As it’s almost 2011, it seems like a good time to continue considering space colonization. I posted below about a spaceship or colony like Biosphere 2, and how many species could survive indefinitely on it. Instead of more than three hundred species of rainforest tree, I imagine a dozen or fewer species could persist in the rainforest because their population sizes would be too small to avoid inbreeding or survive disasters. There are only so many trees that big you can fit into an area less than the size of a football field. From talking to students who do research in the rainforest (e.g. Ty Taylor currently in Scott Saleska’s lab), it sounds like about 400 is the high end of what you could pack in there, and fewer than that would persist even with good care. And that is assuming they get pollinated and make seeds at all – something people would have to help them out with in the absence of the right insects or wind.

Speaking of insects, you could fit a lot more species into the area and have reasonable population sizes, just because they are so much smaller. There are in fact a lot more insect species in the world than there are plants, too – is that for the same reason? Or are other factors, like the genetic structure and the forces that separate and shape populations at the root of such high insect diversity? Biologists are still studying that question.

So what else does thinking about little Biosphere 2 tell us about the big Biosphere all around us (Earth)? Well, assuming Earth is like an island with no immigration, a colony all alone in space, no new species are showing up and evolution happens verrrry slowly. In the meantime, some of the fast changes people are making, like chopping down the Amazon for soybean farms or cattle ranches, like building shopping malls and suburbs in the deserts, like introducing snakes and rats onto islands that have never seen such things – these fast changes are causing a lot of species to go extinct.

How many? Well, about 1% of the total described species. Considering that more than 99.9% of all species that ever existed are extinct, that’s really not a lot. Other people argue that we have only described a small proportion of the diversity in the Amazon, and are changing that habitat at really astonishing rates, causing hundreds to thousands of extinctions a year that we don’t even record.

Is there any reason to worry about this? Why not keep at least the handful of species we actually want – a few individuals in zoos if necessary? Barbara Kingsolver makes a compelling argument for diversity as an insurance policy against disaster and as the raw and holy creative potential invested in the world we live in. Others have described the process like a giant game of Jenga – all these species depend on one another and pulling out a piece at a time, we may eventually cause the structure we depend on to collapse.

Of course, if you live in a space capsule, you can build machines sufficient to produce oxygen, clean your water, fertilize your plants, and other services we get for free from nature in the Big Biosphere here on Earth. As a friend (thanks Gabriel!) pointed out to me, there are aeroponic crop options if you live in low to no gravity – no messy (or free) ecosystem services to worry about. Unfortunately for those of us busily buying things that destroy diversity here on earth, building our own replacements for those services on a planetary scale might be just too expensive.