No species in a community lives completely alone. Organisms rely on other species for food, shelter, pollination and seed dispersal. This is called interdependence.
For example, many flowering plants rely on insects for pollination, so the plants can reproduce. The insects rely on the flowers for nectar, which is their food. Animals eat plants or other animals, and many birds and small mammals use trees and bushes for shelter. Some animals carry seeds to new places, which helps the plants to spread.
Because of interdependence, a change to one species can affect many others. If a predator is removed from a food web, the number of its prey may increase. The prey then eat more of their food, so the producers may decrease. If a disease kills a species, the populations of the species that fed on it can fall. A stable community is one where all the species and the environmental factors are in balance, so the populations stay fairly constant over time.