College reunion

I hadn’t been back to Scripps College since graduating 15 years ago – until last month! I had a great time re-visiting many of the places I loved, like the Motley Coffeehouse, and meeting old friends and making new friends. It was especially wonderful to see my research advisers from that time, Dr. Nina Karnovsky (Pomona) and Dr. Diane Thomson (Joint Science, now becoming Scripps-Pitzer Science).

Thanks to Scripps for the Outstanding Recent Alumna Award! My training and the community there built a strong foundation for pursuing my dreams – and starting to dream even bigger. I’ll make sure it’s not another 15 years before I go back again.

The cost of invasions

The catastrophic human cost of the military invasion is filling the news, but biological invasions also cause damage. A grass from Kenya was bred and planted in the southwestern US and northern Mexico for decades (and is still planted in some places) for cattle grazing, but has escaped cultivation in pastures and begun spreading across the landscape. You can see in these photos the way the bright yellow grass, called buffel grass, fills in the previously empty gaps between the iconic desert cacti and native trees like palo verde. It is already contributing to wildfires in the Sonoran Desert.


A research study I started about a decade ago was (finally!) published last week (, showing that buffel grass is reducing the establishment of native plants where it spreads, even without burning. It’s not just spreading into space that they have vacated.

This scientific article, which formed part of my doctoral dissertation, was the result of a decade of work by not just me, but by a truly tough field crew, advice and help from land managers, mentors official and unofficial who helped and encouraged me, and financial support from the Garden Club of America, Western National Parks Association, the National Science Foundation, the Tindall Conservation Bio Internship from UA EEB Dept, a UA GPSC research grant, the NASA Arizona Space Grant Fellowship, and more I probably forgot.



My colleagues and I just published a new study on what limits microscopic Antarctic life in the tiny oases found on glaciers (cryoconite holes): Unlike much of the Dry Valleys region, “cryo holes” aren’t limited by moisture – so what determines the upper limit of growth there?

Photosynthesis by algae and cyanobacteria forms the basis of the food web, and like primary producers everywhere, key macronutrients like nitrogen (N) and phosphorus (P) can limit their growth.

Multiple lines of evidence in this paper and in past studies show that P is the real limit on primary production and resulting growth cascading through the community, and that at least on some glaciers, N is likely being “fixed” into biologically usable forms from atmospheric N.

Why does any of this matter? It can seem small and insignificant in the face of current geopolitical conflicts. I am posting this on the day that Russia brazenly invaded Ukraine.

Alternatively, our human conflicts can seem small and insignificant in the face of the vast polar regions and the mysteries of nature.

The cryosphere makes up a significant part of our planet, even if we rarely think of it because it’s not so habitable for humans. That makes it globally important, and also an important “natural laboratory” for biology. A natural lab we are rapidly losing as it warms, however.

This paper highlights the need to conduct actual experiments, adding N and P to cryoconite ecosystems to see how they change as a result. I hope to receive funding to do just that in the future 🙂

79 N

I have previously worked in Antarctica’s McMurdo Dry Valleys, at about 79 degrees south. I have finally made it along with a team of colleagues to Svalbard, which is 79 degrees north! This project’s fieldwork has been delayed a year and we are excited to be here.

Some of the landscape feels very familiar from my time in Antarctica, like the bare, rocky mountains with glaciers cascading down through the passes. But there are some key differences! Svalbard is closer to more temperate land masses, only a two hour flight from mainland Norway. It is warmer, and has tundra with grasses and flowering plants growing.

And of course, rather than firearms being banned as they are in Antarctica, they are required in Svalbard for self defense in case of hungry polar bears!

Sledding or not, here we go. Are are headed for the dumps?

When was the last time you went sledding? Doesn’t that sound great right about now, as we’re roasting in summer?

Brandishing my new ice axe before the trip, before slicing my knee open with it sliding down the steep snow. (I’m okay)

I tried to sled – without a sled – over the 4th of July weekend, high in the mountains of Colorado (about 11,000 feet). Technically I was trying to glissade, to slide on my feet or bum down snow so steep I was carrying an ice axe to stop myself if I got out of control. I wasn’t very good at it. I need a sled.

As a kid, I preferred inflatable snow tubes to plastic sleds. My dad would build an epic tube run in the snow from the top of a hill in the backyard. It banked hard around a treacherous curve to avoid a steep drop into the neighbors’ fence, then bounced down a series of stone steps. We called that section “the dumps,” because it wasn’t uncommon to dump there. If you made it around the curve and down the dumps, you hoped the bushes at the end of the yard stopped you before you flew out into the street.

As I grew up, there seemed to be less and less snow. I guess things always seem bigger to littler kids than they do to adults. But I remember building entire cave systems out of the snow piled on the side of the driveway from the piled snow. Maybe I was just much smaller.

Actually, no. I mean, I was smaller, but when you look at the numbers, Salt Lake City (where I grew up) gets less snow. I’m a 90’s kid (born 1985) who definitely went to see the new Lion King already (and was really disappointed by the version of “Be Prepared”). When I was tubing in my backyard on snow days, Salt Lake got on average almost half again as much snow as it gets on average now. Booooo.

And it’s not just Salt Lake. Lots of mountain ranges receive less snow than they used to. My colleagues in Colorado, where I live now, have studied the effects of snowpack on the soil microbiome of the mountains here. Just like the bacteria of our microbiome in our intestines help us absorb and process nutrients, microbes in the soil affect things like water quality and plant growth by processing nutrients.

When our microbiome gets out of balance, it makes us sick (ever heard of “C. diff. infection?”). Our systems don’t function the way we want them to. Changes to the microbiome of soils due to lower snowpacks and other ways in which humans are affecting the planet could change how our ecosystems function. We might not like those changes.

I say “could” and “might” because just like your doctor can’t usually tell you with 100% certainty how your body will respond to, say, antibiotics for a C. diff. infection or exactly when you’ll suffer a heart attack if you don’t change your diet, we don’t understand our microbial ecosystems well enough yet to know how big a deal this will be. Here’s how I think about that:

If I am planning to swimming at my local pool, or at a scenic mountain reservoir, I check the weather forecast. If it’s 30% chance of rain, I’ll probably go anyway and just get out of the water if I hear thunder.

2007-11-17 11-45-22_0013
Rappelling and swimming down Zion’s Pine Creek Canyon in 2007.

But if I am going to rappel down a steep and narrow slot canyon into deep pools, a rainstorm could kill me in a flash flood. The sky might be blue when I start my hike, but a rainstorm even miles away could start a flood that would sweep down the canyon toward me, with walls too steep to climb out. When rain means unavoidable death, 30% chance is too high to even go there.

We don’t understand Earth’s microbiome well enough to know what works and what doesn’t. Heck, we’re only just starting to tweak our own microbiomes inside our bodies, and that’s just one of us at a time. It’s like we woke up sitting in water in the dark and not sure if we’re in a reservoir or slot canyon.  So we might want to treat it like a slot canyon, in case it is. Because sooner or later it’s going to rain.

A bunch of people who make it their jobs to way overthink these kind of numbers agree. I just signed on to the recently published scientific consensus statement called Scientists’ Warning to Humanity: Microorganisms and Climate Change, or “Microbiologists’ Warning” for short.

This statement echos a broader consensus statement I signed in 2017 called World Scientists’ Warning to Humanity: A Second Notice. It’s an update 25 years after a statement from 1992 signed by 1,700 scientists then laying out the problem that we might be sitting in a slot canyon.

The message now? (Signed by >21,000 scientists, including me.) People, we’ve been feeling around and we’re finding walls. This ain’t no reservoir.

It’s time to get out of the water.

A study from 2017 calculated the relative impact of actions you can take to get us up and out of here. Here are the top recommendations:

  • Eat a more plant-based diet (I wasn’t impressed with the much-hyped Beyond Burger, but there are some kick-butt black bean burgers out there…)
  • Avoid airplane travel (want an excuse not to go to that one wedding or meeting?)
  • Live car-free
  • Have one fewer child (fewer people = less impact)

Obviously some of these are a big deal or unrealistic (we can’t all afford to live where we work when that’s Boulder, CO). But every little bit is a start. Try subbing in beans and grilled veggies and mushrooms on burritos one night instead of carne asada.

And tell your stories of what you have seen change. Tell them here. Tell them to your representatives. Tell them over family dinner. Especially when the numbers recorded show that it’s not just you…. there really is less snow.

And thank you. Now let’s go find some snow this winter. Bring your snow tube.

How does hiding from a predator affect biological diversity?

Ecosystems, and the biological diversity they harbor, are complex things. Yet simple mathematical models can often capture important features and teach us about their dynamics.

You might once have learned about food chains in school. For example, plants producing energy from the sun are eaten by rodents which are preyed on by owls. That’s a food chain with three links. Because just about everything has some kind of predator or parasite or other natural enemy, and just about everything must compete for resources of some kind, let’s focus on the middle link in this chain.

To study how many species can be supported in a middle link of such a chain, think first of two species. If each one can invade the system with the other species present, they can coexist. A simple model proposed early in the 20th century by Alfred Lotka and Vito Volterra can be solved for when two species would coexist, increasing biodiversity.

But this model leaves out a major piece of how animals function in the world around them: behavior. What if both kinds of rodents learn to hide from the owls under plants? Does it make them more or less likely to coexist?

In research I did with my doctoral adviser, Peter Chesson, published online recently by The American Naturalist, we show that the answer depends on how much those animals overlap in their resource requirements, like the types of food they like to eat, and in their vulnerability to different predators. When both prey can avoid predators, if they need exactly the same types of plants to survive and ground to dig their burrows, one may drive the other extinct. But if they are more different ecologically in their resource use than in which owls prey on them, then avoiding owls could make them even better able to coexist. (In an appendix, we even show how this scales to more than two species.)

I started this research in 2009 as a brand new graduate student, and worked on it off-and-on for the last decade. Peter’s guidance on this project taught me how to do research, and how to present it and to write about it.

You can see a plain-language summary of article here, or download the paper itself with all the equations here. Feel free to email me for a copy if you don’t have a university hook-up to access it without paying an arm and a leg.



I returned to Colorado almost a month ago now from nearly four months in Antarctica. Some of the samples the team collected from our experiment there recently arrived in Colorado separately, and the rest should arrive this week. I am settling back in to life here, answering four months of mail, getting out in the mountains on my skis, starting to extract DNA from the samples, and continuing to analyze data from field seasons past.

For detailed updates during our season, check out the project blog I kept up almost daily while on the ice (despite the slow internet).

Here are a few highlights:


We found our experimental cryoconite holes (mud puddles on the glacier we had made in a past season)! This was far from a certainty, because our holes look identical to those that form naturally and are difficult to mark accurately without affecting their melt. An organization called UNAVCO provided invaluable help with precision GPS marking our holes, and a way to recalculate their new position – they move about 3-4 inches every day because the glacier ice under them is flowing!


We spent a long season in the field camp, and were able to watch the progression of naturally occurring cryoconite holes. Each of the small, round depressions in the ice at the bottom of the photo above is a cryoconite hole. Notice the ones nearest have a layers of new dust that blew onto their surface after a strong wind storm. When that dust melts through the ice lid, the microbes in it will “invade” the microbial community active in the mud puddle below. Will the new microbes be able to reproduce? Or will the existing community “resist” their invasion? That is one of the questions we hope our experiment will be able to answer.

Our team connected with hundreds of students around the US by Skype to answer their questions about our research and life in Antarctic field camps. I was even able to answer questions live in a Science Riot comedy show at the Clocktower Cabaret in Denver by Skype from camp!

And we looked good doing it all 🙂 After by brother-in-law told me about the fashion insert in the Sunday New York Times featuring layers of jackets as the “it” look this season (left photo above), I did my own fashion shoot on the glacier during a break from fieldwork in my 4-5 layers. Apparently I’m supposed to smile less while modeling. But I think my heals might be as pointy as the model’s.

Just a little luggage

Photo credit: Aleah Sommers. Thanks for the ride to the bus stop for the airport bus, sis!

Well, I am planning to be in a very cold place for more than three months, and camping in New Zealand after that. The trip requires a bit of gear.

I’m headed back to Antarctica for the third and final season of the currently funded research on microbial community assembly in Antarctic cryoconite holes. Check out my previous posts on this blog for more details on life on the ice. I will try to post daily updates and photos, internet speed permitting, at

And if you are a US citizen and haven’t voted yet, do it by the end of the day this Tuesday (Nov. 6th)!

It’s a girl!

A big piece of my stand-up comedy set about my research last month was about how good I am at killing tardigrades, or water bears as they are commonly known, despite their reputation for being indestructible. (They’ve survived five mass extinctions on the planet, but they can’t survive me!)

I have been trying to grow Antarctic tardigrades and their more awesome but less cute metazoan cousins, bdelloid rotifers, in petri dishes in the lab. These microscopic animals are abundant in the glacial ecosystems I use as natural test tubes to understand how ecosystems organize. They are large enough to spot with a dissecting microscope – much lower power than would be required to see individual bacteria – so I hoped they would be useful for more controlled experiments.

However, I was not initially great at keeping the little critters alive, and moreover, having them reproduce to be a population.

Since I am not an expert at tardigrade identification, I thought the best way to isolate different populations of water bears would be to create cultures from individual lineages: meaning I put a single tardigrade on a petri dish and waited for it to lay eggs.

I was fairly certain that any animal whose life plan involved getting dried up and blown into some ice, then waking up when that ice melted into an isolated puddle of water would not have to rely on finding a mate. The chances just seemed too low. The most common tardigrades in Antarctica reproduce by parthenogenesis, laying unfertilized eggs. But after a while without babies, I was starting to wonder if they needed to mate or something.

And then last week, two students working on this project found that a petri dish previously containing a single tardigrade now held three additional tiny tardigrades! Our camera situation is not so great with the petri dishes, so I held my cell phone up to the eye piece to try to snap a picture:


That whitish cigar shaped thing with dark colors in its middle is a tardigrade. The green blobs around it are algae. The dark stuff inside the tardigrade I believe to be algae it ate!

Here is a better image of Antarctic tardigrades I took also using my cell phone, but a microscope in Antarctica:


So I guess the tardigrade really is a “girl” – at least it laid eggs?