Download 2.4.2 Zonation and Succession

2.4.2 ZONATION AND
SUCCESSION
What is Succession

Succession – a predictable sequence of changes,
caused by the living things themselves, where an
ecosystem develops from a simple colonizer
community to a complex climax community.
What is Succession

Succession – Orderly process of change over time in
a community divided into stages called serals
Primary Succession

Involves the
introduction of species
into an area that has
never previously been
colonized
Stages of Primary Succession

Bare inorganic surface: Lifeless abiotic environment
becomes available for colonization by pioneer
plant, animal and lichen species. Soil is little more
than mineral particles, nutrient poor and an erratic
water supply.
Stages of Primary Succession
1.
Stage 1 Colonization: First species to colonizer are
pioneer species adapted to extreme conditions. Pioneer
species are typically r-selected species showing small
size, short life cycles, rapid growth and production of
many offspring or seeds. Simple soil starts from
windblown dust and mineral particles.
Pioneer Species
Stages of Primary Succession
1.
Stage 2 Establishment: Species diversity increases.
Invertebrates (no backbone) begin to visit and live in the
soil, increasing humus (organic material) content and
water-holding capacity. Weathering of rock enriches soil
with nutrients.
Stages of Primary Succession
1.
Stage 3 Competition: Microclimate continues to change as
new species colonize. Larger plants increase cover and
provide shelter, enabling K-selected species to become
established. Temperature, sun and wind are less extreme.
Earlier pioneer r-species are unable to compete with K
species for space, nutrients or light and are lost from the
community.
Stages of Primary Succession
1.
Stage 4 Stabilization: Fewer new species colonize as late
colonizers become established shading out early
colonizers. Complex food webs develop. K-selected
species are specialists with narrower niches. They are
generally larger and less productive (slower growing)
with longer life cycles and delayed reproduction.
Stages of Primary Succession
1.
The final stage or climax community is stable and selfperpetuating. It exists in a steady-state dynamic
equilibrium. The climax represents the maximum possible
development that a community can reach under the
prevailing environmental conditions of temperature, light
and rainfall.
Primary Succession


Occurs in new lakes,
ponds, cooled lava,
sand dunes and bare
rock
Ex - rock -> lichen ->
moss -> grass -> shrub
-> trees -> oak
hickory forest
Secondary Succession

Secondary succession – when an already
established community is suddenly
destroyed/disturbed
Secondary Succession
 Soils
are already developed and ready to accept wind
blown seeds.
 E.g. Forest fire, flood, grazing, deforestation, human
activity (plowing), etc.
The Stages of Succession

During succession, the following changes occur:
 The size of the organisms increases with
trees, creating a more hospitable
environment.
 Energy flow becomes more complex as
simple food chains become complex food
webs.
The Stages of Succession
 Soil
depth, humus, water-holding capacity, mineral
content, and cycling all increase.
 Biodiversity increases because more niches (lifestyle
opportunities) appear and then falls as the climax
community is reached.
 NPP and GPP rise and then fall.
 Productivity: Respiration ration falls.
Climax communities


Not necessarily dense forest.
There is no one climax community.
 Many
stable alternatives
 Dependant on:
 Climatic
factors
 Soil properties
 Random events

**Complex ecosystems are more stable due to the
variety of nutrient and energy pathways.
 If
one collapses its overall effect is low as there are
many others to takes its place.
Secondary Succession


Succession that occurs
where an area has
been disturbed.
Ex - grass -> shrub ->
trees -> oak hickory
forest
Secondary Succession
Annual
weeds
Perennial
weeds and
grasses
Shrubs and
small pine
seedlings
Young pine forest
with developing
understory of oak
and hickory trees
Mature oak and hickory
forest
GPP and NP During Succession
(a summary)
EARLY STAGE
Low GPP but high % of NPP.
Little Increase in Biomass.
Grasses, herbs, small shrubs
grow.
MIDDLE STAGE
GPP is high.
Increased photosynthesis.
Increases in biomass as plants
become larger.
As woodland species and
biomass increases, so does
productivity, but NPP as a %
of GPP falls as respiration
rates increase.
LATE STAGE
Trees reach their maximum
size.
Ratio of NPP to R is roughly
equal.
Both biodiversity and mineral cycling increase strongly as succession progresses.
Biodiversity in Successions

In early stages of succession, there are only a few
species within the community. As the community
passes through subsequent stages, species diversity
increases (to a point).
Secondary Succession

Human activities usually cause secondary succession.
 Cutting
for timber
 Clearing for farming
 Construction

Some Natural Causes
 Forest
fires
 Volcanoes
 Hurricanes
 Tornados
Stages of Succession


Pioneer community –
Earliest seral stage
Early Stages of
Succession:
 Gross
Productivity: low
 Respiration loss: low
 Net Productivity: high
 System: Growing
 Biomass: Accumulating
Stages of Succession


Climax community – Final
seral stage
Final Stages of
Succession:
 Gross
Productivity: high
 Respiration loss: high
 Net Productivity: near 0
 Production/Respiration
Ratio: Near 1
Climax Community

A climax community produced by the action of
humans is called a PLAGIOCLIMAX. This may occur
for the following reasons:
Climax Community

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The introduction on non-native species
The effects of acid rain
The effects of global warming
Deforestation
The planting of crops
Climax Community

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The grazing of cattle
Agricultural operations
Forestry
Deliberate maintenance of grasslands, heathlands
and coppice woodlands
Land clearance
Fire
Zonation
What is Zonation

Zonation –Zonation is the
change in community along
an environmental gradient
due to factors such as
changes in altitude, latitude,
tidal level or distance from
shore/coverage by water.
What is Zonation

Human activities alter
zonation. Road building on
mountains may allow tourism
into previously inaccessible
areas or deforestation or
agriculture.
Zonation
•
•
•
Each species has an ecological niche (boundaries).The
niches change as we increase the altitude.
Temperature – decreases with increasing altitude and
latitude.
Precipitation—Higher up on mountains, the air is too
dry and cold for trees. Most rainfall is in the middle
altitudes where deciduous trees grow.
Zonation
•
•
•
Solar insolation—more intense at higher altitudes and
plants have adapted to this.
Soil type—in warmer zones, decomposition is faster so
soils are deeper and more fertile. Higher up,
decomposition is slow with acidic soils.
Species interactions—competition may crowd out some
species and grazing may alter plant composition.
Mycorrhizal fungi may plan an important role in tree
growth.
Succession vs Zonation
(a comparison)
Succession is how an ecosystem changes in time.
Zonation
Succession
Spatial and Static
Dynamic and temporal (takes place
over long periods of time)
Caused by an abiotic gradient.
Mountains—changes in temperature.
Seashore—changes in time exposure
to water/air.
Caused by progressive changes
through time, eg., as vegetation
colonizes bare rock.
Ex. Rocky Seashore, mountain slopes
Terrestrial
Reproductive Strategies
The Role of r and K strategists in
Succession

Species can be roughly divided into K- and rselected species. K and r are two variables that
determine the shape of a population growth curve.
The Role of r and K strategists in
Succession



K = carrying capacity
r = describes the exponential part of a growth
curve.
K- and r- strategies describe the different
approaches species take to getting their genes
passed onto the next generation and ensuring the
survival of the species.
The Role of r and K strategists in
Succession


S-shape curve
represents a
population that is at
carrying capacity (Kstrategy species)
J-shape curve
represents a
population existing in
an exponential phase
of growth (r-strategy
species)
r-strategist




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Short life
Rapid growth
Early maturity
Numerous and small
offspring
Little parental care or
protection
Little investment in
individual offspring

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Adapted to unstable
environment.
Pioneers, colonizers
Niche generalists
Prey
Regulated mainly by
external factors
Lower trophic level
K-strategist

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Long life
Slower growth
Late maturity
Fewer, but large
offspring
High parental care
and protection
High investment in
individual offspring

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

Adapted to stable
environment
Later stages of
succession
Niche specialist
Predators
Regulated mainly by
internal factors
Higher trophic level
Survivorship Curve


Limiting factors that affect the shape of the curve include
predation, competition, environmental conditions.
Curve II is rare in that species have an equal chance of dying at
any age (ex. Hydra and some bird species).
Activity:

Using sand dunes as an case study (pg. 121)
outline the stages of succession.
Oldest
• For each of the 5 stages outline how the
following change:
• Size and diversity of organisms
• Complexity of energy flows
• Soil
• NPP and GPP (explain why they change)
• Productivity : respiration ratio
Younges
t
Summary of Key Points



Succession is the change in species composition in an
ecosystem over time.
It may occur on bare ground (primary succession)
when soil formation starts the process or where soil
already formed but the vegetation has been
removed (secondary succession).
Early in succession, gross primary productivity (GPP)
and respiration are low and so net primary
productivity (NPP) is high as biomass accumulates.
Summary of Key Points



In later stages, while GPP may remain high,
respiration increases so NPP may approach zero
and the productivity :respiration ratio (P:R)
approaches one.
A climax community is reached at the end of
succession when species composition stops changing.
But there may be several states of a climax
community, depending on abiotic factors.
The more complex the ecosystem (higher
biodiversity, increasing age), the more stable it
tends to be.