New research from the USDA Forest Service Pacific Northwest Research Station, The University of New Mexico's Center for Stable Isotopes (CSI), the UNM Museum of Southwestern Biology, and the University of Texas at Austin adds to the growing body of literature documenting the impacts of climate change on food webs by studying the influence it has had in high-latitude ecosystems.
The research, titled Climate warming restructures food webs and carbon flow in high-latitude ecosystems, is featured in Nature Climate Change. Philip Manlick led the study as an adjunct professor in the UNM Department of Biology and a research scientist with the USDA Forest Service Pacific Northwest Research Station.
Co-authors include Nolan Perryman, who earned his MS in Biology this past spring; Distinguished Professor of Biology and Curator of Mammals at the Museum of Southwestern Biology, Joe Cook; Professor of Biology and Co-Director of CSI, Seth Newsome; and Assistant Professor of Biology, Amanda Koltz, from the University of Texas at Austin.
Their research shows that climate change is significantly affecting ecosystems in Arctic tundra and boreal forests that support animals adapted to the frigid winter temperatures in these northern areas. Warming has altered the food webs these animals have relied on for thousands of years, impacting the entire ecosystem around them.
Rising temperatures are melting the permafrost, or frozen soil, which is allowing bacteria and fungi to break down soil that has been frozen for thousands of years. This has increased "green" plant growth and more "brown" energy, or energy derived from microbial decomposition of permafrost and plant material.
It was previously unknown how these changes in plant and microbial resources impacted animals in these ecosystems, but new research shows that food webs have changed dramatically.
The study focuses on two crucial consumer groups: small mammals in boreal forests, examined over three decades (1990 to 2021), and wolf spiders in the Arctic tundra subjected to experimental warming.
Through stable isotope analysis of museum specimens collected three decades ago and again recently, scientists could track the energy flow through food webs to animals over time.
"Small mammals like shrews and voles that were historically supported by "green" plant-based food webs now acquire almost all their energy from "brown" fungal food webs," Manlick said. "When we looked at experimentally warmed spiders from the Arctic tundra, we saw the same pattern in a controlled environment. This tells us that warming has a consistent "browning" effect on food webs across species and ecosystems and that museums and monitoring programs can be used to track changes in food webs."
Surprisingly, despite the increase in "brown" food webs, the findings showed that animals mainly consume recently fixed carbon instead of ancient carbon from thawing permafrost. This suggests that the impacts of climate change on ecosystems are much more intricate than expected.
It is unknown why there has been such an increase in "brown" food webs, but it is apparent that everything from soil invertebrates to mammals is consuming more fungi than they have historically. The question is, what is supporting the growth of fungi?
"We hypothesized it'd be ancient permafrost, but we don't see that in the radiocarbon data, which was surprising," Manlick explained. "The dynamics of permafrost [carbon] cycling is extremely complicated, though, and our analysis here can't rule out permafrost decay as the driver of food web browning. It does suggest, however, that another mechanism such as increased decomposition of new plant growth could also be contributing to this phenomenon, but we need more research to understand how all these changes are related."
Understanding these changes is vital for determining how these sensitive environments will respond to climate change. As rapid warming continues to reshape high-latitude boreal and tundra ecosystems, these findings provide crucial insights into the intricate interplay of carbon flow, food web structure, and nutrient cycling.
The research provides a foundation for future studies into this topic and sheds light on how essential museum specimens are to understanding the effects of climate change on these sensitive ecosystems.
