(1) The unified whole formed by organisms and the environment in a certain area is called an ecosystem. The components of an ecosystem include biotic parts and abiotic parts. The abiotic parts include sunlight, air, temperature, and moisture. , soil, etc., organisms include producers (green plants), consumers (all animals) and consumers (saprophytic bacteria and fungi,) both of which are indispensable. From the perspective of the components of the ecosystem, the plants in the picture belong to the producers of the farmland ecosystem.

(2) In the ecosystem, the food relationship between producers and consumers forms a food chain. From the perspective of the relationship between organisms and the environment, the relationship between the frogs and insects in the picture is a predatory relationship. ?

(3) In the ecosystem, toxic substances (heavy metals, etc.) are enriched as the trophic level increases in the food chain. The higher the trophic level, the higher the accumulation of toxic substances. This ecosystem contains two food chains, plants → rats → snakes, and plants → insects → frogs → snakes. The longest one is plants → insects → frogs → snakes. Snakes have the highest trophic level in this farmland ecosystem. Therefore, the most pesticides are accumulated.

(4) In this farmland ecosystem, frogs prey on insects. If farmers kill frogs, insects will lack natural enemies and multiply in large numbers. Plants will decrease accordingly, causing an imbalance in the ecological balance.

So the answer is: (1) Producer?

(2) Predator?

(3) Snake?

(4 ) Frog hunting will reduce the number of frogs, insects will breed in large numbers due to the reduction of natural enemies, and crops will be severely damaged, resulting in reduced yields.