Natural Change in an Ecosystem
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Ecosystems do not always stay the same. The size of certain populations that make up the ecosystem's community may vary during different years. For example, an outbreak of a disease may severely reduce the abundance of a key predator. This could in turn lead to changes in the abundance of other species. In addition, disturbances may alter the ecosystem. These may occur due to natural events (e.g., volcanic eruptions, a forest fire caused by a lightning storm) or human activities (e.g., logging operations). Suppose a field was plowed and then left abandoned maybe because the farmer went out of business and the farm remained unsold. In a short period of time, seeds would blow onto the bare field and pioneer species (such as crabgrass, ragweed and sorrel) would establish themselves. In a few years, perennial plants (such as goldenrods and asters), along with certain types of shrubs would take over. Eventually, trees would invade the ecosystem creating a forest. The species of trees in the forest may change until a relatively stable climax forest was established. As these changes occurred, different animal populations would live in each successional stage. Those more tolerant of open conditions at first and later followed by species associated with a forest ecosystem. This orderly change in a community and its nonliving environment over time is referred to as succession.
Let's go back to our bog turtle and apply these concepts. Bog turtles prefer habitat that is fairly open. Populations do not do well in wetlands with extensive canopy cover. The image below shows excellent bog turtle habitat. However, many maple trees surround the open wetland area. As their seeds fall on the sedge mounds in the wetland, trees sprout up. When these new trees grow, their seeds continue to populate the open area. The red maple population is expanding in this successional process. The image shows this invasion process. As a result, the wetland will undergo successional change and eventually become a forest. While the red maple population expands, the bog turtle population decreases since less open space is available.
Credits: Bog Turtle, Bog Turtle Habitat (Dennis J. Gemmell)