Chapter 5: Interactions in the Ecosystem

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Chapter 5 Interactions in the Ecosystem

• 5.1 Habitats and Niches
• 5.2 Evolution and Adaptation
• 5.3 Populations

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Objectives

• Describe the concept of the niche.
• Examine how interactions between a species and
  its environment define the species niche.

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Chapter 5Interactions in the Ecosystem

• An ecosystem is a network of living and nonliving
  things.
• Organisms are connected by food webs and by their
  common needs.
• All organisms need
• A. Food and Energy
• B. Water
• C. Living Space
• D. Appropriate Climate

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Interactions in the Ecosystem (cont.)

• All species have evolved different ways of
  gathering resources from their environment.
• Evolution ties together biology and the physical
  world as ecology ties together the interactions
  between living and nonliving things.
• Therefore, the study of ecosystems is also the
  study of evolution

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5.1 Habitats and Niches

• Ecosystems can be extremely large containing
  many square kilometers and many different
  organisms.
• Environments within an ecosystem vary the
  environment by a stream is different than the
  environment in a forest.
• The organisms in these different environments are
  different from each other. They have adapted to
  the conditions in their particular habitat.

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Niches

• Niche-the role of an organism in the ecosystem.
• The actions of an organism define its role in the
  ecosystem.
• A niche is more than just the habitat an
  organisms lives in it is also what that
  organism does within its habitat

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Niches (cont.)

• A niche includes both the biotic and abiotic
  factors.
• All the biotic and abiotic factors taken
  together define an organisms niche.
• Biotic factors-food source and predators
• Abiotic factors-temperature, amount of sunlight
  and water

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Niches (cont.)

• All members of a species are adapted to the same
  niche.
• No two species can share the same niche in the
  same habitat.
• Two species can occupy niches that are very
  similar to each other.

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Niches (cont.)

• Example Anolis lizards
• The niches of the different species vary only in
  the size of the insects they eat.
• If two species try to share the same niche in the
  same habitat, they will compete for resources.
• This could cause the one specie to have to move
  to another area or the populations to die out.

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Anolis Lizard
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Niches (cont.)

• Competitive exclusion the extinction of a
  population due to direct competition with another
  species for resources.
• Competitive exclusion is the extinction of one
  population in one area not the extinction of a
  whole species.

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Niches (cont.)

• In many ecosystems the niche of one specie can
  effect the niche of another specie.
• Figure 5.3 p. 74 Barnacles

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Barnacles

• Species B (Balanus)was responsible for the niche
  of species A (Chthamalus) and when removed A
  began to grow further down.

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Niches (cont.)

• Fundamental niche-the theoretical niche
• Realized niche-the actual niche

Fundamental Niche
Realized Niche
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Niche Diversity

• Niche diversity is determined by the abiotic
  factors in an ecosystem.
• Predator-an organism that actively hunts another
  organisms
• Prey-the hunted organism
• Predators help to increase the diversity of
  niches by keeping the population of its prey in
  check. This allows resources to be available for
  other organisms.

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Niche Diversity (cont.)

• Keystone predator- a predator that promotes a
  great niche diversity in its habitat.
• Robert Paine and the Sea Stars
• He removed the sea star from a tide pool and as a
  result the mussel population increased until they
  began to out compete the other species.
• The number of species dropped from 15 to 8.

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Sea Stars and Tide Pools
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Review

• What is a niche?
• What effect does a keystone predator have on
  niche diversity?
• What is the difference between a fundamental
  niche and a realized niche?

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5.2 Evolution and Adaptation

• Objective
• Explain how a species adapts to its niche.
• Describe convergent evolution and coevolution,
  and relate each to the concept of niche.

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Evolution and Adaptation

• Ecosystems change over time. Mountains are
  created and eroded, rivers change course forest
  are created and destroyed.
• Changes in environment affect the niches of the
  organisms in that particular environment.
• Changes in the environment affect the evolution
  of populations

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Natural Selection

• http//www.pbs.org/wgbh/evolution/educators/course
  /session4/explore_a.html

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Evolution

• Evolutions is a change in the characteristics of
  a population of organisms over time.
• This occurs when some individuals have genetic
  variations that give them an advantage over other
  organisms.
• Evolution Online Lessons for Students Activity
  4- Flashy Fish

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Evolving in a Niche

• Evolution causes organisms to evolve to a certain
  niche in the environment.
• This reduces competition with other species.
• Fig. 5.5 Warblers
• Specialized species-Koala
• Generalized species-Cockroaches

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Convergent Evolution

• Similar ecosystems often have similar niches.
• Environmental pressures may then select for
  similar adaptations. Resulting in organisms that
  may even look alike.
• Convergent Evolution- the independent development
  of similar adaptations in two species with
  similar niches.
• Examples Figure 5.6 and

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Convergent Evolution
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Convergent Evolution
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Coevolution

• Other organisms may play an important role in the
  life of an organism.
• Keystone Predators
• Species that interact closely may become adapted
  to one another through a process called
  Coevolution.
• Result from Feeding relationships and
  adaptation for mutual benefits.
• Examples

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Coevolution Yucca Moth and Yucca Plant
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Coevolution

• http//www.pbs.org/wgbh/evolution/library/01/3/qui
  cktime/l_013_01.html

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Review

• How do species adapt to the environment?
• What is the difference between coevolution and
  convergent evolution?

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5.3 Populations

• Objectives
• Explain how populations of organisms grow.
• Describe the factors that limit the growth of a
  population.
• Identify the shapes of growth curves that
  represent populations of different organisms.

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5.3 Populations

• The abiotic and biotic factors that define a
  niche also limit the growth of a species.
• Size of a population can be limited by
• Lack of food
• Predators
• Disease

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Population Growth

• Thomas Malthus an English economists studied
  human population.
• He stated
• Human population can quickly grow past the
  environments ability to support it.
• He felt that famine and disease occurred when
  populations became too large.
• Bubonic Plague

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Population Growth

• Malthuss observations influenced a naturalist by
  the name of Charles Darwin.
• On the Origin of Species
• There is no exception to the rule that every
  organic being naturally increases at so high a
  rate, that, if not destroyed, the Earth would
  soon be covered by progeny of a single pair.

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Population Growth

• Important to Darwins theories of evolution was
  the idea that organisms produce more offspring
  than can survive.
• Overproduction of offspring causes
• Selection of the more favorable traits (survival
  of the fittest)

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Population Growth

• Darwin illustrated overproduction with the
  example show in Figure 5.8 p. 80.

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Population Growth

• Exponential Growth- population growth in which
  the rate of growth in each generation is a
  multiple of the previous generation.
• Any population has the potential to increase
  exponentially ifthe perfect conditions exist

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Population Growth

• Although natural population can show exponential
  growth, it occurs only for a short time. This is
  due to the availability of resources and
  restricted geographic areas.

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Carrying Capacity

• As a population grows it takes more from the
  habitat.
• Resources become scarce.
• Scarce Resources Competition
• Death rate increases
• Birth rate decreases
• Growth Slows
• Birth rate Death rate (population growth stops)

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Carrying Capacity

• Carrying Capacity- the number of individuals of a
  species that can be supported by an ecosystem
• Figure 5.9 p. 81

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Limiting Factors

• Forces that slow the growth of a population are
  called the limiting factors.
• Figure 5.10 p. 82
• Examples

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Limiting Factors

• Two kinds of limiting factors
• density dependent limiting factors
• density-independent limiting factors

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Limiting Factors

• Density dependent limiting factors dependent on
  population size.
• Food supply
• Predation
• Disease
• Parasitism
• Living Space
• Water Availability
• Density dependent factors are related to
  competition and other interactions between
  organisms
• As populations grow these factors have a greater
  effect.

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Limiting Factors

• Density-independent limiting factors affects
  the same percentage of a population regardless of
  its size.
• Climate
• Human Disturbances
• Deforestation
• Natural Disasters
• Hurricanes

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Limiting Factors

• Populations controlled by density dependent
  factors show a S-shaped growth curve.
• Populations controlled by density-independent
  factors show a boom-and-bust curve. This type of
  curve represents exponential growth.
• Many insects follow this type of curve.
• Figure 5.11 p. 83

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S-Shaped Curve
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Boom Bust Curve
Population
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Human Population

• Human population has long been an exponential
  one.
• This continuing exponential has continued due to
• Advances in medicine, technology, agriculture,
  energy development, transportation
• However, no population can continue this way.
• Human population growth will level out as
• Use up all the available resources

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Summary

• What is exponential growth?
• What is carrying capacity?
• What are the two types of limiting factors?
• What has allowed human population to keeping
  growing exponentially?