Bioenergy landscapes drive trophic shifts in generalist ants

Journal Article · Mon Dec 14 00:00:00 EST 2020 · Journal of Animal Ecology

DOI:https://doi.org/10.1111/1365-2656.13407· OSTI ID:1764720

Helms, IV, Jackson A. ^[1]; Roeder, Karl A. ^[2]; Ijelu, Selassie E. ^[3]; Ratcliff, Ian ^[4]; Haddad, Nick M. ^[5]

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1. Michigan State Univ., Hickory Corners, MI (United States); Michigan State University W.K. Kellogg Biological Station
2. Univ. of Illinois at Urbana-Champaign, IL (United States)
3. Univ. of Saint Francis, Fort Wayne, IN (United States)
4. Holly Springs, NC (United States)
5. Michigan State Univ., Hickory Corners, MI (United States)

Changes in trophic niche—the pathways through which an organism obtains energy and nutrients—are a fundamental way in which organisms respond to environmental conditions. But the capacity for species to alter their trophic niches in response to global change, and the ways they do so when able, remain largely unknown. Here we examine food webs in three long–term and large–scale experiments to test how resource availability and nutritional requirements interact to determine an organism's trophic niche in the context of one of the largest global trends in land use—the rise in bioenergy production. Here, we use carbon and nitrogen stable isotope analyses to characterize arthropod food webs across three biofuel crops representing a gradient in plant resource richness (corn monocultures, fields dominated by native switchgrass and restored prairie), and to quantify changes in the trophic niche of a widespread generalist ant species across habitats. In doing so, we measure the effects of basal resource richness on food chain length, niche breadth and trophic position. We frame our results in the context of two hypotheses that explain variation in trophic niche—the niche variation hypothesis which emphasizes the importance of resource diversity and ecological opportunity, and the optimal diet hypothesis which emphasizes dietary constraints and the availability of optimal resources. Increasing plant richness lengthened food chains by 10%–20% compared to monocultures. Niche breadths of generalist ants did not vary with resource richness, suggesting they were limited by optimal diet requirements and constraints rather than by ecological opportunity. The ants instead responded to changes in plant richness by shifting their estimated trophic position. In resource–poor monocultures, the ants were top predators, sharing a trophic position with predatory spiders. In resource–rich environments, in contrast, the ants were omnivores, relying on a mix of animal prey and plant–based resources. In addition to highlighting novel ecosystem impacts of alternate bioenergy landscapes, our results suggest that niche breadth and trophic diversification depend more on the presence of optimal resources than on ecological opportunity alone.

• Research Organization: Great Lakes Bioenergy Research Center, Madison, WI (United States)
• Sponsoring Organization: USDOE; USDOE Office of Science (SC), Biological and Environmental Research (BER)
• Grant/Contract Number: FC02-07ER64494; SC0018409
• OSTI ID: 1764720
• Alternate ID(s): OSTI ID: 1786926
• Journal Information: Journal of Animal Ecology, Journal Name: Journal of Animal Ecology Journal Issue: 3 Vol. 90; ISSN 0021-8790
• Publisher: British Ecological Society
• Country of Publication: United States
• Language: English

Related Subjects

59 BASIC BIOLOGICAL SCIENCES
Formicidae
Tetramorium immigrans
biofuels
food chains
food webs
niche breadth
stable isotopes
trophic position