kestrels, nighthawks, and ...friendly invaders?

This is the time of year where migration is evident, even if you aren't really trying.

Duke Farms set a new one day total for stop-over Kestrels, with fifteen(!) working our grasslands this afternoon. We didn't even cover the entire area.

From center bridge in Stockton this evening, I counted sixty two Common Nighthawks.

oh, and somewhere along the way single Nashville and Yellow warblers.

Lastly, in case you didn't catch Tuesday's New York Times this article, titled "Friendly Invaders" is worth a read. As is often the case with the NYT, their bias on invasion science comes out, but it does raise some interesting points.

I'm not going to fly off the handle on this one, but as you read it consider the following:

1. Biodiversity alone is not a good barometer of ecosystem health. So all of these native species of New Zealand are still there, but at what kind of populations? How isolated are they? How have the insects that depend on them been affected? You get the point. There's more to consider than a species list.

2. Biological invasions, especially on large bodies of land, rarely act alone. There is almost always some underlying anthropomorphic disturbance helping to drive the invader's spread. In the Mid-Atlantic, for example, its white-tailed deer and a four hundred year history of screwing up the soil (agricultural land use). I think this idea of strong interactions (such as predation) versus weak interactions (competition) is interesting. I also think its well demonstrated that in an ideal, healthy ecosystem invaders that have to out-compete natives for space either fail to introduce themselves entirely, or manage to assimilate into the ecosystem in some innocuous way. However, disturbed ecosystems are a totally different ball game, and probably better represent reality for most invasion scenarios. Lets face it, there are few places left on earth where we haven't made our mark. Certainly none in New Jersey and I doubt there's very many in New Zealand.

3. These ideas about native snakes rapidly evolving to eat cane toads and the like that Dr. Sax raises throughout this article are hard for me to swallow. There are many excellent scientists who downplay the role of evolutionary history during biological invasions. It is difficult for me to imagine that non-native flora can provide the same value to all of the same species as the plants it replaces. There is two opposing ideas about ecosystems at work here: the ecosystem as the complicated, meticulously constructed natural order that will collapse if disturbed and the ecosystem as the living dynamic thing that will take whatever we can throw at it. Personally, I think its probably somewhere in the middle. The former idea is a little too "Scala Naturae" and the latter stinks of human hubris.

4. Thinking of invasions as a symptom of global change. I think this is a great notion. Species are spreading around the world in unprecedented ways. Dismissing it as another great migration misses the point entirely. We are also exporting nutrients around the world. Nitrogen and Phosphorous are showing up in high concentrations where there should be hardly any at all, largely the result of modern agricultural practices. Of course we are all familiar with the huge net export of Carbon we are putting into the atmosphere, largely as the greenhouse gas Carbon Dioxide. With the science behind these symptoms of global change now universally accepted, does it really make sense to downplay the drastic changes we're seeing in plant and animal communities all over the world? These two elements, the abiotic (non-living) ecosystems components and the biota, are inexorably linked. Change in one will invariably drive change in the other.

Anyway, if you read the article, post a comment and let me know what you think!