TOPIC 2.4: BIOMES,
ZONATION, & SUCCESSION
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
states for a given ecosystem.
■ Ecosystem stability, succession and biodiversity
are intrinsically linked.
Knowledge and Understanding:
1. Biomes are collections of ecosystems sharing similar
climatic conditions which can be grouped into five major
classes – aquatic, forest, grassland, desert and tundra.
Each of these classes will have characteristic limiting
factors, productivity and biodiversity.
2. Insolation, precipitation and temperature are the main
factors governing the distribution of biomes.
3. The tricellular model of atmospheric circulation explains
the distribution of precipitation and temperature
influencing structure and relative productivity of different
terrestrial biomes.
4. Climate change is altering the distribution of biomes and
causing biome shifts.
Knowledge and Understanding:
5. Zonation refers to changes in community along an environmental
gradient due to factor such as changes in altitude, latitude, tidal
level, or distance from shore (coverage by water.)
6. Succession is the process of change over time in an ecosystem
involving pioneer, intermediate and climax communities.
7. During succession the patterns of energy flow, gross and net
productivity, diversity and mineral cycling change over time.
8. Greater habitat diversity leads to greater species and genetic
diversity.
9. r and K strategist species have reproductive strategies that are
better adapted to pioneer and climax communities respectively.
10. 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 productive it high, that is, the system is
growing and biomass is accumulating
Knowledge and Understanding:
11. In later stages of succession, with an increased consumer
community, gross productivity may be high in a climax community.
However, this is balanced by repiration, so net productivity
approaches zero and the productivity: respiration (P:R) ratio
approaches one.
12. In a complex ecosystem, the variety of nutrient and energy
pathways contributes to its stability.
13. There is no climax community but rather a set of alternative
stable states for a given ecosystem. These depend on the
climatic factors, the properties s of the local soil and a range of
random events which can occur over time.
14. Human activity is one factor which can divert the progression of
succession to an alternative stable state, by modifying the
ecosystem, for agriculture, grazing pressure, or resource use
such as deforestation. This diversion may be more or less
permanent depending upon the resilience of the ecosystem.
15. An ecosystem’s capacity to survive change may depend on its
diversity and resilience.
Application & Skills
1. Explain the distributions, structure, biodiversity and relative
productivity of contrasting biomes.
2. Analyze data for a range of biomes
3. Discuss the impact of climate change on biomes.
4. Describe the process of succession in a named example.
5. Explain the general patterns of change in communities
undergoing succession.
6. Discuss the factors which could lead to alternative stable
states in an ecosystem.
7. Discuss the link between ecosystem stability, succession,
diversity and human activity.
8. Distinguish the role of r and K selected species in
succession.
9. Interpret models or graphs related to succession and
zonation.
REVIEW: Biomes
■ BIOME: A collection of ecosystems sharing similar
climatic conditions, e.g. tundra, tropical rainforest,
desert.
■ Although opinions vary we will focus on 5 major
types of biome:
– Aquatic (may split this into freshwater and
marine)
– Forest (tropical, deciduous, coniferous)
– Grassland (savanna and temperate)
– Desert
– Tundra (arctic and alpine)
Aquatic
Aquatic: Mangrove Forest
Distribution
Terrestrial Biomes
See pp 106-113 and student made commercials for comparison of biomes
Major Factors Effecting the
distribution of biomes
■ Insolation (the amount of suns energy reaching
the surface, varies by latitude)
– It is measured by the amount of solar energy
received per square centimeter per minute.
■ Precipitation
– Usually measured in mm per meter squared.
■ Temperature
– Usually measure in degrees Celsius.
Why do the biomes
form in these areas?
Why do the biomes
form in these areas?
Other Factors Effecting the
distribution of biomes
■ Altitude (the higher you rise from sea level, the
colder the temperature)
■ Ocean & Wind Currents
– Distributes heat energy from equator back
towards poles (see tricellular model)
■ Precipitation to Evaporation Ratio (P/E ratio)
– When precipitation is about the same as
evaporation the P/E ratio will be about 1, soil
will be rich and fertile.
Tricellular Model of Air Circulation
■ Winds are due to the movement of air molecules
■ As substance gain heat energy, density decreases so particles rise
■ As you go up in altitude air cools, becomes more dense and falls back
towards earth’s surface.
■ These convection currents drive the Earth’s wind patterns and affect the
biomes.
■ The same phenomena drives ocean currents
Biomes & Productivity
Explain the trends above? How would the Gross
primary productivity compare for the deep
ocean biome? Why?
Climate Change & Biome Shifts
■ “By 2100, global climate change will modify plant communities
covering almost half of Earth's land surface and will drive the
conversion of nearly 40 percent of land-based ecosystems from one
major ecological community type -- such as forest, grassland or tundra - toward another, according to a new NASA and university computer
modeling study.”
http://www.sciencedaily.com/releases/2011/12/111218221321.htm
■ Increasing mean global temperatures and changes in precipitation is
causing biomes to shift locations.
■ Vegetation has been gradually moving toward the poles and up
mountain slopes, where temperatures are cooler, as well as toward the
equator, where rainfall is greater.
http://news.berkeley.edu/2010/06/04/climate/
Zonation
■ Zonation: how an
ecosystem changes
over an environmental
gradient
■ Each species has an
ecological niche.
■ The niches change as
we increase the
altitude.
■ Temperature
■ Precipitation
■ Solar insolation
■ Soil type
www.vcbio.science.ru.nl
■ Species interactions
(including humans)
www.flickr.com
Kite Diagrams
■ A graphical representation of number of species. The width
of the “kite” represents the number of species.
■ Frequently used to show zonation along a transect
Before we move on to succession, you
need to understand the concept of:
K and r reproductive strategies
J-shaped Growth Curve
online.science.psu.edu
• 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)
What are K and r?
■ The two variables that define a population
curve.
■ r = growth rate
■ K = carrying capacity
K-strategists
■ Long life
■ Slower growth
■ Late maturity
■ Fewer, but larger 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 (homeostasis)
■ 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 Curves
Show the fate of a group of individuals in a species
Which represents K selected species?
r- selected?
Succession
■ How an ecosystem changes over time (often
after a disturbance)
■ Two types:
– Primary Succession: Occurs on bare
abiotic surfaces (no soil)
– Secondary Succession: Occurs when an
established ecosystem is destroyed (fire,
flood, human activity), however soil is
still developed and present.
Primary Succession
With a partner, discuss how/when we would have
an ecosystem with NO soil present. How does this
present a problem to an ecosystem?
■ When new land is created (volcanic eruptions,
sand dunes, river deltas)
■ If there is no soil, the first organism that colonize
the new ecosystem must create soil
■ As more soil is formed, more plants can move in
and we have the replacement of one community
by another over time. (this is succession)
Stages of Primary Succession
■ Bare land (rocky/sandy surface) with little nutrients
■ Stage 1- Colonization: Pioneer organisms (first species to
colonize new land) are adapted to extreme conditions.
Usually r-selected species (why?), start breaking down rock
(examples: lichens, mosses)
■ Stage 2 – Establishment: As soil layer forms & improves,
species diversity increases, invertebrates move in and
increase organic matter (humus), water retention improves.
■ Stage 3 – Competition: Larger plants increase providing
shelter and allowing K-selected species to move in, extreme
conditions improved. Competition for resources result in
some early organisms dying out.
■ Stage 4 – Stabilization: Shade developing, complex food
webs forming, specialized niches increase
■ Stage 5 – Climax community: Final stage results in most
adapted organisms occupying each niche. Steady-state
equilibrium obtained
Primary Succession:
Yellowstone National Park
visityellowstonenationalparkyall.weebly.com
Primary Succession:
Yellowstone National Park
visityellowstonenationalparkyall.weebly.com
Primary Succession:
Sand Dunes
hamishnewbysgeographyblog.blogspot.com
Secondary Succession
■ Established ecosystem experiences a disruption
but soil remains intact
■ Could be a fire, flood, humans plowing a field,
human clear-cutting, etc.
■ System is out of balance
■ Will this take more or less time to get to climax
community than primary succession? Why?
Secondary Succession
■ Soil already developed so seeds blow in of wild grasses,
ground cover, and wild flowers
■ Small shrubs start to colonize grassland
■ Eventually trees establish resulting in mature soils and
climax community
Stages of Succession
Bare,
inorganic
surface
Stage 2 –
Establishment
Stage 1 –
Colonization
Stage 4 –
Stabilization
Stage 3 Competition
Climax
community
Primary Succession:
Mt. St. Helens Case Study
Mt. St. Helens, Washington USA 1980 (Pre-Eruption)
en.wikipedia.org
Primary Succession:
Mt. St. Helens Case Study
Mt. St. Helens, Eruption 1980
www.pbs.org
Primary Succession:
Mt. St. Helens Case Study
Mt. St. Helens, After Eruption 1980
http://www.mnn.com
Primary Succession:
Mt. St. Helens Case Study
Mt. St. Helens, After Eruption 1980
Primary Succession:
Mt. St. Helens Case Study
tatesbiology.wordpress.com
Activity:
■ Using Mt. St. Helens as an case study create a
poster outlining the stages of succession.
• 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)
Disturbance in succession
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.