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How Ecosystems Change

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Title: Slide 1 Author: Tom Manning Last modified by: GCPS Created Date: 3/30/2005 11:16:33 PM Document presentation format: On-screen Show Company – PowerPoint PPT presentation

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Title: How Ecosystems Change


1
How Ecosystems Change
  • Understanding how ecosystems change can help you
    predict what can happen to the land around you in
    the years to come.

2
Essential Questions
  • How do ecosystems change over time?
  • How do new communities begin in areas without
    life?
  • How do pioneer species compare to climax
    communities?

3
Ecological Succession
  • Succession refers to the normal, gradual changes
    that occur in the types of species that live in
    an area.
  • Succession is a process by which one biotic
    community is replaced by another until a climax
    community develops.

4
Succession from Rock to Forest
  • Some 240 years ago a glacier began retreating in
  • Glacier Bay, Alaska
  • The glacier left behind a rocky terrain
    completely devoid of organic matter
  • The process that begins in a place without any
    soil is called Primary Succession

5
  • An Example of Primary Succession Glacier Bay,
    Alaska

6
Primary Succession
  • Pioneer organisms such as microbes,
    lichens, and mosses are the first to inhabit a
    rock promoting soil formation.

7
Primary Succession
  • Eventually, enough soil is built up so that
    grasses can succeed the pioneer organisms.

8
Primary Succession
  • Grasses are replaced by shrubs, which are
    replaced by fast-growing trees.

9
Primary Succession
  • Coastal Sitka Spruce Forest, Southeast Alaska

10
Succession occurs differently in different places
around the world.The types of grasses,
fast-growing trees, and climax-community plants
vary with the location and climate of an area.
11
A Climax Community Is Not Truly Final
  • Humans or nature can destroy it.

12
A Climax Community Is Not Truly Final
  • In this case, succession starts over with grasses
    as Secondary Succession.

13
Secondary Succession
  • After a forest fire, not much is left except dead
    trees and ash-covered soil.
  • However, these places do not remain lifeless for
    long.

14
Secondary Succession
  • The topsoil, which may have taken 1000s of years
    to form, is not destroyed.
  • Spores and seeds which lie dormant are then
    allowed to develop.
  • Sequence may be crabgrass, tall grass and
    horseweed, softwood then hardwood.

15
Secondary Succession
  • The soil already contains the seeds of weeds,
    grasses, and trees.
  • More seeds are carried to the area by wind and
    birds.
  • Other wildlife may move in.
  • Succession that begins in a place that already
    has soil and was once the home of living
    organisms is called
  • secondary succession.

16
Secondary Succession
  • Secondary succession occurs faster and has
    different pioneer species than primary succession
    because soil is already present.
  • The cause may be a natural disturbance such as a
    forest fire or farming.
  • In 1850, Connecticut was almost entirely open
    land cleared for farming or timber.
  • Today, Connecticut has been mostly reforested
    through the process of secondary succession as
    farming has left the state since the 1800's.

17
Secondary Succession
  • This photo shows three succession stages.
  • The trees in the background.
  • The area on the right behind the fence, in front
    of the trees.
  • The area in the foreground, in front of the
    barbed wire fence.

18
Secondary Succession
  • In the background are the trees of an eastern
    hardwood
  • forest. This area has not been cleared in over
    fifty years.
  • These trees represent the climax community for
    the rainfall,
  • temperature and soil of this area.

19
Secondary Succession
  • The area on the right, behind the fence, in front
    of the trees, has not
  • been mowed in about ten years. Shrubs and
    evergreen trees have
  • moved in. These are the intermediate species.

20
Secondary Succession
  • The area in the foreground, in front of the
    barbed wire fence, has
  • been mowed within the last year. The plants are
    all annuals or
  • herbaceous perennials. These are the pioneer
    species.

21
Climax Communities
  • A community that has reached a stable stage of
    ecological succession is called a climax
    community.
  • It is a combination of plants and animals that
    use the available resources most efficiently.
  • Diversity and balance are maintained in a climax
    community because as trees die, they provide
    nutrients for new communities of organisms.

22
How do ecosystems change over time?
  • Ecosystems change over time by a process know as
    succession in which one biotic community is
    replaced by another until a climax community
    develops.
  • Succession is often caused by changes in the
    environment brought about by the current
    community.
  • Succession can also occur because of changes in
    climate and natural catastrophes such as fire,
    hurricanes, floods, and volcanic eruptions.
  • Humans cause succession by cutting down forests,
    polluting the environment and overdeveloping an
    area.

23
How do new communities begin in areas without
life?
  • By a process known as primary succession. Pioneer
    organisms such as microbes, lichens, and mosses
    are the first to inhabit a rock promoting soil
    formation.
  • They survive drought, extreme heat and cold, and
    other harsh conditions and start the
    soil-building process.
  • Soil begins to form as lichens and the forces of
    weather and erosion help break down rocks into
    smaller pieces.
  • When lichens die, they decay, adding small
    amounts of organic matter to the rock.
  • Plants such as mosses and ferns can grow in this
    new soil.
  • Thus begins the process for higher order plants.

24
How do pioneer species compare to climax
communities?
Pioneer species are the first organisms to occupy
an area and do not need soil to survive.
Examples of pioneer species would be organisms
such as microbes, lichens, and mosses. Climax
communities are the last communities to occupy an
area. Climax communities are a combination of
plants and animals. They tend to be stable and
self-perpetuating.
25
Ecological Succession
Lichens
Mosses
Microbes
26
Ecological Succession
27
Ecological Succession
28
Ecological Succession
29
Ecological Succession
30
Ecological Succession
31
Ecological Succession
32
Ecological Succession
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Ecological Succession
34
Ecological Succession
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