4_GB_26_Ecol_J

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MAIN TOPICS OUTLINE

26.1 Ecosystems 26.2 Ecological Populations 26.3 Ecological Communities 26.4 The Biosphere

LECTURE OBJECTIVES

01. Recognize the relationships that organisms have to each other in an ecosystem.
02. Understand that useful energy is lost as energy passes from one trophic level to the next (about 90% is lost).
03. Understand that useful chemicals (nutrients) are recycled.
04. Understand that humans have converted natural ecosystems to human use.
05. Understand that organisms interact in a variety of ways within ecological communities.
06. Recognize that ecological communities proceed through a series of stages to stable climax communities.
07. Name and list characteristics of the major biomes
08. Recognize that ecological populations vary (in gene frequency, age structure, sex ratio, density)
09. Describe the characteristics of a typical population growth curve.
10. Understand why populations grow.
11. Recognize the pressures that ultimately limit population size.
12. Understand that human populations obey the same rules of growth as populations of other kinds of organisms.
13. Define selected key terms.

Key Terms

26.1 Ecosystems
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26.21 Biotic Structure

26.22 Abiotic Structure

26.21 BIOTIC STRUCTURE

Biotic factors: living parts of the environment
Abiotic factors: nonliving part of the environment

26.21.1 Categories of Organisms

26.21.2 Feeding Relationships

26.21.1 CATEGORIES OF ORGANISMS

A. Producers

B. Consumers

• All ecosystems (with a few exceptions) must have an input of energy from the sun!

- energy flows through an ecosystem (one-way)

A. Producers

• Organisms that can use energy from the sun directly: Autotrophs -- self-feeders

def. Autotrophs: organisms capable of producing its own food from inorganic materials & sunlight.

• In ecological terminology these are called: Producers

def. Producers: organisms that obtain energy from sunlight by photosynthesis

def. Photosynthesis: the conversion of light energy to chemical energy (stored in glucose produced) from carbon dioxide and water.

Photosynthesis

B. Consumers

• Organisms that cannot use the sun directly -- must feed on something: Heterotrophs

def. Heterotrophs: organisms incapable of producing its own food, and therefore depend directly or indirectly on producers to
meet their food requirements.

• In ecological terminology these are called: Consumers

def. Consumers: organisms that obtain energy by feeding on the tissues of other organisms.

- - - - - - - - - - - - - - -
• Various kinds of consumers:
General types:
def. Herbivores: animals feeding on plants.
def. Carnivores: animals feeding other animals.
def. Omnivores: animals feeding both on plants and other animals.

Special types:
def. Decomposers: organisms that use dead organic matter as a source of energy (organisms whose feeding actions results in decay or rotting of organic material (mainly fungi and bacteria).
def. Scavengers: animals that feed on food left by other animals.
def. Parasites: Ecological relationship between two organisms where only one organism benefits, by deriving nourishment from the other, without killing it (at least not immediately) but usually doing harm to it.

26.21.2 FEEDING RELATIONSHIPS 6

A. Food Chains B. Trophic Levels C. Food Webs & Ecological Communities D. Energy Flow Through Ecosystems E. Ecological Pyramids

A. Food Chains (Interconnecting paths of energy flow)

• Producers and consumers are connected by food chains.

Producers - 1st Consumer - 2nd Consumer

def. Food chains: A sequence of organisms that feeds on one another, resulting in a flow of energy from a producer through a series of consumers (flow of energy as each one feeds upon the next).

i. Grazing Food Chain (Energy from the sun):

Photosynthesizer (producer) - Herbivores - Carnivores

grass - cow - human

leave - caterpillar - mouse - hawk

ii. Detrital Food Chain (Energy from dead organic matter):

Decomposer (producer of detritus) - Detritus feeder - Carnivores

fungus - earthworm - beetle

soil bacteria - earthworm - beetle

B. Trophic Levels (Feeding levels in a food chain)

• Each step in a food chain is known as a trophic level ("FEEDING LEVEL")

A trophic level is composed of all organisms that feed at a particular link in a food chain.

def. Trophic levels: a step (feeding level) in the flow of energy through an ecosystem (Organisms that photosynthesize are at the first trophic level, organisms that feed on first trophic level organisms are at the second level.)

1st trophic level: Producers -- AUTOTROPHS algae
2nd trophic level: Herbivores (primary consumer) -- HETEROTROPHS small fish
3rd trophic level: Primary carnivores (secondary consumer) -- HETEROTROPHS big fish
4th trophic level: Secondary carnivore (tertiary consumer) -- HETEROTROPHS shark
5th trophic level: Tertiary carnivore (quaternary consumer) -- HETEROTROPHS human

GRASS - COW - HUMAN

1st trophic level - 2nd trophic level - 3rd trophic level

Producer - Herbivore - Carnivore (or Omnivore)

Producer - Primary Consumer - Secondary Consumer

Autotroph - Heterotroph - Heterotroph

C. Food Webs & Ecological Communities

def. Community: a collection of interacting populations within an ecosystem.
(The populations of all species occupying a habitat.)

• Organisms in populations form many food chains that interlock -- food webs.

def. Food web: a system of interlocking food chains (the combination of all the feeding relationships that exist in an ecosystem).

BECAUSE OF COMMUNITY AND ECOSYSTEM INTERLOCKING, CHANGES IN ONE PART OF THE FOOD WEB CAN HAVE EFFECTS ELSEWHERE.

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D. Energy Flow Through Ecosystems

• Energy flows into the food webs of ecosystems from an outside source -- usually the sun.

• Energy flow is a one-way system and leaves ecosystems as

1. waste (dead tissue, urine, feces)

2. heat (metabolic heat generated by the organisms)

• The amount of useful energy flowing through the food web (consumer trophic levels) declines at each energy transfer.

(Each time energy passes from one trophic level to the next, 90% of the energy is lost as
-- heat, or waste.

E. Ecological Pyramids

• Ecosystems usually have a larger producer base -- more 'plants'

Only about 90% of the energy of one trophic level is NOT available at the next trophic level. An ecosystem can be illustrated a a pyramid. A pyramid is broad base, necessary to support the upper levels of the structure.

i. Energy Pyramid -- Energy losses between trophic levels result in pyramids based on amount of energy available.

ii. Number Pyramid -- Energy losses between trophic levels result in pyramids based on number of organisms that can feed at each level. (Some exceptions exist.)

iii. Biomass Pyramid -- Energy losses between trophic levels result in pyramids based on biomass (dry weight of a collection of designated organisms).

• At each level of the pyramid there is a 90% loss of energy:

Producer - Herbivore - Carnivore (or Omnivore)

grass - cow - human

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26.21.3 NON-FEEDING RELATIONSHIPS

-- (see Ecological Communities)

def. Community: a collection of interacting populations within an ecosystem. (All “animals” & “plants” in an area.)

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26.22 ABIOTIC STRUCTURE

26.22.1 Limiting Factors 26.22.2 Biogeochemical Cycles

Biotic factors: living parts of the environment
Abiotic factors: nonliving part of the environment

i. Climate (rain, temperature, wind, light)

ii. Chemistry (minerals, pH, salinity)

iii. Topography (physical barriers)

iv. Environmental events (fire, volcanic eruptions)

26.22.1 LIMITING FACTORS

Limiting factor: The environmental factor (the primary influence) that limits population growth.

A. Availability of raw materials
-- water

-- minerals

-- materials for the nest (the home)

B. Availability of energy
-- autotrophs: light

-- heterotrophs: food

C. Disposal of waste products
-- harmful toxic products (kill, sterilize >>> death phase)

D. Interaction with other organisms (nonfeeding interactions)
-- Competitive relationships (predation, parasitism, competition)

-- Supportive relationships (mutualism)

>>> see Ecological communities (Non-feeding relationships)

26.22.2 BIOGEOCHEMICAL CYCLES

• Energy flow (one way) vs. Nutrient recycling (cyclic, repeated)

def. Nutrient cycle (biogeochemical cycle): Repeated (cyclic) pathway of particular elements from the nonliving environment to living organisms, and then back to the nonliving environment (e.g., carbon cycle, nitrogen cycle, phosphorus cycle, water cycle).

A. Water cycle -- Cyclic flow of the water from the nonliving environment to living organisms, and then back to the nonliving environment.

B. Carbon cycle -- Cyclic flow of the element carbon from the nonliving environment to living organisms, and then back to the nonliving environment; tied to the Oxygen cycle; related to the greenhouse effect.

C. Nitrogen cycle -- Cyclic flow of the element nitrogen from the nonliving environment to living organisms, and then back to the nonliving environment; tied to the Oxygen cycle; related to the greenhouse effect.

Nitrogen fixation: Process in the nitrogen cycle where nitrogen gas N2 (for most organisms unusable) from the atmosphere is converted to nitrates NO3- and ammonia NH3 (usable forms); by lightning; by nitrigen fixing bacteria, e.g., Rhizobium, Cyanobacteria

26.3 Ecological Populations
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26.31 Population Distributions 26.32 Population Size 26.33 Population Regulation

DEFINITION:
def. Population: A group of organisms of the same species, located in the same place at the same time, and therefore can freely interbreed.

LEVELS OF BIOLOGICAL ORGANIZATION:
1 Subatomic particle, 2 Atom, 3 Molecule, 4 Macro-molecule, 5 Organelle,

6 Cell, 7 Tissue, 8 Organ, 9 Organ system, 10 Organism,

11 Population, 12 Community, 13 Ecosystem, 14 Landscape, 15 Biosphere

EVOLUTION:
Populations Evolve (Individuals do NOT evolve)

1. Individuals pass on their genes (alleles) to future generations of the population
2. If the frequency of certain alleles of a trait change in the population, then
3. Future generations of the population change, they EVOLVE

26.31 POPULATION DISTRIBUTIONS

• Population distributions depends on:

i. # of individuals/ area
ii. limiting factors
iii. pattern of dispersal of individuals within an area

• Kinds of population distributions:

i. uniform distribution (golden eagle, creosote brush, RARE)
AVOIDANCE
-- competition (territoriality, plant chemicals)

ii. random distribution (moose, spiders, EXTREMELY RARE)
NEITHER AVOIDANCE, NOR ATTRACTION

iii. clumped distribution (conifers, apes, MOST POPULATIONS)
ATTRACTION
-- form social groups

26.32 POPULATION SIZE -- # of individuals contributing to the population's gene pool.

Biotic potential (Reproductive capacity): The potential of a species for increasing its population (and distribution). Given optimal conditions all species will increase.

Exponential growth: Population growth that result in a J-shaped curve, in which numbers double at regular intervals and therefore accelerates over time, a type of growth that reflects a populations theoretical biotic potential -- w/o environmental resistance.
Logistic growth: Population growth that result in a S-shaped curve, a type of growth that results when environmental resistance comes into play.

A. Unregulated population curve J-shaped curve
TWO PHASES:

LAG -- growth is slow because the population is small

EXPONENTIAL GROWTH -- growth is accelerating
B. Regulated population curve S-shaped curve
FOUR PHASES:

LAG -- growth is slow because the population is small

EXPONENTIAL GROWTH -- growth is accelerating

DECELERATION -- growth slows down due to environmental resistance

STABLE EQUILIBRIUM -- no growth because births and deaths are about equal

26.33 POPULATION REGULATION

• Two kinds of population regulation factors:

Density-dependent population regulation factor: Biotic factor that affects the population size, e.g., disease, competition.

Density-independent population regulation factor: Abiotic factor that affect the population size -- independent of the density, e.g., fire, flood

• Population curve key terms:

Biotic potential (Reproductive capacity): The potential of a species for increasing its population (and distribution). Given optimal conditions all species will increase.

Carrying capacity: The maximum population of a given species that an ecosystem can support over a long period of time, without being degraded or destroyed.

Environmental resistance: The factors that tend to cut back population size (e.g., climate, lack of food, lack of water, lack of space, predators, disease).

26.33.1 CARRYING CAPACITY (REINDEER POPULATION)

26.33.2 CARRYING CAPACITY (HUMAN POPULATION)

26.33.1 REINDEER CARRYING CAPACITY (on Pribilof Island)

• The carrying capacity of any environment is the maximum number of individuals of a given species the environment can support.
The closer a population size gets to the carrying capacity, the greater the environmental resistance will be.

REINDEER POPULATION ON PRIBILOF ISLAND (ST. PAUL ISLAND), ALASKA, 1910 - 1950

1910 -- 26 reindeer (4 males, 22 females introduced to the island)
1920 -- 300 reindeer

about 1928 ?overshoot of the carrying capacity (more than 300 reindeer)?

1938 -- 2000 reindeer
1950 -- 8 reindeer (after population crash)

26.33.2 HUMAN CARRYING CAPACITY (on “Earth Island”)

A. Human Population Growth

B. Age Distribution

C. Present and future growth (I)

D. Present and future growth (II)

E. The Human System

F. The end of an orgy...

A. Human population growth

SOME STATISTICS:
-- present Earth population approx. 6.3 billion
-- annual growth increase approx. 100,000,000
-- 5 billion live on 10% land surface
-- 3 billion live w/in 480km (300 miles)of the sea
-- billions are malnourished or starving

Double the food supply -- million would still be starving

Question: What would happen if the Human population doubled?

B. Age distribution

• Age distribution contribute to our understanding of the past and future history of a population’s growth.

Age Distribution Diagram: A demographics display of the age groups of a population.

Pre-reproductive age group large

pyramid shaped diagram

>> expanding population

Pre-reproductive age group same as reproductive age group bell shaped diagram (most ages same)

>> stable population

Pre-reproductive age group small urn shaped (almost upsidedown pyramid) diagram

>> diminishing population

C. Present & future growth of the human population (I)
(Source: Starr & Taggart; some Hardin)

500,000 yrsa	less 1 million	doubling time: 233,333 years
10,000 yrsa	5 million	doubling time: 1000 years
1804	1 billion	doubling time: 123 years
1927	2 billion	doubling time: 47 years
1960	3 billion	doubling time: 33 years
1974	4 billion	doubling time: 37 years
1987	5 billion	doubling time: 38 years
1999	6 billion	doubling time: 40 years
2008	7 billion?	doubling time: 40 years?
2011	8 billion?	doubling time: 40 years?
2040	12 billion?	doubling time: 40 years?
2080	24 billion?	doubling time: ?

D. Present & future growth of the human population II
(Source: Garret Hardin)

• Population increase has been slow during most of human history.

(From the chapter “End of an Orgy”, by Hardin, G. 1972. Exploring New ethics for Survival: The Voyage of the Spaceship Beagle. Penguin Books, Harmondsworth, Middlesex, England. 273 pp.)

During the last 1 million years of human existence on earth, the first 700,000 years the doubling time was 233,333 years!

The doubling time then decreased and reached a 994 years temporary low 10,000 years ago. This low occured during the time we call “agricultural revolution” -- when Man learned to grow plants for his/her needs.

Another low, 33 years, was reached between 1950 - 1960.

“This is (undoubtedly) the fastest growth rate the world population will ever experience.

• From now on population growth will diminish -- until it reaches zero.

It is even probable that it will swing below zero until the total population reaches a lower level, more adequat for Spaceship Earth’s ability to sustain life.

If the worst happens, population may reach zero, at which point all talk of growth rates and doubling times stops.”

“Most men, having only an imperfect understanding of biology and history, incorrectly thinks that population growth is normal.”

• "FUN (?) WITH NUMBERS?" Some hypothetical future population numbers -- if the world continues the present growth rate:

CONDITION

POPULATION

TIME

DATE REACHED

BACKWARD TIME EQUIVALENT DATE

Standing room only (land areas only)

8.27 x 10¹⁴

615 years

2585 A.D.

1355 A.D.

Standing room only (incl. oceans)

28.34 x 10¹⁴

677 years

2647 A.D.

1293 A.D.

All earth converted to human flesh

1.33 x 10²³

1557 years

3527 A.D.

413 A.D.

Human_Flesh_Table

• The real reason for the mathematical exercise above:

To change peoples “laissez-faire attitude about population growth (refusing to face the hard choices of population control).”

Some people think that since it is ridiculous to say that people would ever allow themselves to be packed together like sardines, population problems does not exist.

During the past few centuries coitus interruptus (“withdrawal”) has been the most common method of birth control, and today the most single used method of birth control is abortion. (Chapter Parenthood: Right or Priviledge?)

E. The Human System

• Is the human system a true ecosystem (and therefore natural)?
Should we be concerned about what the human species is doing to the planet?

-- Another way to ask the same thing:

• Is the human system sustainable? (A true ecosystem is always sustainable.)

Answer: NO, because

1. it fails to break down or recycle wastes

pollution

2. it relies on non-renewable energy sources -- 'fossil fuels'

global warming, destruction of the ozone layer

• If the population problem does exist and Hardin (1972) lists the following hard questions humankind must answer:

1. What is the optimum level of population?

2. What standard of living is that decision based on?

3. How do we choose from among alternate standards?

4. How do we deal with differences of opinion?

5. How do we control breeding?

6. How do we justify coercion?

7. Who decides?

• However, if “there is no population problem, there is no need to face these fearful questions” above.

• If we say that the population problem does NOT exist, Hardin lists the conclusions as “reductio ad absurdum” below:

1. Assume that there is no need for change, i.e., > 48 BILLION PEOPLE -- NO PROBLEM!

2. Grant the most unbelievable technological possibilities, e.g., turning granite into food, i.e., NO PROBLEM WITH THE CARRYING CAPACITY.

3. At some time in the future, about six hundred years, an abrupt change will be forced upon us, i.e., we will have STANDING ROOM ONLY.

4. Refusing to change voluntarily will result in change being forced upon us, i.e., ENVIRONMENTAL RESISTANCE OUT OF OUR CONTROL.

A change of our own choosing can be pleasanter than the unavoidable change that will be forced upon us if we refuse to make a choice. Loss of freedom to breed is less horrible than massive death by starvation, epidemics, social chaos, and insanity.(Hardin, 1972).

F. The end of an orgy... (Principles of sustainability)

• We DO have the knowledge & the technology to create an ecologically sustainable human system.

def. Sustainable agriculture: Agriculture that maintains the integrity of soil and water resources such that it can be continued indefinitely. (Much of modern agriculture is depleting these resources on which it depends.)
def. Sustainable society: A society that functions in a way so as not to deplete energy and material resources on which it depends.
def. Sustainable yields: The taking of a biological resource (e.g., fish or forest) that does not exceed the capacity of the resource to reproduce and replace itself.
def. Sustainable: Something that can be maintained indefinitely without being depleted.
def. First basic principle of ecosystem sustainability: Ecosystems dispose of wastes and replenish nutrients by recycling all elements.
def. Second basic principle of ecosystem sustainability: Ecosystems use sunlight as their source of energy.
def. Third basic principle of ecosystem sustainability: Ecosystems maintain consumer populations at a proper size so that overuse does not occur.
def. Fourth basic principle of ecosystem sustainability: Ecosystems maintain a workable biodiversity.

Principles of sustainability

1. Wastes & nutrients (recycled)
2. Energy source (sunlight)
3. Consumer population level (size so overuse do not occur)
4. Biodiversity (maintained)

• No intelligent decision should be made “in economics, politics, or anything else that touches on human welfare”, unless the following is taken into account (Hardin, 1972):

We live in a spaceship. Men can escape from it -- find another planet, but mankind cannot.

The past two hundred years have been an absolutely exceptional period in the million-year history of Homo sapiens. It has been an orgy of expansion and exploitation of irreplaceable environmental riches.

We are only a few moments away from the end of the orgy...

...which will never be repeated.

The rich mineral deposits lying near the surface, the apparent boundless virgin forests, the increadable concentration of marine fish...

-- all, all will be gone, never to return.

Are we doomed or is there a solution?

Chemostat?

Not On-Line

CNN: Plants to Mars

../CNN_Starr_Taggart_f/26_Ecol_PlantsToMars.mov

26.4 Ecological Communities

26.41 Feeding Relationships

26.42 Non-Feeding Relationships

26.43 Succession

BECAUSE OF ECOSYSTEM INTERLOCKING, CHANGES IN ONE PART OF THE FOOD WEB CAN HAVE EFFECTS ELSEWHERE.

Organisms going extinct in one part of the world, may affect organisms in another part of the world.

----Tropics--------------------------......----------------USA----

Rainforest Plant >> Insect >> Songbird......Songbird << Insect << Crop Plant

Human

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26.42 NONFEEDING RELATIONSHIP
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def. Niche: The specific functions of an organisms -- the "job" of an organism. (Total of all relationships that determines how an organism do in an ecosystem, including both biotic and abiotic factors.)
def. Habitat: The specific environment of an organisms -- the "home" of an organism.
def. Mutualism: Relationship between two organisms where both organisms benefit.
def. Commensalism: Relationship between two organisms where one organism benefits without harming the other one.
def. Predation: Ecological relationship between two organisms where only one organisms benefit, by deriving nourishment from the other, by killing.
def. Parasitism: Ecological relationship between two organisms where only one organisms benefit, by deriving nourishment from the other, without killing it (at least not immediately) but usually doing harm to it.
def. Interspecific competition: competition between species in a community
def. Intraspecific competition: competition within (a population of) a species
def. Camouflage: A defense against being eaten in which organisms mimic materials in the environment in an attempt to be invisible.
def. Mimicry: Superficial resemblance to an unrelated species.
def. Warning coloration: A bright, memorable design that helps the predator remember which prey to avoid.

A. Mutually Supportive Relationsships

-- mutualism
-- commensalism

B. Competitive Relationsships

-- predation
-- parasitism

C. Predator Prey Interactions

-- Camouflage
-- Mimicry
-- Warning Coloration

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26.43 ECOLOGICAL SUCCESSION (Community change over time)
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def. Succession: Gradual changes in the structure of a community, due to some abiotic change, ultimately leading to a climax community.
- - - - - - - - - - - - - - -
def. Primary succession: Ecological succession to a climax ecosystem in an area that has not been occupied before (e.g., rock face).
def. Secondary succession: Ecological succession to a climax ecosystem in an area that has been occupied before (e.g., an area that has been cleared).
def. Climax community: Last stage of succession, a relatively stable long-lasting community of organisms.
def. Climax ecosystem: An ecosystem with a climax community, the last stage in ecological succession. (An ecosystem in which populations of all organisms are in balance with each other and with existing abiotic factors. The biomes are climax ecosystems for their particular areas.)
def. Pioneer species: Early colonizer of barren or disturbed habitats that usually has rapid growth and high dispersal rate.
def. Fire climax ecosystems: Ecosystems that depend on the recurrence of fire to maintain balance.
def. Aquatic succession: Ponds and lakes gradually filled in and invaded by the surrounding land ecosystem.
def. Immediate disturbance hypothesis: moderate disturbance is required for a high degree of community diversity.

--- CLIMAX VEGETATION

• Ecological communities change over time. In primary succession a new community form where no community previously existed (e.g. a new island, or bare rock after a volcanic event -- the first species to invade is called a pioneer species); in secondary succession the types of species change after a disturbance in the area (e.g. after a forest fire, or agriculture), with some soil and life remaining.

• Succession often leads to a climax community, which is a community that remains fairly constant as long as climate does not change or a major disturbance does not occur. The climax community is often a type of forest.

26.51 Climate and Topography

26.52 Biomes and Mountain Life Zones

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def. Biomes: A group of large regional communities ("ecosystems") that are related by having a similar type of vegetation governed by similar climatic conditions (e.g., arctic grasslands ("tundra"), temperate grasslands ("prairies"), tropical grasslands ("savannas"), deserts, tropical rainforests).
def. Climate: Prevailing weather conditions for an ecosystem (incl. temperature, humidity, wind speed, cloud cover, and rainfall).
def. Succession: Gradual changes in the structure of a community, due to some abiotic change, ultimately leading to a climax community.
def. Climax community: Last stage of succession, a relatively stable long-lasting community of organisms.
def. Rain shadow: A reduction in rainfall on the leeward side of high mountains, resulting in arid or semiarid conditions.
def. Biosphere: Portion of Earth inhabited by life; all of the earth's waters, crust, and atmosphere in which organisms live.

A Biomes

B. Distinct climax vegetation

C. Mountain Life Zones

D. Deserts

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A. Biomes (Terrestrial size communities)

• A biome is characterized by the climax vegetation adapted to living under certain environmental conditions.

• The distribution of the biomes can be described as bands going east - west along the latitudinal gradients of the planet. However, there is no definite demarcation but rather a gradual change from one biome to another. Also, the bands are irregular, affected by altitude (mountains) which change the climate expected at certain latitudes (mainly temperature and rainfall).

1. Polar biome (latitude ≈ N 90° / S 90°)

-- snow and ice

2. Tundra (latitude ≈ N 70° / S 70°)
-- Arctic circle 66° 33 min

3. Conifer forest (latitude ≈ N 60° / S 60°) (annual rainfall 25 - 60mm)

4. Temperate broadleaf forest
-- (e.g., Temperate Deciduous forest, temperate rain forest) (annual rainfall 60 - 3000mm)

5. Temperate grassland
-- (e.g., Prairie, Pampas)

6. Desert (latitude ≈ N 30° / S 30°) (annual rainfall < 25mm)
-- Tropic of Cancer N 23° 27 min, Tropic of Capricorn S 23° 27 min

7. Tropical grassland
-- (e.g., Savanna)

8. Tropical broadleaf forest ( latitude: 0° -- equator) (annual rainfall 2000 - 4000mm)
-- (Tropical Deciduous forest, Tropical rainforest)

B. Distinct climax vegetation

• Distinct climax vegetation prevail at certain latitude and altitudes

-- latitudes -- gives temperature, precipitation (rain/moisture) and wind variation

-- altitudes -- gives temperature, precipitation (rain/moisture) and wind variation

- short, less leafy plant species prevails in

-- dry regions

-- high latitudes / high altitudes

- tall, very leafy plant species prevails in

-- wet regions

-- low latitudes / low altitudes

• The distribution of biomes is therefore determined by climate (temperature, precipitation and wind) and latitude & altitude.

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C. Mountain Life Zones

• Compare biomes with mountain vegetation zones. High mountains show the same kind of vegetation subdivisions called Life Zones.

D. Deserts

def. Rain shadow: A reduction in rainfall on the leeward side of high mountains, resulting in arid or semiarid conditions.

• At the equator and at 30° latitudes certain climate factors persist:

-- at the equator, air heats up at the equator-picks up moisture-rises to cooler altitudes - RAIN

-- at 30° latitudes, dry air moves away from the equator-descends at 30° latitudes-warms up - DRY

Deserts are therefore usually found at latitudes of about 30° north and south on the planet. The winds that descend at 30° latitudes lack moisture (annual rainfall 250mm). Also, because of very little cloud cover days are hot -- the sun’s rays reach the surface easily, and nights are cold/cool -- heat escapes easily into the atmosphere.

• Deserts form:

-- at 30° latitude by prevailing dry wind patterns caused by climate factors (as discussed above)

-- at other latitudes with rain shadow created by a mountain range

When winds from the direction of the sea cross a costal mountain range (the windward side), the winds rise and release moisture when coolong down (condensation). The other side of the mountain range (the leeward side) receives no or very little rain. This side is said to be in a Rain Shadow.

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Copyright 2002, 2003, Jan A. Nilsson. Web page layout and design © and intellectual property Jan A. Nilsson. All rights reserved. Reproduction of the whole or any part of the contents without written permission is prohibited. Page created 10.XII.2002, last updated 30.V.2003, most likely during the wee hours of the morning on a G3 PowerBook owned by Jan A. Nilsson. Please send comments and suggestions to: J.A. Nilsson

-- Disclaimer: "Dr. Nilsson's CyberOffice", at the time of writing located as a file under the South Texas Community College's (STCC) web server with the general URL http://stcc.cc.tx.us/, is the intellectual property of Dr. Jan A. Nilsson, member of STCC biology faculty. The content of Dr. Nilsson's CyberOffice does not necessarily reflect the opinions and beliefs of the STCC faculty, staff, administration, and Board of Trustees.