how do changes in species interactions affect ecosystem functioning?
Experimental plots near Toolik Lake, Alaska.
My research focuses on two fundamental questions in Ecology: (1) How do biological communities respond to changes in the environment? and (2) What are the consequences of changes in species interactions for the cycling of energy and nutrients within ecosystems? I work across disciplinary boundaries and use a combination of observational and experimental approaches to address these questions. I especially enjoy targeting organisms, often little ones, that are widely distributed, sensitive to change, and linked to ecosystem services of importance to humankind.
Cascading effects of wolf spider predation
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, which could affect their population densities. Likewise, larger spiders might choose different prey, which could alter their top-down effects on the food web. 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 our recent paper in Frontiers in Ecology and Evolution on the variation in egg sac parasitism experienced by wolf spiders across Greenland.
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, which could affect their population densities. Likewise, larger spiders might choose different prey, which could alter their top-down effects on the food web. 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 our recent paper 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, 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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Quantifying effects of parasites on ecosystems
Parasites are well-known for having direct negative impacts on host individuals and populations, but they can also affect host behavior, physiology, and demography. By altering the ecological roles of their hosts, changes in host-parasite interactions also have the potential to impact ecosystem functioning. The link between disease ecology and ecosystem ecology has not received much attention to date, but a framework for quantifying such effects is critical as changing environmental conditions affect the abundance and diversity of parasitic species across the globe. With funding from The Living Earth Collaborative at Washington University in St. Louis, our interdisciplinary working group of disease ecologists, animal health specialists, community and ecosystem ecologists, and theoreticians is developing such a framework by using ungulates and their diverse parasites as a model.
See more about this project here: Small but mighty: Measuring parasites' footprints
