Download pioneer species

Unit 3 Topic 6
Changes in a community
Ecological succession
Ecological succession:
• Natural, gradual changes in the types of
species that live in an area; can be primary or
secondary
• The gradual replacement of one plant
community by another through natural
processes over time
Primary Succession
•
Begins in a place without any soil
– Cooled lava flows
– Bare rock exposed from: massive flooding & mudslides, glacial
retreats
Primary Succession
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Starts with the arrival of living things such as lichens that do not need soil to survive
(Called PIONEER SPECIES)
Soil starts to form as lichens, microbes & the forces of weather/erosion help break
down rocks into smaller pieces
Lichens die & decompose, adding small amounts of organic matter (more soil)
Simple plants like mosses and ferns can grow in the new soil
The simple plants die, adding more organic material
Primary Succession
• The soil layer thickens, and grasses, wildflowers, and other
herbaceous plants begin to take over
• Now insects, birds and small mammals can inhabit the field.
• These plants die, and they add more nutrients to the soil
Primary Succession
• Shrubs and tree seedlings can now survive
• The habitat can support a wider diversity of small animal species.
Primary Succession
• Trees with high disperal abilities can colonize.
• Those that are fast growing and early maturing will dominate.
• Now larger mammals and birds can be supported by the young
forest.
Primary Succession
• Trees that are shade tolerant start to dominate the community.
• The forest transitions into a “climax” forest, in which, large, slow
growing and long-living species dominate.
• Mature forests sustain a diverse community of animal fauna, often
different than that of the field and shrublands communities.
Climax Community
• A stable group of plants and animals that
is the end result of the succession process
• Does not always mean big trees
– Grasses in prairies
– Cacti in deserts
Summary of changes in biodiversity over time
Generally, biodiversity increases over
time.
Succession of species
pioneer species
lichens & mosses
compete well in high sunlight
grasses
climax forest
shade tolerant species
stable community
bushes & small trees
trees
What causes succession?
• Tolerance
– early species are “weedy”
– tolerant of harsh conditions
• Facilitation & Inhibition
– early species facilitate habitat changes
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build soil
increase nutrient and water retention of soil over time
change soil pH
change light levels
– allows other species
to out-compete
Changes in abiotic factors over time
Abiotic
factor
How it
changes
Soil
quantity
Increases
Soil
quality
Improves
Soil
water
retention
Increases
Why it changes
Benefits to
succession
More detritus
increases
humus
Provides more area
for plants to anchor
their roots in
Gains
organic
matter
Provides more
nutrients for
plant growth
Increased organic
matter retains more
water; shading
decreases evaporation
More water
is available
for plants
Changes in abiotic factors over time
Abiotic
factor
How it
changes
Why it
changes
Light
availability Decreases
Shading
increases
over time
Temperature
Shading
increases
over time
Decreases
Nitrogen or
phosphorus
Increases
Increased N
fixation,
Increased
decomposition
Benefits to/
impacts on
succession
Favors shade-tolerant
species and inhibits
shade-intolerants
Favors heat-intolerant
species and inhibits
plants that need higher
temps.
Favors plants with
higher N or P
requirements
Secondary succession
• Occurs after a disturbance that leaves the soil intact
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Fire
Massive storm
Forest clear-cutting
Death of a large mature tree
Also occurs in abandoned agricultural fields
Soil is intact
Often there is a seed bank
Starts with annual plants (wildflowers, herbs)
Lots of organic matter for nutrient recycling
Can help to maintain regional biodiversity
Disturbances as natural cycle
• Disturbances are often necessary for community
development & survival
- release nutrients
- increases biodiversity
- increases habitats
- rejuvenates
community
Fire climax species
adaptations to survive
and reproduce in
areas that experience
frequent fires
Jack
Pine
Scenarios
• A massive landslide
occurs leaving completely
bare bedrock behind.
• A forest is completely
uprooted by a tornado.
• What is the immediate
effect on the ecosystem?
• What are the ongoing
long-term effects on
succession?
• What is the immediate
effect on the ecosystem?
• What are the ongoing
long-term effects on
succession?
.