Biological warfare: is it for you?

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.”

Garden Envy

I have mad garden envy of my friends who can garden. My friend Jonathan puts a lot of work into his, from hauling in pick-ups full of eye-watering not-quite-ready compost to determinedly watering the blank spot where his pipe vine used to be before his vacation until it re-sprouts. A former housemate, Emma, harvests greens and strawberries and radishes from a plot in a community garden (and blogs about it!).

By contrast, my yard is a haven for whatever can survive the brutal Arizona heat and the adorable trampling of my housemate’s dogs. I have yet to figure out how bribe myself to work out there. The tentative promise of plump cherry tomatoes I ate from our backyard a kid just doesn’t do it. That’s what grocery stores are for, right?

The fruits of my labor, or lack thereof, in my Tucson yard.
The fruits of my labor, or lack thereof, in my Tucson yard.

My point is that different houses offer very different growing conditions. A watermelon seed falling in Jonathan’s little Eden may live to grow and produce fruit. I can spit all the seeds I want into my backyard, secure in the knowledge that they won’t stand a chance.

Seeds can arrive not only through loving planting and tender care, but also via birds pooping, the wind blowing, or children playing. Ecologists call this process seed dispersal, as the seeds disperse themselves throughout your neighborhood (or the radius of the hardware store where you bought the packet).

Here is another ecologist-y phrase to describe the collection of well-watered manicured gardens and the dandelion-spotted lots you see as you bike around a city: spatial variation. Means that in some yards roses grow better than dandelions (in Tucson it’s probably only if some human is maintaining their water supply), but in other yards the dandelions win.

Spatial variation can promote biodiversity. You can see more species along a street with a range of landscaping preferences or conditions than you might in a neighborhood where everyone has picture-perfect Bermuda grass coating every inch of space. It is a common phenomenon in nature, too, one I observed in the Rocky Mountains on a recent vacation to Banff. Different trees and plants dominate the dry, windswept ridges than do the pockets in alpine meadows that remain swampy from melted snow. We can see with our own eyes that species have their own specific responses to environmental conditions.

Hiking in Banff National Park, Alberta, Canada, I observed spatial variation in environmental conditions and levels of competition.
Hiking in Banff National Park, Alberta, Canada, I observed spatial variation in environmental conditions and levels of competition.
Snow pockets provide wet conditions, favoring species who compete well with plenty of moisture.
Snow pockets provide wet conditions, favoring species who compete well with plenty of moisture.

But if that seems too obvious, environmental conditions are only part of what determines which species can coexist. The other major part is competition. As gardeners who start their delicate basil plants indoors know, if you sprinkle several seeds into each tiny pot, you’re almost sure to get at least one sprouting (that’s called bet hedging, and plants do it, too). But very likely, you will have a number of seedlings poking out their first shoots and leaves in every pot, as Emma’s April 21st photos show. As they grow larger, not all of them can survive. There is just not enough room, never mind nutrients, light, moisture, or other things plants need.

This process ecologists (and gardeners) call thinning. If the gardener does not pinch off the smaller plants early, they will die out eventually, but only after a long and grueling battle with its siblings, sapping the energy of the survivors, reducing its eventual output. This is competition, a familiar word from sports and family life, but much closer in meaning ecologically to the way we use it to talk about economics. Remember Adam Smith and his “invisible hand?”

Just as a University neighborhood (or gloomy sky like Seattle’s) may provide fertile grounds for coffee shops, yet a plethora of espresso joints ensures stiff competition and low profits, so do plants that find the choicest habitat have to battle contenders for space, for water, for light, for nitrogen, for pollinators, and the list goes on and on. (Check out Emma’s March 1 photo of a field of daffodils in Washington for an image of competition!) Environment and competition are obviously related and can determine local coexistence (and larger regional biodiversity). But how? Should a “good” environment be more diverse or less diverse than “poor” habitat?

In introductory biology classes, we received this answer a maddening amount of the time: it depends. But that just leads to more questions, the most obvious being: it depends on what?!

That’s where biology starts to get fun, but you’ll have to excuse me for a bit. The monsoon has started here in Tucson (raining in small patches, providing more spatial variation!), and I have a garden to go imagine. Stay tuned.