The Pith: The Amazon Rainforest has a lot of species because it’s been around for a very long time.
I really don’t know much about ecology, alas. So my understanding of evolution framed in its proper ecological context is a touch on the coarse side. When I say I don’t know much about ecology, I mean that I lack a thick network of descriptive detail. So that means that I have some rather simple models in my head, which upon closer inspection turn out to be false in many specific instances. That’s what you get for relying on theory. Today I ran into a paper which presented me with some mildly surprising results.
The question: why is the Amazon Rainforest characterized by such a diversity of species? If you’d asked me that question 1 hour ago I would have said that it was a matter of physics. That is, the physical parameters of a high but consistent rainfall and temperature regime. This means the basic energetic inputs into the biome is high, and its consistency allows the organisms to plan their life schedule efficiently, maximizing the inputs. All that naturally produces a lot of diversification in the “climax” ecosystem. To some extent I would acknowledge this was pretty much a “Just-So,” but I’d have thought it was a good shot, and probably representative of the internal logic of many people.
But no, a new paper in Ecology Letters seems to imply that that the answer we must look to is history and not physics. From the perspective of someone who is rooted in are reductionist conception of evolutionary biology this isn’t the answer I was “rooting” for, but if it is, it is. What’s their logic?
Yesterday I alluded to the Court Jester hypothesis of evolutionary change, which is often contrasted with the Red Queen hypothesis. The main embarrassment for me as a person who fancies himself a fan of evolutionary process is that I hadn’t ever heard of the Court Jester Hypothesis before yesterday. Therefore I went back to the paper which outlined many of the basic ideas of the model in 2001, Distinguishing the effects of the Red queen and Court Jester on Miocene mammal evolution in the northern Rocky Mountains. To be fair, the hypothesis itself is a tightening of a range of ideas which were long in the air. I did know, for example, about the Turnover-pulse hypothesis. These are all a set of models which emphasize the abiotic selective pressures on life forms, as opposed to the biotic ones. An abiotic pressure would be something like the Younger Dryas cold snap. A biotic pressure might be an exotic invasive species spreading through the landscape.
In my own mind selection is selection, so I didn’t distinguish them too stridently. In fact, most people seem to have abiotic pressures in mind when they conceive of natural selection, so I generally prefer to emphasize the competition and cooperation between and within species. Additionally, it seems that biotic models are more formally tractable and elegantly constructed (I know much of climate change is cyclical, but I assume that “catastrophe” exhibits a poisson distribution?). I generally lack the “thick” knowledge to really make sense of a lot of detailed natural historical treatments, so I probably avoided them because I didn’t think I’d get much out of them. In hindsight, this seems foolish and shortsighted. Rather like economists focusing on equilibrium states because of their ease of modeling when periodic exogenous shocks are a major variable within our real lives.
In yesterday’s link dump I expressed some dismissive attitudes toward the idea that loss of linguistic diversity, or more precisely the extinction of rare languages, was a major tragedy. Concretely, many languages are going extinct today as the older generation of last native speakers is dying. This is an issue that is embedded in a set of norms, values which you hold to be ends, so I thought I could be a little clearer as to what I’m getting at. I think there are real reasons outside of short-term hedonic utility why people would want to preserve their own linguistic tradition, and that is because I am no longer a total individualist when it comes to human identity. I have much more sympathy for the French who wish to preserve French against the loss of their linguistic identity against the expansion of English than I had a few years ago.
Language is history and memory. When the last speaker of English dies, or, when English is transmuted to such an extent that it is no longer English as we today understand it, our perception of the past and historical memory, our understanding of ourselves, will change. There is a qualitative difference when Shakespeare becomes as unintelligible as Beowulf. Though I tend to lean toward the proposition that all languages are a means toward the same ends, communication, I agree that there are subtleties of nuance and meaning which are lost in translation when it comes to works of literature and other aspects of collective memory. Those shadings are the sort of diversity which gives intangible aesthetic coloring to the world. A world where everyone spoke the same language would lose a great deal of color, and I acknowledge that.