abundant invertebrate predators.
Wolf spiders outnumber wolf populations in the Arctic. Given their high population numbers, it is likely that disturbances to their lifecycle will have broader implications for the tundra. As the Arctic warms, wolf spiders are getting bigger, reproducing more, and developing a new taste for a familiar prey – their own species, according to new research published in the Journal of Animal Ecology.
“Although cannibalism is probably not the best dietary choice for these spiders, our field and experimental data suggest that when there are lots of spiders around, they turn to cannibalism more frequently,” said Amanda Koltz, first author of the new study, in a statement. “It’s likely a reflection of increased competition among the spiders for resources.”
The wolf spiders (Pardosa lapponica) are ectothermic, also known as cold-blooded animals, which means they regulate their body temperature externally in response to their surrounding environment, making them more likely to undergo physiological changes in response to warming temperatures. For example, some spiders in the Arctic are larger than they have been in the past as summers get longer and warmer. As climate change warms the Arctic, spiders will likely get bigger and their ability to reproduce will increase.
Researchers at Washington University in St. Louis collected wolf spiders at two sites in the Alaskan Arctic, where individually body size varies naturally. Collected specimens were compared against those that had been placed in what is known as a mesocosm experiment, an enclosed outdoor environment meant to mimic their habitat without all of its associated variables. Researchers were able to manipulate and control environmental conditions to determine how higher population densities altered the dietary behavior of the spiders.
Larger wolf spiders were associated with fewer juvenile spiders, a surprising discovery given that females with larger body sizes produce more offspring on average. When researchers tracked the flow of nutrients through the food web via stable isotope analysis, it was determined that the site with larger females were more apt to dine on their own species.
“Wolf spiders that were experimentally exposed to higher densities underwent a dietary shift similar to that of the field population where females were bigger – and where we would expect competition and cannibalism among wolf spiders to be highest,” Koltz said.
Wolf spiders in southern latitudes have been shown to exhibit similar behavior, but it remains unknown how the behavior affects natural populations. One theory is that it may help regulate wild populations and, though it reduces competition in the short-term, wolf spiders who dine only on their own species tend to have shorter lifespans.
What happens in the Arctic doesn’t stay in the Arctic, remind the researchers. “The results from our study are a reminder that changes in invertebrate body size driven by climate change could have widespread ecological consequences, including shifts in intraspecific competition, diet and population structure,” said Koltz.
