Title: How Ecosystems Change
1How Ecosystems Change
- Understanding how ecosystems change can help you
predict what can happen to the land around you in
the years to come.
2Essential Questions
- How do ecosystems change over time?
- How do new communities begin in areas without
life? - How do pioneer species compare to climax
communities?
3Ecological 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.
4Succession 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
6Primary Succession
- Pioneer organisms such as microbes,
lichens, and mosses are the first to inhabit a
rock promoting soil formation.
7Primary Succession
- Eventually, enough soil is built up so that
grasses can succeed the pioneer organisms.
8Primary Succession
- Grasses are replaced by shrubs, which are
replaced by fast-growing trees.
9Primary Succession
- Coastal Sitka Spruce Forest, Southeast Alaska
10Succession 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.
11A Climax Community Is Not Truly Final
- Humans or nature can destroy it.
12A Climax Community Is Not Truly Final
- In this case, succession starts over with grasses
as Secondary Succession.
13Secondary 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.
14Secondary 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.
15Secondary 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.
16Secondary 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.
17Secondary 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.
18Secondary 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.
19Secondary 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.
20Secondary 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.
21Climax 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.
22How 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.
23How 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.
24How 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.
25Ecological Succession
Lichens
Mosses
Microbes
26Ecological Succession
27Ecological Succession
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29Ecological Succession
30Ecological Succession
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34Ecological Succession