CHAPTER 5
Interactions in the
Ecosystem
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SECTION 3.3 - THE ECOSYSTEM
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SECTION 3.3 - THE ECOSYSTEM
Levels of Organization
• Individual – one organism from a species.
• Species – a group of organisms so similar to one another that they can breed
and produce fertile offspring.
• Since they all have the same needs they compete with one another for food,
shelter, space, mates, etc.
• Populations – All the members of a species that live in the same
geographic area, a group of the same species.
• Communities – are made up of different populations of organisms that
interact in the same area at the same time.
• Ecosystems – are large places where all the biotic factors and abiotic
factors interact with one another.
• Abiotic factors generally cause environmental differences.
• Biome – made up of ecosystems: grasslands, savannah, desert.
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SECTION 5.1 – HABITATS AND
NICHES
• Habitat – the specific environment in which a
particular species lives.
• Within their habitat individual organisms find the
appropriate food, shelter, temperature and other
factors needed to survive.
• Niche – the role or actions of an organism in an
ecosystem; what the organism does in its habitat.
• An organisms niche is defined by all the biotic and
abiotic factors in the environment.
• Competition occurs between species when they try
to share the same niche.
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SECTION 5.1 – HABITATS AND
NICHES
• Competitive Exclusion – the extinction of a population due to direct
competition with another species for a resource in the same area.
• Not the extinction of the whole species!
• The presence of one species might limit the niche of another.
• Fundamental niche – a theoretical niche of an organism.
• The realized niche of an organism is an organisms actual niche.
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SECTION 5.1 – HABITATS AND
NICHES
Predator vs. Prey
• Predator – an organism that actively hunts other organisms.
• Prey – the organism that is hunted.
• Predator vs. prey relationships help keep environments
stable.
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SECTION 5.1 – HABITATS AND
NICHES
• Keystone predator – a predator that promotes a great
niche diversity in its habitat.
• It increases the biodiversity in a habitat.
• If they are removed from an environment; it often
decreases the overall diversity of organisms because
a chain reaction of events will occur.
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SECTION 5.2 – EVOLUTION AND
ADAPTATION
Ecosystems change over time
• Change in an environment will affect the niches of organisms.
• Changes in the environment affect the evolution of populations
• Evolution – a change in the characteristics of a population of organisms
over time.
• Evolution happens when some individuals have genetic variations that
allow them to produce more offspring with a certain trait or gene that is
more advantageous for survival.
• “Survival of the Fittest”
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SECTION 5.2 – EVOLUTION AND
ADAPTATION
Evolving in a niche
• Specialized species – an organism with a small
niche.
• Koala and eucalyptus trees.
• Pandas and bamboo.
• Vulnerable to extinction.
• Are less able to tolerate habitat disturbance, so
would thrive in an area with outside human
activity.
• Living on an island without human involvement.
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SECTION 5.2 – EVOLUTION AND
ADAPTATION
Convergent Evolution
• If niches in two ecosystems are similar, the organisms that evolve there
may also look alike.
• It is the independent development of similar adaptations (traits) in two
species with similar niches.
• Wings of birds and wings of bats (mammals) because both their niches
require flight.
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SECTION 5.2 – EVOLUTION AND
Coevolution
ADAPTATION
• Organisms that live closely together and interact may have evolutionary
responses to one another.
• Coevolution – species that interact closely may become adapted to one
another through this process.
• Clown fish and sea anemone.
• Acacia (uh-kay-sha) tree and stinging ants.
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SECTION 5.3 - POPULATIONS
Population Growth
• Populations can quickly grow past the environment’s ability to support
it.
• As a result of growing populations, organisms experience increased
competition for resources.
• So populations can continually grow exponentially unless prevented by
limited resources.
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SECTION 5.3 - POPULATIONS
Carrying Capacity
• As a population grows it takes move from its habitat and resources
become scarce.
• The death rate rises because those who cannot compete die and the birth
rate starts decreasing.
• The growth of the population slows down.
• The population will stop growing altogether because the number of births
equal the number of deaths.
• Carrying capacity – the number of individuals of a species that can be
supported by an ecosystem for a species.
• The carrying capacity for a species is usually determined by the
ecosystem’s resources.
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SECTION 5.3 - POPULATIONS
Carrying Capacity
• The S-shaped curve represents the change
in the size of a new population over time.
• The population starts out small and then
increases rapidly.
• As the size of the population approaches
carrying capacity, the growth rate slows
down.
• The population stops growing when it
reaches the carrying capacity and levels
off.
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SECTION 5.3 - POPULATIONS
Limiting Factors
• Limiting factors – the force that slow the growth of a population.
Human
Densitydependent
Disturbance
Climate
Natural
Disasters
Density
Independent
Predation
Population
Size
Parasitism
Disease
Food
Competition
Water
Availability
Living
Space
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SECTION 5.3 - POPULATIONS
Limiting Factors
• 2 Kinds
1. Density-dependent limiting factors – limiting factors that are dependent on
population size.
- Examples include: food supply, predation, and
disease.
- Are related to competition and other interactions
between organisms.
- Usually when one population declines, another
declines.
population also
2. Density-independent limiting factors – a limiting factor that affects the same
percentage of a population regardless of its size.
- Examples include: Natural disasters, climate and
human disturbance.
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