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Printable Handouts
Navigable Slide Index
- Introduction
- Why is the world green?
- Brown areas of the world
- White areas of the world
- Blue areas of the world
- Why are parts of the world green?
- What happens to primary production?
- Population size and productivity
- What does theory say?
- Bottom-up control: things that limit plant growth
- Temperature and precipitation determine biomes
- Terrestrial primary production is about water
- Limiting factors (water)
- Marine primary production is about nutrients
- Secondary production and trophic transfer
- Evidence for bottom-up control
- Bottom-up control is clearly important
- Top-down control: things that affect mortality
- Two sources of top-down control
- Herbivores can take a bite out of plants
- NPP consumption by herbivores
- Can plants defend themselves?
- Trophic cascades: do predators rule the world?
- Trophic cascades in kelp forests
- Trophic levels or trophic tangles?
- Classic examples of trophic cascades (otters)
- Otters increase fish, bacteria and viruses
- Classic examples of trophic cascades (lakes)
- Predators and climate in mountain lakes
- Trophic cascades (Yellowstone National Park)
- Are trophic cascades stronger in water or on land?
- Practical implications: Eutrophication
- Practical implications: Fisheries
- Top-down, bottom-up, or both?
- Conclusions
Topics Covered
- Regulation of primary and secondary productivity
- Different kinds of resources
- Herbivory and productivity
- Predators and trophic cascades
- Applied issues
Talk Citation
Shurin, J. (2017, September 28). Why is the world green? Top-down and bottom-up controls on ecosystems [Video file]. In The Biomedical & Life Sciences Collection, Henry Stewart Talks. Retrieved November 9, 2024, from https://doi.org/10.69645/XMEJ5817.Export Citation (RIS)
Publication History
Financial Disclosures
- Prof. Jonathan Shurin has not informed HSTalks of any commercial/financial relationship that it is appropriate to disclose.
Other Talks in the Series: Ecology
Transcript
Please wait while the transcript is being prepared...
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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