Topic 2.4:
Biomes,
zonation and
succession
Starter:
Using the world map outline try
break the world up into its
different biomes.
Shade them in different colours.
E.g. Tropical rainforest, Desert,
Tundra, Savana, Deciduous forest.
Significant Ideas
• Climate determines the type of biome in a given area,
although individual ecosystems may vary due to many
local abiotic and biotic factors.
• Succession leads to climax communities that may vary
due to random events and interactions over time. This
leads to a pattern of alternative stable steady states for
a given ecosystem.
• Ecosystem stability, succession and biodiversity are
intrinsically linked.
Applications and Skills
• Explain the distributions, structure, biodiversity and relative
productivity of contrasting biomes.
• Analyze data for a range of biomes.
• Discuss the impact of climate change on biomes.
• Describe the process of succession in a name example.
• Explain the general patterns of change in communities
undergoing succession.
• Discuss the factors which could lead to alternative stable
states in an ecosystem.
• Distinguish the roles of r and K selected species in succession.
• Interpret models or graphs related to succession and zonation.
Knowledge and Understanding
• Biomes are collections of ecosystems sharing similar climatic
conditions which can be grouped into five major classesaquatic, forest, grassland, desert and tundra. Each of these
classes will have characteristic limiting factors, productivity
and biodiversity.
• Insolation, precipitation, and temperature are the main factors
governing distribution of biomes.
• The tricellular model of atmospheric circulation explains the
distribution of precipitation and temperature influencing
structure and relative productivity of different terrestrial
biomes.
• Climate change is altering the distribution of biomes and
causing biome shifts.
• Zonation refers to changes in community along an
environmental gradient due to factors such as changes in
altitude, latitude, tidal level or distance from shore (coverage
by water).
• Succession is the process of change over time in an ecosystem
involving pioneer, intermediate and climax communities.
• During succession, the patterns of energy flow, gross and net
productivity, diversity, and mineral cycling change over time.
• Greater habitat diversity leads to greater species and genetic
diversity.
• r and K strategists have reproductive strategies that are better
adapted to pioneer and climax communities respectively.
• In early stages of succession, gross productivity is low due to
the unfavorable initial conditions and low density of
producers. The proportion of energy lost through community
respiration is relatively low too, so net productivity is high,
that is, the system is growing and biomass is accumulating.
• In later stages of succession, with an increased consumer
community, gross productivity may be high in a climax
community. However this is balanced by respiration, so net
productivity approaches zero and the productivity:respiration
(P:R) ratio approaches one.
• In a complex ecosystem, the variety of nutrient and energy
pathways contributes to this stability.
• There is no one climax community but rather a set of
alternative stable states for a given ecosystem. These
depend on the climatic factors, the properties of local soil
and a range of random events which can occur over time.
• Human activity is one factor which can divert the
progression of succession to an alternative stable state, by
modifying the ecosystems, for example the use of fire in
an ecosystem, use of agriculture, grazing pressure, or
resource use such as deforestation. This diversion may be
more or less permanent depending upon the resilience of
the ecosystem.
• An ecosystem’s capacity to survive change may depend on
its diversity and resilience.
Biomes:
• A collection of ecosystems sharing similar climatic
conditions, e.g. tundra, tropical rainforest, desert.
• Although opinions vary there are 5 major types of
biome:
•
•
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•
•
Aquatic (some split this into freshwater and marine)
Forest—tropical, temperate and boreal (taiga).
Grassland—tropical or savanna and temperate.
Desert—hot and cold.
Tundra—arctic and alpine.
For the five major classes of biome what are the
characteristic limiting factors, productivity and
biodiversity.
Different factors govern the distribution of biomes.
• Insolation (the amount of suns energy reaching the
surface)
• It is measured by the amount of solar energy received per
square centimetre per minute.
• Precipitation
• Usually measured in mm per metre squared.
• Temperature
• Usually measure in degrees Celsius.
Each biome we will look at has specific limiting factors,
productivity, and biodiversity.
Map of World Biomes
Biomes are where they are due to climatic conditions (temperature and precipitation)
Why are Biomes Where They Are?
Climate: The temperature is hotter
near the equator and generally gets
cooler towards the poles. At the poles,
the rays of the sun hit the Earth at an
angle and so are spread out over a
greater area.
Latitude: Distance north and south
from the equator.
Altitude: Height above sea level. Air is
less dense at higher altitudes.
Ocean Currents and Winds: Winds
cause ocean currents and ocean
currents distribute massive amounts
of heat from the equator towards the
poles.
Insolation, Temperature and Precipitation/Evaporation are the most important
physical factors influencing biomes.
Productivity
• Productivity is greater in low altitudes (nearest the
equator) where temperatures are high throughout the
year, sunlight input is high and precipitation is high.
These conditions are ideal for photosynthesis.
Complete the biome handout/chart using
pages 106-113 of your textbook. If needed,
use the internet.
Climate Change and Biome Shift
With an increase in mean global temperature and changes
in precipitation, evidence suggests biomes are moving. The
climate is changing in these ways:
Temperature increase of 1.5 – 4.5 degrees Celsius by
2100 (IPCC Report).
Greater warming at higher latitudes.
More warming in winter than summer.
Some areas are becoming drier, others warmer.
Stronger storms.
Organism cannot adapt (evolutionarily) this quickly. They
must, if they are able, migrate.
Climate Change and Biome Shift
• Organisms are moving towards the cooler poles.
• Organisms are moving to higher altitudes—500m m of
altitude results in a 3 degree drop in temperature.
• Organisms are moving towards the equator where it is
wetter.
Examples of Shifting Biomes:
In Africa, in the Sahel region, woodlands are becoming
savannas.
In the Arctic, tundra is becoming shrubland.
Plants migrate very slowly, but animals can migrate longer
distances. There are barriers to migration, however.
Climate Change and Biome Shift
There are hotspots—areas predicted to have a high
turnover of species due to climate change.
The Himalayas – species can move no higher than the land mass.
Equatorial Eastern Africa – with a very drought-sensitive climate.
The Mediterranean Region(s) – drought, high temp.
Madagascar – more extreme weather events.
The North American Great Plains and Great Lakes .
Up to one billion people live in regions which are vulnerable to biome
change.
• Drilling for oil under the Artic Ocean is becoming possible with the
decrease in sea ice.
• The North-West Passage for ships between the North Pole and
North America could become an ice-free trade route.
The Tri-Cellular Model of atmospheric circulation.
(see page 105 in your book)
• The Tri-Cellular Model of atmospheric circulation explains the
distribution of precipitation and temperature influencing structure
and relative productivity of different terrestrial biomes.
The Coriolis Effect
(see page106 in your textbook)
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.
Human activities alter zonation. Road building on
mountains may allow tourism into previously
inaccessible areas or deforestation or agriculture.
Zonation
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•
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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.
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.
Zonation
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
Stages in Primary Succession
(see figure 2.4.20 in textbook)
Primary succession occurs on a bar inorganic surface
(rock). It involves the colonization of newly created land
by organisms. It occurs as new land is either created or
uncovered such as river deltas, after volcanic eruptions,
on sand dunes.
The process of succession results in a natural increase in
complexity to the structure and species composition of a
community over time.
Stages of Primary Succession
1.
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.
2.
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.
3.
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.
4.
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.
5.
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.
6.
The final stage or climax community is stable and self-perpetuating. 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.
Succession in Water
Secondary Succession
• Secondary succession – when an already established community
is suddenly destroyed/disturbed
• 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.
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.
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).
The Role of r and K strategists in
Succession
Species can be roughly divided into K- and r- selected species.
K and r are two variables that determine the shape of a
population growth curve.
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
• We saw these population
growth curves before.
• 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)
K-strategist
• Long life
• Slower growth
• Late maturity
• Fewer, but large offspring
• High parental care and
protection
• High investment in
individual offspring
• Adapted to stable
environment
• Later stages of succession
• Niche specialist
• Predators
• Regulated mainly by
internal factors
• Higher trophic level
r-strategist
• Short life
• Rapid growth
• Early maturity
• Numerous and small
offspring
• Little parental care or
protection
• Little investment in
individual offspring
• Adapted to unstable
environment.
• Pioneers, colonizers
• Niche generalists
• Prey
• Regulated mainly by
external factors
• Lower 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
Youngest
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.
• 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.
• In agricultural systems, humans often deliberately stop
succession when NPP is high and crops are harvested.
• Sometimes the ecosystem recovers from this interruption
and succession continues, sometimes the interruption is
too great and the system is less resilient and so
succession is stopped.
• Species biodiversity is low in early stages and increases as
succession continues, falling a little in a climax
community.
• The higher the diversity, the higher the resilience.
• Mineral cycling also changes over the succession,
increasing with time.
Bill Nye on Why We Have Seasons