living things require water for survival & water is a kind of natural resource ->  water is a kind of resource that living things require for survival  water is a kind of resource that living things require for survival & when available resources decrease in an environment , organisms have to conserve those resources ->  when the availability of water decreases in an environment, living things in that environment must conserve water to survive  a dry environment is low in availability of water & a desert environment is a dry environment ->  a desert environment is low in availability of water  when the availability of water decreases in an environment, living things in that environment must conserve water to survive & a desert environment is low in availability of water -> living things in a desert environment must conserve water to survive