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Ecological Succession
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Ponder this…. Do communities change?
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Ponder this…. Do communities change? yes, of course What makes them change?
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Ponder this…. Do communities change? yes, of course What makes them change? something about the environment changes, may be huge or small, natural or man-made, sudden (a disturbance) or gradual (abiotic factors change as the community changes) How do they change?
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Ponder this…. Do communities change? yes, of course What makes them change? something about the environment changes, may be huge or small, natural or man-made, sudden (a disturbance) or gradual (abiotic factors change as the community changes) How do they change? gradual change over time as species are replaced by other species
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Ponder this…. Do communities change? yes, of course What makes them change? something about the environment changes, may be huge or small, natural or man-made, sudden (a disturbance) or gradual (abiotic factors change as the community changes) How do they change? gradual change over time as species are replaced by other species For a given area, is change predictable?
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Ponder this…. Do communities change? yes, of course What makes them change? something about the environment changes, may be huge or small, natural or man-made, sudden (a disturbance) or gradual (abiotic factors change as the community changes) How do they change? gradual change over time as species are replaced by other species For a given area, is change predictable? sort of…. If you could stand in a cleared field in Georgia for 500 years, what would you expect to see?
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disturbance This change in a community over time is called ecological succession
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Ecological Succession Definition: a gradual process of change and replacement of the types of species in a community The sequence of changes is somewhat predictable May take place over hundreds or thousands of years
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Two types of ecological succession Primary succession: occurs on a surface where no ecosystem existed before (no soil) Secondary succession: occurs on a surface where an ecosystem has previously existed but has been disturbed (soil is present)
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Primary Succession On new islands created by volcanic eruptions On sand dunes
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Primary Succession Where glaciers have retreated
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Primary Succession Paved areas that are abandoned
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Primary Succession Begins with pioneer species (defined as the first species to colonize a disturbed area), like lichens, that can grow directly on rock; begin the breakdown of the rock to form soil
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Primary Succession Once rocks begin to weather and crack, soil forms and small plants can take root
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Primary Succession Larger plants continue to move in until the bare ground is covered with life
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Secondary Succession Definition: type of ecological succession that occurs on a site where an ecosystem previously existed (soil is present) Due to a disturbance to the ecosystem – something upsets the natural balance May be natural or man-made (anthropogenic) disturbances Think of examples of each….
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Examples of natural disturbances tornadoes, floods, trees falling, fire, hurricanes, disease
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Examples of man-made (anthropogenic) disturbances deforestation, pollution, urbanization, harvesting
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‘General Ecology’, D.T. Krohne
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Secondary Succession After a disturbance, pioneer species move in, followed by other species in a somewhat predictable sequence
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Typical stages of secondary succession in woodlands Early: plants typically small with short lifecycles (annuals, grasses), rapid seed dispersal, environmental stabilizers (pioneer species) Middle: plants typically longer lived, slower seed dispersal, and usually larger Late: plants and animal species are those associated with older, more mature ecosystem: larger, slower dispersal, better competitors, slower growth Climax community: final stage of succession that will last as long as there is no disturbance
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Each stage of succession brings about changes in the ecosystem that enable or prevent certain species from moving in – better soil, less light, more competition as ecosystem matures Some changes may help other species – called facilitation (example: dogwood trees grow well under the shade of larger trees) Some changes may hinder other species – called inhibition (example: black walnut produces a chemical that keeps other plants from growing near it)
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Even though the stages can be generally predicted, stages of succession can vary, depending on local conditions Amount of rain, temperature, terrain, latitude, altitude, soil type, human impact
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Succession in two forests: What causes the difference in these climax communities? Succession in the boreal forest (for example in Canada) – climax species are fir, spruce, hemlock For example, eastern U.S. - climax species are oak, hickory, maple
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Even in one location, the climax community depends on many factors
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Current way of thinking: instead of one stable, final climax community, there are patches that are constantly changing within an ecosystem (called patch dynamics)
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Identify the “patches” around this school in the southeastern U.S. Although in the “deciduous forest”, it is not that simple….
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We can see changes in the animal communities over time, too
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© 2003 John Wiley and Sons Publishers Fig 10.7 Diagram of bog succession. Ecological Succession can occur in aquatic ecosystems
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© 2003 John Wiley and Sons Publishers Fig 10.8 Graphs showing changes in biomass and diversity with succession. Changes in Biota
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© 2003 John Wiley and Sons Publishers Fig 10.9 Changes in soil nitrogen and phosphorus. Changes in Abiotic Factors
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