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.”
Over the past few years, I have tried to post once every month or at least every other month with updates from my research or outreach. This came to a crashing halt after BioBlitz last year as I finished off the last few sections of my dissertation and prepared to defend.
After a successful defense, I am happy to say that I am now, officially, a PhD! Graduate school has been quite the adventure. I was fortunate to work with some great people, visit some amazing places, and do some really cool science. And that brings me to the next step….
I will be starting a new position as a postdoctoral research with Dr. Alexandra Harmon-Threatt (Click here for the HT lab website) in the Entomology department at the University of Illinois May 1st! I have known about this for a while but have been waiting until I defended/passed to announce it. I will have more information on the project soon, but we primarily will be looking at ecosystem services of insects in woody perennial polyculture systems. This is an exciting step for me as it not only represents something completely different from my dissertation research, but it also fills this nagging itch I have had to do more applied research. Look out for updates, pictures, stories and more from this summer’s field season!
Once a year, there is an annual Bioblitz that takes place in different locations, generally parks or natural areas that are protected, around Oklahoma. These have occured for the past 15 years in this state and I think really help bring together a diversity of people who love nature. Priscilla Crawford leads the organization of these large events and has this to say…
“BioBlitz! is a rapid inventory of biological diversity. Biologists and citizen scientists count as many species as possible in a given period of time, traditionally large BioBlitz! events are for 24 consecutive hours. Anyone who is interested participate in a BioBlitz! – university professors to boy scouts to high school students to enthusiastic retirees.
Bioblitz is a fun and exciting event to educate people about the natural diversity “in their back yard.” BioBlitz offers a hands-on scientific experience and a chance to learn more about the diversity of life where people live.”
This year’s BioBlitz took place at Greenleaf State Park in Eastern Oklahoma where we actually got to observe the American Burying Beetle, a federally protected species since 1989. During our 24-hr period we collected ~20 ant species including some really neat army ants from the genus Neivamyrmex! Check out some pics from this year’s blitz and hopefully next year you will join in.
2018 BioBlitz: Greenleaf State Park
You can learn more about the Oklahoma BioBlitz here
A slight delay in posts as I have been gone or busy writing up portions of my dissertation. In September, our lab finished off the last sampling on the SALT grant for the year at three locations in the midwest United States. Having never visited two of these states before, I was quite excited to see what Kansas and Nebraska had to offer. And they did not disappoint! We visited the Konza LTER and two Nature Conservancy sites in Nebraska on the Platte and Niobrara rivers. The goal was to measure how invertebrates and plants are responding to macro and micronutrient additions in long term plots that were first established earlier this year. Will be exciting to see the results as the grass and forb composition, and their respective heights, were quite different at each site. Check out some pictures below to see where we were working…
Third paper of 2018 is out in Ecological Entomology! Here we look at daily temperature changes, and how such changes regulate activity of red imported fire ants and other native species. This was a pretty fun project that arose from observations during data collection for my first dissertation chapter. Specifically, I was noticing that fire ants were not active at the hottest parts of the day, but many native species that co-occur were. We started to quantify these observations by first measuring ant activity on baits over a month long period during the summer of 2016. The figure below shows some of these results.
We hypothesized that fire ants likely compete with species that have similar traits such as body size and thermal tolerance as these often are correlated with diet and activity, respectively . Dormyrmex flavus was the most similar ant species, so we set up a field based competition experiment to see if fire ants competitively displaced our native D. flavus from resources near their nests. Turns out…they do!
So how does D. flavus coexist in similar environments with fire ants? We argue that dietary differences may be one way and use stable isotope analyses to show that red imported fire ants and D. flavus have different dietary niches. Combined, we believe this study is a nice example of observations leading to ecologically relevant patterns that we test the mechanism of using additional field and lab experiments.