As you enter a natural community, you may notice some plants and animals that seem to be the most abundant. These are generally the most conspicuous and can be indicators of a type of ecosystem. Many of the plants found in a particular natural community are seldom found elsewhere.
Plants are dependent on a particular soil type, topography and climate through biological adaptation. Because of their immobility, plants generally require those components that are specific to a site. You would not expect to see a large stand of sugar maples growing in the sandy soils of a jack pine forest.
Certain animal life is also characteristic of natural communities. For example, bluebirds seek standing snags with shallow cavities for nesting and roosting and wont be found in communities without these or a suitable alternative.
Indicator species are used as a standard in identifying similar communities. Their decline may indicate a disturbance that alters the ecosystem. Disturbances may result from natural events: glaciation, climatic changes, volcanic activity, fires, floods, disease and wind; or man-made events: development, over-harvest, alterations to hydrology or other ecological processes including fire-suppression, introduction of non-native species.
Some species depend on a frequent disturbance, while others cannot tolerate any disturbance.