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Transcript
35.5 Disturbances are common in communities Objectives • Describe how disturbances can have positive and negative effects. • Compare primary and secondary succession. • Explain how human activities can affect species diversity. Vocabulary • ecological succession • primary succession • secondary succession • introduced species Disturbances to Communities • continually changing – fires, floods, droughts, etc. • not always negative • sometimes human-caused Ecological Succession • The series of predictable changes that occurs in a community over time is called succession. • To remember: Think of succession as it relates to monarchies (governments based on kings and queens). Primary Succession • primary succession: the series of changes that occur in an area where no ecosystem previously existed • Examples: new island, area of rock uncovered after ice melts Pioneer Species • pioneer species: the first species to populate an area • To remember: The Wright brothers were pioneers of aviation. Pioneer Species • These are often lichen and mosses carried by wind and water. • little needed to survive • They break rock as they grow. • In death, they provide nutrients to develop soil. So what happens next? • Plant seeds land in this soil. • Over time, soil grows richer. • Eventually the community becomes stable unless disrupted. • Stability can take centuries! Secondary Succession • secondary succession: the series of changes that occur after a disturbance in an existing ecosystem • causes: fires, hurricanes, tornadoes, farming, logging, mining • faster than primary succession Human Activities and Species Diversity • humans have greatest impact on communities • 60% of Earth’s land used by humans • negative effects on diversity Clearing the Land • forests cut down • plains used for farming • diverse forest or grassland used to grow single crop Introduced Species • organisms that humans move from native location to a new area • intentional and accidental • can disrupt ecosystem for native organisms
