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Why is the world green? Top-down and bottom-up controls on ecosystems

Published on September 28, 2017   54 min

A selection of talks on Plant & Animal Sciences

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0:00
I'm Jonathan Shurin. I'm a Professor of Ecology, Behaviour and Evolution at the University of California in San Diego, and I'll be talking today about the question of, "Why is the world green?", or in more scientific terms about the topic of top-down and bottom-up controls on ecosystems.
0:20
So, this question of "Why is the world green?", it sounds like the sort of question a small child might ask their parents and they would have to go and google it or make up something smart sounding. But it's in the scientific world that's usually traced back to an essay that was written by Hairston, Smith and Slobodkin in 1960. And these three were professors at the University of Michigan, Ann Arbor, Michigan and they wrote this essay about, "Why is it that so much of the plant material in the world appears to go to waste?" in the sense that it is not consumed by any sort of herbivorous animals and instead dies and becomes part of the soil or decomposes over time. And if you lived in Michigan, this question might make a lot of sense. So, this picture is taken at Michigan State University's Biological Field Station. I actually did my Ph.D research there. And Michigan is in fact, at least for half of the year or so, a very green and leafy place with lots of green plants around. And so this cow is staring out onto this pasture and wondering why is it that it is unable to eat all of this grass that is growing in front of it and pondering this question of, "Why is the world green?" But depending on where you're listening to this lecture and where you live, this question might make not as much sense as it did to these three.

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