Month: September 2010

Invasion

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The sun beat down on the small crew of volunteers armed with six-foot segments of Rebar. When I say the sun beat down, I mean the Arizona sun. It beat the volunteers as if with Tasers and billy clubs. It was seven o’clock in the morning.

So why the volunteers for this torment? They were fighting – and apparently winning – a small but significant skirmish in a war with an illegal invader that is threatening the very homeland they have inherited, or for the most part, adopted. And yada yada yada about the war and menacing alien metaphors. The popular literature on buffelgrass is already pregnant with them. I doubt I can add much, either to that or to the raft of comedians using Arizona crazy as their favorite subject of jokes these days.

Buffelgrass is a bunch grass originally from the African savannah, as far as I can find out. It was – and is still – widely planted in North America, especially in Texas and Sonora, primarily for cattle forage. But in Arizona, it has taken on a life of its own and been declared a noxious weed. Biologists fear the choking, fire-prone grass that spreads here on its own could wipe out the iconic species and forever change the ecosystems. Nothing against African savannas, but picture Arizona without the branched saguaro cactus, or tentacle-like ocotillo or broccoli-green trunked palo verde. People here are understandably concerned.

The Sonoran Desert Weedwackers are a volunteer group that has taken matters into its own hands – in coordination with the Desert Museum, Pima County, and other relevant authorities. Marilyn Hansen, who has been organizing and compiling a really remarkable data set on what the Tucson Mountain Park chapter has accomplished, beamed as she told me about the reaction she had gotten from local officials before clearing so much area, and such dense stands.

“They said this was impossible. Well, to Weedwackers, those are fighting words.”

That may be a point of pride to someone with the time and drive to spend at giving it a shot, but others have to calculate if the resources are worth the risk. Upon mentioned of the project my Conservation Bio students will do on biodiversity in the wake of buffelgrass removal, an outdoors trip leader in the area recently asked me,

“Do you think we can get ever get rid of it? Or is it a lost cause by now?”

I gave him my best scientific answer: I shrugged.

But it is something worth giving more thoughtful consideration to: should we spend the tens of thousands of dollars to spray Roundup from helicopters, ask the scores of volunteers to labor under the vicious Arizona sun, bulldoze acres and acres of buffelgrass covered land to replant natives?

Katriona Shea and Peter Chesson published a paper in 2002 titled “Community ecology as a framework for understanding biological invasions.” In it, they provide a brief run-down of the models and parameters that matter most to determine local coexistence, exclusion, and invasion processes. They claim you can divide an invasion into two parts: arrival and spread. While Mexico’s government continues to pay ranchers to plant buffelgrass, there is little we can do to slow seeds blowing in over the border. But what happens when they arrive? This is the community ecology part, where we look at the grass’s response to the environment, to competitors, and how it shakes up the predation pyramid.

I may spend some more field time in the near future examining the trophic (fancy word for “food web”) interactions, and the way it competes with natives for water and other resources. But a quick and dirty equation can provide at least the trivial answer the trip leader’s question: Under what circumstances can the Weedwackers win?

Population growth = birth rate – death rate.

When the Weedwackers, along with the county, private landowners, and others can drive the death rate (pulling, spraying, etc.) of buffelgrass higher than its recruitment rate (germinating seeds from populations in Arizona), no matter how many seeds blow over the border, they will not find a “niche opportunity,” as Shea and Chesson (2002) put it.

Impossible?

Tell that to the Weedwackers.

[Note: I had a bunch of great photos of a small desert tortoise we found, rebar use, before-and-after shots, etc. But… in my sleep-deprived haze this week I apparently cleared my camera card memory after only examining them on my laptop, not saving the photos. Note to self: sleep more.]

Step 1 to being America’s Next Top Biologist

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Excerpt from my field journal.

Being a respected biologist these days usually requires a little more training than natural historians of the past would have encountered. We have to learn stories at the molecular and cellular levels, up through what we can touch and feel and see, and above to the population and ecosystem levels. There are statistics and politics and grant writing skills.

But I propose that Step 1 to being America’s Next Top Biologist is to keep a field journal. This is hardly an original idea. Most biologists in the past did so, and most do today. Charles Darwin, arguably one of the most famous biologists ever, published his field notes as a book titled The Voyage of the Beagle. It is full of maddeningly narrow-minded commentary, especially at first, but it is a fascinating read about an adventure and a world that today we can only approximate.

I have one quibble with Darwin’s journal, too, which is the lack of drawings included. I suppose he may have done them, and just not have included them in the final version. I can commiserate. I’m more than a little embarrassed about the quality of my field journal drawings.

But the point of field drawings for a biologist is not just the aesthetic quality of the finished image. It is the process of looking more closely at a plant or animal. It is the difference between noticing or missing that every flower on this plant has five petals, or that something has been chewing on the leaves.

All our fancy statistics and abstract theory come to very little use without the details of what is happening, and being done by whom and how and where in the natural world. To be a big picture thinker, you still have to remember to look at the details once in a while. And there is no better time than while watching bugs in your classroom, strolling around your neighborhood, or backpacking through remote and wild territories. It’s something everyone can do, whether or not you are a professional.

I’ve shared a few images of my journal here. I mostly included the pictures because they’re more interesting to look at than my hurried handwriting. In the trade-off between being more organized and being more accessible, I tend to the immediate and hence lack some recording detail and standard format. That’s something I might work on.

Do you keep a field journal? Who knows, you could be America’s Next Top Biologist. What have you recorded lately?

Biological warfare: is it for you?

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An Arizona black rattlesnake (Crotalus cerberus) hanging out on the side of the train in the morning.

Over the Labor Day weekend, I went backpacking in the Catalina Mountains with some friends. It was a beautiful night, with a nearly new moon and Jupiter gleaming brightly in the sky, so most of us left our tents in the car and slept outside. Or in my case, lay around outside, stiff as a board, fearing one of the rattlesnakes or scorpions we had run into earlier would try to snuggle up in my sleeping bag with me.

But the real trouble started for me just as it began to get light and I started to relax. A slight whining noise increased in volume until it reached screaming pitch and I realized a mosquito was dive bombing straight into my right ear. I took immediate evasive maneuvers, and managed to thwart the attack. But it was either a very nimble insect, or prepared with hefty backup, because no sooner had I declared the immediate vicinity of my head a Green Zone but a double strike was ordered on my left ear. Again I warded off insect penetration of my blood supply – or so I thought. The game of cat and mouse continued until it became too bright to continue the charade of sleep, whereupon I found the facial squadrons had been mere decoys to distract me from the devastation being wrought upon my arms and ankles. I have been painfully avoiding scratching in the days since.

Back in July, intern Janet Fang of Nature wrote a brief news article on the research and development of large scale mosquito eradication efforts. She asked several researches what might be the impacts of eradicating all 3,500 or so species of mosquitoes worldwide (of which a couple hundred bite humans and a handful of those carry disease, like malaria). Unlike other pesky bugs, like no-see-ums, mosquitoes are not the exclusive pollinators of cacao or other any other valuable crops. They do not by themselves support any endangered species that we are aware of. In fact, the brief survey of research in the Nature article made it sound like mosquitoes are mostly generalists (as opposed to specialists) and that theoretically, their disappearance would allow competitors to take their place with little ecological impact.

This is the kind of near-term thinking we humans are good at. If there are no immediately obvious consequences, we deem it relatively harmless. As long as no people live right where we dump the rocket fuel or test the nuclear weapons, it should be okay, right? We forget that it might migrate into the water table and travel. As long as no one dies of carbon dioxide poisoning, we see little harm in burning fossil fuels, and miss the slow and insidious creep of average temperatures and extreme weather events. If farm workers fail to die from pesticide exposure, it is hard to claim damages for their children’s IQ being lowered by 30 points due to impeded mental development. But studies of larger scale can sometimes capture these indirect impacts.

Likewise, a species’ mere presence can restructure the ecological community around it. I have been doing some theoretical research (read: math) on how hiding from predators affects two competitors’ ability to coexist. (More on that soon, I’m meeting with my advisor tomorrow!) For example, grasshoppers change which leaves they hang out on depending on whether they are hunted by ambushing spiders or by roaming spiders, and that has cascading effects on what plants thrive there (Schmitz 2008). Aldo Leopold wrote about what happened in the mountains of Arizona and New Mexico when the wolves were extirpated there. Although he thought the mountainsides were stripped by deer no longer consumed by wolves, he would have found poetry in the notion the damage was worse because they were no longer hiding from wolves either. Just because we cannot predict the effects of wiping out mosquitoes does not necessarily mean there will be none. In fact, maybe I will try my hand at that after this predator avoidance project.

I should mention there is also an ethical dimension to this. An entire field has emerged, known as Conservation Biology, that really holds at its core the preservation of biological diversity. Back to Leopold again – he writes of the killing of what may have been the last grizzly in Arizona. The world afterwards seems a smaller, sadder place. Barbara Kingsolver (a Tucson homegirl) also makes more explicit and practical, though no less impassioned, arguments for biodiversity.

What do you think? Would it be wrong to erase all mosquito species from the face of the earth instead of slapping them one by one like I did all night? Would it be a good idea? After all, we did it with smallpox. I don’t think it will be a matter of “can” for long, but “should.”

What bike crashes and tarantulas have in common

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Here I am prepping for a night lap in a 24 hour race in February with my great big headlight. It's important to be a responsible mountain biker: stay on trails, don't ride them if they're wet and you will destroy them, brake for wildlife. Biking can have a negative impact on the environment, though nowhere near the impact motorized vehicles have off-road.

I recently went out into the desert after dark and bashed myself against the rocks for a few hours. By this I mean I went on a mountain bike ride. I had a good light; the problem really lay in my not having ridden on trails for six months and being off balance. I failed to hit any saguaro or other types of cactus, so I considered the night a major win.

Over the course of the ride, my riding companions and I stopped several times. Once was to observe from a safe distance the Mojave rattlesnake coiled at the side of the trail. Another stop or two were to observe male tarantulas crossing our path. I assume they were male because the males crawl out from their holes in force during late summer to wander in search of a mate. The third and longest break was to fix a broken bike chain. As I watched the others struggle with the chain tool that was produced, I tried and failed to discern what they were doing with it. Much like the tarantula with a nice deep hole and plenty of prey, if my chain were to break when I was out alone, having a chain tool would be insufficient to succeed in life. Just as he must find one more thing – a mate – in order to pass on his genes, were I to find myself with a broken chain and a tool to fix it, I would still need to hunt down someone who knew how to use the tool.

Okay, so that’s a bad analogy. But at least give me this: both of us are stranded in the Arizona desert with little to no water, and if we stay stranded alone for too long it can be bad for what biologists call “fitness” (and everyone else calls “the chance to have babies”). And both of us need more than one scarce resource to get de-stranded. In fact, if you break it down, we both need many resources over the course of our lives to survive and pass on our genes.

Pierson and Turner (1998) showed saguaro cactus populations grown in spurts when conditions are good. "Good" for a saguaro mean rain, temperatures above freezing, plenty of seeds landing under other plants ("nurse plants"). You can think of conditions being "not bad," meaning no freezing or drought, but that implies some kind of maximum that might not be realistic.

Tarantulas, people, and other animals all need shelter, need water, need energy and need nutrients. The iconic saguaro cacti I rode past last night need water and need nutrients, and when they are little baby cacti, they need shelter, too, from another plant (a nurse plant). Basically, plants and animals almost always compete for more than one resource. Elizabeth Pierson and Ray Turner found in a 1998 paper in the journal Ecology that saguaro populations have massive numbers of seedlings surviving in wet years without bad freezes. Some ecologists, like David Tilman, have looked at coexistence of several species as results of their limiting factors (Tilman 1990 in Oikos), where limiting factors might be water, or nurse plants. It’s sort of analogous to cooking: you have enough of everything except flour to make a full batch of cookies. So you have to limit yourself to a half batch.

However, the number of environmental factors (like temperature or humidity) that an animal or plant experiences, and the importance of each one, can make one daunting laundry list. That is why I prefer the approach Peter Chesson (as in his Annual Review of Ecology and Systematics article in 2000) takes in describing the “environmental response” of a plant or animal without specifying the environment necessarily. His models deal with the way growth rate changes based on the environment with some probability of a “favorable” year, whatever that may be, coming up so often, like your odds on a slot machine.

In the meantime, I think I will learn to repair a chain. Fun as slot machines may be, I’d rather have greater certainty in my ability to return from a bike ride than the gamble I can find that other individual out in the desert who can help me.