An area being taken over by outside species is one major cause of ecological succession. Depending on the species, this can take place rapidly or gradually. For a species to continue flourishing in a certain location, an assortment of environmental factors must remain constant. The introduction of a new and unfamiliar species into a habitat has the power to throw the current occupants' lives into disarray.
There are three stages involved with invasion by other species: migration, ecesis and aggregation. The first stage refers to the arrival of a new species into an already occupied area. The second stage refers to how well the new species adjusts to the area's ecosystem. The third stage involves the reproduction of the species after it has familiarized itself with its new place of residence.
Human interference is another major cause of ecological succession. This type of ecological succession tends to be more rapid than natural forms of succession, because of the use of heavy machinery, pesticides and controlled fires. Species that have inhabited certain areas for many years can be driven from their homes overnight if human interference takes place on a large enough scale.
There are varying degrees of human interference. Cutting down some trees in your yard to make room for a vegetable garden or storage shed is a prime example of small scale human interference. Larger scale human interference takes place in the form of leveled forests and drained lakes. Sometimes human interference occurs accidentally, as is the case with forest fires.