How do changes in species interactions
affect ecosystem functioning?
affect ecosystem functioning?
Experimental plots near Toolik Lake, Alaska.
Cascading effects of predation in the Arctic
The Arctic is warming faster than any other biome on the planet, which underscores the critical importance of understanding the influence of warming on ecosystem processes in this region. In particular, arctic warming could increase microbially-mediated decomposition of the vast amounts of carbon stored in permafrost soils. Increased decomposition would result in higher levels of atmospheric carbon dioxide and methane, which are heat-trapping pollutant gases that endanger public health and welfare, and potentially create positive feedbacks to climate change. Decomposition rates are strongly determined by microbial community composition, and consequently, many studies have addressed the effects of climate change in the Arctic by focusing on microbial responses to warmer temperatures and greater resource availability (e.g. due to deeper permafrost thaw). Although we know that the composition and activity of the microbial community can be modified by micro- and macro- invertebrates in the soil, and that soil invertebrates themselves are regulated by generalist predators like spiders, it's unclear how microbial responses to warming in the arctic are being affected by the broader food web.
Generalist-feeding spiders are among the most abundant predators globally. Their behavior has been shown to indirectly influence decomposition rates, nutrient cycling, and the composition, diversity, and productivity of plant communities in temperate ecosystems. Potential shifts in spider feeding ecology as a result of climate change could therefore have important and far-reaching consequences for arctic community dynamics and ecosystem processes as well.
Through this work, my research has shown that when densities of wolf spiders are higher, decomposition in the tundra happens faster (Koltz et al. 2018 PNAS). However, this pattern is reversed when we experimentally warm the tundra -- under warmer conditions, as wolf spider densities increase, decomposition slows due to a shift in predator-prey interactions between the wolf spiders and their Collembola prey. These results suggest that if wolf spider densities increase in the future, they could potentially help buffer carbon losses from arctic soils due to warming.
The Arctic is warming faster than any other biome on the planet, which underscores the critical importance of understanding the influence of warming on ecosystem processes in this region. In particular, arctic warming could increase microbially-mediated decomposition of the vast amounts of carbon stored in permafrost soils. Increased decomposition would result in higher levels of atmospheric carbon dioxide and methane, which are heat-trapping pollutant gases that endanger public health and welfare, and potentially create positive feedbacks to climate change. Decomposition rates are strongly determined by microbial community composition, and consequently, many studies have addressed the effects of climate change in the Arctic by focusing on microbial responses to warmer temperatures and greater resource availability (e.g. due to deeper permafrost thaw). Although we know that the composition and activity of the microbial community can be modified by micro- and macro- invertebrates in the soil, and that soil invertebrates themselves are regulated by generalist predators like spiders, it's unclear how microbial responses to warming in the arctic are being affected by the broader food web.
Generalist-feeding spiders are among the most abundant predators globally. Their behavior has been shown to indirectly influence decomposition rates, nutrient cycling, and the composition, diversity, and productivity of plant communities in temperate ecosystems. Potential shifts in spider feeding ecology as a result of climate change could therefore have important and far-reaching consequences for arctic community dynamics and ecosystem processes as well.
Through this work, my research has shown that when densities of wolf spiders are higher, decomposition in the tundra happens faster (Koltz et al. 2018 PNAS). However, this pattern is reversed when we experimentally warm the tundra -- under warmer conditions, as wolf spider densities increase, decomposition slows due to a shift in predator-prey interactions between the wolf spiders and their Collembola prey. These results suggest that if wolf spider densities increase in the future, they could potentially help buffer carbon losses from arctic soils due to warming.
Setting pitfall traps near the Arctic National Wildlife Refuge. Photo: Nick LaFave
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Sorting spider samples.
Photo: Nick LaFave
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Variation in population structure and trophic ecology of wolf spiders
In addition to understanding how wolf spiders can have cascading effects on food webs and ecosystems, I am interested in how these predators themselves are responding to the rapid changes occurring in the Arctic. For example, wolf spiders are growing larger in response to the longer summers brought on by warming. Bigger spiders produce more offspring (Høye et al. 2020), which could affect their population densities. Likewise, larger spiders might choose different prey, which could alter their top-down effects on the food web. For example, wolf spiders are density-dependent cannibals -- so what will having bigger spiders that reproduce more but also cannibalize more mean for wolf spider populations in the future? Likewise, how will predators of those wolf spiders (e.g., parasitic wasps) respond to higher prey availability? This area of my research program is focused on understanding the abiotic and biotic drivers of variation in wolf spider population structure and trophic ecology so that we can better predict the strength of wolf spider predation impacts across the landscape. See recent publications in the Journal of Animal Ecology on the impacts of wolf spider body size on cannibalism and juvenile abundances and in Frontiers in Ecology and Evolution on the variation in egg sac parasitism experienced by wolf spiders across Greenland.
Female wolf spider with spiderlings
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Sarah and Kiki set pitfall traps along the Dalton Highway, N. Slope of Alaska
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Community responses to disturbance
Through several other ongoing projects, my collaborators and I are quantifying how the structure and function of aboveground and belowground invertebrate communities are affected by disturbances such as warming, fire, nutrient addition, and changes in snow melt in the Arctic and elsewhere. See my relevant publications in Royal Society Open Science, Oikos, Current Opinion in Insect Science, Ambio, and Ecology and Evolution on these topics.
Collaborator Ashley Asmus and Amanda at the site of the Anuktuvuk Fire in N. Alaska
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Hard at work sorting vacuum samples!
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Parasite effects on ecosystems
Parasites are well-known for their negative impacts on the physiology and behavior of individual hosts, but these effects are rarely considered within the context of the broader ecosystems they inhabit. Yet in a similar way to predators, changes in parasite-host interactions can also have cascading effects on ecosystems. Understanding the links between disease ecology and ecosystem ecology is especially critical now as changing environmental conditions alter the abundance and diversity of parasitic species in both natural and managed systems across the globe. With funding from The Living Earth Collaborative at Washington University in St. Louis, I'm currently leading an interdisciplinary working group that uses ungulates and their diverse parasites as a model for investigating the extent to which parasite-host interactions impact ecosystem nutrient cycling.
See recent coverage of our working group: Small but mighty: Measuring parasites' footprints
This work is in collaboration with Vanessa Ezenwa (University of Georgia), Rachel Penczykowski (Wash U), Sharon Deem and Maris Brenn-White (Saint Louis Zoo), David Civitello and Matthew Malishev (Emory University), Aimée Classen (University of Michigan), Brandon Barton and Zoë Johnson (Mississippi State University), Daniel Becker (Indiana University), Susan Kutz (University of Calgary), Daniel Preston (University of Wisconsin-Madison), and J. Trevor Vannatta (Purdue University).
Our newest paper in TREE, led by Vanessa Ezenwa, describes how increasing prevalence of infectious diseases could lead to higher methane emissions from ruminant livestock, thereby accelerating climate change.
See the Press release here
