1. Constructing a DN explanation for Leopold’s article “Thinking Like a Mountain”;
For the original text, see http://www.pep.com.cn/200406/ca429154.htm
1) Any animal’s survival requires enough food. —— universal law
2) Any animal can obtain food only within its own range of activity. —— universal law
3) If there is not enough food within its range of activity, then that animal cannot obtain enough food. —— corollary of 2
4) If there is not enough food source within its range of activity, then that animal cannot maintain survival. —— corollary of 1 and 3
5) If a group of animals remains stable in a certain place, then there must be a stable and sufficient food source there. —— corollary of 4
6) Every individual animal needs to consume a certain amount of food independently. —— universal law
7) The greater the number of individuals in an animal population, the more food it consumes. —— corollary of 6
8) If one kind of animal takes another kind of animal as its main food source, then the former is called the latter’s natural enemy. And if one kind of animal takes another kind of plant as its main food source, then here too the former is simply called the latter’s “natural enemy.” —— definition
9) The existence of natural enemies constrains the number of offspring produced by that animal (or plant). —— corollary of 7 and 8
10) The increase in the number of an animal population (or plant population) is determined by its reproductive rate, while the speed of that increase is constrained by the rate at which it is preyed upon by natural enemies, the rate of natural death, and other losses such as dying of hunger due to food scarcity (or, in the case of plants, nutrient scarcity, etc.). —— universal law
11) The maintenance of numerical stability by an animal population (or plant population) in a certain region means that its rate of increase and rate of death are in mutual balance. —— reasoning obviously true from the definition and mathematical truth
12) An animal population (or plant population) maintains numerical stability in a certain region if and only if its reproductive rate and various constraining conditions remain in balance. —— 10, 11
13) If, while the reproductive rate, natural death rate, and other constraining conditions all remain stable, there is only a drastic change in the single constraining condition of being preyed upon by natural enemies, then the original balance will be broken. —— corollary
14) If natural enemies greatly decrease or even disappear, then the population’s increase will lose sufficient constraint, leading to a large increase in numbers. —— corollary of 13
15) If natural enemies greatly increase, then the population’s increase will be overconstrained, leading to a large decrease in numbers. —— corollary of 13
16) Wolves and deer are both animals; deer are food for wolves; grass, shrubs, saplings, leaves, and so on are food for deer. —— empirical fact
17) There are some mountains in the following condition. —— real observation (boundary conditions)
a) These mountains originally had wolves, and aside from wolves there were no natural enemies of deer
b) These mountains originally had deer, and aside from deer there was no suitable and stable source of food for wolves
c) These mountains originally had plenty of grass, shrubs, and saplings
d) State after state eliminated all of their wolves
e) All edible shrubs and saplings were eaten, first becoming useless things, and then dying.
f) Every edible tree lost most of its leaves, leaving only leaves above the deers’ heads.
g) Large numbers of deer died
18) The wolves, deer, and plants on these mountains were originally relatively stable. —— 17abc
19) Wolves are the deer’s natural enemies. —— 8, 16
20) The number of the deer population’s natural enemies suddenly decreased greatly or even disappeared. —— 17d
21) The deer population’s reproduction lost its constraint, and its numbers increased greatly. —— 14, 20
22) Deer are the “natural enemies” of grass, shrubs, saplings, leaves, and so on. —— 8, 16
23) The “natural enemies” of these plants increased greatly, leading to a large decrease in their numbers. —— 15, 22
24) 17ef verifies the inference in 23. —— and at the same time, 23 is an explanation of 17ef
25) Damaged grasslands are difficult to restore for decades. —— universal law
26) The deer population lost a sufficient food source. —— 23, 25, 17b
27) If there is no stable and sufficient food source, a group of animals will find it difficult to remain stable. —— 5
28) The deer find it difficult to remain stable on those mountains. —— 26, 27
29) Large numbers of deer died. —— 28
30) 17g verifies the inference in 29. —— and at the same time, 29 is an explanation of 17g
31) An incidental conclusion: the deer died because there were too many of them. —— 21, 29
Translated from the Chinese original with AI assistance. The original text is authoritative.
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