The Kaspari Lab
Potassium as a game-changer in prairie food webs
We all know how sports drinks full of sodium (Na) and potassium (K) can rescue your performance on a hot day. But what if you’re a plant? Let me tell you about an experiment with Dr. Ellen Welti that shows the super-powers K gifts to plants. Plants use K as their primary way of keeping cells hydrated, plump, and working. But K is slippery—it’s so soluble that it leaks out of plants and must be constantly resupplied. K today, gone tomorrow. PDF: https://bit.ly/3G9SKwO
Plants often get their K pre-packaged with Na in urine. But plants don’t need the Na, and we’ve shown it attracts herbivores who, like us, eat plants and need both. What gives? So, we set up an experiment at @KonzaLTER to find out. #NSFFunded
We monthly fertilized 7×7 m plots w the Na and K you’d find from a herd of bison —or just the Na or K—vs controls. We watched what happened to the chemistry of the plants, and numbers of bugs on the plots. @OUBiology
On control plots, we see the natural course from May through September. Plants get bigger and drier, and a mouthful of May grass is much more nutritious than that in Aug/Sept. Nutrients are diluted in time. PDF: https://bit.ly/3yc5Y6s
But look what happens to all those elements on plots fertilized with K, Na, NK! With repeated fertilization, the net effect sizes become strongly positive by July. The grasses seem to be using the K to help pump nutrients into foliage. By September those same treatments have *lower* nutrients than control plots. NaK is a ‘sports drink’ for prairie plants, allowing them to mobilize nutrients up to leaves when they need them, and down to roots when they need to store them.
Now look at the bug densities: almost the opposite pattern. When the nutrients are high on +KNa plots, the bugs are suppressed. As they decline, the bugs rally, until they are sequestered below round, when they decline again.
One more thing. Perhaps the reason one-time applications of K rarely show an effect in big experiments like #NutNet is that they are applied, w N and P, in May. K is so soluble that it doesn’t stick around. But areas with repeated urine applications—like Bison Lawns and Vole latrines— may be the place to find plants that are true masters of their ionomic domain. But areas with repeated urine applications—like Bison Lawns and Vole latrines— may be the place to find plants that are true masters of their ionomic domain.
All that is green is not nutritious or, The importance of peeing earnestly
Grasslands can be zen places: hectares of rolling prairie. But to an herbivore, all that is green is not nutritious. In a recent paper led by NSF REU Katerina Ozment mentored by Dr. Ellen Welti of OU_Biology we reveal how drought & Bison combine to create a nutritional patchwork.
The paper (PDF:https://bit.ly/39c4cHB) began as a 2018 study of Bison Lawns at
@KonzaLTER, patches revisited by the big herbivores, where they eat, poop, and pee. The bison get a dependable, high nutrient food supply; the local grasshoppers do too. Win:Win!
But 2018 was also a *big* drought year. Enter Nutrient Dilution: where lotsa plant biomass dilutes with carbs the other essential nutrients in a bite of grass *and visa versa*. 2018 nitrogen supplies *off* bison lawns were like those of bison lawns in *normal* years.
So Ellen and I revisited the same 10 bison lawns in 2019, a normal rainfall year that would 1) reduce nutrient densities with the increased biomass, and 2) exacerbate (we predicted) the consequences for grasshoppers of *not* taking advantage of Bison pee-supercharged grass.
Combined, the 2 years tell a story of grasshoppers minding their nutrients. In the wet year (triangles) bison lawns were ‘hopper hotspots in a green desert; in the drought year, where nutritious grass was everywhere (just less of it), grasshoppers were less discriminating.
Katerina’s honors project revealed the interaction of subtle (rainfall) and not so subtle (bison) factors in generating a prairie patchwork for grasshoppers, and the counter-intuitive result that a lush green prairie may not necessarily be a herbivores cup of tea.
Bite by bite: why North American herbivores confront such a variable diet
As you travel across North America, grasslands are everywhere, from roadside strips to boundless open prairie. It is easy think of acres of grass and forbs (flowering herbs) as just mouthfuls of forage for local herbivores. Give me a moment to present the more beautiful truth.
In a recent paper in Ecology, Dr. Ellen Welti, Dr. Kirsten de Beurs and I analyzed data we gathered visiting 54 grasslands in the summer of 2016. In each, we cut 0.1m2 strips of vegetation—clip plots—to study food web nutrition. As always, we are grateful for funding support from the National Science Foundation. You can download the paper for your personal use from the publication page of this website, here.
Now, if you want to get *realllly* fundamental you can think of the vegetation from these grasslands following the same recipe of 25 chemical elements. We asked if a grasshopper or bison munched away in each grassland, how nutritious would they be? Why and how are some grasslands more yummy?
Above, we plot average element ppm (parts per million) in the plants against the avg in the soils; elements above the dashed line are accumulated by plants. The standbys NPK accumulate, also B(oron) and Mo(lybdenum). Plants tend to *avoid* animal essential nutrients except Na.
But then we looked for patterns *across* North America grasslands and found the same element could vary 1000-fold in ppm (amount per bite). The Supply Side hypothesis reasonably predicts that this is caused by soils—where a soil is rich in element R, it is often so in its plants.
This is where the first difference between grasses and forbs emerged. Forbs tended to be pickier, harvesting more universal nutrients where available. Grasses, on the other hand, were more indiscriminate, harvesting even non-essential nutrients like Cd and Sr when available.
A second hypothesis, championed by Dr. Puni Jeyasingh up the road at Oklahoma State suggests that the availability of macronutrients like N and P—that build our metabolic machinery—drives the need for the other nutrients. This too, won some support: grasslands rich in N and P increased uptake of catalysts like Zn and Cu.
A third idea: nutrients are recycled by herbivores in the form of poop and pee. Sadly (in retrospect) we called this the ‘Grazing Hypothesis’, not ‘PoopPee’. Grazing by cattle increased plant ppm in elements like Fe, Cu, and Cr: straight outta the colon and its own microbiome.
Finally, we looked for Nutrient Dilution: how increases in plant biomass dilute its nutrition per bite. This is where the second diff between forbs and grasses emerged. Forbs, richer in nutrients in the first place, tend to decline in ppm when they grow more. Less so, grasses.
The upshot? Plant nutrient density—not just biomass—is key to herbivore health. We found the 2 plant groups followed different rules. Since forbs are more prone to Nutrient Dilution, increases in CO2, temperature, and precipitation likely target forb-feeders more.
More generally we provide a framework of four hypotheses to explore the geography of nutrition for Earth’s consumers, and show that plants don’t slavishly track the nutrients in the soil, but create their tissues by integrating across the entire abiotic and biotic environment.
The Great Diverse North? Flipping the latitudinal gradient.
Every student of Ecology learns that the variety of species declines as you move north or south from the equator. In a new paper led by Dr. Michael Weiser @NEONAnts we show the truth is more delightfully complex. And we do it for the most diverse set of animals on Earth! As always, we thank the National Science Foundation @NSF for their support, as well as our friends in the Department of Biology at the University of Oklahoma @OU_Biology.
In a new paper in Oikos, Mike, me, Dr. Cam Siler, Sierra Smith, Dr. Katie Marshall, Dr. Matt Miller, and Dr. Jess Mclaughlin show the diversity of invertebrates from a huge network of pitfall traps *increases* as you go from south to north. To download a copy for your personal use, click here.
Why do we think this study is important? Five reasons.
The scale
The taxa
The community
The methods
The future
The Scale: the paper exploits a series of standardized trapping grids across much of North America. Every terrestrial habitat—from deciduous forest to desert shrub—is sampled the same way. These traps capture all manner of invertebrates that move across the soil surface, adding their data to the large compendium of geographic patterns for trees, mammals, birds…the big stuff. In this way, we give a first, comprehensive look at patterns of diversity measured via passive traps that rely on Activity Density: the rate that critters move across the landscape.
The Taxa: The invertebrates are the most diverse group of animals and have thus far been incompletely sampled, with a few groups well sampled nearly everywhere (e.g., ants, butterflies) and most groups known well from far fewer locales. We explore how diversity varies for the summed diversity of all invertebrates plus 12 common taxa, from springtails to grasshoppers to spiders. Collectively, rather than declining toward the poles (the classic “Latitudinal Diversity Gradient” documented at the scale of latitude/longitude grid cells) we show that diversity increases from Puerto Rico through the American South northward, attenuating or dipping only in the Arctic. The pattern is consistent at multiple taxonomic scales (i.e., counting species, genus, family, and orders) and is true for a variety of subgroups.
In short, we flip the latitudinal gradient on its head! Take a look:
The Community: Why do our results diverge from one of the oldest ecological patterns in the book? We think the big reason is that we are sampling discrete communities around each trap grid—only a few hundred square meters. Communities differ from grid cells like those at the top of this post. Grid cells encompass, and hence tally, species across a variety of habitat patches (each with their own complement of bugs). Community diversity focuses on a more limited suite of species: those that are living and interacting in the same place.
The science of community ecology is all about the processes that limit the number of critters that can coexist, a suite of processes that follow different rules than those determining the ranges of all those species. A variety of processes—like the existence of food plants, nearby competitors, predators, and mutualists, or local moisture and temperature—all serve to filter that pool to a smaller subset. Our results suggest that those filters are stronger toward the equator. So much so, that even with more species available, communities from the warm subtropics are more rigorous at kicking out species that don’t “fit”.
A second, complementary hypothesis, is that communities closer to the poles have more mobile species (and thus more colonists from the wider species pool coming to visit)…
Or perhaps northern communities are more likely to be disturbed by cold temperatures that knock down populations and open up resources…
Regardless, the flip in the community diversity curve from that often found in the grid cell diversity curve was quite a surprise.
The Methods: We obtained the NEON pitfall samples from their storage facility at ArizonaState. We use a combo of eDNA (extracting info from the alcohol) and machine learning from images (ditto for pictures) to nondestructively analyze their contents.
The Future: With this pipeline we provide tools to ecologists for monitoring Earth’s invert populations in this era of Insect Declines. We are discovering the rules for insect communities differ from “common knowledge”. Next: the geography of invasive species and size!
Oh, and one more thing.
We are proud to publish these cool results in the journal Oikos—rather than the countless spinoffs of journals beginning w ‘Sci’ and ‘Nat’—because we support scientific societies like the Nordic Society Oikos, the British Ecological Society, and the Ecological Society of America that in turn support the ecological community.
On the challenge of interpreting Activity Density from NEON’s pitfall arrays
As fossils fuels burn—with all the attendant effects—we are becoming increasingly concerned with how Earth’s insects—the little things that run the world—may be declining. Follow along, and let met tell you about a wee complication toward understanding what’s happening.
In a new paper in Ecology we use NEON‘s network to explore how changes in climate affect insect communities monitored via Activity Density PDF: https://bit.ly/3IThjfu.
Frequently insects are monitored with traps—like these malaise traps that capture flying insects, and NEON’s pitfall traps that capture bugs running on the ground. In each case traps catch more when 1) bugs are more abundant and/or 2) bugs move around more.
This gets tricky when we use the traps to say something about insect populations. Why? Because ecologists know that bugs (as ectotherms) can move more when its warm, and can reach higher numbers in productive, rich environments. Hence Activity (movement) Density (abundance).
Consider, when
Kirsten DeBeurs and I reanalyzed a global dataset from tundra to rainforest, the number of ants running across branches, sure enough, increased predictably as the plant production grew richer. PDF: https://bit.ly/3wOOfDC
But here’s the complication. A lot of other things change as you go from deserts to forest including the ability to move, unimpeded, thru the environment. Our dear ant would be slowed by a lot more stuff on the way to a trap in forest litter compared to desert pavement.
And the pitfall traps in the NEON network sample from *all* major habitat types, often more than 1 at a site. High in the Rocky Mountains, for example, the NIWO site samples grasslands and evergreen forests. Could these habitats yield different responses to changing climate?
When we—Cam Siler, Michael Weiser, Kirsten de Beurs and Katie Marshall—examined the effects of a site’s mean temperature and productivity on its bug community’s Activity Density, we got very different results for each.In desert scrub, as temp increased so did activity density. In grasslands this increase plateaus. Now look at forests: AD increases to a peak, then declines as temps warm. A global monitoring network, this suggests, promises all sorts of responses to an increase in temperature.
Warming in the desert scrub may continue to generate higher AD, with or without changes in abundance, simply because bugs move faster along desert pavement. Forests? 1°C of warming may increase—or decrease—AD, with or without changes in the numbers of bugs.
Why is this important? If we use traps to monitor Earth’s bugs populations—particularly if we want to see how forest bug populations are changing relative to desert bugs—we need to be *very careful* to consider their habitat and how bugs move through it. More on this soon.
Introducing “Ecology Stories”
Debby Kaspari and I are pleased to announce the first “episode” of our ongoing series of illustrated essays on Ecology. Our goal is to introduce fascinating topics in a style accessible to audiences from middle-school through undergraduate science classrooms, and just about any reader that may be wondering about what is going on with our planet Earth. The first episode can be downloaded as a 12-page PDF here and is freely available on a Creative Commons license that asks you to attribute the work to Debby and myself, not create mash-ups, nor make people pay for it.
The work is a labor of love between an artistically inclined scientist and a scientifically inclined artist. It is inspired by great graphic novel collaborations that know how to tell a story with pictures and words. It is firmly grounded in our appreciation of the #SciArt and #SciComm community. It was made possible in part through funding from NSF (DEB-1702426), and was made so much better through consultations with science teacher extraordinaire Lauren Niemann, and scholar-poet-science student, Tom Kaspari.
We are especially excited about highlighting the work of ecologists from around the world. Our first guest scientist is Dr. Andrea Lucky from the University of Florida, who describes her work as an ant taxonomist. Other scientists that show up in the first episode are Dr. EO Wilson, Dr. Winnie Hallwachs, and Dr. Dan Janzen.
One of the most fun parts of the collaboration is seeing Debby’s magnificent work—from pencil sketches, inked cartoons, pastels, watercolors, to computer generated art—used to illuminate concepts in ecology. You can find a lot more of Debby’s work on her website Drawing the MotMot.
For example, one challenge in talking about biodiversity is its nomenclature. Debby’s poison dart illustration captures one of our favorite taxa from the Neotropics—poison dart frogs—toward capturing the essence of genera and species.
Even Gizmo the cat gets her opportunity to shine. As this is the first in a planned series, we’d love to find out how “Episode One: What is Biodiversity” plays in your classroom or with your Sci-curious niece. Get back to us here with comments, suggestions for improvement, or potential story ideas. What are ideas, challenges in ecology that everybody needs to know more about? How can we help you communicate ecology in a colorful, accessible, and hopefully, just a bit entertaining way?
Grasshopper Declines and the perils of Nutrient Dilution
Grasshopper numbers at a tall grass prairie have declined ca. 2% per year. Ellen Welti leads in identifying a likely culprit: increasing CO2 is diluting plant nutrients, making each bite less and less nutritious over the years. This open access paper at PNAS https://www.pnas.org/content/pnas/117/13/7271.full.pdf earned the 2020 finalist for the Cozarelli Prize for the best PNAS paper in the Environmental Sciences.
An intensive program of sweep netting at @KonzaLTER revealed 37% decline over 22 years. This decadal decline is similar to those found for butterflies, suggesting a common cause. Konza-a large preserve-isn’t destroying habitat or using pesticides. But…
Konza also harvests plants every season to measure production. We show over this time how grass production has ca. doubled. And with no corresponding added nutrients the concentration of nutrients is declining in dominant grasses: grasshopper food. Hence the Dilution Hypothesis.
We are left w the working hypothesis that 5-year fluctuations in climate combine with long-term accumulation of CO2 to reduce the capacity of this tall grass prairie to support a dominant herbivore. How common is Nutrient Dilution? And how do we fix it? Stay tuned.
Originally tweeted 9 March 2020
The Kaspari Lab 