From the mathematical model in (1) diagram, it can be seen that when the number of predators decreases in the section of N 1 ~ N2, the number of predators also decreases, and the number of predators will not increase with the increase of the number of predators; From N3 to N4, when the number of prey increases, the number of predators also increases. However, when predators reach a certain level, the number of prey is decreasing. This trend reflects the widespread negative feedback regulation in the ecosystem.

(2) When the number of prey population increases, the number of predator population increases, so that the number of prey population decreases, so that the number of predator population decreases, and finally the number of prey population increases. In this way, the number of the two populations can be kept relatively stable through continuous circulation.

(3) Through the analysis of the model, if the number of predators falls below a certain threshold, the number of food species arrested will increase, while if the number of predators increases, the number of food species arrested will decrease. On the contrary, if the number of food species caught rises to a certain threshold, the number of predators will increase, while if the number of food species caught is small, the number of predators will decrease. In other words, if the number of food species caught exceeds N2, the number of predators will increase. When the number of predator population exceeds P2, the number of prey decreases, and they interact to keep the number of prey and predator in a dynamic balance at N2 and P2 levels.

(4) The relationship between predator and prey is gradually formed through long-term co-evolution. The existence of predators is also beneficial to prey, because predators mostly feed on the old, weak, sick and disabled individuals in prey, and often prey on arrested food species with large population.

So the answer is:

(1) mathematical negative feedback

(2) Increase of prey population → Increase of predator population → Decrease of prey population → Decrease of predator population → Increase of prey population → Recycle.

③N2？ P2？

(4)*** Old, sick and young in the same year? big