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3.1 How Changes Occur Naturally in Ecosystems
• How do you think mature forests, such as the temperate rainforests
of coastal British Columbia, change over time?
 They change over time by developing a larger biodiversity.
• Read Chapter 3.1 and answer the following
• How does an organism change over time? What is this process
called?
• How do organisms adapt to change?
• How does an ecosystem change over time?
• Specifically how do biotic characteristics change?
• What is this called?
• How do natural events effect/change ecosystems? Examples?
(c) McGraw Hill Ryerson 2007
1. As a glacier retreats, the process of primary succession will occur.
Describe the various stages that lead to the development of a
mature community.
2. After a forest fire, not much is left except ash and burnt trees.
Describe the sequence of events that will occur during secondary
succession.
3. For each event summarize the effects on a mature community
1.
Fire, Flooding, Tsunami, Drought, Insect infestation
(c) McGraw Hill Ryerson 2007
3.1 How Changes Occur Naturally
in Ecosystems
• When an organism is born, it belongs to a species,
but it also is born with unique characteristics.
 Sometimes, these unique characteristics give organisms an advantage within
their niche. For example, a salmon with a slightly larger tail may be able to swim
a little faster or a little farther in a river.
• Natural selection is the process where
individuals with advantages are better able
to reproduce and pass along their traits.
 Those with unfavourable characteristics have
less chance to reproduce and pass along
A salmon with a large tail may be able
their traits.
to swim faster and farther.
 A salmon with a smaller tail may never have a chance
to spawn because it cannot swim to the correct location.
How Organisms Adapt to Change
• The Galapagos Islands, off the coast of Ecuador, are a
famous example of natural selection.
 Many species on these islands are very similar to each other
but different from species on the South American continent.
 There are 13 species of finches on the islands.
 Each is descended from a finch species from the
mainland.
 Each species has unique characteristics that allow
it to thrive in its own niche and not compete with
other finches for resources.
• Adaptive radiation describes the type of
natural selection where many different
species appear from one original species.
Galapagos
finches
How Ecosystems Change Over Time:
Primary Succession
• Ecological succession refers to the changes in the biotic
characteristics in an area over time.
 There are two types of ecological succession:
1. Primary succession begins with bare rock
such as where glaciers scrape away dirt
or a volcano erupts. (no soil exists)
Bare rock.
 Wind carries spores of lichens and organisms that can survive and eventually,
combined with the weathering of rock, help form soil.
 The first organisms to survive and reproduce are pioneer species.
 Pioneer species alter the abiotic and biotic environment in some way.
 Soil improves, plants are able to grow and animals begin to appear.
 Primary succession occurs in all parts of the world.
 This stage can last for hundreds of years, until a mature community eventually
forms.
How Ecosystems Change Over Time:
Secondary Succession
•
Mature communities are very stable and can appear
to be unchanging over long periods of time.
 These are also known as climax communities, but “mature” correctly implies
that there are still changes occurring.
2. Secondary succession occurs after a major disturbance in an area
that already has soil and once had living organisms.
 Forest fires are the most common reason for
secondary succession.
 The soil remains for plant growth and contains
seeds, micro-organisms, earthworms,
and insects.
 Secondary succession is much more rapid than
primary succession because soil, seeds and
insects are already present.
Secondary succession.
How Natural Events Affect Ecosystems
• Many other disturbances can affect mature communities.
• Flooding
• Tsunami
• Drought
• Insect infestations