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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But salmon, when they come upstream to spawn, and when those salmon are then taken, for example, by predators and eaten on stream banks and all that sort of stuff, a lot of the nutrients that they bring from the ocean get into the forest, and you can map those nutrients right into the growth of those trees.
So it turns out that salmon are like a conveyor belt for nutrients coming from the ocean into these trees.
forests alongside these rivers so who would have thought that right I mean it's just sort of stunning to think that trees are somehow influenced by salmon yeah and as you know a lot of those rivers have been dammed that's blocked off the salmon well that has effect on the rivers that has effect on the forests around those rivers and so again there's a lot now there's a huge movement
There's a lot of dams being taken down in the West and biologists are monitoring what's going on. And as the salmon populations come back, you can actually see the nutrients moving up those rivers again. So these strong indirect effects, the idea is that salmon would influence trees or that otters would influence the kelp forest. For example, the number of
will the beast on the serengeti influences the numbers of giraffe i can go through that again that explanation as well these strong indirect effects these domino effects that that ripple through a system they're they really were unexpected and they it you know it's it so almost everyone is a sort of just surprised when it's discovered that um these the dependence of species on each other are not obvious uh you have to sort of map these out
yeah that's part that's partly why they're doing well but the hunting really wouldn't have been that significant until the deer herds exploded in the early part of the 20th century so deer when you know when wolves roamed the lower 48 and abundant and you know in large numbers uh deer numbers were i'm going to take a stab at maybe a 50th or a hundredth of what they are now i spent a lot of time in the state of wisconsin
And I mean, the annual deer hunt is a huge thing culturally and the deer herd is enormous, but some of the pioneering ecologists of the 20th century understood that that was a huge change from say that from the 19th century and that deer exploded when you took away their predators.
so predators have a big role in controlling the size of populations of their prey and take away the top predators and you can have an explosion in the number of their prey so really deer numbers are abnormal all over the country because they have no essentially no significant natural predators i mean there are a few you know wolves are coming back in various places but they're not making a dent
now deer have spread over all these you know suburban and urban populations and they're making a living on our gardens right so um yeah so so deer you can i know they're cute uh but they are essentially an invasive species um or at least they're a species that's out of control um out of natural control so you know i think deer are with us to stay in these large numbers but
That's a great point, Mike. In fact, essentially the third rule. And that third rule is that the density of populations is sort of self-limiting. So when there's a lot of food, abundant food and populations are small, they will grow explosively.
But as that sort of population fills up the space and as food starts to become limiting, that will slow or in fact sort of reverse that to a population decline. So lots of things are density regulated. And so deer are, you know, have expanded their habitat. They're filling, you know, our suburban areas and things like that. But there's still limits on deer in terms of food abundance.
And there's also, you know... there's cars you know as you know there's lots of collisions and things like this so there's various things that are um constraining the deer population as well as disease, you know, because they have certainly acquired some diseases now that they're in close contact with humans.
So, yeah, so this, the general concept is that in no area will be, there is a limit to how much can be carried by, the population can be carried in any given area, you know, limited particularly by food supply.
That's a hugely important, maybe sort of philosophical question. I think, you know, you said earlier about how nature kind of works these things out. Let's take something like a beaver and you could say, all right, a beaver builds a dam and that dam diverts some water. And, you know, does that impact other creatures? It certainly does.
um and and maybe it impacts you know the ability of fish to get around in some places and things like that but it also in creating these wetlands you see all sorts of plant life that thrives in the wetlands and then creatures that invade these places and um or exploit these places and so
beavers you know are often referred to as you know one of nature's engineers you know their net effect is you know to create habitat for lots of different things so we you know in a lot of places we took out beaver and we straightened out rivers we straightened out waterways we didn't want beaver dams on our you know on our on our waterways um we wanted you know unfettered access to this but
You know, it's hard for me to see the beaver in a negative light because, you know, it has done this particular job for eons and all sorts of creatures became dependent upon that job. And then we came in and essentially took the beavers out of the picture and lots of things, you know, suffered for that.
So it's, it's often the case, you know, it's, I mean, I'm going to try to see if I can come up with some other example where you might wonder about, I'll jump through to elephants. Okay. You can look at elephants are incredibly majestic creatures, but they're pretty tough on forests. Elephants are, We'll knock down a lot of trees.
And I've been in areas in Africa where it's pretty astounding what elephants can do to a forest and probably can do it in a fairly short period of time. And if you're knocking down trees, you're probably taking away nesting sites from birds. You may be taking away food from other animals. So.
the knock-on effects of some of these creatures are negative for for other creatures but you know take away the elephants and then you don't get the turnover of the forests and you don't get uh you know fertilization you know through their dung and that supports all sorts of other communities and you know and so on and so forth so it it takes some
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