The Kaspari Lab
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.
A short essay on Koechner’s Criterion and its relationship to success in Grad School
During a layover at DFW airport, I opened Twitter to find a lively discussion spurred on by Terry McGlynn, @hormiga, who (and I paraphrase) encouraged grad students to seek mentors who encouraged living normal lives, using the specific example that Saturday work days should not be mandatory.
The thread quickly expanded into one about work/life balance in academia, many of the arguments and counterarguments (in the form of tweets and counter-tweets) appeared to hang on definitions both of success and what “normal” looks like or should look like in a better world. All of it had the subtext that bubbles under many such discussions—“Am I working hard enough?”. In my experience, there are few more troubling questions to an academic scientist, or any creative person.
I dedicated a blog to this and related subjects in the (my gawd) late 2000’s called “Getting Things Done in Academia” (rebranded “Survive and Thrive in Grad School”) that is moribund but still out there, and hopefully moderately useful.
So there I was, sitting in the airport, waiting for my flight to OKC, and reading tweets and counter-tweets on an important subject that I obsess about. What was I to do? I tweeted the longest thread of my TwitterCareer, I think. Three whole tweets. I started with the proviso that Twitter is a mixed bag for holding such discussions (Boy Howdy, nothing like leading with understatement). Then, because I found it an intense distillation of one view, I quoted EO Wilson’s comment from Advice to a Young Scientist, that said for a real scientist, every vacation should be a “working vacation”. I ended with my thoughts on that key question “How hard should I work as a grad student/academic?”.
I thought I’d add a few observations. In the spirit of Twitter, they will not be organized into a coherent whole ;-). I suppose I could blast out a thread, but it is easier to get some thoughts down in one place, as a blogpost, and link to them. (I wonder if such a stratagem, once things get hot, might be a productive way to carry on the discussion. As good as Twitter is for starting a discussion, I would rather read one continuous argument).
Assumptions and Definitions
1) The best definition of a successful life, that I’ve yet heard at least, is from the comedian David Koechner, @DavidKoechner, who said
“If you are doing what you love and have someone to share it with, congratulations, you are a winner.
I think this should be called Koechner’s Criterion. I mean, does it set up a discussion of work-life balance, or what?
2) Scientists are scientists because they are intensely curious about how Nature works, and want to discover new stuff and share those discoveries with others, particularly those that are curious about the same stuff. The most successful scientists, however we define them, do this discovery/sharing stuff more and better than others. They also have a higher probability of getting jobs where they are paid to do science.
3) We live in a stochastic universe where sheer dumb random luck can be important and bad luck is rampant.
4) There are skills, mental attitudes, and societal tweeks that, once achieved, improve our chance of being successful.
5) We spend much of our lives pursuing 1, desiring 2 as part of 1, fearing 3, and seeking 4.
Observations
1) There are as many formulae to being a scientist (or artist, teacher, craftsperson) as there are people. But I think that all routes to mastery include a passion for the subject, an aptitude for it, and a desire to create the opportunities that will allow one to develop and prosper. For many people, this leads to a more or less single-minded devotion early in their careers to master a difficult task. However, the diversity of humankind guarantees that there are other folks whose sheer brilliance will allow them to succeed without breaking a sweat. There are still others who are amazingly effective, doing a lot with less time, because of, not in spite of, their strong relationships. Against that diversity of approaches all are judged by a common outcome: the discovery of new things and sharing them with an interested audience.
2) There are also a lot of ways folks decide to share their lives together (including living alone), and the best institutions honor that variety. Family leave, maternity leave, equal pay for equal work, are all hallmarks of a civilized society, in no small part because they help each person fulfill their potential.
3) The happiest biology departments I know find a way of of making steady progress toward maximizing Koechner’s Criterion for their faculty, post docs, staff, and students.
Conclusions in the form of suggestions to Grad Students
1) A key task in a young scientist’s career is to find a mentor who is the best match for the way they seek to develop their career and maximize Koechner’s Criterion. The single best way to find that match is to talk to the graduate students and post docs of possible mentors.
2) It is an old, but true adage that its not just the time you put it, but how you use that time (i.e., working hard versus working smart). If you haven’t already done so, read these two books: The Seven Habits of Highly Effective People by Stephen Covey, and Getting Things Done by David Allen. Seven Habits focuses on the strategy of designing a creative life, GTD is about tactics. There’s work-life balance baked into both of them.
3) Unplug. Daydream. Daily. One key element of Zen Meditation is to calm the Monkey Mind. Twitter and Facebook are the Monkey Mind incarnate. Your best ideas will come to you when you release yourself from the data stream. That also means your best ideas will likely come to you on vacation, so don’t forget to bring a notebook.
4) One good way to center yourself and set your own expectations is to read memoirs of scientists. Sapolsky’s A Primate’s Memoir, Fortey’s Trilobite, and, of course, Jahren’s Lab Girl are all awesome and different.
5) I would be remiss if I didn’t conclude this essay by plugging EO Wilson’s Advice to a Young Scientist. Since when does one read an advice book in which you agree with everything in it? The book presents a series of chapters that have got a lot of discussion going (one review). Find a new or used copy, or check it out from the library. Or start with Wilson’s Ted Talk on the subject.
Herbivores like a little salt with their protein
One of the questions that drives a lot of our work is “Of the 25 elements required to build organisms, how many of them help regulate the abundance, activity, and diversity of organisms in ecosystems?”. In a freely available paper just out as a Report in Ecology, we provide a framework for the many ways that nutrients can interact, then test how Sodium (an AntLab favorite) and Nitrogen+Phosphorus (the preferred pair of the “Stoichiometric-Set”) interact to shape the abundance of the invertebrates above- and below-ground.
We were particularly keen on seeing if Na acts as a catalyst, increasing an insect’s ability to efficiently convert Nitrogen and Phosphorus into more insects, or if the two sets of nutrients acted more or less independently.
Four possible ways that two sets of nutrients can interact. We were betting on Serial C0-limitation, where Sodium catalyzes access to N and P. Didn’t always turn out that way.
The experiment was pretty classic field ecology: we furnished m2 plots with either water, N+P in the quantities used by the NutNet experiment, 1% NaCl solution, or both. We measured the soil and plant responses, and bugvac’ed the above-ground invertebrates with a modified leafblower (see picture above). For below-ground invertebrates, we used a very messy, but unfortunately best method available, flotation extraction of soil cores from the center of each plot.
A soil core from one of the experimental plots. Somewhere in there lurk oribatids, collembola, and other tiny inverts.
As an aside, as someone who cut his ecological teeth in the Nebraska Sandhills for his undergrad and master’s work at the University of Nebraska (see below), and has spent a good fraction of my days since then in the tropics, I am very much enjoying spending time in grasslands again. An NSF project with Nate Sanders on the role biogeochemistry plays in grassland food webs will keep me in the grass for the next few years.
A 21-year version of Mike Kaspari above WhiteTail Creek in the Sandhills of Nebraska. Note the Nikon K-100 camera, and the spiffy digital watch. And yes, those are cutoff jeans. It was a different time then.
After the sampling came the microscope work. Leafhoppers are by far the most common insects in the aboveground samples, and their mobility and subsequent ability to respond quickly to manipulations is something we want to investigate further. As predators go, spiders were common and diverse, and clerids were the most common beetle group.
Looking forward to getting to know the leafhoppers, a group whose English name is simple, and whose latinate name defies easy memorization.
One of the big questions going forward is how quickly predators accumulate on plots that first attracted their prey. The spiders were dauntingly diverse on this patch of Oklahoma prairie.
One of the greatest pleasures of invertebrate microscope work is getting acquainted with taxa like these clerid beetles that are common, but that I’ve never had the occasion to look at before.
Results: Both sodium and N+P shape both communities, but in different ways
In the grass and forbs above-ground, all three treatment plots differed from controls. Adding salt increased the abundance of insects, and adding N+P increased it even more so. However, these effects seemed to be independent of each other (strike one for the Na as a catalyst hypothesis). Since plant height and mass increased on N+P plots and not on Na plots (suggesting that while NP was a nutrient for the plants, adding Na had no negative effect on the first trophic level), we think that NP provides a double bonus of more food, and more habitat, while Na just provides the food. We will test this idea more this coming summer.
Below-ground, however, was a different story. Here Na seemed to act like a catalyst. Alone it had no effect on the oribatids and collembola that dominated belowground. But combined with NP, it boosted the modest increase of abundance where NP was added by itself. Here, our working hypothesis is that NP fertilization increases the food supply, and thus increases the demand for Na. We are keen to follow this up this summer as well.
So there it is, so far. The plans are to expand both the kinds of experiments and their distribution, to add experiments farther north in more Na-deprived grasslands. One project has a particular appeal: as NP + NaCl is roughly the recipe for urine, and urine is the single most effective way to fertilize a patch of prairie, how do community dynamics respond to a splash of Bison Piss? Is there a predictable succession? And how do the hundreds of species find, exploit, and deplete this resource? What are the patterns of succession? Lots to learn.
When the science news is bad, write your local paper
Note
Recent events have found me struggling to find some way to be useful. I decided that one thing I could do was to write–on a regular basis– a letter to the editor of the The Norman Transcript, our local paper. The bad news from Crowther et al in Nature served as the grist for this week’s letter. Writing it scratched a number of itches: it gave me a shot at explaining negative and positive feedback, it provided readers with actual phone numbers (not just the link in this version) to phone the local offices of our Senator’s and Representative, and it pressed the notion that there is always hope when people engage, even when times are dark. Below is a slightly modified version of the letter.
To the Editor:
Last week was a bad one for Planet Earth. While her workings are pretty complex, it has long been evident that when we pump millennia-old carbon into the atmosphere we warm the planet. Many of us scientists had hoped that this warming would be slowed by a variety of feedbacks. Trees, after all, scrub CO2 from the atmosphere; more gets sucked up by our oceans. That, we hoped, may buy us more time to move away from fossil fuels and build the solar panels and windmills that are springing up over the state. These natural feedbacks protect us in the same way that, when you notice a bridge is out, you step on the brakes long before catastrophe strikes.
Well, there is another kind of feedback, and for that we can thank the microbes. Boatloads of carbon rest in the cold earth. And, just as we keep our bacon in the fridge to keep it from rotting, that cold earth has kept its microbes from chewing through the countless tons of dead carbon just below our feet. Now, 49 scientists have together revealed in the journal Nature that the warming Earth is waking the microbes from their cold torpor. And they are hungry. As the microbes break down the soil CO2 pours into our atmosphere. This warms the Earth and makes the microbes even hungrier…
You are, by now, beginning to see how this other feedback works. It is as if, back in the car, you stomp on the brake pedal. Or…what you *thought* was the brake pedal. The car lurches forward, racing toward the chasm. So you stomp harder! (Why aren’t these brakes working??) In the same way that the car accelerates toward the chasm, every fraction of a degree that we further warm the planet drives Earth’s microbes to empty one of its last storehouses of carbon, making the problem even worse.
Bad timing, right? Just as we should be redoubling our efforts to find a solution, prez-elect Trump calls climate change “bunk” and his advisor on NASA wants to delete such “politicized science” from its budget. This is code for the hundreds of satellites that watch our Earth, informing our farmers about soil moisture, our sailors about sea ice, our friends and neighbors about approaching storms. All because some of that data is used by scientists to diagnose our warming planet. It is bad enough our car is hurtling toward a cliff. Trump’s NASA policy would disable the speed gauge and paint over the windows.
Now more than ever we need to phone our Senators and Representative. We need to urge them to preserve NASA’s world class Earth Observatory program. Why do I think you and I can convince climate change deniers that we need to do more, not less? Because over the past 23 years at OU I have had the privilege of teaching science to thousands of Oklahomans. These young citizens see the evidence, and in our conversations (and in anonymized polling) overwhelmingly agree humans are warming the Earth and that there is still time to save it. Full stop. These same people are our future governors and legislators, will be paying taxes when some of us are retirees, and are thinking about raising families of their own. I suspect these are some of the same people who will be answering the phone when you make those calls. They are our future. They are our hope.
Mike Kaspari
Norman Oklahoma
One way to build a dietary generalist
By Karl Roeder
We are incredibly excited to announce that our work on fire ants and isotopes has just been accepted in Ecology! The work primarily revolves around understanding trophic variation across a population of one of the model organisms of myrmecology: the red imported fire ant, Solenopsis invicta. Essentially, we are looking at where you rank in a food web and what did you eat to get there. To expand upon this, we had been thinking about ways to understand the how, what, why, and where of stable isotope variation that regularly occurs in the published literature. Stable isotope analyses have increased in their use in ecological studies as a tool where nitrogen (d15N) can be used to understand trophic position/structure and carbon (d13C) can be used to map out where the dietary source came from, in this case C3 or C4 plants.
Despite a lot of myrmecologists loving morphological measurements, it seems few had tested how size, both body and colony, may affect trophic variation within a species. A question that we were intrigued with. Perhaps even more surprising was a real lack of good information at the colony level, as most stable isotope studies with ants focus on differences across species in an assemblage or community. We set out to answer these question by measuring a variety of different sized workers and colonies across multiple time periods throughout a year in a small 0.5-hectare old field in Oklahoma. To our surprise, we found an unprecedented range of values occurring within a population. A range that was comparable to whole ant assemblages from prairies to tropical rainforests. The red imported fire ant, while acting as a generalist at the species level, may in fact be specializing on particular dietary items at the colony level.
While there are still mechanisms to work out, we believe this is a wonderful step towards disentangling the trophic ecology of the red imported fire ant and potentially other invasive species. Given the wide diet breadth we observed in such a small area, we hope this will encourage researches to think more about the natural history of their study species, and combine this information with physiological measurements to really attack questions surrounding their biology.
This work was generously funded both by the National Science Foundation and a University of Oklahoma Biological Station summer fellowship.
