Natural family planning

 　　When discussing ecological balance, the reproductive capacity of organisms naturally comes to mind. In reality, besides natural predators, the population size of each organism is also constrained by its own reproductive capacity. A close observation of the living world reveals an interesting fact: the lower the organism, the stronger its reproductive capacity; for example, bacteria can divide at an extremely rapid rate. Conversely, the higher the organism, the weaker its reproductive capacity; for example, humans' reproductive capacity is vastly different from that of bacteria! Furthermore, generally speaking, plants have a strong reproductive capacity while animals have a weak one, and herbivores have a strong reproductive capacity while carnivores have a weak one. Thus, nature seems to be implementing a form of family planning, setting a limit on the number of each organism—what we might call a "life switch."

　　To illustrate this, let's look at the African savanna. On that vast plain, one often sees several lions or a pack of hyenas chasing hundreds or thousands of buffalo or zebras. Then, a buffalo or zebra is caught in the jaws of a predator. It howls in agony, struggling desperately, while its kin turn a blind eye, as if nothing has happened. Before long, the tragedy will repeat itself. Can you imagine that this life-or-death struggle has been going on for hundreds of thousands, even millions of years? Logically, even the most foolish creature should be able to learn from this, summarize some experience. Not to mention using sharp teeth and claws to fight off predators, even if they all joined forces and charged at lions or hyenas, they would crush them into mincemeat. However, buffalo and zebras continue to be eaten, their only resistance being to reproduce, as if they were born solely to fill the bellies of lions and hyenas.

　　If you have the opportunity to go to the Arctic, it's even more interesting, with its unique ecosystem. Because of the hundreds of meters of permafrost underground, as hard as stone, tree roots cannot penetrate, so there are no trees, only wild grass, forming a thin layer of turf. Due to the short summers and low temperatures, the variety of wild grasses is limited and their growth is slow, making it impossible to support as many herbivores as in Africa. Only lemmings, hares (limited in number), caribou (migrating), and musk oxen (nearly extinct) survive. Among them, lemmings are the most important herbivores in the Arctic, as they must provide sufficient food for weasels, foxes, skuas, and snowy ospreys. Thus, the tiny lemming becomes a crucial link in maintaining the ecological balance of the Arctic. However, nature faces a significant problem: if there are too many lemmings, they will devour all the grass, cutting off the food supply for the herbivores; if there are too few, weasels, foxes, skuas, and snowy ospreys will go hungry. Therefore, nature employs a cruel solution: endowing lemmings with an extremely high reproductive capacity, but when their numbers exceed a certain limit, they are forced to commit mass suicide.

　　A lemming litter can produce a dozen or more offspring, which mature in 20 days and then begin to reproduce. If they were allowed to reproduce freely, the original two could multiply into hundreds of thousands in a year. At that point, if you went to the Arctic grasslands, you'd see lemmings bustling about everywhere. However, the Arctic grassland vegetation, with its short growing season and limited growth, couldn't possibly feed them all. So, the lemmings were forced to commit suicide. They could form massive herds of hundreds of thousands, traversing mountains and rivers, attacking anything they encountered, even cars. Their final destination was the sea, where they would leap in without hesitation, huddling together, leaving the ocean filled with the bodies of their fallen comrades. This scene has been observed in Norway, Finland, Sweden, Russia, and Alaska.

　　However, not all lemmings joined the suicide charge; some survived and continued to reproduce. Strangely, lemmings don't reproduce in such large numbers every year; it's cyclical, with periods of both large and small populations. In a small year, lemmings are few in number; you could walk for a long time on the grasslands and not encounter a single one. In years like these, foxes and snowy ospreys suffer greatly. They not only starve themselves but also endanger their offspring, forcing them to reproduce less or not at all. For example, in the Arctic Circle region of Alaska, lemmings have been scarce in recent years, leading to a

　　significant decline in fox populations, while snowy ospreys have virtually disappeared. This strange "life switch" isn't limited to lemmings; foxes also experience this. In years when lemmings reproduce freely, foxes also multiply due to abundant food. However, when their numbers or density reach a point that threatens the ecological balance, they contract a strange disease called "mad dancing," causing them to dance wildly until they die of exhaustion.