Sean B. Carroll
speaker
52 appearances
1 recordings
1 series
first heard Jan 2025
last heard Jan 2025
Sean B. Carroll’s voice in public audio — every appearance, attributed to the second.
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Appearances
And one of my favorite examples is the influence of salmon in western rivers on tree growth. And you're like, what? Yes, trees need salmon. So who would have thought that?
Let's start with one rule, which is really some animals are more important than others, or if you want to use the Orwell saying, are more equal than others. There's sort of a poetic description sometimes of nature, that everything matters and everything has its role. But it turns out that some creatures have a really outsized role in the diversity and stability of their ecosystems.
When ecologists started to discover this, it was even to their own surprise, well, the consequences are great. So that if you think about, for example, people may be familiar with the story of both the
eradication and then the later reintroduction of wolves in the yellowstone ecosystem so in the early part of the 20th century there was a great effort to eliminate wolves virtually everywhere in the lower 48 states you know because they were Disliked by humans, their effect on livestock, they were scary, et cetera, et cetera.
What we didn't understand what we were doing was we were taking a creature that had a really outsized impact on the stability and diversity of its ecosystem. We were taking it out of the picture and this had huge consequences. One of those consequences we can still see all over the place, which is, for example, the enormous numbers of deer that are in many states.
those deer in turn have enormous consequences on uh plant diversity because they mow down the plants and forests etc etc so the discovery that some creatures have these outsized effects um was a surprise it's sort of they were about these sort of hidden connections in in ecosystems and then we understand that if we can replace some of these things maybe we can reverse
some of the some of the changes that um some of the unwanted changes that have happened in places so it's i give you the wolf example but you know in the tide pools on the pacific coast that certain starfish in the serengeti it's the wildebeest that the massive numbers of wildebeest just munching the grass have an enormous impact on the diversity and stability of that ecosystem.
So this gives us insight into really how these systems work and how we can better manage them in the future.
Well, I mean... You know, nature was around a long, you know, we're late comers to nature, right? Humans and human population growth is very, very recent. So most of these places, you know, have operated on their own without human intervention for hundreds of thousands or millions of years.
And then we came along and, you know, in either in settling these places or in wanting to exploit them, for example, think of things like the fur trade and things like this, where we took specific creatures because we wanted we wanted them for our own gain. We've disrupted the balance in in those systems. So from nature's point of view, these creatures are all good.
From our point of view, they were either bad or desirable for other reasons. And we You know, we eliminated them. And then we've really sort of, you know, tip these systems into a different place. So it's rethinking our relationship to nature, you know, not to not to make ourselves out as the, you know, as bad and evil or anything like that. It's just we're doing this unwittingly.
We just didn't understand our impact when we, for example. eliminated most of the sea otters, for example, from the Pacific coast. And what that did amazingly to kelp forests, you know, you'd sort of think, I mean, why would, why would sea otters have any influence on kelp forests? Well, it turns out they eat the things that eat the kelp forests.
And if you don't have sea otters, the kelp forests can't grow. And those kelp forests are great habitat for fish. And those fish are great food for bald eagles, et cetera, et cetera. So there are all these domino effects that removal of these, what are called keystone species, uh,
Keystones, dubbed after the name of the keystone in a Roman arch, removal of these keystones have really outsized effects on systems. And so their restoration can have outsized effects on the restoration of the health of these ecosystems.
It's a very competitive world out there, yeah. And creatures are competing with each other of different kinds and of their own kind for resources, et cetera. And these are very complex web of interactions that's going on anywhere, in a coastal system, in a forest, in a pond, out on a plains.
But that web, there are certain components of those systems that when you remove them, the web sort of collapses. And that's what humans were doing unwittingly for, I think, a good part of the 19th and 20th centuries.
And it was a bunch of biologists, a bunch of ecologists studying these systems over long periods of time in the last four or five decades of the 20th century that put together, essentially from studying different systems, an understanding of these rules that sort of knit life on a large scale together. And understanding these rules then, of course, empowers us with a better understanding of life.
What's our best long-term behavior?
Yeah, let's go with one. So one rule are these certain species that have these outsized effects called keystone species. Another rule is there's sometimes really strong indirect effects between species. And one of my favorite examples is the influence of salmon in Western rivers on tree growth. And you're like, what? Yes, trees need salmon. How does that work?
Well, it turns out that those rivers, think of things like the Columbia or Snake, sort of majestic rivers in the Pacific Northwest, those rivers don't carry a lot of nutrients.
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