Chapter 865 Levi's Flight

In front of the narrow cave entrance, Bifang identified the footprints of animals coming and going here.

Some of these footprints have been preserved for a long time.

The surface of the African savannah in the dry season is dry and hard, and rarely leaves footprints, unless it is a giant reptile like the Komodo dragon, whose sharp claws will leave a row of small holes on the hard ground under the action of its huge weight.

Most of what everyone saw at the entrance of the cave were left in the wet season.

There are fresher footprints, claws, and hoof prints in the cave.

"There are no large carnivores."

After looking for a long time, Bifang confirmed this.

Then he checked the surrounding environment and confirmed that there was only one entrance to this underground river within a certain range, so he took Harley to hide behind a pile of rocks, ready to wait for the opportunity.

Bifang sat on the ground next to the stone, polishing his spear.

"The quality of human life has greatly improved in recent decades - high-rise buildings, bustling streets, and beautiful night scenes are no longer new things."

"The rapid development of science and technology has made our life taste higher and higher. Things that were considered luxuries in the past can now be easily achieved."

"For three meals a day, we are no longer just pursuing a full stomach, but have higher quality requirements for taste. We pursue "delicious food."

"However, for wild animals that also live on the earth, filling their stomachs is still their primary contradiction."

"Herbivores or omnivores are optimistic. Food sources are relatively abundant. As long as they are not born in deserts or places like the Gobi Desert, there is always something to eat."

"The requirements for carnivores are relatively high. They must obtain food through hunting."

"During the hunting process, predators need to compete with prey in wits and courage, which is a double test of energy and physical strength. Even if the hunt is successful, the food obtained cannot be preserved for a long time, and there is even a risk of being robbed."

[Cheetah: I agree with both hands]

[Cheetah: That's it]

[Why x-on:Cheetah (dog head)]

[If you have discrimination, you can speak up, everyone, hahahaha]

[Harley: What B netizen]

Bifang carried the polished spear on his back, and then looked for some plants with strong smells nearby to cover his body.

Perhaps because it was close to the water source, these plants growing in the cracks of the rocks were green, much more vibrant than the bright yellow hay seen on the grassland before.

"One of our main tasks in the African savannah this time is to teach Harley how to hunt, so that he won't be stupid and can't even get meat when he lives alone on the savannah."

"But different types of predators have different temperaments, tastes and physical conditions, and their hunting styles are naturally different. We also have to demonstrate according to the characteristics of the animals themselves."

"For example, the difference in hunting styles between lions, tigers and wolves reflects the difference between cats and canines."

"Lions and tigers are very strong and agile, and the latter like to be alone; gray wolves are weaker in size and speed than lions and tigers, but living in groups greatly improves the hunting efficiency of gray wolves."

"When Canadian gray wolves capture bison, in a natural environment covered with ice and snow, they will constantly use double-teaming harassment tactics to cause the bison herd to fall into chaos, and wait for an opportunity to attack the lone bison."

"Like Big Gray Wolf, who wants to sweep the sheep village by himself This is a rare situation. "

[This example is good]

[Fang is always good at giving examples]

"Compared with wolves, tigers, as cats, seem much more arrogant. Even among the lions that hunt in groups in the public's impression, there are many male lions and a few female lions who like to act alone."

"Cat hunting emphasizes ambush, which emphasizes speed, ruthlessness and accuracy. Even if the cheetah is the king of speed, it can often catch up with it by hard pursuit, but that is actually an extra cost. Ambush is the best choice."

"So, the focus of our demonstration is on ambush."

"However, a good cook cannot cook without rice. No matter what strategy is adopted, there is a big premise for predation, that is, first of all, it must be able to find prey, otherwise, no matter how strong the predation ability is, it is just talk on paper."

"For wild animals, the most natural foraging strategy is actually to simply follow Brownian motion and Levy flight."

Brownian motion?

Levi flight?

When Bifang was talking about how to find prey, he suddenly heard a physical concept, and many viewers were a little confused.

[What is Brownian motion? 】

【Brownian motion is irregular, right? This doesn't seem to match Fang Shen's thinking. Didn't we all look for traces and tracks in the past?】

【So, can anyone tell me what Levy flight is?】

【I don't have much education, tell me quickly】

"That's right, but the subject who looks for traces and tracks, and finally determines the direction is me - a human being."

"For animals, it is really a test of their brain capacity to clearly grasp these things."

"Most animals at the top of the food chain, such as lions, tigers, wolves, eagles, crocodiles, etc., actually rely mainly on vision to find prey."

"There is no gradient difference in visual signals. If you can't see it, you can't see it. No animal has a perspective eye."

"Birds of prey like eagles have a wide field of vision and don't need to make a big fuss about foraging, but land animals like lions and tigers have to consider foraging strategies."

"Brownian motion is the most natural method without knowing the exact location of the prey."

But before Bi Fang finished explaining, the audience was even more confused.

[I’m not sure about lions and tigers, but don’t wolves rely on their sense of smell? How did it become visual? 】

[My cognition has been greatly challenged]

[Is the water in the underground river poisonous, and Fang Shen was confused after drinking it? 】

【Are you lying to me】

For a time, the barrage was filled with voices of doubt or inquiry.

"Hey, actually everyone knows too little about the world of smell."

Bi Fang scratched his head. After all, the audience did not have the same keen sense of smell as him.

The gap in perception makes everyone seem to be separated by two worlds.

After thinking for a while, he gave an example that he thought was more appropriate.

"Let's put it this way, if an alarm clock is placed in a room on the second floor of a villa, and you sit in the living room on the first floor and rely solely on hearing, can you accurately determine which room on the second floor the alarm clock is in?"

"I think most people can't do it. In the animal world with a keen sense of smell, their sense of smell plays the same role as our hearing at this time. They know that the prey is on the second floor, but they don't know In which room, and smell is more ambiguous than hearing.”

"As long as you stay in one place for a long time, you can create two birthplaces with strong smells. This is impossible to do in the world of sound."

[A little confused, but I feel like I’ve caught something again (face covering)]

[It seems to make sense]

[unclear]

"Everyone should be familiar with Brownian motion. It is the never-ending irregular motion of particles suspended in liquid or gas, a continuous random process."

"In fact, Brownian motion may seem inconspicuous, but its discovery is a major development in physics and has had a huge impact on human understanding of the universe."

“The behavior of many creatures in nature also obeys this point invisibly. Animals that perform Brownian motion are like coming to the second floor and randomly entering a room to search. And from a data perspective, this is the most efficient one. way.”

"Its step length obeys a normal distribution, just like a random walk, its step length and direction are discrete. Although Brownian motion and random walk are two concepts, they have each developed a different set of theories. But the mathematical nature of the two is the same, and there is virtually no difference in the efficiency of finding prey regardless of which foraging strategy the predator uses."

"But if a predator really does Brownian motion aimlessly like a headless fly, can it really find its prey very effectively?"

Bi Xiang asked the audience a question.

But you don’t need to answer to know that the answer is no.

"It can be proved mathematically that Brownian motion is the same as the free diffusion of molecules. The average displacement of molecules with unit speed in time t is only square root t."

"If a predator uses this method to find prey, it may have to travel across thousands of mountains and rivers to succeed."

"So before that, there is another way to determine which villa in the community the alarm clock is in. This is another mathematical concept, Levi's flight."

“The person who discovered Levi’s flight was Paul Pierre Levi, the mentor of the French mathematician Benoit Mandelbrot. He first discovered that many random movements of life belong to Levi’s flight, and also contain a small part of Brownian motion. "

"This is a relatively complex concept, so I won't explain it in detail, but there is an example that everyone should be familiar with. The flight trajectory of flies is based on Levi's flight. This principle makes their flight trajectories elusive and helps flies Avoiding predators and humans trying to knock their little heads off.”

"Levi's flight is a fractal, which means that no matter how many times it is magnified, it still looks similar to the original pattern."

"More importantly, Levi's flight is a random walk, which means that its trajectory cannot be accurately predicted and is as ghostly as the pace of a fly."

"Brownian motion has a characteristic, that is, the step length of each step is concentrated in a region, and the graph is a bell-shaped curve."

"That's not the case with Levi's flight. In the Levi's flight diagram, the distance traveled per step follows a power law."

"In other words, most of the steps in exercise are short, but a small number of steps are very long."

[I’m not good at math, you’re right]

[That’s it, another lesson on listening to the Book of Heaven]

[Damn it, without some knowledge of physics and mathematics, can’t you survive in the wilderness? 】

Most of the viewers in the live broadcast room were basically confused when they heard this.

“The different nature of the steps of Levi flight and Brownian motion directly results in Levi flight being more efficient than Brownian motion.”

"When walking the same number of steps or distance, Levi's flight displacement is much larger than that of Brownian motion, and it can explore a larger space."

"This is critical for creatures that need to navigate uncharted territory."

"For example, marine predators such as sharks use Brownian motion when they know there is food nearby, because Brownian motion helps 'disc' - opening and clearing a small area of ​​hidden food."

"But when food becomes scarce and new territory needs to be colonized, marine predators abandon Brownian motion and adopt Levi's flight strategies."

[I wish I had said this earlier, it was just a matter of luck]

[Summary: Try your luck when shopping]

[I would like to call Fang Shen’s room juxtaposed with Schrödinger’s cat! 】

[Black bitter buckwheat tea is given to the anchor yacht*1 - although I don't understand, I give a thumbs up to Fang Shen's professionalism. ]

Behind the stone, Bifang and Halley, who was resting again, looked around to see if there were any prey coming.

At the same time, they continued to chat with the audience.

"In 2008, a research team from Central China and the United States published a study in Nature: 55 different marine predators in the Atlantic and Pacific Oceans, including silky sharks, swordfish, blue marlin, yellowfin tuna, turtles and penguins, were given trackers to track their movements for 5,700 days."

"After analyzing their movements 12 million times, it was found that most marine predators prefer Levy-style movements when food is scarce."

"What's more interesting is that the distribution of prey, such as krill, also conforms to the characteristics of Levy flight."

"Not only that, the routes of amoeba, plankton, termites, bumblebees, large terrestrial herbivores, birds, primates, and indigenous peoples in the soil when foraging also have similar patterns."

"Levi flight seems to be a biological phenomenon when resources are scarce common law of survival in an environment lacking food."

"For wandering animals, finding the next meal depends not only on luck, but also on advanced mathematics."

"With almost no knowledge of the distribution of prey, the efficiency of Levy flight is much higher than that of Brownian motion. This may be the reason why they will switch to Levy flight mode when they try their luck."

"Therefore, biologists later proposed the Levy flight hypothesis to summarize the coquettish movements of animals when they leave everything to fate."

"However, just because wild animals leave everything to fate does not mean that Halley has to leave everything to fate. We can help it realize that the probability of encountering prey in some places will be greater, and it can just do Brownian motion in a few fixed locations to help it survive better on the grassland."

[Referee, I report the opponent for cheating!]

[Report invalid!]

[What a boast, you are the first anchor I have ever seen who talks about math knowledge seriously outside the outdoor board]

[It's true that if you learn math, physics and chemistry well, you won't be afraid to travel around the world. 】

[You think that math, physics and chemistry cannot survive in the wilderness, but in fact, you just know too little and haven't learned them thoroughly (funny)]

After sitting behind a rock with Harley for a long time, Bifang finally encountered his first real prey on the grassland at noon.

An ostrich!