Ecological Succession


General Definition: The gradual change over time in the species that form a community1



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*You should watch from 4:31 if you don't want to watch the whole thing. He does a great job of explaining
the appearance and disappearance of species. It's something you should know.


PRIMARY SUCCESSION

  • Definition: succession in an area that has no plants, animals or soil1
  • Takes place on barren rock/mineral deposits1
  • Thermal energy, ash and lava from a volcano eruption destroy all living things and cover existing soil which makes a site for primary succession1
  • Lifeless surfaces exposed by retreating glaciers or explosions also create a site for primary succession1
  • Primary succession begins when pioneer species colonize a bare surfaceSuccession increases the biodiversity of an environment1
    • The type of species that will colonize depends on the environment - temperate forest trees won't colonize in the Tundra, it's too cold1
  • Succession changes the biotic/abiotic factors of an ecosystem1
    • Biotic changes are most obvious - species and their population change throughout succession1
    • Abiotic changes include acidity, type, and temperature of the soil. It also includes the availability of sun light and water1
  • As biotic/abiotic factors change, the type of species change - some species favour a different type of environment, resulting in their decline1

Example of Primary Succession: (takes about 200 years)
  1. A glacier retreats, land is exposed - there's no shade, soil, or shelter1
  2. Pioneer organisms, such as lichens, colonize the rock1. They don't need soil to get nutrients1. They secret acid which erodes the rock, creating soil1.
  3. Mosses/very small plants colonize the area1. They keep water in the soil, stablizing it1. Insects, birds, and small animals feed on the plants1. Plant/animal decomposition builds soil1.
  4. Small herbaceous plants replace mosses1. Their roots break up the rock below1. They add nutrients when they decompose, further building soil1. Plants provide food/shelter for more species e.g. worms, small mammals1
  5. Large herbaceous plants/small shrubs begin to grow1. More shelter is available for more species1. Plants provide food/habitat for a wider range of mammals1. Waste/decomposition from these species further enriches the soil1.
  6. Trees/ Larger shrubs provide more shade and moderate wind/temperature1. Plants cycle nutrients and water through community1. A climax community has been formed3.
*NOTE: once the community is fully developed and stable, it will still respond to environmental changes e.g. Global Warming1. The environment will become warmer and dryer, giving rise to species that are drought resistant1.


SECONDARY SUCCESSION (see figure 1)

  • Definition: succession in an ecosystem that has been disturbed by a natural event or human activity1.
  • Natural events include: forest fires, floods, and violent storms (tornadoes, hurricanes)1.
  • Human activities include: forest harvesting, clearing land for agriculture/construction1.
  • Secondary succession does not take place on a barren surface1. It happens where there is soil that still has some organic matter or small plants in it1.
    • This allows plant populations to establish more quickly in secondary than primary1.
    • Pioneer species also occur in secondary succession1
  • Secondary succession can also happen in an aquatic environment1.
  • Abiotic/biotic factors of the environment are influenced by secondary succession1

external image succession.jpg
Figure 1 4 - Example of Secondary Succession


HUMAN ACTIVITY AND SUCCESSION

Humans get in the way of succession1. We limit it through our activities1.One common example would be your front yard and back yard1. Both are dominated by grass, and you would not let any other species of plant grow there, such as weeds, etc.1. You would stop them from colonizing the grass by weeding or using a herbicide1. This decreases the biodiversity of plants and animals1. As a solution, some home owners allow native species to colonize their gardens1. It reduces negative effects on succession1. Another example would be forestry1. Instead of cutting down all trees and limiting succession (those tress won't be able to colonize the land, slowing down succession), companies are cutting down specific trees of a special size1.On the other hand, humans can help advance succession (see figure 2)1. Parks and school yards are planting species that would rise eventually due to succession1. This helps it along1. However, it is important not to plant species that would rise in later stages of succession1. The ecosystem won't be able to support those species1. Plants that would occur in the early next stages should be planted1.
external image 1164719_f23c5826.jpg
Figure 2 5This sign is preventing humans from entering so they won't disturb the development of the ecosystem, a.k.a. succession


MINI QUIZ


  1. Where does Primary Succession occur?
  2. What creates a site for primary succession?
  3. Where does Secondary Succession occur?
  4. Give examples of situations that allow for secondary succession to occur.
  5. What is a pioneer species and how is it effected by the type of environment?
  6. Explain abiotic and biotic changes within succession. Give an example of each.
  7. How do humans effect succession? Give an example with the solution.



Answers

  1. On barren rock/mineral deposits
  2. glaciers retreating or volcanoes
  3. On surfaces where the soil is still there. The soil would still have some organic matter to it and maybe small plants
  4. Tornadoes, forest fires, etc...
  5. Pioneer species = first species to colonize the area. The abiotic/biotic factors effect which type of organism colonizes the area. Some organism don't like the heat or cold and won't colonize those type of places.
  6. Biotic - species change through out succession. Some trees populations will decrease due to bigger and stronger trees taking their place. Abiotic - acidity of soil, temperature, etc... changes throughout succession. With the addition of trees, the availability of sunlight decreases, resulting in a cooler climate
  7. Humans limit succession. Through forestry,companies cut down many trees, slowing down succession. To fix the problem, some companies only cut down trees of a specific size.


References


1 Dulson J, Douglas F, LeDrew B, Vavitsas A. Biology 11. Toronto, Canada: Nelson; 2011
2 Anderson P. Ecological Succession [pod cast on the internet]. Montana, USA: youtube, 26 April 2012. Available from:http://www.youtube.com/watch?v=V49IovRSJDs
3 N.A. Ecological Succession [Internet]. Pennsylvania, USA: Pennsylvania State University; 2002 [updated 2009 July 12, cited 2012 June 17]. Available from:
http://www.psu.edu/dept/nkbiology/naturetrail/succession.htm
4 Denali Biome Project [Internret]. Available from: http://denalibiomeproject.wikispaces.com/Succession
5 Embleton B. Geograph [Internet]. Worcestershire, Great Britain. Available from: http://www.geograph.org.uk/photo/1164719