Workbench
09.17.2009, 11:32 AM

How are urbanization and other human influences affecting the biodiversity and health of ecosystems? Seed visits urban entomologist James Danoff-Burg in the field and takes a peek at the core field equipment that he is using to investigate this critical question. Danoff-Burg collects and studies cosmopolitan critters in an attempt to quantify human impacts on the environment so that we can better mediate them. From tracking invasive ant species in street medians throughout Manhattan with repurposed coffee cups and salad lids to identifying the correlation between biodiversity and street garbage, the Columbia University professor combines a decidedly low-tech toolkit with rigorous scholarly analysis to tease apart the interaction of plants, animals, and humans within an ever-changing urban ecosystem.

Interview by Greg Boustead
Photographs by Nikki Schiwal

Beating Insects

The square white sheet is called a beating sheet, an oft-used tool in collecting specimens. We hit the branches of plants and trees to dislodge any insects, arthropods, or other creatures onto it. Then we can easily collect specimens off of the stark white sheet.

Not for Smoking

The aspirator is the single most important item in the entomologist’s tool kit. This is the primary equipment for collecting insects that are crawling about. You put the rubber tube into your mouth and inhale quickly. It creates a vacuum inside the bottle, and that vacuum is released by pulling air in through the metal end so the insects shoot into the vial. If the filter inside the rubber tube falls off, you often end up inhaling dirt, even the specimens themselves. I can’t tell you the number of things that I’ve accidentally eaten as a result. Its peculiar—or potentially illegal—appearance sometimes raises suspicion. I actually had a cop stop me and say, “What are you doing?” “I’m collecting insects.” “Ah, okay, fine.”

A Soft Touch

The soft forceps in my toolkit are fantastic because they won’t squish most insects: Dismembered specimens aren’t as useful as intact ones. The curved forceps are for shoveling underneath things during collection. Insects are like little flying jewels, but they’re often surprisingly soft-bodied and delicate. So we have to be very judicious in how we handle them. With the larger ones, we can actually identify them in the field and then let them go. But the vast majority of species are maybe half the size of a rice grain.

The Pitfalls of Collection

I dig holes and sink plastic cups into them to create pitfall traps. The dirt has be level around the lip so that it’s a continuous path until the insects arrive at the cliff. They wander around in their search for food, nests, or mates and then they fall into the cup, which is filled about a third of the way up with water, soap, and salt. The soap is there to break the surface tension, so that when insects fall in, they can't get out. The salt stops the bacterial activity that would otherwise start decomposing the body. We mostly get ants, spiders, and, of course, beetles. Beetles are everywhere. There are about a total of 1.6 million named species, including plants, animals, bacteria, fungi, protists—the whole shebang. About 48 percent of all those species are insects. Even more remarkable, one in five named species are beetles. So a fifth of known life is beetles.

Repurposed Garbage

That’s a pan trap—its purpose is to provide a larger surface area for trapping more aerial, agile insects. It’s filled with the same solution as the pitfalls. Often we’ll paint the bottoms yellow because insects seem universally attracted to that color. In urban settings like here, I get a lot of parasitoid wasps, which are beneficial insects that lay their eggs in crop-eating pest insects. People shoot us dirty looks sometimes because they think we’re just littering, not knowing that we’re actually setting up biodiversity data collection sites. It’s understandable—a lot of the components literally are repurposed garbage. This pan trap is a lid from a salad I had the other day, for instance.

Sifting through the Data

This contraption is used for separating insects out from the leaf litter. The beating sheet is useful for pulling insects off of leaves, but in the litter there are at least as many species of insects, most of which we’d never see unless we isolated them. So you won’t usually see these sorts of insects walking around. We grab handfuls of the leaf litter, put it into the sifter, and then shake. The insects pass through the sifter filter, but the leaves stay behind. I use my beating sheet as a recipient for the “siftate,” the stuff that falls through.

Trashy Biodiversity

I use this 50-meter measuring tape to figure out the sizes, distances, and widths of just about everything in the field. Aside from things like leaf-litter depth, I need to record the number and size of plants and other flora at a collection site. According to island biogeography, we would expect a strong correlation between high biodiversity and large areas filled with plants and close to parks or other insect “reservoirs.” But that’s not what we found in urban settings. The single strongest predictor of overall biodiversity in our New York City research wasn’t increased space or plant life. It was garbage. It represents a surprising and initially counterintuitive result.

Keep Out

Almost all of the insects we find are invasive. Normally in an ecosystem that’s been around for a while, native species have a leg up...or six, as it were. But if you cut everything down, put some dirt on it, and plant some stuff, you’re turning the ecological clock back to zero; succession and evolution happen equally for all species, natives and invasives. If we can detect an invasive species before a population gets established, then we should intervene and attempt to remove it. But it’s probably too late for New York City. The invasive species found here, like the Argentine ants—forget about it. We’ll be stuck with this ecosystem for a good while. And the truth is, we don’t yet know what the larger consequences of invasive dominance are.