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Fish Markets: Cooperation and Competition in the Undersea "Economy"

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You probably know that hermit crabs live in shells. What you might not know is that really nice shells to call home are a scarce commodity, and hermit crabs consequently have some pretty cool ways of optimizing the ways they acquire and occupy their shells.

A study of the purple-clawed hermit crabs (Coenobita clypeatus) on an island off the Belizean coast reveals that the crabs fill shells using "vacancy chains"—social structures through which vacancies in certain resources propagate through a population, like the ways humans fill jobs and apartments.

Synchronous and Asynchronous Vacancy Chains

The hermit crabs were observed to use two types of vacancy chain: synchronous and asynchronous. An asynchronous chain is when one crab moves into a new, empty shell and abandons its old one to be found by another crab, which abandons its own for another crab to find, etc. With this type of chain, shell switching is sequential and the crabs experience little to no interference or competition. They have the opportunity to investigate any vacant shells they find and can directly compare their current shell with a new shell by switching back and forth between the two. It's sort of like when you look at apartments that have just been moved out of and are available immediately or in the near future. If you take one of those apartments, someone else can check out and move into yours, someone else will move into theirs, etc., in an orderly fashion.

Synchronous vacancy chains are more social and much more interesting. They start off with "waiters," crabs that hang around a shell that's too big for them, and wait for a bigger crab to come along so that if the big crab moves in to the vacant shell, the waiter can grab their more appropriately-sized hand-me-down shell. (The researchers note that the decision to wait, and how long to wait, based on previous experience, provides some evidence that the crabs are smarter than we thought.)

As a crowd gathers—a crowd always gathers, but no one knows how; the researchers think the waiters may use vocal or chemical signals to draw attention to the vacancy—the crabs queue up by size, from largest to smallest. Once the largest crab switches into the vacant shell, each crab climbs into a new shell as it's vacated by the slightly larger crab ahead of it, quickly shuffling vacancies (literally) down the chain. A similar type of chain happens in college towns across America every fall. Students spend months "lining up" by finding apartments, packing and labeling boxes, and then—BAM!—a few thousand kids move in and out of apartments in one day.

Here's a synchronous chain in action.

The Undersea Service Industry

Moving away from real estate and into the service industry, animals still behave kind of like humans. They partner with other animals that provide the high-quality goods and services, cheat each other, and then threaten to take their business elsewhere in order to get what they want.

"Cleaner fish," which remove dead skin and parasites from other fish in a mutually beneficial relationship (they get a meal, and the other fish get groomed), have been known to make their "clients" wait for service and cheat them by feeding on healthy tissue or mucous instead of parasites. Clients don't have many options for ensuring good service. They can't demand their mucous back or complain to the Better Business Bureau. What they can do is go get cleaned somewhere else.

A study by a University of California, Santa Barbara biologist found that individuals of one type of cleaner fish near French Polynesia, the luestreak cleaner wrasse, have to compete for access to their preferred clients, the ornate butterfly fish. This competition gives clients with easy access to multiple "cleaner stations" - areas where the cleaner fish hang out and do their thing - the ability to get better service from cleaners, who apparently are cued to the fact that their customers can easily take their business elsewhere and are discouraged from cheating them.

This story originally appeared in a different format on Matt's website.

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Man Buys Two Metric Tons of LEGO Bricks; Sorts Them Via Machine Learning
May 21, 2017
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iStock // Ekaterina Minaeva

Jacques Mattheij made a small, but awesome, mistake. He went on eBay one evening and bid on a bunch of bulk LEGO brick auctions, then went to sleep. Upon waking, he discovered that he was the high bidder on many, and was now the proud owner of two tons of LEGO bricks. (This is about 4400 pounds.) He wrote, "[L]esson 1: if you win almost all bids you are bidding too high."

Mattheij had noticed that bulk, unsorted bricks sell for something like €10/kilogram, whereas sets are roughly €40/kg and rare parts go for up to €100/kg. Much of the value of the bricks is in their sorting. If he could reduce the entropy of these bins of unsorted bricks, he could make a tidy profit. While many people do this work by hand, the problem is enormous—just the kind of challenge for a computer. Mattheij writes:

There are 38000+ shapes and there are 100+ possible shades of color (you can roughly tell how old someone is by asking them what lego colors they remember from their youth).

In the following months, Mattheij built a proof-of-concept sorting system using, of course, LEGO. He broke the problem down into a series of sub-problems (including "feeding LEGO reliably from a hopper is surprisingly hard," one of those facts of nature that will stymie even the best system design). After tinkering with the prototype at length, he expanded the system to a surprisingly complex system of conveyer belts (powered by a home treadmill), various pieces of cabinetry, and "copious quantities of crazy glue."

Here's a video showing the current system running at low speed:

The key part of the system was running the bricks past a camera paired with a computer running a neural net-based image classifier. That allows the computer (when sufficiently trained on brick images) to recognize bricks and thus categorize them by color, shape, or other parameters. Remember that as bricks pass by, they can be in any orientation, can be dirty, can even be stuck to other pieces. So having a flexible software system is key to recognizing—in a fraction of a second—what a given brick is, in order to sort it out. When a match is found, a jet of compressed air pops the piece off the conveyer belt and into a waiting bin.

After much experimentation, Mattheij rewrote the software (several times in fact) to accomplish a variety of basic tasks. At its core, the system takes images from a webcam and feeds them to a neural network to do the classification. Of course, the neural net needs to be "trained" by showing it lots of images, and telling it what those images represent. Mattheij's breakthrough was allowing the machine to effectively train itself, with guidance: Running pieces through allows the system to take its own photos, make a guess, and build on that guess. As long as Mattheij corrects the incorrect guesses, he ends up with a decent (and self-reinforcing) corpus of training data. As the machine continues running, it can rack up more training, allowing it to recognize a broad variety of pieces on the fly.

Here's another video, focusing on how the pieces move on conveyer belts (running at slow speed so puny humans can follow). You can also see the air jets in action:

In an email interview, Mattheij told Mental Floss that the system currently sorts LEGO bricks into more than 50 categories. It can also be run in a color-sorting mode to bin the parts across 12 color groups. (Thus at present you'd likely do a two-pass sort on the bricks: once for shape, then a separate pass for color.) He continues to refine the system, with a focus on making its recognition abilities faster. At some point down the line, he plans to make the software portion open source. You're on your own as far as building conveyer belts, bins, and so forth.

Check out Mattheij's writeup in two parts for more information. It starts with an overview of the story, followed up with a deep dive on the software. He's also tweeting about the project (among other things). And if you look around a bit, you'll find bulk LEGO brick auctions online—it's definitely a thing!

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May 23, 2017
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