The Kaspari Lab
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
As ecosystems heat and green, ant abundance and diversity increases; but too much heat and these communities lose colonies and species.
One paradox in the recent flurry of papers reporting insect declines is that insects—ectotherms that rely on external sources of heat—are often predicted to benefit as their environment warms. In an open access paper accepted as a Report in the journal Ecology our team of ecologists—including Michael Weiser, Jelena Bujan, Karl Roeder, and Kirsten deBeurs—all from the University of Oklahoma, help resolve that paradox.
Ants are diverse and abundant in terrestrial ecosystems. They act as nature’s cleanup squad, and are threaded throughout her food webs. Understanding how their abundance and diversity is changing as Earth heats up is a major challenge to ecologists. Images used by permission of Alex Wild @Myrmecos.
In a resurvey of 34 North American ecosystems after 20 years—both surveys funded by the National Science Foundation and that contribute to the NEON continental observatory—ant communities from deserts to forest have increased their abundance and diversity, but only up to a point.
The ants living in 34 ecosystems across North America were first surveyed in the 1990s, and then again 20 years later.
The desert, tundra, grassland and forests resampled by the Kaspari lab as we explored 20-year changes in the ant communities. Image by Karl Roeder.
To get these ecological “before” and “after” pictures, our team of post docs, graduate students, and undergraduates, traveled across North America in 2016 and 2017. We used the same methods of sampling ants from the same field stations, parks, and forest service districts that Weiser and I, along with Leanne and Alfonso Alonso, had sampled back in the mid 90s.
The 34 sites were on average 1°C warmer with higher estimates of plant production. Both trends are predicted to increase the numbers of ant colonies, and numbers of ant species in the ecosystem.
Twenty years later, these sites were different in important ways. First, they averaged 1°C warmer, with some much warmer than that. This evidence of global heating, differentially expressed, allowed us to evaluate a key theory underlying global change. that systems where ecotherms run the show should increase their activity and production—in fact accelerate it—before they suddenly crash. Second, they tended to be more productive–that is plants were producing more food, in the form of sugars, than before.
A graphical prediction from Thermal Performance Theory, that systems accelerate before they crash. In this case, it predicts that smaller increases in temperature are likely to enhance ant abundance, but bigger temperature increases will cause abundance to suddenly decline.
This second snapshot of the ant communities revealed that ant abundance at most sites had increased, and increases in the number of ant species had increased even more consistently.
The distribution of observed 20-year changes in North American ant communities. Left of the blue line, communities are losing colonies and species. To the right, they are gaining.
Ant colonies tended to be more abundant in ecosystems that had warmed by a degree or so. However, those few that had warmed more—and some forest sites were up to 2.5°C hotter—suffered big declines in colony numbers. This result supports an important ecological theory: that when you warm a system composed of ectotherms it often accelerates. But beyond a certain temperature, it crashes.
Dr. Jelena Bujan sampling a one m2 plot for ant colonies at the Jornada field station in southern New Mexico. Photograph by Josh Kouri.
The number of species found in each community—a measure of its biodiversity—was in turn sensitive to these changes in abundance. The communities that increased their abundance were able to support more biodiversity, on average 2 more species on our sample transects after 20 years.
Dr. Michael Kaspari using an aspirator, or “pooter” to suck up ants at the Ordway Swisher field station in northern Florida. Photograph by Deborah Kaspari.
Such data on insect changes—collected all in the same way and over a large geographic area—are still relatively rare, making generalizing about insect declines difficult, and contentious.
But ants are an important test case. They are ecologically dominant and widespread. Their apparent increases—when studies of say, butterflies often show decreases–also likely arise because ants tolerate higher temperatures than other insect groups. Moreover, ants tend to be diet generalists, eating plants, animals, and carrion, and many colonies can seek respite underground from the hottest parts of the day. All of these traits combine to make them relatively resistant to moderate increases in temperature.
However, the precipitous decline of ant communities at temperature increases > 1.5° C is a cause for concern. We will all be watching how this unfolds over the next 10 years.
Dr. Michael Weiser, inspects the ants active at night from a plot at the Sevilleta National Wildlife Refuge. Photo by Josh Kouri.
Arts and Sciences
Caption: Debby Kaspari (of Drawing the Motmot) provided this sketch for a seminar of mine in the 90’s, an update of the parable of the blind men and the elephant.
One of my favorite classes is “Principles of Ecology”, a venerably old course at the University of Oklahoma whose structure and focus has long been shaped by the professor in charge that semester.
One of my tweaks to PE in Fall 2017 was the addition of a list of the Ten Principles of Ecology around which to structure the course. This experiment generally paid off, I think, as it gave students ten solid memes to take away at the end of the semester. And there was a bonus: the ten were also a great way to structure PE’s final capstone project. Students have one of three options: 1) write a 500 word letter to the editor, 2) record a 15 minute teaching video aimed at middle school students, or 3) create a work of art. Each should celebrate and makes concrete why knowledge of one of those principles is a good thing.
To my delight, an increasing number of students have been creating art. Moreover, “Option 3” consistently yields some of the most intense and novel work. I’d like to share with you and honor five of those works of art here. The following gallery could easily be three times as long.
The instructions
Create a piece of art that captures one of the ten ecological principles. Create a description of the piece that would hang next to it and that includes the name of the piece, the name of the artist, the date it was created, and a short description of the materials, the process by which you created it, and the principle it was meant to capture.
A Cog in the Moo-chine by Miranda Hannon
“The cow itself was laser etched on a ½ in thick piece of plywood, using a table saw to get the plywood the correct size. The gears were 3D printed out of PLA on a MakerBot Replicator 5th Generation. The wood was lightly stained and the cow was covered in painter’s tape to give contrast. It represents Ecology Principle #3: Organisms are chemical machines that run on energy. While the interior mechanisms may differ, we are all bound by the laws of physics. Most energy ultimately originates from the sun (Principle #2), and organisms are the machines that must process that energy into a format that’s usable for them.”
Reference
Freevector. Cow Silhouette Graphics [Online Vector]. Retrieved December 4, 2017 from https://www.vecteezy.com/vector-art/78846-cow-silhouette-graphics
Pleppik. (2012) Sam’s Gears [3D Model]. Retrieved December 4, 2017 from https://www.thingiverse.com/thing:30981
Organized Chaos by Makenna Hukill
“This piece represents Principle 8 of the 10 Principles of Ecology that states, “Ecosystems are organized into webs of interactions.” I never realized how important species interactions truly were until taking Principles of Ecology. Measuring and understanding species interactions is one way to determine the health of a biome or ecosystem. Also, the more species interactions there are the more stable an ecosystem is. I used String Art to illustrate species interactions. I would also like to point out that I used slices of wood in this piece. I did this purposely and with meaning. Examining and measuring details in wood slices is a way to determine if a terrestrial biome has been healthy over an extended period of time. Although this piece focuses on the importance of species interactions, the take home message is having healthy biomes and ecosystems through the examination of fine details and organized chaos.”
Materials:
- Wood (from the tree cutters at McKinley Elementary School)
- Cotton Yarn
- Decorative Nails or Tacks
- “T” Brackets and Screws
Interactions by Nicole Nguyen
“Acrylic paint was used to first paint the different organisms. The different organisms were then labeled with their name painted on the backs of them. Interaction arrows were also painted with acrylic paint, and the backs of those were also labeled with the type of interaction being shown. All of this was then connected by ribbon. There were three ribbons total, which were then all tied to a rod. Another piece of ribbon was tied to the rod so that this piece of artwork could be hung up. The principle it was meant to capture was principle 7, which states that organisms interact – do things to each other – in ways that influence their abundance.”
The Sunflowers of Life by Bahar Iranpour
“Materials: As an artist, my favorite media to use is paint, specifically oil paints and watercolor. However, oil paintings take up to a week to dry, so I chose to make my project using water colors. I actually prefer using water colors when drawing nature sceneries because I like how light it appears and how easy it is to mix the colors together. It makes the painting look more realistic because nature and our ecosystem is just as mixed in together and intertwined. As you can see in the painting, there is no specific line or division between the flowers and the field, the mountains and the sky. It was my way of showing through the material I chose that everything is complete when together as a whole.
Principle: I chose principle 2– The sun is the ultimate source of energy for most ecosystems. Life runs on carbon rich sugars produced by photosynthesis; every ecosystem’s sugar output depends on how much solar energy and precipitation it receives. I thought this was the most important principle because it serves as the base for all the other principles. If there was no sun, there would essentially be no life, so we would not have any organisms, hierarchies, species interactions, etc that the rest of the principles discuss. The sun allows photosynthesis to occur in plants. These plants are then able to make glucose and grow, which provides food for herbivores. These herbivores eat the plants, grow, and then carnivores come and eat the herbivores. This cycle consistently continues, providing energy to all levels on life.
Process: I definitely wanted to paint a nature scene for the principle I chose. However, I didn’t want to just paint a sun in the middle of my art. I wanted it to be more interpretive. I chose to draw sunflowers because it reminds me of when my mom used a sunflower as an example to teach me about photosynthesis when I was a child. My grandfather always had sunflowers in his garden. I remember my mom pointing out how the sunflowers would position themselves toward the sun in order to obtain its energy and go through photosynthesis. Then at night, the sunflowers would turn around again. This process was very beautiful to me, so I wanted to depict it in my painting. That’s why I drew the sunflowers facing different directions.
This taught me to appreciate the world around me, and how something as simple as the sun does so much for us. I feel that society is so invested in other things, that we take our environment, our sun, etc for granted. One day it may go away, and all life will be gone too. This is why I chose to not make the sun so apparent and clear. I painted a faint, yellow shadow in the middle of the sky, behind the mountains and clouds, to show that the sun is present and providing energy to the plants and flowers in the painting, yet it may go away one day and not be able to provide its energy.
I drew a variety of things like flowers, grasses, plains, shrubs, mountains, water, etc to show that the sun is important to all of these and many more. The small little plants on the mountains and even the small little plants in the water all need the sun’s energy to live. I included a body of water in my painting to also show the importance of water in photosynthesis—water is also needed for photosynthesis to occur. I also wanted the painting to be mostly yellow in order to emphasize the sun and its color, which is why I chose to paint a sunflower field.”
Human. Expansion. Landscape. Permutation. by Sierra Smith
“This piece was intended to capture Principle Nine of the Ten Principles of Ecology. In short, the ninth principle states that humans have an enormous influence on the Earth’s biosphere due to the large population size and technological advances the species has achieved. For hundreds of years, this influence has been used to reshape the Earth’s landscape, scatter species, and destroy diversity. This piece depicts a side by side view of what the natural Earth looks like in comparison to an Earth shaped by humans. To create my piece, I began with a blank, white poster board and used water based, twin tip Fineline Markers. I used these markers to draw the pine trees in addition to the bison and deer herds. Also, these markers were used to outline everything from the roads to the buildings to the mountains. To color everything in I used regular Crayola colored pencils.
I began the process by using the markers to draw the outlines of the buildings and the mountains to establish the two different sides of the piece. Next, I drew the road dividing the sides, and outlined it with the gray marker. Then, I drew all of the trees surrounding the mountains. I made sure to leave a space for the deer and bison herds. There was a more open space left for the bison herd in order to create a prairie environment. I moved on to the city side of the piece by drawing windows on the buildings and coloring them in. The BP building is a representation of a time humans had a detrimental effect on the environment due to the BP oil spill. After this, I drew and colored in the river. The river that runs through the city is a darker shade than the side that runs through the natural environment because of the pollutants and junk that humans release into the water systems, causing murky water. I drew the cargo ship as a representation of one way humans have used the rivers for our advantage. Then, I created the three billboards on the sides of the road. One billboard reads: “IPhone 10 On Sale Now” to signify the advanced technology the human race has developed over time. The next reads: “Land for Sale: 20 acres” which represents the fact that humans will commonly come into a natural environment and change it to their liking, regardless of its effect on the natural life inhabiting the land. The last sign reads: “Eat low fat bison burgers” to depict the human consumption of many animals, including bison. These three signs are representations of common human-imposed environmental change described in Principle 9.”
Toward a MacroEcology of Some of the Little Things that Run the World
Caption: Five Geographical Ecologists from OU’s Dept. of Biology and investigators on our new macrosystems grant. L-R: Michael Kaspari, Matt Miller, Michael Weiser, Katie Marshall, and Cam Siler.
The backstory behind our latest NSF-Macrosystems funded project
Insects are among the most abundant and ecologically important animals in the biosphere. Insects pollinate plants and decompose them back into soil. They include serious crop pests and invasive species that cause countless millions in damage. A key goal of macroecology is to understand how and when the number and activity of insects change as one moves from place to place across the U.S., and why those numbers fluctuate from year to year. Such an understanding can help predict insect pest outbreaks, the spread of invasive species, and changes in an ecosystems ability to provide food and fiber and conserve soil nutrients.
Yet macroecological datasets vastly underrepresent the terrestrial invertebrates. This reflects a lack of sampling effort (boots on the ground collecting insects) and identification expertise (eyes in the lab counting and recording them).
Thanks to the NEON pitfall network, 47 invert sampling arrays now span the U.S.’s major ecosystems, collecting insects in pitfall traps. These traps–sunk flush with the soil surface–capture biweekly samples throughout the growing season of each site. We believe these samples are the first step toward a new flourishing invertebrate macroecology. But, beside the carabid beetles, these samples currently consist of jars of bugs in alcohol. For the first time, we have the potential to understand both seasonal and annual invertebrate dynamics at a continental scale. If we could just count, size, and identify all those bugs in all those jars.
The geography of the NEON pitfall trap network. (A) Distribution of monitoring sites in the NEON Pitfall Network (Note: Sites outside of continental US not shown above). (B) Example of site-specific pitfall array. (C) Illustration of individual, pooled jar of macroinvertebrates collected in pitfall array.
The second step
We call the project NEONinverts*. We will endeavor to develop two complementary technologies to turn NEON’s jars of bugs into some classic macrecological variables–abundance, diversity, and body size–and then to test some big continental questions (see below). Each NEON jar is a two-week sample from one of ten arrays from 1 of 47 sites. Only the carabid beetles have been removed. This is an astounding library of ecological information.
In NEONinverts, we will develop two pipelines–a g’mish of technology, databasing, and best practices–that will count, size, and identify taxa from these samples. The first half of our project will be to test, hone, and validate these protocols.
The big picture of our pipeline development.
Environmental Barcoding will extract insect DNA from the alcohol in which the insects steep and use that DNA to put names on the inverts found therein. Environmental barcoding (EB) is a set of tools that allows the identification of biota, not from their tissue, but from the media in which they exist. It has been used to screen for aquatic invasive and endangered species from water samples. More recently, several studies have used EB from arthropod “biodiversity soup”—homogenized samples from insect traps.
We propose to take on the hard problem of non-destructive quantification of diversity and composition from pitfall samples using the ethanol supernatant of preserved macro-invertebrate samples. In doing so, we hope to develop a robust pipeline for characterizing taxonomic diversity not only from pitfall traps, but from any fluid preserved mixed-invertebrate sample. This includes quantifying the nature and magnitude of biases, both taxonomic and environmental.
Image Analysis is a second, complementary method for quantifying pitfall traps samples. It starts with spreading trap contents on a white gridded surface with trap labels and ruler placed in a standard location. Images are captured with an articulating system of 10 PowerShot G7 X Mark II cameras, each with a resolution of 20.1 megapixels from fixed tripod arms with constant lighting conditions. Our first goal will be to use these images to quantify abundance and body size distributions.
The low down on Image Analysis as a tool to identify bugs.
We will then use machine learning–automated algorithms for pattern recognition and classification–to explore our ability to identify taxonomic groups. While machine learning methods for classification are not as accurate as expert examination, they classify orders of magnitude faster than an expert. Like the EB methodology, one of our chief goals is to see how far we can get with current technologies. Just quantifying the the dynamics of different invertebrate orders in time and space will be a huge step forward, but we are confident we can go further than that.
Together, these two pipelines hold the promise of automate and streamlining NEON’s monitoring network, providing the first such nationwide dataset on abundance, activity, and diversity of the U.S.’s soil insects.
Answering macroecological questions with invertebrate data
These data will be potentially valuable to a variety of stakeholders: ecologists testing and refining models that predict future insect communities; land managers who want to know the likelihood of a pest eruption; conservation biologists and urban planners hoping to anticipate spread of invasive ants and beetles.
We are focusing on one uber-question: how do Earth’s great abiotic drivers–temperature, precipitation, and biogeochemistry–govern how ecological communities of individuals and species vary from place to place and over time? The few existing arthropod datasets suggest that as one travels from deserts to rainforests, terrestrial arthropod communities vary by orders of magnitude in abundance (the number of individuals), size (mass per individual), activity (the rate at which individuals do work on the system), and diversity (the number of species/forms). A better understanding of the drivers of each–applied to groups as different as spiders, ants, collembola, and tiger beetles–should help us understand how these taxa regulate ecosystem processes like decomposition, herbivory, and seed dispersal.
Stay tuned.
*Yeah, we know. We are not completely happy with “NEONinverts”. But at least the twitter handle was available.
The Ten Principles of Ecology
I have been teaching a course called “Principles of Ecology” at OU since 1996. It was a traditional two one-hour lecture, one three-hour lab for most of those years. In 2013, I decided to flip the course, converting the lectures to workshops, and asking students to do more reading outside of class. The goal is to allow for more hands on “learning by doing” activities in the workshops, and to more tightly linked lab and fieldwork to workshop data analysis and interpretation. All in all it has been an exciting, often unnerving, but very satisfying transformation. One that is ongoing.
All along it occurred to me that the title of our course strongly implies that there is a finite number of useful principles that our students should internalize. Moreover, if the list and the principles themselves are sufficiently pithy, we should be able to cover them at the beginning of the course, rather than unveil them, one after the other, as the course proceeds. The advantage there would be that students get the big picture early, allowing us to revisit and recombine different suites of principles to build and explore new concepts and ideas. That’s the idea, at least.
I had two inspirations for this venture. One was Eugene Odum’s classic “Fundamentals of Ecology”, the famous “yellow book” that was the go-to text for much of ecology’s early years. Odum organized the book around chapters with titles that begin “Principles and concepts pertaining to….” (e.g., “Limiting factors). He would then carve each chapter into a series of expositions each with a “Statement”, followed by an “Explanation” followed by “Examples”. I just love Odum’s book and this organization because it fits so well how I organize my own thoughts. I recommend finding a used copy. It holds up remarkably well.
The second inspiration was Meghan Duffy’s and colleagues’ recent discussion of how to organize an Intro Bio version of Ecology. I think I lifted Principle 2 and 4 directly from that blogpost. Lots of good pedagogy there.
So here is my working list of the Ten Principles of Ecology, stated first as tweet-worthy statement, followed by a short explanation of each. The idea is that my 48 students will be seeing this the first week of class and we will sample, expand on, and recombine them throughout the rest of the semester. I realize every ecologist is different, and that this lays bare my own intellectual DNA on the subject. None-the-less, I’d love to see more lists like this.
Also, has anyone else tried a similar approach to structuring their class? That is, start with the big picture, then backfill? I’d love to hear about it.
The Ten Principles of Ecology
1. Evolution organizes ecological systems into hierarchies.
Individual organisms combine into populations, populations combine into species, species combine into higher taxa like genera and phyla. Each can be characterized by its abundance and diversity (number of kinds) in a given ecosystem or study plot. How and why abundance and diversity vary in time and space is the basic question of ecology.
2. The sun is the ultimate source of energy for most ecosystems.
Life runs on the carbon-rich sugars produced by photosynthesis; every ecosystem’s sugar output depends on how much solar energy and precipitation it receives.
3. Organisms are chemical machines that run on energy.
The laws of chemistry and physics limit the ways each organism makes a living and provide a basic framework for ecology. The supply of chemical elements and the sugars needed to fuel their assembly into organisms limit the abundance and diversity of life.
4. Chemical nutrients cycle repeatedly while energy flows through an ecosystem.
The atoms of elements like C, N, P, and Na go back and forth from spending time in living to spending time in dead parts of an ecosystem. But the photons of solar energy can be used only once before they are lost to the universe.
5. dN/dt=B-X+I
The rate that a population’s abundance in a given area increases or decreases reflects the balance of its births, deaths, and net migration into the area. Individuals with features that improve their ability to survive (i.e., not die) and make copies of themselves will tend to increase in that population.
6. dS/dt=D-X+I
The rate that the diversity of species in an area changes reflects the balance of the number of new forms that arise, those that go extinct, and those that migrate into the area. Individuals and species that have features allowing them to survive and reproduce in a local environment will tend to persist there.
7. Organisms interact—do things to each other—in ways that influence their abundance.
Individual organisms can eat one another, compete for shared resources, and help each other survive. Each pair of species in an ecosystem can be characterized by the kind and strength of these interactions, measured as their contribution to dN/dt.
8. Ecosystems are organized into webs of interactions.
The abundance of a population is influenced by the chains of interactions that connect it to the other species in its ecosystem. This often leads to complex behavior, and a key challenge in ecology is to determine what patterns of abundance and diversity can be predicted.
9. Human populations have an outsized role in competing with, preying upon, and helping other organisms.
Humans are one of millions of species embedded in Earth’s ecosystems. The ability of humans to change the planet, abetted by our large population size and technological prowess, increases our ability to shape the biosphere’s future. Humans, through principles 1-8, are currently changing the climate, re-arranging its chemistry, decreasing populations of food, moving around its species, and decreasing its diversity.
10. Ecosystems provide essential services to human populations.
These include products like timber, fiber and food, regulating water and air quality, and cultural benefits like recreation. A key goal of ecology is to use principles 1-9 to preserve ecosystem services.
A slightly less paradoxical paradox
All organisms are built from the same recipe of 25 or so elements, and so it makes sense that as you increase the supply of those building blocks to an ecosystem, you should be able to increase the number and variety of organisms that ecosystem supports. Deserts vs. rainforests, right? In a paper just out from a terrific collaboration, we show, it turns out, things are not quite that simple.
The background
Michael Rosenzweig
In 1971, Michael Rosenzweig (MikeK’s Ph. D. advisor and friend of the Kaspari lab) used a suite of differential equation models to explore why adding nutrients to an ecosystem so often reduced, not enhanced, the number of species. He coined the term “Paradox of Enrichment” to capture this incongruity. Since then Rosenzweig and a who’s who of ecologists–particularly terrestrial botanists–have documented this Paradox and compiled a long list of mechanisms that could explain it.
A few years ago, our lab joined a team of collaborators to take on the relationship between nutrient availability and diversity in tropical soils. We did so using a grand experiment initiated by Joe Wright and colleagues at the Smithsonian Tropical Research Institute in Panama. Since 1998, we have been fertilizing 40×40 m plots with the “big 3” nutrients–Nitrogen, Phosphorus, and Potassium–as well as a cocktail of micronutrients from Boron to Zinc. In 2012, as part of an NSF MacroSystems grant, we visited each of these plots, sampled soil and litter, and used a variety of molecular and traditional methods to count the number of species of bacteria, fungi, and invertebrates on the essentially 9 different kinds of tropical soils generated by this experiment. I would say that our results, out early online in the journal Ecology, were surprising, but, what happens when you quantify the absence of a paradox?
The Gigante Fertilization Experiment, one of the largest, and longest running such planned experiments on Earth. (You can say that humans are actually doing a pretty good job of adding Nitrogen and Phosphorus and a variety of metals to Earth’s ecosystems in a less scientific, tho none-the-less deliberate manner).
The results are wonderfully complex, but here are some highlights.
Bacteria, Fungi, and Invertebrates each had their own “biogeochemical niche”.
If you plot out the magnitude of diversity responses to nutrients–positive or negative–the resulting fingerprint differed among the big three soil supertaxa. Everybody’s diversity suffered when nitrogen alone was added. This is as close as you get to a uniform Paradox of Enrichment. After that, Bacteria increased the most (and modestly) with phosphorus (P), fungi were all over the map but tend to do better with potassium (K), and invertebrates showed the biggest increases when combinations of nutrients were applied.
Why does nitrogen do a number on soil diversity? The standard explanation is that there are a handful of weedy taxa that just thrive when nitrogen is superabundant (fertilize a prairie with urea and you wind up with tall, green patch of invasive grass). But we find little evidence for that: things that increase on N plots tend to be rare, and increase when any nutrient is added (and some of them are icky. See below).
Instead, we suggest that nitrogen, which tends to acidify the soil, sets off a chain reaction by which aluminum–a toxin to most life–leaches into the water supply and bathes the unfortunate members of the brown food web in a bath of metal. In other words, nitrogen doesn’t seem to favor a suite of nitrogen specialists, it releases an all-purpose toxin that stresses everybody out. That’s our new working hypothesis. It needs to be tested.
A summary of our results. The Effect Size is a way of uniformly expressing the change in diversity, positive or negative ,of a fertilizer compared to unfertilized plots. For example, fertilizers tend to have a bigger effect on invertebrates than bacteria. More and more complex fertilizer combos are arrayed toward the right.
Combo’s of nutrients often enhance diversity more than individual nutrients.
One common pattern among plants is that if adding one nutrient, say nitrogen, drops diversity in a prairie, adding two, say nitrogen and phosphorus, does so even more. We don’t find much evidence for that. Instead, the two groups with big, complicated genomes–the fungi and invertebrates–show the largest increase in species diversity when micronutrients are added. Invertebrates do almost as well when the big three nutrients, N, P, and K, are added in tandem. What is it about nutrient combos that favor mushrooms and ants?
We suggest that one reason is that critters with large genomes need a ready supply of chemical elements to build and maintain their more complex metabolisms. It is fun to ponder such a link between an organism’s metabolic diversity–the number of enzymes it has linked together in intricate pathways (many of which require a metal like Zinc or Copper to operate properly) and its metal-craving. Again, this is a working hypothesis. But we have already shown that decomposition in this system–the combined action of the metabolisms of the brown food web–shows big increases on the +Micronutrient plots in the Gigante experiment.
Of the three soil supertaxa, the bacteria and invertebrates have the most similar biogeochemical niches.
One might have guessed that fungi and bacteria–both “microbes” that break down “detritus”*–might respond similarly to the same nutrients, but this doesn’t seem to be the case. Fertilizers with a strong effect on bacterial diversity tended to have little effect on fungi, and visa versa. On the other hand, the fertilizers that really knocked down bacterial diversity, N and NK, did the same for invertebrates.
Many soil inverts have rich microbiomes in their guts that allow them to make a living in the brown food web. Could this be one cause of their similar responses. Does the gut flora of millipedes also suffer in bacteria-poor soil?
When you contrast the effect of a fertilizer on diversity between each combo of the soil supertaxa, fungi and prokaryotes (bacteria) do their own thing, while bacteria and invertebrates tend to response more similarly.
There are weedy taxa in each of the three supertaxa
Which taxa thrive regardless of what nutrient you drop on the soil? It is somehow satisfying to find that among the invertebrates, the Blattaria (aka roaches) can’t say no to any fertilizer.
It is a little more chilling that among the fungi, only the Chytrids, a phylum that contains the infamous B. dendrobaditis, a deadly pathogen of amphibians, increases in diversity in response to almost any fertilizer. We are fertilizing the planet. Just a pattern thus far. Someone should look into it.
Subtaxa of the soil supertaxa that respond positively or negatively to a given fertilizer by at least one standard deviation over controls. See paper to suss out all the abrev’s.
What’s the take home?
Humans are rearranging Earth’s biogeochemistry–depleting fertile soils through erosion and dumping enormous quantities of N, P, and C and a mess of metals into the biosphere. Our study contrasted three grand hypotheses for how fertilization shapes diversity–by increasing abundance, by favoring a subset of competitive species, or by acting as toxins. Much of what we ecologists know about these nutrient effects comes from the experiments of our botanical colleagues. And those experiments consistently point to fertilizers favoring a subset of high-nutrient specialists that drive other species locally extinct. The Paradox of Enrichment is thus an inevitable result of simplifying the environment with fertilizers to favor a handful of species.
But by focusing on three soil supertaxa–the bacteria**, fungi, and invertebrates–that account for most of the diversity of life on dry land, we find evidence for some nutrients enhancing abundance, others acting as toxins and for combos of nutrients ameliorating toxic effects. For some of the reasons why, check out our Discussion. Not surprisingly, spatial scale comes into play. And how metabolisms are rejiggered.
An enduring question is how the combined diversity of life in any given ecosystem–from trees to mites to microbes–will respond to the slings and arrows of anthropocene fortune. The answer “it’s complex” shouldn’t surprise. At the same time, one path ahead, we think, lies in contrasting how tiny organisms with effectively infinite population sizes and evolutionary potential to match respond to global change compared to their large colleagues that can be comfortably enumerated with m2 quadrats.
*Combining fungi with bacteria** as “microbial” is akin to combining petri dishes and planets as “matter-intensive phenomena”. Likewise “detritus” can be anything from a dead leaf to a dead armadillo. *Celebrate* the diversity.
**Again, I beg forgiveness from microbial ecologists for using the shorthand “bacteria” or “prokaryotes” to lump together the archaea and eubacteria. I was raised by ornithologists.
The Kaspari Lab 