@article {6106, title = {Electrolytes on the prairie: How urine-like additions of Na and K shape the dynamics of a grassland food web}, journal = {Ecology}, volume = {104}, year = {2023}, pages = {e3856}, abstract = {

The electrolytes Na and K both function to maintain water balance and membrane potential. However, these elements work differently in plants\—where K is the primary electrolyte\—than in animals\—where ATPases require a balanced supply of Na and K. Here we use monthly factorial additions of Na and K to simulate bovine urine inputs and explore how these electrolytes ramify through a prairie food web. Against a seasonal trend of increasing grass biomass and decreasing water and elemental tissue concentrations, +K and +Na plots boosted water content and, when added together, plant biomass. Compared to control plots, +Na and +K plots increased element concentrations in aboveground plant tissue early in summer and decreased them in September. Simultaneously, invertebrate abundance on Na and K additions were sequentially higher and lower than control plots from June-September and were most suppressed when grass was most nutrient rich. K was the more effective plant electrolyte, but Na frequently promoted similar changes in grass ionomes. The soluble/leachable ions of Na and K showed significant ability to shape plant growth, water content, and the 15-element ionome, with consequences for higher trophic levels. Grasslands with high inputs of Na and K\—via large mammal grazers or coastal aerosol deposition\—likely enhance the ability of plants to adjust their aboveground ionomes, with dramatic consequences for the distribution of invertebrate consumers.

}, keywords = {LTER-KNZ}, doi = {10.1002/ecy.3856}, url = {https://onlinelibrary.wiley.com/doi/10.1002/ecy.3856}, author = {Kaspari, Michael and Welti, E.A.R.} } @article {6027, title = {How and why grasshopper community maturation rates are slowing on a North American tall grass prairie}, journal = {Biology Letters}, volume = {18}, year = {2022}, abstract = {

Invertebrate growth rates have been changing in the Anthropocene. We examine rates of seasonal maturation in a grasshopper community that has been declining annually greater than 2\% a year over 34 years. As this grassland has experienced a 1\°C increase in temperature, higher plant biomass and lower nutrient densities, the community is maturing more slowly. Community maturation had a nutritional component: declining in years/watersheds with lower plant nitrogen. The effects of fire frequency were consistent with effects of plant nitrogen. Principal components analysis also suggests associated changes in species composition\—declines in the densities of grass feeders were associated with declines in community maturation rates. We conclude that slowed maturation rates\—a trend counteracted by frequent burning\—likely contribute to long-term decline of this dominant herbivore.

}, keywords = {LTER-KNZ}, doi = {10.1098/rsbl.2021.0510}, url = {https://royalsocietypublishing.org/doi/10.1098/rsbl.2021.0510}, author = {Kaspari, Michael and A. Joern and Welti, E.A.R.} } @article {6120, title = {How and why plant ionomes vary across North American grasslands and its implications for herbivore abundance}, journal = {Ecology}, volume = {102}, year = {2021}, pages = {e03459}, keywords = {LTER-KNZ}, doi = {10.1002/ecy.3459}, url = {https://esajournals.onlinelibrary.wiley.com/doi/10.1002/ecy.3459}, author = {Kaspari, Michael and Beurs, Kirsten M. and Welti, E.A.R.} } @article {KNZ002056, title = {Sodium addition increases leaf herbivory and fungal damage across four grasslands}, journal = {Functional Ecology}, volume = {35}, year = {2021}, pages = {1212-1221}, abstract = {

\ \ \  1. Sodium (Na) is an essential element for all animals, but not plants. Soil Na supplies vary geographically. Animals that primarily consume plants thus have the potential to be Na limited and plants that uptake Na may be subject to higher rates of herbivory, but their high Na content also may attract beneficial partners such as pollinators and seed dispersers.
\ \ \  2. To test for the effects of Na biogeochemistry on herbivory, we conducted distributed Na press experiments (monthly Na application across the growing season) in four North American grasslands.
\ \ \  3. Na addition increased soil and plant Na concentrations at all sites. Grasses in Na addition plots had significantly higher herbivore damage by leaf miners and fungal pathogens than those in control plots. Forbs with higher foliar Na concentrations had significantly more chewing insect herbivore and fungal damage.
\ \ \  4. While no pattern was evident across all species, several forb species had higher Na concentrations in inflorescences compared to leaves, suggesting they may allocate Na to attract beneficial partners.
\ \ \  5. The uptake of sodium by plants, and animal responses, has implications for the salinification in the Anthropocene. Increased use of road salt, irrigation with saline groundwater, rising sea levels, and increasing temperatures and evapotranspiration rates with climate change can all increase inputs of sodium into terrestrial ecosystems.
\ \ \  6. Our results suggest increasing terrestrial sodium availability will benefit insect herbivores and plant fungal pathogens.

}, keywords = {LTER-KNZ}, doi = {10.1111/1365-2435.13796}, url = {https://besjournals.onlinelibrary.wiley.com/doi/10.1111/1365-2435.13796?af=R}, author = {Welti, E.A.R. and Kaspari, Michael} } @article {KNZ002057, title = {Studies of insect temporal trends must account for the complex sampling histories inherent to many long-term monitoring efforts}, journal = {Nature Ecology \& Evolution}, volume = {5}, year = {2021}, pages = {589{\textendash}591}, keywords = {LTER-KNZ}, doi = {10.1038/s41559-021-01424-0}, url = {http://www.nature.com/articles/s41559-021-01424-0}, author = {Welti, E.A.R. and A. Joern and Ellison, Aaron M. and Lightfoot, David C. and Record, Sydne and Rodenhouse, Nicholas and Stanley, Emily H. and Kaspari, Michael} } @article {KNZ002046, title = {Tracking nutrients in space and time: Interactions between grazing lawns and drought drive abundances of tallgrass prairie grasshoppers}, journal = {Ecology and Evolution}, volume = {11}, year = {2021}, pages = {5413-5423}, abstract = {

1. We contrast the response of arthropod abundance and composition to bison grazing lawns during a drought and non-drought year, with an emphasis on acridid grasshoppers, an important grassland herbivore.
2. Grazing lawns are grassland areas where regular grazing by mammalian herbivores creates patches of short-statured, high nutrient vegetation. Grazing lawns are predictable microsites that modify microclimate, plant structure, community composition, and nutrient availability, with likely repercussions for arthropod communities.
3. One year of our study occurred during an extreme drought. Drought mimics some of the effects of mammalian grazers: decreasing above-ground plant biomass while increasing plant foliar percentage nitrogen.
4. We sampled arthropods and nutrient availability on and nearby (\“off\”) 10 bison-grazed grazing lawns in a tallgrass prairie in NE Kansas. Total grasshopper abundance was higher on grazing lawns and the magnitude of this difference increased in the wetter year of 2019 compared to 2018, when drought led to high grass foliar nitrogen concentrations on and off grazing lawns. Mixed-feeding grasshopper abundances were consistently higher on grazing lawns while grass-feeder and forb-feeder abundances were higher on lawns only in 2019, the wetter year. In contrast, the abundance of other arthropods (e.g., Hemiptera, Hymenoptera, and Araneae) did not differ on and off lawns, but increased overall in 2019, relative to the drought of 2018.
5. Understanding these local scale patterns of abundances and community composition improves predictability of arthropod responses to ongoing habitat change.

}, keywords = {LTER-KNZ}, doi = {10.1002/ece3.7435}, url = {https://onlinelibrary.wiley.com/doi/10.1002/ece3.7435}, author = {Ozment, Katerina A. and Welti, Ellen A. R. and Shaffer, Monica and Kaspari, Michael} } @article {KNZ001995, title = {Bottom-up when it is not top-down: Predators and plants control biomass of grassland arthropods}, journal = {Journal of Animal Ecology}, volume = {89}, year = {2020}, month = {1286-1294}, abstract = {

1) We investigate where bottom-up and top-down control regulates ecological communities as a mechanism linking ecological gradients to the geography of consumer abundance and biomass. We use standardized surveys of 54 North American grasslands to test alternate hypotheses predicting 100-fold shifts in the biomass of four common grassland arthropod taxa\—Auchenorrhyncha, sucking herbivores, Acrididae, chewing herbivores, Tettigoniidae, omnivores, and Araneae, predators.

2) Bottom-up models predict that consumer biomass tracks plant quantity (e.g. productivity and standing biomass) and quality (nutrient content) and that ectotherm access to food increases with temperature. Each of the focal trophic groups responded differently to these drivers: the biomass of sucking herbivores and omnivores increased with plant biomass; that of chewing herbivores tracked plant quality; and predator biomass did not depend on plant quality, plant quantity, or temperature.

3) The exploitation ecosystem hypothesis (EEH) is a top-down hypothesis that predicts a shift from resource limitation of herbivores when plant production is low, to predator limitation when plant production is high. In grasslands where spider biomass was low, herbivore biomass increased with plant biomass, whereas bottom-up structuring was not evident when spiders were abundant. Furthermore, neither predator biomass nor trophic position (via stable isotope analysis) increased with plant biomass, suggesting predators themselves are top-down limited.

4) Stable isotope analysis revealed that trophic position of the chewing herbivore and omnivore increased significantly with plant biomass, suggesting these groups increased scavenging and meat consumption in grasslands with higher carbohydrate availability.

5) Taken together, our snapshot sampling documents gradients of food web structure across 54 grasslands, consistent with multiple hypotheses of bottom-up and top-down regulation.

}, keywords = {LTER-KNZ}, doi = {10.1111/1365-2656.13191}, url = {https://onlinelibrary.wiley.com/doi/abs/10.1111/1365-2656.13191}, author = {Welti, Ellen A. R. and Prather, Rebecca M. and Sanders, Nathan J. and deBeurs, Kirsten M. and Kaspari, Michael} } @article {KNZ002005, title = {Nutrient dilution and climate cycles underlie declines in a dominant insect herbivore}, journal = {Proceedings of the National Academy of Sciences}, volume = {117}, year = {2020}, pages = {7271-7275}, abstract = {

Evidence for global insect declines mounts, increasing our need to understand underlying mechanisms. We test the nutrient dilution (ND) hypothesis\—the decreasing concentration of essential dietary minerals with increasing plant productivity\—that particularly targets insect herbivores. Nutrient dilution can result from increased plant biomass due to climate or CO2 enrichment. Additionally, when considering long-term trends driven by climate, one must account for large-scale oscillations including El Ni{\~n}o Southern Oscillation (ENSO), North Atlantic Oscillation (NAO), and Pacific Decadal Oscillation (PDO). We combine long-term datasets of grasshopper abundance, climate, plant biomass, and end-of-season foliar elemental content to examine potential drivers of abundance cycles and trends of this dominant herbivore. Annual grasshopper abundances in 16- and 22-y time series from a Kansas prairie revealed both 5-y cycles and declines of 2.1\–2.7\%/y. Climate cycle indices of spring ENSO, summer NAO, and winter or spring PDO accounted for 40\–54\% of the variation in grasshopper abundance, mediated by effects of weather and host plants. Consistent with ND, grass biomass doubled and foliar concentrations of N, P, K, and Na\—nutrients which limit grasshopper abundance\—declined over the same period. The decline in plant nutrients accounted for 25\% of the variation in grasshopper abundance over two decades. Thus a warming, wetter, more CO2-enriched world will likely contribute to declines in insect herbivores by depleting nutrients from their already nutrient-poor diet. Unlike other potential drivers of insect declines\—habitat loss, light and chemical pollution\—ND may be widespread in remaining natural areas.

}, keywords = {LTER-KNZ}, issn = {0027-8424}, doi = {10.1073/pnas.1920012117}, url = {http://www.pnas.org/lookup/doi/10.1073/pnas.1920012117}, author = {Welti, Ellen A.R. and Roeder, Karl A. and de Beurs, Kirsten M. and Anthony Joern and Kaspari, Michael} } @article {KNZ002030, title = {Salty, mild, and low plant biomass grasslands increase top-heaviness of invertebrate trophic pyramids}, journal = {Global Ecology and Biogeography}, volume = {2958}, year = {2020}, pages = {1474 - 1485}, keywords = {LTER-KNZ}, doi = {10.1111/geb.13119}, url = {https://onlinelibrary.wiley.com/doi/10.1111/geb.13119}, author = {Welti, Ellen A. R. and Kuczynski, Lucie and Marske, Katharine A. and Sanders, Nathan J. and Beurs, Kirsten M. and Kaspari, Michael}, editor = {Madin, Elizabeth} } @article {KNZ001935, title = {A distributed experiment demonstrates widespread sodium limitation in grassland food webs}, journal = {Ecology}, volume = {7113}, year = {2019}, pages = {e02600}, abstract = {

Sodium (Na) has a unique role in food webs as a nutrient primarily limiting for plant consumers, but not other trophic levels. Environmental Na levels vary with proximity to coasts, local geomorphology, climate, and with anthropogenic inputs (e.g., road salt). We tested two key predictions across 54 grasslands in North America: Na shortfall commonly limits herbivore abundance, and the magnitude of this limitation varies inversely with environmental Na supplies. We tested them with a distributed pulse experiment and evaluated the relative importance of Na limitation to other classic drivers of climate, macronutrient levels, and plant productivity. Herbivore abundance increased by 45\% with Na addition. Moreover, the magnitude of increase on Na addition plots decreased with increasing levels of plant Na, indicating Na satiation at sites with high Na concentrations in plant tissue. Our results demonstrate that invertebrate primary consumers are often Na limited and track local Na availability, with implications for the geography of invertebrate abundance and herbivory.

}, keywords = {LTER-KNZ}, doi = {10.1002/ecy.2600}, url = {https://esajournals.onlinelibrary.wiley.com/doi/full/10.1002/ecy.2600}, author = {Welti, Ellen A. R. and Sanders, Nathan J. and Beurs, Kirsten M. and Kaspari, Michael} }