New paper out! Micronutrients enhance macronutrient effects in a meta-analysis of grassland arthropod abundance

A meta-analysis led my myself, Karen Castillioni, and Ellen Welti is now out in Global Ecology and Biogeography! This paper examined the effects of micro- and macronutrient fertilization in grasslands on plant biomass, plant nutrient content, and on the abundance of six arthropod trophic groups.

We found the interesting result that micronutrients applied alone had no effects on plant biomass or arthropod abundance. However, when added with macronutrients (such as nitrogen, phosphorus, and potassium), micronutrients amplified the effect of N, P and K in promoting arthropod abundance, a synergy that did not affect plant biomass (Figure 1).

Figure 2. Forest plot showing effect sizes (Cohen’s d) of (a) plant biomass and (b) total arthropod abundances by fertilizer type. Red stars denote significant effect sizes, while black circles indicate non-significant effect sizes. We included fertilizer types used in > 5 studies. The number of replicates provided within the figure refers to the number of experimental responses containing each fertilizer type. Error bars are the standard error of the mean of the effect sizes of individual experiments

Micronutrients catalyzed the ability of macronutrients to promote arthropod abundance across all arthropod guilds studied (Figure 2).

Figure 2. Forest plot showing effect sizes (Cohen’s d) of arthropod trophic group abundances by fertilizer type. Responses are provided for the trophic groups of (a) chewing herbivores, (b) sucking herbivores, (c) pollinators, (d) omnivores, (e) predators, and (f) detritivores. Red stars denote significant effect sizes, while black circles indicate non-significant effect sizes. We included fertilizer types used in ≥ 5 studies. Number of replicates provided within the figure refers to the number of experimental responses containing each fertilizer type and trophic group. Error bars are the standard error of the mean of the effect sizes of individual experiments

This paper was a result of a collaboration with Dr. Lara Souza and Dr. Mike Kaspari at OU and Dr. Chelse Prather and Ryan Reihart at the University of Dayton. We highlight a stoichiometric mismatch between limits of plants and arthropods for metal cations whose biogeochemistry, along with N and P, are being actively rearranged in the Anthropocene.

You can read the paper here. https://rmprather.files.wordpress.com/2020/10/prather-et-al.-2020-geb-meta-analysis.pdf

New paper out! The economics of optimal foraging by the red imported fire ant.

New paper out in Environmental Entomology! This is the 3rd publication for 2020, a surprisingly productive year.

Karl Roeder sums up the paper nicely, “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 optimal foraging theory 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. We argue this hypothesis 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. 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.”

You can read the paper here.

New paper out! Bottom-up when it is not top-down: Predators and plants control biomass of grassland arthropods

New paper out in Journal of Animal Ecology! This paper surveyed 54 North American grasslands to investigate whether bottom-up or top-down control regulates ecological communities. We examined the biomass of four common grassland arthropod taxa— Auchenorrhyncha, sucking herbivores, Acrididae, chewing herbivores, Tettigoniidae, omnivores, and Araneae, predators.

We found that sucking herbivores and omnivores tracked plant biomass and chewing herbivores tracked plant quality. In addition, we found that when spider biomass was low, herbivores increased with plant biomass but this didn’t happen at high spider abundances. Furthermore, stable isotope analysis showed that neither predator biomass nor trophic position changed with plant biomass, suggesting predators themselves are top-down limited. Finally, the trophic position of chewing herbivores and omnivores increased with plant biomass, suggesting increased scavenging in grasslands with increased carbohydrate availability.

This was a fun paper to work on. You can click here to read the whole paper.

 

New paper out! Abiotic factors and plant biomass, not plant diversity, strongly shape grassland arthropods under drought conditions

My third dissertation chapter is now out in Ecology! This paper used a factorial experiment of precipitation manipulation and human management (hay harvest) in a temperate mixed-grass prairie to examine 1) how two drivers, altered precipitation and biomass removal, can synergistically affect abiotic factors and plant communities and 2) how these effects can cascade upward, impacting the arthropod food web.

This paper was a result of a collaboration with Dr. Lara Souza’s lab and I worked closely with her Ph.D. candidate, Karen Castillioni. At Kessler Atmospheric and Ecological Field Station, the Souza lab set up a seven-level precipitation manipulation gradient. Using rain-out shelters, they excluded up to 100% of precipitation on plots in addition to adding +50% precipitation to other plots (Fig. 1).

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I collected arthropods from plots in 2017 and 2018 and tested 3 non-exclusive hypotheses detailing how direct and indirect effects of drought and hay harvest work synergistically to affect the plant and arthropod communities in a mixed-grass prairie. I found that both drought and hay harvest increased soil surface temperature while drought decreased soil moisture. Arthropod abundance decreased with low soil moisture and, contrary to our predictions, decreased with increased plant biomass. Arthropod diversity increased with soil moisture, decreased with high surface temperatures, and tracked arthropod abundance but was surprisingly unaffected by plant diversity or quality. Our results demonstrate that arthropod abundance is directly constrained by abiotic factors and plant biomass and in turn constrains local arthropod diversity.

This was a fun project to work on. You can click here to read the full paper.

New paper out! Plants regulate grassland arthropod communities through biomass, quality, and habitat heterogeneity

My second dissertation chapter is now out in Ecosphere! This paper used a factorial experiment of NPK fertilization and clipping (to mimic grazing) to manipulate plant biomass, habitat heterogeneity, and plant quality and quantify their effects arthropod abundance and diversity. Thus, I demonstrate the direct and indirect effects of plants on grassland arthropod communities. I ran this experiment at the University of Oklahoma Biological Station in the summer of 2017. I used both pitfall traps and bugvacs to show that grassland insect community abundance, activity, and diversity respond to fertilization and simulated grazing via effects on microclimate, habitat space, and nutrient quality. I also show how nutrients buffer microclimate via increased plant volume.

Fig. 1 with caption.jpg

This was a fun project to work on and resulted in a lot of lab time – I had to count and identify >150,000 arthropods. You can read the full paper here.