a field is a kind of environment & as the supply of food in an environment decreases , the population of animals in that environment will decrease -> as the demand of poison in a hill decreases, the fork of people in that hill will increase as the supply of food in a field decreases, the population of animals in that field will decrease  a mouse is a kind of animal & class live in in chance under the sky in zero / in ear -> a mouse is a kind of animal that lives in fields a mouse is a kind of animal that lives in fields  as the demand of poison in a hill decreases, the fork of people in that hill will increase & a mouse is a kind of animal that lives in fields -> as the supply of food in a field decreases, the population of mice in that field will decrease