IB Diploma Environmental Systems and Societies

1. Topic 2
2.4 Biomes, zonation and succession

3. Biosphere and Biomes
• Biosphere – Regions of the planet able to
support life
• Biome – A large patch of land with similar
conditions throughout which characteristic
plants are adapted to survive
• You can show the positions of different
biomes on a climograph

4. A Climograph

5. Biomes
• There are 3 factors which determine a biome:
– Amount of water (rainfall)
– Amount of sunlight (insolation)
– Temperature
• All of these factors affect photosynthesis
• The rate of photosynthesis determines the net primary
productivity (NPP) of a system and therefore
determines the location and make-up of a biome
http://www.windows2universe.org/earth/ecosystems.html
http://www.marietta.edu/~biol/biomes/biome_main.htm

6. Different Biomes
BIOME CLIMATE ADAPATED PLANT
LIFE
Tropical rain forest 20oC
Rainfall throughout the year. Short
dry season
Very diverse
Savanna 25-35oC
Semiarid – low rainfall in winter and
heavy in summer
Perennial grasses
Temperate deciduous forest -5 – 25oC
Snow in winter and moderate
summer rain
Rich diversity of
trees and shrubs
Grassland 0 – 25oC
Low rainfall
Diverse grasses,
sedges broad leaved
plans
Cold desert 0 – 22oC
Very low rainfall
Few species of
plants and shrubs
Tundra -22 – 5oC
Very low rainfall
Few species of
shrubs, mosses and
lichens

7. A Climograph

8. http://www.marietta.edu/~biol/biomes/biome_main.htm

9. The Tri-cellular Model
• The distibution of biomes can be understood by
looking at patterns of atmospheric air circulation
• The most used model is the ‘tri-cellular’ model:

10. The Tri-cellular Model
• There are 3 cells types (one of each in the northern and southern hemisphere:
– The Hadley Cells
– The Ferrel Cells
– The Polar Cells
• In the Hadley Cells (close to the equator), air heats up, rises, then cools and
condenses, forming large cumulonimbus (rain) clouds. Pressure is low as air
rises. Due to the high temperatures and high rainfall, tropical rainforest biomes
form
• In the Ferrel Cells (approx 30o N and S of the equator), the air cools and starts
to descend. Descending air causes high pressure. Since the air has lost its
moisture, it causes desert biomes to form.
• Air now heads either back to the Hadley Cell at ground level, or to polar
regions as warm winds (south-westerlies in northern hemisphere and north-
easterlies in the southern hemisphere). When the air reaches the poles, it
forms the Polar Cells (approx. 60o N and S of the equator). The air cools as it
hits colder winds. It condenses and rain falls. These conditions create
temperate forest biomes.

11. The Tri-cellular Model

12. Climate Change and Biomes
• There is clear evidence of climate change
– Global temperature increase of 1.5 – 4.5°C by 2100 (predicted by IPCC)
– Higher latitudes have greater warming and sea ice is breaking up
– Warmer winters across the globe
– Storms are increasing in intensity
– The mosquito line is decreasing
• There is evidence that biomes are beginning to shift
– In Africa, forest biomes are turning into savannah
– In the Arctic, tundra is turning into taiga
– There are areas of rapid species loss which can be accredited to climate
change: The Himalyas, East Africa, The Mediterranean, Madagascar, The Great
Plains of North America
• Shifts are occurring very quickly (within decades)
• Organisms evolve over thousands or millions of years and are therefore
unable to adapt to them
• One billion people live in areas where biomes are shifting and will have to
change their ways of life as a result

13. Questions
1. What is the difference between a biosphere, a biome
and an ecosystem?
2. Make a table to show the following biomes, with
information about insolation, precipitation and
temperature for each:
- Tropical rainforest
- Desert
- Tundra
- Temperate forest
3. Which biomes have (a) the highest (b) the lowest net
primary productivity? Why?

14. Zonation
• Zonation is the change in an ecosystem along an environmental
gradient
• Zonation is a product of each species possessing its own ecological
niche.
• As conditions along an environmental gradient change the available
niches change and therefore so do the species able to survive there
– Temperature
– Precipitation
– Insolation
– Soil type
– Biotic factors such as competition
Change in species over DISTANCE
https://www.youtube.com/watch?v=zLTw5VbGtf4

15. Zonation

16. Zonation
Kite diagram for a rocky shore in a temperate biome

17. Succession
• Primary Succession
– Occurs on a previously uncolonised substrate (e.g. a
newly formed bit of bare igneous rock, newly exposed
surfaces such as landslips, newly quarried rock face,
newly exposed sanbanks or sanddunes)
• Secondary Succesion
– Occurs in places where a previously existing
community has been destroyed (e.g. by a forest fire,
newly exposed sediment at the edge of a lake)
– This occurs faster since soil and seed already exist
Change in species over TIME

18. Succession Model (Lithosere)
Bare uncolonised rock exposed
Colonisation by lichens, weathering of rock and build up of dead organic material
Growth of moss, further weathering; soil begins to form
Growth of small plant such as grasses, leading to further improvement of soil
Larger plants can grow in the deeper and more nutrient rich soil
Climax Community of shrubs and trees

19. Succession
• Succession occurs in stages
• The first colonisers are pioneer species
– Fast growing species such as lichens and mosses which don’t require thick
soil
• Secondary species (especially grasses) then take over
– These are slower growing and are able to outcompete the pioneer species
for light and nutrients
• Tertiary species (especially herbaceous plants) then take over
– These take advantage of thicker soil appearing as litter breaks down
• Quaternary species then take over
– Largely shrubs appear which are able to outcompete the herbaceous
plants
• Finally a climax community is produced (e.g. oak forest)
– Thick soil has been produced, trapping more moisture and nutrients
– A community of soil organisms develops
– An animal community develops to exploit the available niches
http://edroness.blogspot.mx/2014/02/ecological-
succession.html
Private Life of Plants – episode 4

20. Succession
Feature Start of Succession End of Succession
Amount of organic matter Small Large
Amount of Nutrients Small Large
Nutrient conservation Poor Good
Amount of detritus Small Large
Niches Few but wide Many but small
Size of colonisers Small Large
Life cycles Simple Complex
Growth patterns r-strategists dominate K-strategists dominate
Diversity Low High
Stability Low High
Productivity Low and unstable High and stable
pH High Low
Biodiversity Low High

21. Productivity
• In the early stages of succession, GPP is low due to the low
density of producers. However, NPP is fairly high due to the
low respiration rates in the whole community
• As succession proceeds, GPP increases as soils become
more structured and the density of organisms increases.
NPP stabilizes as niches become occupied
• The ratio of GPP/NPP is called the P/R ratio. In the climax
community, overall productivity is balanced by overall
respiration – therefore as succession proceeds, the P/R
ratio approaches a value of 1

22. Productivity

23. Productivity
1
time
P/RRatio
0
Climax Forest
Agricultural Crop

24. Plagioclimax
• An interruption to succession is termed plagioclimax
• Humans are often the source of this
• Sometimes it is accidental and sometimes on purpose (e.g.
farmers do not want forests to become established on their
land)
• The greatest impact is through direct deforestation
• Humans also affect succession by:
– Erosion of footpaths
– Trampling of plants
– Hunting
– Land clearance
– Introduction of grazing animals

25. r- and K-Strategists
• Slow growing, long-lived species which exploit S-curve
growth are called K-strategists
• Fast growing, short-lived species which exploit J-curve
(boom and bust) growth are called r-strategists
• Species which employ a strategy somewhere between
these extremes are called C-strategists
• K-strategists tend to be large, have a small number of
offspring and high level of parental care (e.g. mammals)
• r-strategists tend to be small, have large number of
offspring and very little parental care (e.g. insects)
• Pioneer species tend to be r-strategists
• Climax community species tend to be K-strategists
K stands for ‘Kapazitätsgrenze’ (capacity limit)
r stands for ‘reproductive focus’

26. r and K Survivorship Curves
1000
100
10
1
0 50 100
Percentage of lifespan
Numberofindividualssurviving
K-strategists
C-strategists
r-strategists

27. r and K Survivorship Curves
• K-strategists tend to survive for their entire
potential lifespan and then die over a short time
period (e.g. humans, salmon)
• r-strategists tend to die at a young age, and those
that don’t are likely to live a long time (e.g.
turtles, oysters)
• Limiting factors that affect the shape of the curve
include:
– Competition for resources
– Adverse environmental conditions
– Predator-prey relationships

28. Questions
1. Briefly describe the stages of primary
succession
2. What is P/R ratio and how does it change as
succession proceeds
3. List the characteristics of a typical climax
community
4. What is plagioclimax. Give examples of how
humans may cause it