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CHAPTER 5 Evolution and Community Ecology 5-4 Community Stability A 2010 report on invasive species suggests that they cost the U.S. $120 billion a year in environmental losses and Invasive kudzu Lesson 5.4 Community Stability Ecological Disturbances • A community in equilibrium is generally stable and balanced, with most populations at or around carrying capacity. • Disturbances or changes in the environment can throw a community into disequilibrium. • Severe disturbances can cause permanent changes to a Forest fire Lesson 5.4 Community Stability Primary Succession • Occurs when there are no traces of the original community remaining, including vegetation and soil • Pioneer species, such as lichens, are the first to colonize. • The environment changes as new species move in, adding nutrients and generating habitat. QuickTime™ and a decompressor are needed to see this picture. Lesson 5.4 Community Stability Secondary Succession • Occurs when a disturbance dramatically alters a community but does not completely destroy it • Common after disturbances such as fire, logging, or farming • Occurs significantly faster than primary succession QuickTime™ and a decompressor are needed to see this picture. Lesson 5.4 Community Stability Succession in Water • Primary aquatic succession occurs when an area fills with water for the first time. • Disturbances such as floods or excess nutrient runoff can lead to secondary aquatic succession. QuickTime™ and a decompressor are needed to see this picture. Lesson 5.4 Community Stability Climax Communities • Ecologists once thought succession leads to stable “climax” communities. • Today, ecologists see communities as temporary, everchanging associations of species. • Communities are influenced by many factors and constant Beech-maple forest, a classic “climax community” Lesson 5.4 Community Stability Invasive Species • Nonnative organisms that spread widely in a community • A lack of limiting factors such as predators, parasites, or competitors enables their population to grow unchecked. • Not all invasive species are Did You Know? Although the European harmful. honeybee is invasive to North America, it is beneficial because it pollinates our agricultural crops.