Biodiversity: the Blog

Does this landscape make you wonder how so many species can coexist? Well, it’s no tropical rain forest, but the San Simon Valley in southeastern Arizona IS home to a long term study on annual plant diversity and the rodent species that feed on their seeds. I posted below about the difference in winter and summer annual plants in the Sonoran Desert. While this field site is in the Chihuahuan Desert, it also has a distinct winter community.

I helped a post-doctoral researcher (Pirate Danielle in the second picture) finish the census in March, as she and other graduate and undergraduate students measured literally thousands of teeny tiny plants that had grown all winter in these 80cm x 80cm squares. These were long days, starting at 6am for a three hour drive to the site, followed by eight or more hours crouched on the ground counting or recording, with the return drive looming! If Danielle’s new job as faculty at Smith College doesn’t work out, maybe she’ll publicize the “Portal Workout.” It involves assuming a position on the ground with your weight cantilevered forward, then holding for approximately eight hours. She was pretty strong by the end of the field season. 

The Tucson Gem and Mineral Show is long over, and with it those flocks of “snow birds” – sixty-degrees-and-sunny-weather chasers down from Minnesota and Ohio for the winter – will head back up north to avoid the scorching Arizona summers.

Plants here have learned this trick, too. An entire “guild,” or group with similar life histories, of “winter annuals” exists. These are plants that germinate, grow, flower, and set seed all within the winter rainy season. They vanish with the winter rains during that arid foresummer of April and May, much like the retirees. I visited my field site a few weeks ago, only to find an entirely new set of green things “carpeting” (for Arizona, anyway) the hillside. With an early end to the rains, many are flowering now – Tumamoc Hillis covered in something yellow with purple highlights! The wildflower fans I know are planning their weekend excursions now, nearly a month before expected – so hurry outside! The bloom won’t last.

It’s raining in Tucson again! These are the winter rains, which typically yield a very different pool of germinating seedlings. Since I am focusing on the summer community, I am not counting the seedlings, but looking forward to checking in on what the plots look like during the other part of the year. If these rains keep up until January when La Nina effects kick in, the rumor goes among ecologists, we could have a particularly spectacular spring wildflower crop. I wonder if the soil chemistry, or remaining vegetation structure of dead annuals, will affect my summer germination next year?

You can now watch a 4 1/2 minute video of me presenting my preliminary results from this summer’s field study on an invasive grass. I’m going back through the data, analyzing how meaningful the differences I saw were, given the massive variation. So keep in mind these are preliminary, not yet peer reviewed, conclusions.

I point out at the end of the talk that my results pave the way to ask more questions I am interested in.

One of those questions that needs to be answered (before I can get to the real questions) is what a few of the plants I saw out there are… most of them I only saw in seedling stage. Seedlings lack reproductive parts (flowers), which are pretty critical for identification. But it gets worse. They also lack other major structures like adult stem structures (woody or not?), and even basic things like leaves. So I may not get much more specific than genus, but that would be pretty good itself – especially since we know mostly what species are present in my study site, so I can make an educated guess about what members of the genus I might be seeing.

Biosphere 2 was in the news in the last few days throughout their Earth Day celebration and the 20th anniversary of the original biospherean missions, in which people tried to live inside the sealed, regenerative system in the early 1990’s.

One of the main lessons learned from those missions was the importance of Biosphere 1: the earth. So it is appropriate to celebrate both anniversaries at the same time. While the article today suggests the structure could serve as an “ark” for endangered plants, it is clearly not large enough to support self-sustaining populations of large forest trees. The inability of scientists who study ecological communities to predict the interactions of all the species from around the world meeting one another for the first time inside Biosphere 2 clearly pointed out how far we had to go to in understanding ecology.

That is why I am working on my PhD, to contribute to a better understanding of populations’ interactions, especially in the case of new interactions. I plan to study how invasive plants affect the populations of native species when they spread out of control, as many grasses and thistles have done in North America (and worldwide really).

What does my homemade pasta have to do with biology? That they are both green? Well, sure. That energy is being transferred up the food chain from the producers (the dandelion greens, spinach, frisee, and flour) to a consumer (me)?  Yep. And energy is also being transferred from a consumer (a chicken) through its attempts to reproduce (eggs) to me, a secondary consumer. And by the time you have also considered the bacteria living in my digestive tract that help me digest food, we have a whole complex ecology of multiple trophic levels and a symbiosis.

Pasta making can be as frustrating and baffling as trying to penetrate nature’s secrets, and, like all biology, pasta obeys laws of physics and chemistry. The first time I made past from greens, eggs, flour, and salt, it turned out inexplicably perfect and delicious. The green dough formed long strips of fettuccine that curled delicately on the plate. The second time, for whatever reason, the gooey mass that I attempted to slice stuck together in strips and balls, and when I boiled it became warty. Like any science experiment, the first results seem eerily irreproducible – but I have a hypothesis as to why. I suspect I did not add enough flour. Although I measured the requisite number of cups in, more flour gets incorporated as you pat the dough out on a floured surface, then fold it over to pat it out again. Or perhaps I failed to pat and fold the dough long enough for that gluten to bind to the other ingredients.

Maybe next time I can do an experiment to test that: divide the batch into several portions, to which I’ll add varying amounts of flour, patting and folding for a fixed time. Another set of portions will have a set amount of flour to be incorporated during varying lengths of patting and folding.

And if this whole PhD thing doesn’t work out, maybe I can get a job as a pasta chef.

Since spring break is just finishing at some schools and just about to start at others, I have been thinking about islands. Lots of people will go on cruises, or to spend the week on an island, scuba diving or just surfing or lounging. But all those visitors have had some serious effects on biodiversity on those islands. Since the 1600s, when humans first caused the extinction of the island bird called the dodo by bringing dogs, pigs, rats, and other animals that found eggs lying on the ground an easy breakfast, island birds have gone extinct in great numbers. Guam’s native birds were wiped out by the introduction of the brown tree snake, and avian malaria has done a number on unique Hawaiian birds.

Plants, on the other hand, have not gone extinct in large numbers on islands due to introduced species. That is according to a 2008 study by Dov Sax and Steven Gaines. There are certainly examples where domestic goats have run wild and eaten off virtually all of the remaining slow-growing and unique silverswords in Hawaii. Rob Robichaux, a faculty member at University of Arizona, along with a number of other scientists and dedicated volunteers and professionals, are trying to save those silverswords.

So why do introduced plants tend to naturalize without causing extinction of native plants? Maybe they are using resources in a different way and will continue to coexist. They certainly can change the ecosystem’s look, structure, and functioning (how much biomass grows, how humid the climate is, etc.). So maybe they are causing extinctions, just more slowly than a disease epidemic. The paper by Sax and Gaines asks some of those questions, but scientists do not know the answers yet.