1. Every environment is a result of a delicate balance of organisms, nonliving objects, landforms, weather and climate. Any adjustment to any of these factors can result in a dramatic change in an environment’s appearance or composition. Many influences on an environment can come from nature itself. The environment of the far north tundra of North America is very different in July than it is in January. In July the ground is covered with green foliage, and animals forage and graze. In January the ground is frozen and desolate, and the animals have migrated to warmer locations. Even in more temperate areas, summer brings warmth, greenery, and an abundance of insects, and winter produces chilly weather and the grass and plants become brown and dormant.

2. These changes in temperature and plant life have a dramatic effect upon many species of animals living in an ecosystem. Some animals, such as bears, amphibians and reptiles, move into a state of hibernation after finding a safe place of refuge away from predators and weather. Other animals, such as geese, ducks, and elk, migrate to warmer locations to spend the winter in a warmer location with appropriate food sources and then return when the weather warms in the spring. The physical characteristics of an environment can also determine the suitability for life of organisms. The high, craggy mountains are ideal habitats for mountain goats, whereas the rolling plains are the environment of choice for the pronghorn antelope.

3. Sometimes rapid environmental changes can change an ecosystem dramatically. When a hurricane crashes ashore bringing with it a huge amount of salty, ocean water, the freshwater ecosystem that existed before the storm will be affected. In areas of severe drought, the ecosystem which was dependent upon a plentiful supply of water will disappear, and plants and animals which can exist on far less water will move in. When an ecosystem changes rapidly, an existing organism is faced with one of two fates. If the organism has the ability to move it may migrate, seeking a more compatible ecosystem. If it cannot change locations, however, it may die. Its destruction results from lack of food, suitable water, or some other change in the ecosystem composition.

4. Beyond natural changes to an ecosystem, living organisms themselves can alter an environment and affect other organisms. In a forest a group of beavers builds a dam across a small stream creating a small pond or lake. The pond attracts more animals because of the availability of water, and the populations of fish, frogs, and other aquatic animals flourish. A swarm of locusts invades a field of grain stripping every leaf from the plants, and small animals which depended upon the plants for food are forced to migrate elsewhere. Humans are dramatically changing environments in many different ways. Trees and plants are cleared to build homes, shopping malls, and roads, that all change or affect the ecosystem.