There are an extraordinary number of life forms on the face of the earth. I mean, just staggering. Somewhere in the neighborhood of 2 million species have been described, depending on how species designations change as we get new information. That’s a hard number to wrap our heads around.  Most of us have probably never seen 2 million somethings at one time (not counting bacteria and other stuff not visible to the naked eye).

All those species have no business being alive and well! Didn’t Darwin’s theory of evolution suggest that when species compete, one of them wins and the other, well… tough luck? In Princeton biologists Rosemary and Peter Grant’s Galapagos study made famous in Jonathan Weiner’s Pullitzer winning The Beak of the Finch, people actually watched species converge and differentiate due to resource competition. So does that mean that each of these two million species is part of a neat little food chain, with each having their very own food, their very own kind of home, the predators that are only hunting them?

Walk outside and look around. Along my street in Tucson, Arizona, there are plenty of empty lots, populated by weeds despite the brutally hot summers here – not many plants, and not many species, but certainly more than one. Rarely do I see a monoculture occur naturally. If you live near the Pennsylvania temperate forests, take a hike in the game lands and look at all the different trees and shrubs. Up in the Rocky Mountains, the fields of summer wildflowers are multicolored because of all the different species. The same holds true in Californian tidal pools, and in rainforests from Portland to Panama.

It seems that a neat little picture of who lives where and eats what will not suffice to explain the world around us. Biodiversity is somehow maintained while species compete ferociously. A species’ ecological niche is not a tidy little box, but overlaps generously and unevenly with its competitors.

How is this biodiversity was maintained? Why are those weeds coexisting in the empty lot next door? Or are they? Any why aren’t any petunias coexisting with them? I hope studying mechanisms of local coexistence will help us understand its loss and what that means.

Species are vanishing faster than humans have ever experienced, and we are contributing to that. (Throughout the fossil record, but well before we were around, there have been 5 really big extinctions, of which the well known dinosaur extinction was one. We may be approaching a sixth.) Well-studied birds and mammals have been disappearing at roughly a species a year, and those are just the ones we know about. Thousands of square miles of Amazon rainforest is cleared every year, which, in such a lush and diverse ecosystem may be spelling extinction weekly for localized plants or beetles. It’s like we are playing a giant game of Jenga. We remove structural supports of this great towering network of ecosystems one by one, hoping it won’t collapse.  Of course, if we keep going and keep going, eventually we would collapse, but are we really going to get to that point? Scientists are trying to answer that question: how much diversity is enough?

That’s why I’m studying coexistence mechanisms in Peter Chesson’slab at the University of Arizona for my PhD. Members of our lab study the storage effect, relative nonlinear responses to competition, covariance of environment and competition, nonlinear competitive responses, and other fun mechanisms in variable environment ecological models.

Still trying to figure out what that mouthful means? So am I.