The cold Locke-Voltaire equations

April 27, 2018 2:52 PM

Leaving populations to boom and bust on their own is currently gruesome in the Netherlands, economically advantageous in Sussex, and contentious where reintroduced Yellowstone bison can be hunted.

Here's a summary of definitions, attempts, and problems from Current Biology and a similar essay concentrating on network theory as a method for biological understanding from Perspectives in Ecology and Conservation.

posted by clew (20 comments total)

The title is a creaky joke about the Lotka-Volterra equations, which are the simple model explaining why we expect population booms and starvation in any predator-prey system (as in the first link). Should we cultivate the world as a garden? Do we expect famines even in the best of all possible worlds? Would even perfect empiric knowledge of ecology answer either question?
posted by clew at 2:53 PM on April 27, 2018 [6 favorites]

Thanks for this corrective to my perhaps-overly-optimistic Knepp post the other day.
posted by clawsoon at 3:30 PM on April 27, 2018

The title made me think of this.
posted by stevil at 3:37 PM on April 27, 2018

Half-baked idea after reading half of the articles: Maybe rewilding would work better if the animals involved were small enough to allow predators to be part of it. Instead of deer starving to death because there isn't enough room for wolves, have weasels ripping hares apart. No muss, no fuss.
posted by clawsoon at 3:46 PM on April 27, 2018 [1 favorite]

A less-controlled rewilding experiment
posted by clawsoon at 3:48 PM on April 27, 2018 [2 favorites]

I thought that would be a link to High-Rise.
posted by GenjiandProust at 3:53 PM on April 27, 2018 [1 favorite]

Aw, sorry, clawsoon, I assumed you had rewilding as a tag in your post. I can't find any reporting about Knepp that seems to have been done by ecological science standards, so was riffing on the meat-selling part -- AFAICT they're economically sustainable because they can sell fancy beef, which means that as usual humans are the top-down predator. (Which explains the other reference too, stevil.)

Weasels and rabbits sounds manageably Wind in the Willows, but what if we got Australian rabbit disasters instead?
posted by clew at 3:54 PM on April 27, 2018

Tags added. When I posted the story, I didn't know the right word. :-)
posted by clawsoon at 3:58 PM on April 27, 2018

The Dutch example of Oostvaardersplassen says (to me, at least) you can't do rewilding halfway. If you're going to attempt to restore a natural ecosystem (or in the Netherlands example create one for the first time) you've got to go all the way and introduce predators as well as herbivores. And introducing predators mandates a need for space. Just slipping an ecosystem into a pocket of land that happens to be available isn't going to work. I'm not sure if anyone knows the minimum required space for an ecosystem, but in Oostvaardersplassen the marshland appears adequate while the grassland/forest is much too small.
posted by Kevin Street at 5:39 PM on April 27, 2018 [1 favorite]

I just read clawsoon's post, and there seems to be two big differences between the Knepp Castle Estate and Oostvaardersplassen: the Tree family left their farm alone (not introducing any animals and not planting anything, but just letting natural succession happen), and it is a farm surrounded by other farms instead of a pocket of land located between cities. The size of their farm may not be large enough for a full ecosystem, but it's located in an area where animals and plants have free access and is not an island.
posted by Kevin Street at 5:56 PM on April 27, 2018

It seems I was wrong, Knepp did introduce herbivores. So maybe the main difference is their respective locations and the land around them.
posted by Kevin Street at 6:11 PM on April 27, 2018

And Knepp does have carnivores: humans. They talk about culling the cattle herd when it reaches the land's carrying capacity.
posted by maxwelton at 7:14 PM on April 27, 2018 [2 favorites]

To me, ‘rewilding’ mainly conjures up Monbiot’s proposal that the U.K. should stop using subsidies to keep unnatural and uneconomic flocks of sheep scouring the hills bare in a way which is historically recent.

Knepp Castle Estate and Oostvaardersplassen seem almost quixotic by comparison, ‘rewilding’ small areas with no recent history of wildness.
posted by Segundus at 8:38 PM on April 27, 2018

It was pretty clear in the links that Clawsoon made in their post that the Knepp estate was controlling animal numbers by culling (and selling the meat). If you don't cull & don't have an apex predator population, then your outcomes are going to be Malthusian.
posted by pharm at 4:27 AM on April 28, 2018 [4 favorites]

The amount of large herbivores in the Oostvaardersplassen project just seems wildly out of scale, even at the new level. The EU has some rules for animal welfare, and they are naturally designed for farm animals who are fed corn and hay in addition to (or in place of) grass and other plants. As far as I can see the number of animals in Oostvaardersplassen fit more to those EU levels than what the natural unfertilized habitat would be able to carry. I'm sorry I can't find the particular recommendations in English, but it's like 2 cows with calves on a hectare, or 4 mares with foals. If a lot of the land is marsh that is inaccessible to the big grazers, there isn't even enough room with supplemental food, and absolutely not without.
Also, there doesn't seem to be much shelter in the park. It's not that you need built structures, but you do need relatively dense forest for the winter months. Which is a thing they seem to be doing better at Knepp.
posted by mumimor at 5:42 AM on April 28, 2018 [2 favorites]

Famines happen without human management, is the thing. That's one of the basic ecological facts ilustrated by the Lotka-Volterra eqns.; even though they assume a steady supply of food for the species counted as prey, it only takes one more trophic level to have starvation-caused population crashes. In a real ecosystem, the photosynthesisers aren't even guaranteed equally good years every year, so they're the prey, and we go up one trophic level to the browsers or grazers and they have crashes. I think this is not paywalled?

And even the melioristic Knepp story has this, but it;s hard for humans to see because we think some creatures are prettier than others. That "nature fixed itself" section when an invasive weed is controlled by a flood of butterflies? That's equivalent to "there were a lot of grazers here and then a year of lethal botfly infestations, and now the grazers are a small population".
posted by clew at 11:32 AM on April 29, 2018 [1 favorite]

Famines happen without human management, is the thing.
Yes, but famine because of extreme overpopulation managed by humans is not that thing. Where I live I'm used to rather large fluctuations in populations of hare, deer, fox, migrating birds and various insects, and obviously plants, specially invasive plants. But none of these situations lead to dead animals and trees lying about as in the link from the Netherlands. I've never seen anything like it, and I live on the edge of a wilderness/national park where I've been in every corner.
If there is an overpopulation of hare, they will be eaten by an overpopulation of various predators, and the next year, when there are less hares, there will be far less predators. As for the big herbivores, I've never ever seen a dead animal like in those images, though we definitely are on the edge of what the land can take. Partly because there is a better balance of animals and land, and partly because there are obviously more carnivores to eat whatever dead animal there might be.
posted by mumimor at 12:58 PM on April 29, 2018

With predators, you trade grazer starvation in the first low-NPP year for predator starvation in the *second* low-NPP year. And there are a lot of deaths of hungry grazers by predation in the first low-NPP year. Trophic cascades are all death.
posted by clew at 6:59 PM on April 30, 2018 [1 favorite]

clew: With predators, you trade grazer starvation in the first low-NPP year for predator starvation in the *second* low-NPP year. And there are a lot of deaths of hungry grazers by predation in the first low-NPP year. Trophic cascades are all death.

Do either of territoriality or long childhoods limit predator population growth rates and subsequent predator death rates?
posted by clawsoon at 9:56 AM on May 1, 2018

They might, but if the predator population can't grow proportionally with the herbivore population during good grass-and-browse growth, we're back to unpredated herbivores starving to death when a bad-growth period follows a good-growth period. (Possibly with predators eating only the best bits, without killing them immediately. A bobcat in my childhood kept eating the back half of the geese.)

If the herbivores are K-selected it takes a longer boom-bust cycle to induce a starvation crash, but iirc there's usually a greater risk of the population not being able to recover from a low level. Every evolved life history strategy is a balance of resource optimization and risk management.
posted by clew at 7:33 PM on May 1, 2018 [1 favorite]