35.5 Disturbances are common in communities
Feb 15, 2016
35.5Disturbances 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