Wednesday, October 1, 2008

Longhorns and snakeheads and bees- Oh my

Over the weekend, I found a moment to peruse the Sant Ocean Hall online exhibit on the National Museum of Natural History website. I'm thinking ahead to some opportunities to get the little one to an exhibit that will catch his attention. I happened upon a page about the rapa whelk, a fairly recent exotic pest (some might say a menace) in the Chesapeake Bay region. It's been in various conservation groups' publications for a while.
What in the heck is a rapa whelk? It's a type of marine snail that has some nifty adaptations that allow it to spread itself around very quickly. Unfortunately, it's not from around here. It hails from Asia, almost certainly arrived in the bilge water of ships, preys on clams and oysters, and is a threat to the local marine snails. This presents yet another problem for the region's shellfish industry, not to mention the already badly degraded Chesapeake Bay ecology.
The rapa whelk is what's known as an invasive exotic species. This isn't a new idea. You've probably heard of many others, perhaps without realizing it: The fire ant, the Asian long-horned beetle, the gypsie moth, the zebra mussel, the European house sparrow, &c. This short list is merely the tip of the iceberg.
There are others that don't get peoples' hackles up, though: The honey bee, chickory, and the cattle egret, for instance. These pollinate many of our crops, make a proper cup of coffee for folks in New Orleans, and get rid of some of the fire ants that wouldn't have been here in the first place if we hadn't been so careless. (And, while we're at it, basically everything we eat comes from somewhere other than here.) These species are our friends, right?
I put some questions to the reader: Is it worth the effort to try to stop exotic species from invading new areas or to drive them out before they take hold? Is it appropriate to get rid of exotics that have been in an area for a long time? Does the usefulness or harm of the new species weigh on this? Should we hesitate to introduce an exotic crop? Should we simply accept that people will change the biosphere and make do with those changes?

Image source: Smithsonian Institution, National Museum of Natural History, Sant Ocean Hall


Sue said...

This reminds me of a post I made several years ago criticizing the whole idea of "native" plants and animals. All definitions of nativity for plants an animals make implicit, generally unexamined assumptions about time limits, i.e., that the plant or animal existed in a particular location prior to some unspecified point in time. For example, most discussions about "native" plants in North America implicitly use 1492 as the cut off date. We have no way of knowing what plants or animals may have been brought by humans entering the Americas by the land bridge across the Bering straight (what seeds and spores came on their clothing, and possessions). As for animals, how many actually began their evolutionary development on the land base we call home? And at what point in time -- when all the continents were connected as Pangea? Since that time? How many animals or their ancestors crossed land bridges, rode on flotsam across waterways?

The only legitimate basis for judgements about "invasive" species is what is destructive to existing patterns of human society. Since clams and oysters have food and economic value in our society today, the rapa welk is "invasive." No one is particularly worried about the house sparrow, because it has little economic or social impact.

Not too long ago, I was made aware that a lovely tree, the mimosa or silk tree, that can be seen all over eastern Kentucky, is an "invader," but since it primarily supplants other trees such as dogwood whose value is mostly ornamental, it seems silly to me to get all upset about it. Indeed, the expansion of the mimosa, and the decline of dogwood in this area, seems to be more connected to changing climate (longer, drier summers) than to the "invasive" nature of mimosa.

When you get right down to it, every species was an "invader" at some point in time.

E. R. Dunhill said...

I had a biology professor who contradicted the sentiment that the species is the most biologically significant unit in evolution, with the assertion that the individual is the most (or only) biologically significant unit in evolution. His reasoning was that species is an abstract construct, while the individual is actually competing to pass on its genetic material.
Also, the people who lived in the Americas intentionally moved species long before contact with Europe. As you're no doubt aware, maize was originally cultivated in what is now central Mexico (caveat, caveat, caveat), but was traded to the north, south, east, and west.
With these two ideas in mind, I think you're right that it's tough to call something native. When we muddy this with species that were clearly brought by Europeans (honey bees, earthworms, and certain grasses, &c) centuries ago and which have fundamentally changed the Americas' ecology, the issue of native identity and the right to be here becomes even more difficult.
I'm not sure how much supercontinents weigh on whether or not something is native. The vast majority of extant species have evolved since the Jurassic, though there are some trememdously hip old-timers still with us (among my favorites: brachiopods, crinoids, horseshoe crabs, ginkos, and cycads). It is an interesting question, though: Where is a horseshoe crab "from", given that none of our modern continents were configured as they now are, the equator was in a different place, and much of the rock that forms continental shelves and fills-in gaps between landmasses was yet to be deposited? Where is "here" in paleogeography? This was one of my favorite questions as an undergrad. (Reunite Gondwanaland!) Obviously, I've begun to split hairs.
I think what it means to be invasive does come down to a question of values. I'm not about to squash honey bees because they come from Eurasia, but I am likely to pull kudzu or put-down a snakehead if I come across it.
This all raises another question: I scatter my crums for the house sparrows in my yard, but I know some birders who carry slingshots and don't hesitate to kill them. Whose value judgment do we use in deciding what's invasive?

E. R. Dunhill said...

...sorry about the long response...

Pat Jenkins said...

are you insinuating that man's actions create these problems erd? whether limiting the spread of disease, or curtailing "bugs", interaction between groups is a must. which means it is almost impossible to stop the flow of harmful influences.

E. R. Dunhill said...

I'm not insinuating. I'm saying flat-out that people move a lot of exotic species, whether by accident or by design. I'm trying to find out what people think and how people feel about this.