The 6th and likely last pub for 2020 was just published in Journal of Animal Ecology. Led by Jackson Helms IV, this paper investigates isotopic and trophic relationships of ants in corn, switchgrass, and restored prairies in Michigan. A summary from Jackson in JAE…
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.
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.
After a brief delay, we are back. Please welcome Jesse Daniels as the 1st member of our research team! We are incredibly excited to have him join us in Brookings and are looking forward to what the future will hold.
Jesse joins us from the Appalachian Mountains. His prior research experience involved analyzing plant-pollinator interactions and trophic networks to better understand invasive species’ effects on flowering plant communities. Previously, Jesse worked as an adjunct faculty member at Mountain Empire Community College in Big Stone Gap, VA and an environmental interpreter at Natural Tunnel State Park in Duffield, VA. As a family man, Jesse is enthusiastic about sharing new adventures and opportunities with his expecting wife and one year old son.
Lots of big, exciting changes happening right now! Once we get settled more details will follow, but I think you can guess based on some of the updates here that I have taken a job with USDA as a Research Entomologist. Unfortunately, it may be a while till I get the website formatted to the way I like it. More hopefully soon!
Our second NEON ants and 5th pub for 2020 was just published in Global Ecology and Biogeography. Led by Jelena Bujan, this is our first paper linking physiological traits like critical thermal max and min (CTmax and CTmin ) to different environmental abiotic conditions at a large geographical scale. A summary from Jelena in GEB…
“In ectotherms, gradients of environmental temperature can regulate metabolism, development and ultimately fitness. The thermal adaptation hypothesis assumes that thermoregulation is costly and predicts that more thermally variable environments favour organisms with wider thermal ranges and thermal limits (i.e., critical thermal minima and maxima, CTmin and CTmax) which track environmental temperatures. We test the thermal adaptation hypothesis at two biological levels of organization, the community and species level. We used ramping assays to measure CTmax and CTmin for 132 species of North American ants across 31 communities spanning 15.7° of latitude.
Ants were cold tolerant in cooler environments particularly at the community level where CTmin was positively correlated with the maximum monthly temperature (CTmin = 0.24Tmax − 0.4; R 2 = .39, p < .001). In contrast, most ant communities included some highly thermophilic species, with the result that CTmax did not covary with environmental temperature means or extremes. Consequently, we found no evidence that thermally variable environments supported ant communities with broader thermal ranges. We found a strong phylogenetic signal in CTmax but not CTmin. Species level responses paralleled community data, where maximum monthly temperatures positively correlated with species CTmin but not CTmax, which was significantly lower in subterranean species.
Our results suggest a large fraction of continental trait diversity in CTmax and CTmin can be found in a given ant community, with species with high CTmax widely distributed regardless of environmental temperature. Species level analyses found the importance of local microclimate and seasonality in explaining thermal tolerances. Frequent invariance in CTmax of insects at a large scale might be caused by (a) local adaptations to a site’s microclimates and (b) species acclimation potential, both of which cannot be accounted for with mean annual temperatures.”
Great to see another publication out from one of my favorite places to do field work, the University of Oklahoma Biological Station. This is the 4th pub for 2020, which is shaping up to be quite the productive year! Recently published in Ecology, Jelena and I were interested in seeing if thermal tolerance, an important trait for understanding activity patterns of ants, changed over the seasons with temperature. We collected ants across three seasons in Oklahoma across a range of temperatures finding some pretty interesting results. A summary from Jelena…
“Analyses of heat tolerance in insects often suggest that this trait is relatively invariant, leading to the use of fixed thermal maxima in models predicting future distribution of species in a warming world. Seasonal environments expose populations to a wide annual temperature variation. To evaluate the simplifying assumption of invariant thermal maxima, we quantified heat tolerance of 26 ant species across three seasons that vary two‐fold in mean temperature. Our ultimate goal was to test the hypothesis that heat tolerance tracks monthly temperature. Ant foragers tested at the end of the summer, in September, had higher average CTmax compared to those in March and December. Four out of five seasonal generalists—species actively foraging in all three focal months—had, on average, 6°C higher CTmax in September. The invasive fire ant, Solenopsis invicta, was among the thermally plastic species, but the native thermal specialists still maintained higher CTmax than S. invicta. Our study shows that heat tolerance can be plastic, and this should be considered when examining species‐level adaptations. Moreover, the plasticity of thermal traits, while potentially costly, may also generate a competitive advantage over species with fixed traits and promote resilience to climate change.”
It has been a busy March as our third paper of 2020 was recently published in Environmental Entomology! This was a fun collaboration with Wyatt Hoback at Oklahoma State University, who I first met while working on our Ants of Oklahoma project. We decided to tackle a data set that had been collected almost 15 years prior from one of his MS students looking at how invasive saltcedar and drought may combine to shape ant communities and isopod abundance in Nebraska. Abstract below from Wyatt…
“The establishment and spread of non-native species often results in negative impacts on biodiversity and ecosystem function. Several species of saltcedar, Tamarix spp. L., have been recently naturalized in large portions of the United States where they have altered plant and animal communities. To test the prediction that saltcedar negatively affects invertebrates, we measured ant genera diversity and the activity density of the exotic isopod Armadillidium vulgare Latrielle (Isopoda: Oniscoidea) for 2 yr using pitfall traps located within 30 5-m2 plots with or without saltcedar at a south-central Nebraska reservoir. From 2005 to 2006, we collected 10,837 ants representing 17 genera and 4,953 A. vulgare. Per plot, the average number of ant genera was not different between saltcedar (x̅ = 3.9) and non-saltcedar areas ( x̅ = 3.9); however, saltcedar plots were compositionally different and more similar from plot to plot (i.e., they had lower beta diversity than control plots) in 2005, but not in 2006. Isopods were likewise temporally affected with higher activity density (+89%) in control plots in 2005, but higher activity density (+27%) in saltcedar plots in 2006. The observed temporal differences occurred as the drought that initially enabled the saltcedar invasion became less severe in 2006. Combined, our results suggest that invertebrate groups like ants, which are generally omnivorous, may be better equipped than more specialized taxa like detritivores to withstand habitat changes due to invasions by non-native species, especially during extreme weather events such as prolonged droughts.”
Second paper of 2020 is out in the Proceedings of the National Academy of Sciences of the United States of America (PNAS for short)! Ellen Welti sums up the work nicely here…
“Parsing variation in long-term patterns underlying insect abundances and assigning mechanisms are critical in light of recent reports of dramatic insect declines. Grasshopper abundances in a North American prairie exhibited both 5-y cycles and >2%/y declines over the past 20 y. Large-scale climate oscillations predicted the cycles in grasshopper abundances. Moreover, plant biomass doubled over the same period—likely due to changes in climate and increasing atmospheric CO2—diluting the concentrations in plant tissue of key nutrients which in turn predicted the declines of a dominant herbivore. Nutrient dilution, like CO2 enrichment, is likely a global phenomenon, posing a challenge to Earth’s herbivore populations.”
First paper of 2020 is out in Environmental Entomology! Here we look at how the red imported fire ant, Solenopsis invicta, regulates its foraging behavior. This was an interesting project that we first piloted back in 2015 and built on all the way through the summer of 2018. We were interested in testing ideas from from optimal foraging theory (Figure 1 below) and developed the Diminished Returns Hypothesis that posits for social insects (1) foraging investment levels increase until diminishing gains result in a decelerating slope of return and (2) this investment level is a function of the size of the collective group. This hypothesis we argue is an analog to Charnov’s Marginal Value Theorem and in testing it we found that fire ants forage as predicated in a particular manner.
However, fire ant foraging behavior was also regulated, at least in part, by the size of the colony. We posit this is possibly why large fire colonies have been so successful in their invasion of the United States and compared values with native co-occuring species in southern Oklahoma (Figure 2 below). We found that fire ant foraging mass was greater than the estimated colony mass for 45% of the co-occurring native ant species (10 of 22), many of which are small myrmecines from the genera Monomorium, Myrmecina, Pheidole, Strumigenys, and Temnothorax.The estimated average colony mass of fire ants, on the other hand, was greater than 95% of the co-occurring species (21 of 22)—the lone exception being the red harvester ant, Pogonomyrmex barbatus, whose workers are often 20-fold larger than fire ants.
Taken as a whole, our results suggest that substantial biomass differences between invasive and native ants are likely one of the key reasons that species like red imported fire ants are able to dominate novel environments. A pretty fun paper overall and our first foray into the realm of testing optimality models. Check back for more updates and you can view the whole paper at the link below.
The Harmon-Threatt lab at the University of Illinois Urbana-Champaign is seeking a motivated, hardworking undergraduate student to join our team for the spring 2020 semester. The successful candidate will work with Dr. Karl Roeder on a recently funded project examining if multifunctional woody polycultures increase insect biodiversity and food web stability.
The position will mostly involve sorting insects to family, measuring traits of insects, and preparing samples for carbon and nitrogen stable isotope analysis. Experience in insect identification is required, however training will be provided. The candidate must be well organized, keep meticulous datasheets, and be comfortable working in Microsoft Excel.
This successful candidate’s wages will be $10/hour and they will be expected to work 10 hours per week during standard business hours (M-F, 8 am to 5 pm). Scheduling is otherwise flexible and will accommodate the student’s class schedule and U of I holidays/breaks. There is also the potential for continued employment through the summer if desired. To apply, send your resume and a short cover letter describing why you are interested in the position and why you are a strong candidate to Karl Roeder; firstname.lastname@example.org.
Our newest paper of 2019 and the first NEON ants paper is out in Ecology!!!
“In an era of rapid climate change, and with it concern over insect declines, we used two theories to predict 20‐year changes in 34 North American ant communities. The ecosystems, from deserts to hardwood forests, were first surveyed in the 1990s. When resurveyed in 2016‐2017 they averaged 1°C warmer with 200 gC/m2/y higher plant productivity. Ant colony abundance changed from ‐49% to +61%. Consistent with Thermal Performance Theory, colony abundance increased with temperature increases <1°C, then decreased as a site’s mean monthly temperature change increased up to +2.4°C. Consistent with Species Energy Theory: 1) ant abundance tracked changes in a measure of energy availability (Net Aboveground Productivity, gC/m2/y), and, 2) increases in colony abundance drove increases in local plot‐ and transect‐level species richness but not that of Chao 2, an estimate of the size of the species pool. Even after accounting for these drivers, local species richness was still higher ca. 20 years after the original surveys, likely due to the increased activity of ant workers. These results suggest community changes are predictable using theory from geographical ecology, and that warming can first enhance but may ultimately decrease the abundance of this important insect taxon.”