Transcript Ecological Succession

Ecological Succession
Natural Changes in Ecosystems
1. Natural selection - species change (adapt) to
their environment
2. Adaptive radiation - new species arise.
3. Ecological succession – changes the types of
organisms that live in an ecosystem.
Slide 1
Ecological Succession
Changes in the types and amount of species in an ecosystem
over time.
Changes in biodiversity in an ecosystem over time.
Two Types of Succession:
1. Primary Succession
2. Secondary Succession
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Primary Succession
• Change in community composition on a site which previously
has had no living organisms.
• Very gradual, species introduced slowly.
Slide 3
Example: Colonization following a large scale disturbance
(volcanic eruption)
Primary Succession
time
Slide 4
Example:
Glacial Retreat
Slide 5
Lichen
Lichens are an example of Mutualism
• 2 organisms, both benefit
• fungus and algae
•Lichens secrete (release) chemicals
that break down rock.
•This type of weathering (plus wind,
rain and freezing) helps produce soil.
Pioneer species: organisms like lichen and plants that are the first
organisms to survive and reproduce in an area.
Pioneer species: change environment by producing soil and providing
food for other organisms.
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Pioneer Species
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First plants to colonize an area: mosses, lichens & herbs
Rapid colonizers
Rapid growth (opportunistic)
Relatively poor competitors in established environments
Due to symbiotic relationship (algae use photosynthesis),
they can survive in low nutrient environments.
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Climax communities = a mature community
Tropical rainforests, grasslands and deserts are all examples of
climax communities.
Appear to be unchanged but this is a mistaken assumption.
HOW MIGHT CLIMAX COMMUNITIES CHANGE OVER TIME?
Slide 10
Climax community??
Difficult to identify
May take 100’s or 1000’s of years to reach this stage
Stage at which system has reached steady state
equilibrium
Most permanent of all the stages
Determined by climatic or soil factors
unless humans interfere (e.g. poor
soil quality, grazing, preventing forest
fires, selective logging)
Slide 11
Secondary Succession
Succession in an area that has been cleared or modified
by a disturbance and already has a soil base in place
Slide 12
An example of
secondary succession
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Oldfield (farming)
succession
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Changes During Succession
Graphs showing
changes in biomass
and species
composition with
succession.
Slide 17
Other Ecological Pyramid Changes during Succession
Slide 18
How Natural Events Affect Ecosystems
• Include events such as storms, fires, flooding,
Tsunamis, droughts, overgrazing, and human
activities
– They damage
biological
communities
– They remove
organisms from
communities
– They alter the
availability of
resources
Slide 19
Succession due to Natural Events
Slide 20
How Natural Events Affect
Ecosystems
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Read p. 115 – 116
List at least one affect of each of the
following on an ecosystem
1. Flooding
2. Tsunamis
3. Drought
Insect Infestations
Mountain Pine Beetle
Insect Infestations
• Read the article on the mountain pine
beetle and complete the attached
assignment.
Insect Infestations
The mountain pine beetle is a small insect, less than a
centimetre long, which lives most of its life under the bark
of pine trees, including lodgepole, ponderosa and western
white pine. Normally these insects play an important role in
the life of a forest. They attack old or weakened trees,
speeding the development of a younger forest. However,
unusual hot, dry summers and mild winters in central
British Columbia during the last few years, along with
forests filled with mature pine trees, have lead to an
epidemic.
To date, beetles have destroyed millions of lodge-pole pine
in BC – the province’s most commercially harvested tree.
How Does the Beetle Damage the
Pine Tree?
The mountain pine beetle is as small as a grain of rice, but in large
numbers it can take down the pine from the inside.It accomplishes this
by attacking the trees in large groups. A female beetle starts the
process by licking trees until it finds a pine mature enough — at least
80 years old. Once it has located the tree, the female begins boring
through the bark, while at the same time secreting a pheromone that
attracts male beetles to the site. When the males join in the attack, they
too release a pheromone to attract more females, who in turn attract
more males until a large enough population descends on the tree. The
tree, however, is far from helpless. In response, it secretes a highly
toxic resin similar to pitch to kill the beetles. Should the number of
beetles attacking the tree be too few, the tree can usually withstand it.
An example of mutualism.
But swarming isn't the only tactic the beetle has: a symbiotic relationship with a
blue-stained fungus also gives it another advantage over the trees. The beetles
carry spores of this fungus in compartments in their mouths, and as they tunnel
their way underneath the bark of the tree, they release these spores into the
tree. As the fungus spreads through the tree, it stops the spread of the toxic
resin and lets the beetles continue tunnelling.
The fungus and the beetles work their way through the tree, with the beetles
laying their eggs in hollows created underneath the bark. The larvae born from
these eggs feed on the fungus as part of their development into adults and in
the process, carry away spores from the fungus inside their mouths. When the
beetles emerge from the now-dead tree in search of a new host, they'll be
armed with their symbiotic partner. "They are more of a complex than two
separate organisms," said Allan Carroll, a research scientist with the Canadian
Forest Service. "The beetle needs the fungus to feed and to stop the resin and
the fungus couldn't get anywhere without the beetles."
Why has the beetle spread?
The spread of the beetle can be traced to two separate issues: forest
management and climate change. Forest management practices designed to
limit forest fires have inadvertently supplied the beetles with an overabundance
of mature pine to feast on. As part of an evolutionary tactic to spread at the
expense of other trees, pine cones don't release their seeds until heated by fire.
When other trees begin crowding a pine stand, the dense forest becomes more
susceptible to forest fires. When fires do happen they clear out the old forest
but leave behind the released pinecone seeds, allowing a new stand of pine
tree to grow where the old one existed, unimpeded by other trees. But forest
management practices geared towards preventing forest fires has allowed the
trees to mature beyond their expected age, making the forests older and thus
more desirable to the beetles. Carroll estimates that less than one per cent of
the pine that would have historically burned from forest fires burns today. While
the abundance of food is behind the population explosion, a lack of cold winters
to wipe out the beetles and curb the infestations is also to blame. Pine beetles
die when temperatures get below -30 C. Warming of the region brought on by
climate change has also helped the beetles survive in climates it would
normally find inhospitable, such as forests east of the Rockies like the Peace
River valley.