FE2.7 - Kelp Worlds- Trophic Cascadia (Part 1)
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Notes
New!
- Seems to use some statistical physics language to describe these ecosystems
- E.g. talking about these "stable states" and that you need to reach a critical threshold of external pressure in order to move from one stable state to another
- This is very different from how I'm used to thinking about ecology. I've always thought of it as these balances being sort of smooth functions of each other: as a predator declines, its prey will increase smoothly, and vise versa.
- However, what we see here is that, even as a predator declines, the prey might not be able to mount a full comeback, until you get a shock to the system, or the predator declines past from critical threshold
- Sort of like the difference between kinetic vs static coefficient of friction
- Or like the concept of activation energy: where, sure, there might be another equilibrium now with a lower free energy, but to get there requires catalysis.
- trophic downgrading and this notion of parity of the number of predation levels which determines the prevalence of plants.
- If there's an even number (e.g. just plant an herbivore, or an additional even number of predation levels above that), then herbivores will dominate, while if there's an odd number, than plants will dominate.
- This seems maybe somewhat intuitively believable, but only under very strong assumptions. Honestly, I'm very surprised that it seems like they're claiming this is an empirical phenomenon?
Interesting tidbits
- Kelp are algae
Highlights
people tend to be concerned about things that are cute and cuddly naturally.
Even though there are relatively few starfish compared to all the other species, they play this critical, previously invisible role. To
he used the term keystone species, which is like a cool reference to the central stone in an arch. Without that stone, the whole structure collapses.
not from the perspective of how the system's affecting otters, but from the perspective of how the otters are affecting the system.
He writes in his book, which is called Serendipity,
And I thought, my gosh, what an amazing natural experiment to go to some of these places where otters had once been and simply look at it and see is it any different from the places that they have recovered?
Note: Something like this in human level?
While we refer to kelp ecosystems as forests, kelp aren't trees or even what we commonly think of as plants. They're actually algae, specifically, brown algae. They're distinct from green and red algae and considerably more complex morphologically
Note: Kelp are algae! And there’s different kinds of algae!
Remove the otters, and the kelp begins to disappear, eventually resulting in an urchin barren,
Note: But won’t the urchin die out then?
When does an ecosystem really need more than 2 species??
We waste so much time not learning interesting things, but, you know, trying to make sure we're not wrong about things that we're almost certainly not going to be wrong about.
So wait, are you telling me this is how sea otters return to BC? Totally. They're fluffy refugees of us nuclear testing, like.
So, 89 sea otters are dropped off at the west coast of Vancouver island at a place called Checklist Bay, and that becomes ground zero, if you will, for sea otter recolonization of the BC coast.
He really knew how to give a complicated idea a snappy name.
trophic cascade, the basic idea that changes in the abundance of one species at one end of a food chain could have dramatic domino effects throughout the system,
Note: Is there a physics version?
Okay, so there's a bit of inertia in the system. It kind of wants to stay in one state. Yeah. Once it's in that state, it wants to stay there. And to get from one stable state to the other, the system has to undergo something called a phase shift,
Note: Weird here though…
So hysteresis means that there's this lag time that until the otter population reaches a critical threshold, this system just won't flip from being urchin dominated to being kelp dominated.
so that when there is an even number of trophic levels, that is two or four or six or eight, you're going to have a world in which the herbivores are limiting the plants. And when you have an odd number of trophic levels, that is one with just plants or three predators, herbivores and plants, you're going to have a world that is very much like the one without any herbivores in it at all. And so that's the basic theory.
trophic downgrading, then, is when there's a change up top that cascades down the system, affecting the plants negatively. In fact, the notion of trophic downgrading is a little more complicated than that. It could operate in any number of different detailed ways, but that in every particular case, if you perturb these higher trophic level species, expect to see big changes.