A new study published on July 23rd in the Proceedings of the National Academy of Sciences (1) highlights the potentially positive impact of the increasing wolf spider population (a member of the Lycosidae family) on the rapidly warming Arctic climate. As temperatures in the region continue to rise, the number of these tiny predators is growing but surprisingly, instead of reducing the number of springtails (Collembola) – small insect-like arthropods that are their usual prey – the number of springtails may actually be increasing. Springtails in turn feed on the soil-dwelling fungi responsible for producing potent greenhouse gases, including carbon dioxide and methane, thus, the wolf spider may indirectly be affecting greenhouse gas emissions in the region, resulting in cooler temperatures overall.
In the Arctic region, faster decomposition of stored soil carbon is expected to result in so-called “positive carbon feedbacks to the atmosphere” pushing the climate in the direction of warming, but these adverse changes can also be minimized or prevented by certain internal factors, such as decomposition, root competition, or the types of species present. Researchers wanted to study one internal system in particular, which may be involved in negative feedback, that is, the predator-prey interactions between the aggressive predatory wolf spider and the fungus-munching springtail.
While the wolf spider may come in a tiny body ― 1.25 centimeters long ― in some parts of Alaska they are abundant and have around 80 times more biomass (kilogram per kilogram) than the entire gray wolf population. Dr. Amanda Koltz and her colleagues from the University of Washington spent several weeks near the Brooks Range mountains in Alaska, collecting hundreds of wolf spiders and placing them into 30 different 1.5-meter experimental enclosures. The temperature and number of spiders in each enclosure was then varied in order to investigate the effects of warmer temperatures and different densities of spiders on the number of springtails.
Contrary to the original hypothesis, the number of springtails in higher-temperature enclosures with a greater number of spiders increased. It’s theorized this may be due to infighting between the spiders owing to the larger population and the competition may actually be causing the spiders to prey each other. Koltz suggests these altered predator-prey interactions may have a cascading effect on soil decomposition and could prevent some of the effects of greenhouse gas emissions on global warming in the Arctic region. Thus, it is hypothesized that the increase in the wolf spider population as a result of warmer temperatures will mean fewer greenhouse gases are produced by decomposing plant matter.
This study highlights the important role that spiders, and indeed many species, play in communities and ecosystems. However, the effects of global warming on any population or region is difficult to predict, and until researchers can pinpoint exactly why the wolf spider’s predatory behavior is changing, applying the results of this one small study to larger regions will be a complex task.
(1) Koltz, KM., Classen AT., and Wright, JP. Warming reverses top-down effects of predators on belowground ecosystem function in Arctic tundra. PNAS (2018). DOI: 10.1073/pnas.1808754115