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 & Skills1. Explain the distributions, structure, biodiversity and

relative productivity of contrasting biomes. 2. Analyze data for a range of biomes3. 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■ Species interactions

(including humans)www.vcbio.science.ru.nl

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

• We saw these population growth curves before.

• S-shape curve represents a population that is at carrying capacity (K-strategy species)

• J-shape curve represents a population existing in an exponential phase of growth (r-strategy species)

J-shaped Growth Curve

online.science.psu.edu

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 CurvesShow 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

■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)

With a partner, discuss how/when we would have an ecosystem with NO soil present. How does this present a problem to an ecosystem?

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?

■ 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

Secondary Succession

Stages of SuccessionBare,

inorganic surface

Stage 1 – Colonization

Stage 2 – Establishme

nt

Stage 3 - Competition

Stage 4 – Stabilization

Climax community

Primary Succession: Mt. St. Helens Case Study

en.wikipedia.org

Mt. St. Helens, Washington USA 1980 (Pre-Eruption)

Primary Succession: Mt. St. Helens Case Study

www.pbs.orgMt. St. Helens, Eruption 1980

Primary Succession: Mt. St. Helens Case Study

http://www.mnn.com/Mt. St. Helens, After Eruption 1980

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.