An ecosystem is the combination of all living and non-living things functioning within a particular habitat. Natural ecosystems are, of course, our life support system, providing basic requirements such as oxygen, food, and water. In the Houston region, natural ecosystems have been lost and most, if not all, have been degraded to some extent. It is difficult to repair or replace ecosystems. Thus, habitat alteration and loss is one of the four highest environmental risks facing the Houston region.
Evolution continues to take place within native ecosystems, but only gradually over many centuries.
Rapid loss of habitat, such as occurs in urbanizing areas, is a threat because the ecosystem cannot easily recover. Once an ecosystem is lost it is unlikely to be regained. A particular ecosystem or group of ecosystems provides several functions. For example, barrier islands are actually a system of ecosystems that have worked together to withstand hurricanes for thousands of years. They also aid in flood control and irrigation by removing water from surrounding land.