a lake is a kind of body of water & a body of water is a kind of environment ->  a lake is a kind of environment  a lake is a kind of environment & as population of predators increases , the population of prey will decrease in an environment ->  as the population of predators in a lake decreases the population of prey will decrease in that lake  as the population of predators in a lake decreases the population of prey will decrease in that lake & population is a measure of the number of a species in an environment ->  as the number of predators in a lake decreases the number of prey will decrease in that lake  predators eat prey & if an animal eats other animals for food , then the animal will be the predator ->  if an animal eats another animal then the animal will be the predator and the other animal will be the prey  if an animal eats another animal then the animal will be the predator and the other animal will be the prey & fish eat insects ->  fish are predators to insects and insects are prey to fish  as the number of predators in a lake decreases the number of prey will decrease in that lake & fish are predators to insects and insects are prey to fish ->  as the number of fish in a lake increases the number of insects in that lake will decrease  as the number of fish in a lake increases the number of insects in that lake will decrease & if something decreases in number then there will be fewer of that something -> if the number of fish in a lake increases there will be fewer insects in that lake