ECOSYSTEM DYNAMICS I pp. 405-410

Stability and Change Ecosystems are characterized by both stability and change Change can be a healthy component of the ecosystem as long as an ecosystem is resilient (ability to recover) The resilience of an ecosystem depends on three factors: biodiversity, health, and disturbances

Biodiversity Biodiversity is a measure of the variety of organisms in a given area The greater the biodiversity, the more the roles in a food web to create stability

Ecosystem Health A healthy ecosystem usually recovers quickly because they have more options for dealing with different types of disturbance or even disease

Disturbance Frequency A disturbance is an event that changes a community, removes organisms from it, and alters resource availability Moderate levels of disturbance can foster greater diversity than high or low levels of disturbance Disturbance may promote slow-growing species and inhibit dominant species from excluding less competitive species

Index of disturbance intensity (log scale) 10 0.9 1.0 1.1 1.2 1.3 1.4 Figure 54.20 35 30 25 Number of taxa 20 15 Figure 54.20 Testing the intermediate disturbance hypothesis. Index of disturbance intensity (log scale) 10 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2.0

Succession The natural, sequential, and gradual growth and change of a community There are two types of succession, primary and secondary succession

Primary succession occurs when land is first formed due to glacial retreat or as new land forms (ex. Volcanic activity) Microbes, lichens and mosses must create soil before other plants can grow. Pioneer species: first species to dominate early in succession (small and fast growing)

Secondary succession occurs when succession must start over after the destruction of a climax community A climax community is marked by the domination of long-lived species and great diversity. Takes place on sites that have already supported life Fire is a significant disturbance in most terrestrial ecosystems. In some ecosystems, fire is needed for seedlings to germinate