Ecosystem Balance

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Chapter 6

• Ecosystem Balance

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Ecosystem Balance

• 6.1 Relationships in the Ecosystem
• 6.2 Ecological Succession
• 6.3 Stability in the Ecosystem
• 6.4 Land Biomes

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6.1 Relationships in the Ecosystem

• Objectives
• Explain the relationship between the population
  sizes of predator and prey.
• Define symbiosis and describe several symbiotic
  relationships.

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Relationships in the Ecosystem

• A complex web of relationships exist among all
  the species in an ecosystem.
• Scientists study these relationships by
• Studying how two populations interact with one
  another.
• Expanding the knowledge they have gained to other
  parts of the ecosystem.

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Predator and Prey

• One of the relationships ecologists study is that
  of predator and prey.
• Define Predator.
• Define Prey
• Examples

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Predator and Prey
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Predator and Prey

• The sizes of predator and prey populations are
  closely linked.
• Figure 6.1 p. 89
• Prey experience populations cycles.
• A predators populations cycle mimics that of its
  prey.

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Parasitism

• Some animals do not kill the prey they feed on.
• Parasitism-an organism that feeds on the tissue
  or body fluids of another organism
• Host-the organism the parasite feeds off of
• Examples

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Parasites-Tapeworms and Roundworms
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Symbiosis

• Symbiosis-a relationship in which two species
  live closely together
• Three types
• Parasitism-one is helped and the other is harmed
  (typically)
• Commensalism- one organism benefits and the other
  is neither helped or harmed
• Examples
• Mutualism-both organism benefit
• Examples

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Commensalism
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Mutualism
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Questions

• What is the relationship between the population
  sizes of predator and prey.
• Define Symbiosis
• What are some examples of symbiotic relationships?

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6.2 Ecological Succession
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Objectives

• Contrast primary and secondary succession.
• Describe the sequence of ecological succession in
  a lake and on an island.

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Ecological Succession

• Organisms affect their environment
• Example Plants ? Soil
• Changes are not always beneficial
• Old niches are replaced by new niches.
• Other forces can cause change in the environment.
• Example Forest Fire

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Ecological Succession

• As environment change the communities living in
  that environment change as well.
• In many cases different communities follow one
  another in a definite pattern, this is called
  succession.

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Volcano Eruption

• A volcano erupts leaving the land covered in bare
  black rockit is lifeless.
• Does it stay this way?

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Volcano Eruption (cont)

• No
• Almost immediately organisms begin to inhabit the
  area.

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Primary Succession

• Define Primary Succesion
• Examples Cooled lava fields and exposed rock
  from retreating glaciers.

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Primary Succession

• Primary succession is an orderly process.
• Follows the same general pattern in most
  ecosystems.

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Step 1

• Colonization by new organisms and formation of
  soil from exposed rock.
• On land this is done by lichens.
• Define lichens.
• Lichens can live on bare rock.

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Step 1 (cont)

• Lichens secret acids that break down the rock and
  form organic material by photosynthesis.
• Weathering also breaks down rocks.
• Soil is formed by the actions of the lichens and
  weathering.

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Pioneer Community

• Lichen Community
• First community to colonize the area.

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Step 2

• Once soil is formed, grasses and other small
  plants begin to grow.
• Root growth and accumulation of dead leaves ?
  Soil formation
• Plants grow dense ? lichen disappear

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Grass Community

• Survives for many generations and makes the soil
  deeper and more fertile.
• Soil is deep enough ? Growth of nonwoody plants
  with deep roots (Heath Mat).
• These plants are taller and shade out the
  grasses.
• Since the grass/shrub community is not diverse a
  small disturbance may cause drastic change.

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Pines and other tress

• Pines or other trees with shallow roots are next.
• Trees shade out the heath mat.

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Broadleaf and Hardwood Trees

• As the soil deepens even further broadleaf and
  hardwood trees take over.
• Hardwood forest in the final stage of succession
  in many areas.

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Climax Community

• A community that does not undergo further
  succession.
• Climax communities are usually highly diverse and
  can often survive even severe local disturbances.

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Primary Succession
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Primary Succession

• Only occurs on freshly exposed rock or in places
  where a severe disturbance has occurred.
• However most disturbances are not this drastic.

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Secondary Succession

• A fire may kill many plants but leave the soil in
  place.
• Living things can quickly colonize these types of
  areas.
• Define Secondary Succession.
• Examples Storms, Fires and human activity

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Deforestation
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Secondary Succession

• Secondary succession resembles the later stages
  of primary succession.
• 1st to colonize are
• Next to colonize
• Final to colonize

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Secondary Succession

• Research has shown that many habitats never
  develop climax communities.
• Why?
• Example

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Secondary Succession
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Aquatic Succession

• Newly formed mountain lake.
• Low nutrient levels
• Supports few organisms.
• Reeds and other aquatic plants.
• Organic matter builds up and lake fills with
  sediment.
• Nutrient rich water
• Increase in wildlife
• Water plants cover the surface.
• Lake fills with sediment ?Marsh
• Land plants begin to colonize
• Finally ?Fertile Meadow (possibly a forest)

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Island Succession

• Similar to succession on the continents.
• Any organisms found on an island must have
  ancestors that were
• Carried by water
• Carried by wind
• Carried by other organisms
• Many islands have large bird populations.

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Island Succession

• There are many unfilled niches on islands.
• Organisms can evolve to fit many niches.
• When a population of organisms adapted to their
  new niches new species are formed.
• Example Figure 6.9 p. 95

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Review

1. How does primary and secondary succession differ
   from each other?
2. What is a climax community?
3. What is a pioneer community?
4. Describe the sequence of ecological succession in
   a lake and on an island.

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6.3 Stability in the Ecosystem
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Objectives

1. Explain the concept of ecosystem stability.
2. Characterize the effects of disturbances on the
   ecosystem

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Stability is a measure

• of how easily an ecosystem is affected by a
  disturbance.
• how quickly it returns to its original condition
  after a disturbance.
• Conditions include biotic and abiotic factors,
  patterns of energy flow and nutrient cycling.

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More stable ecosystem

• Will return steady pattern of energy flow
• Experience fewer food web changes.
• Fewer evolutionary changes
• Fewer changes in the abiotic environment.

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Stability in the Ecosystem

• Determined by the complexity of food web
• Manages the systems energy flow and nutrient
  cycles.
• More connectionsstability
• Impact of disturbance is less.

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Equilibrium

• State of balance
• Changes counteract other changes.
• Weather cooling is counteracted by the
  evolutionary adaptation to cold weather.
• Disturbed ecosystem returns to a state of
  equilibrium (balance).

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Ecosystem Function

• Scientist do not understand every detail of how
  even simple ecosystems function.
• They do understand that a change in one part of
  triggers a change in another.
• Scientists are trying to apply the chaos theory.

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Chaos Theory

• A type of mathematics
• Suggests that ecosystem may be sensitive to even
  small changes
• The beginning state of an ecosystem is crucial to
  its later development.

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Species Extinction

• Species are becoming extinct at an alarming rate.
• Fastest since the extinction of dinosaurs.
• Possible causes
• Human Growth
• Habitat destruction
• Introduction of foreign species
• Pollution of fresh water

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Thought

• It is difficult for scientists to predict the
  long-term effects of humans on the biosphere.
• And for them to predict the ability of the
  biosphere to support human population.

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Review

• What makes an ecosystem stable?
• What happens to a stable ecosystem when a
  disturbance occurs?
• What happens to a ecosystem that is unstable when
  a disturbance occurs?

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6.4 Land Biomes
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Objectives

• Explain the concept of the biome, and name the
  eight major land biomes.
• Name an area in which each type is located.

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Biomes

• Earth is very large and diverse
• Environments range from the ice of Antarctica to
  the heat and rain of the Amazon.
• Difference in temperature and rainfall create a
  vast array of conditions.
• Life has adapted to almost all of these
  conditions.

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Biomes

• Definition-major type of ecosystem with
  distinctive temperature, rainfall and organisms.
• Either terrestrial or aquatic.

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Biomes

• Biome is the largest general category used to
  classify ecosystems
• Conditions may vary from place to place
• Smaller ecosystems within a biome may have
  different habitats with different conditions and
  organisms.
• Every habitat on Earth is different.
• Term Biome is useful when discussion related
  habitats.

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Aquatic Biomes

• Determined by
• Water depth
• Nutrients
• Nearness to land

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Terrestrial Biomes

• Determined by
• Average temperature
• Amount of precipitation
• 8 major types of land biomes
• Desert
• Tundra
• Coniferous forest
• Deciduous forest
• Rain forest
• Steppe
• Prairie
• Savanna

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Desert

• Low humidity
• High summer temperatures
• Low annual rainfall
• Supports only a small amount of biomass
• Deserts cover 25 of Earths land surface
• Deserts contain only 1 of Earths biomass
• Plant life is scarce in a desert due to lack of
  water

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Desert in Australia
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Tundra

• Cold
• Windy
• Dry
• South of polar ice caps in Alaska, Canada,
  Greenland, Iceland, Norway and Asia
• Very little plant life due to lack of water

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Tundra
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Forest Biomes

• Contains 75 of Earths Biomass
• Three types
• Coniferous forest- containing conifers.
• Deciduous forest containing deciduous trees.
• Rain forest dense canopy of evergreen, broadleaf
  trees that receives at least 200 cm of rain each
  year.

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Deciduous Forest
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Coniferous Forest - Yosimite
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Amazon Rain Forest
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Rain forest

• Covers only 6 of Earths land surface.
• Contains more than 50 of all Earths biomass.
• Most diverse biome.
• Destruction of the rain forest is a HUGE
  environmental problem

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Grasslands

• Cover 22 of Earths land surface
• Contain 8 of Earths biomass.
• Grasslands receive less precipitation than do
  forests and may have long dry seasons.
• May experience frequent fires
• Home to large herds of migrating herbivores
• Three types
• Steppe
• Prairie
• Savanna

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Steppe

• Grassland Biome
• Receives less than 50cm of rain per year
• Characterized by short bunchgrasses.

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Steppe
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Prairie

• Grassland Biome
• Characterized by
• Rolling hills
• Plains
• Sod-forming grasses

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Prairie
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Savanna

• Grassland Biome
• Tropical
• Ranging from dry scrubland to wet, open woodland

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Savanna - Africa
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Review

• What is a biome?
• What are the 8 major types of land biomes?
• What type of land biome covers the largest land
  area?
• What type of land biome contains the most biomass?