SPECIES AND POPULATIONS

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SPECIES AND POPULATIONS

• Obtained through World of Teaching and
  revised by J. Jernigan

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SPECIES

• Species an organism that can interbreed and
  produce viable offspring

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Specie Types

• Native species A species that normally lives
  and thrives in a particular community
• Nonnative species - invasive species or alien
  species A species that was introduced into a
  particular community
• These can be beneficial or harmful

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• Indicator Species - Species that are used to warn
  of damage to an ecosystem
• Example Birds, frogs, butterflies
• Keystone Species Species that are key to a
  community and if lost could cause significant
  loss of other species
• Example bees, hummingbirds, bats, alligators,
  wolf, sharks
• Foundation Species A species that helps to
  shape a community by enhancing the community
• Example elephants, bats and birds

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Specie Interactions

• Predation predators feed directly on all or
  part of a living organism of another species
  (prey)

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• Parasitism a species (parasite) will feed on
  part of another organism (host) while usually
  living on that host.

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• Mutualism Two species that interact with each
  other where both benefit

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• Commensalism an interaction between species
  where one species benefits and the other is
  little or slightly affected.

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POPULATIONS

• Population-all of the individuals of a species
  that live together in one place at one time.
• Demography-the statistical study of populations.
  It is used to predict how the size of a
  population will change.

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KEY FEATURES OF POPULATIONS

• 1. Population size
• is the number of individuals in a population.
• has an important effect on the ability of the
  population to survive.
• A small population is more likely to become
  extinct
• -in the case of random events or natural disaster
• -due to inbreeding where the population is more
  genetically alike. Recessive traits are more
  likely to appear.
• -with reduced variability it is harder to adapt
  to changes.

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KEY FEATURES OF POPULATIONS, cont

• 2. Population density
• the number of individuals in a given area.
• if they are too far apart they may only rarely
  encounter one another resulting in little
  reproduction.

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Population size is limited by

• density-independent factors
• Volcanic eruptions
• Temperature
• Storms
• Floods
• Drought
• Chemical pesticides
• Major habitat disruption (as in the New Orleans
  flooding)
• Most are abiotic factors

• density-dependent factors
• Disease
• Competition
• Predators
• Parasites
• Food
• Crowding
• The greater the population, the greater effect
  these factors have.
• Ex. Black plague in the Middle Ages more deaths
  in cities

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• 3. Dispersion
• the way in which the individuals are arranged.

Most common
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PREDICTING POPULATION GROWTH

• Model
• A hypothetical population that has key
  characteristics of the real population being
  studied.
• Used by demographers to predict how a population
  will grow.

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PREDICTING POPULATION GROWTH, cont

• Nearly all populations will tend to grow
  exponentially as long as there are resources
  available.
• Two of the most basic factors that affect the
  rate of population growth are the birth rate, and
  the death rate. Two other variables will include
  emigration and immigration
• r(rate of growth)birth rate death rate

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PREDICTING POPULATION GROWTH, cont

• Exponential growth curve population growth
  plotted against time.
• As a population gets larger, it also grows at a
  faster rate.
• This is the maximum population growth under ideal
  circumstances.
• Includes plenty of room for each member,
  unlimited resources (food, water) and no
  hindrances (predators).

FACT No population exhibits this type of growth
for long.
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PREDICTING POPULATION GROWTH, cont

• Logistic model This model accounts for the
  declining resources available to populations as
  they grow.
• It assumes the birth and death rates are not
  constant.
• As the population grows, births decline and death
  rises.
• Eventually birthdeath so the population stops
  growing.
• Carrying capacity (K) The number of organisms of
  one species that an environment can support
  indefinitely.

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PREDICTING POPULATION GROWTH, cont Two modes of
population growth.
The Exponential curve (also known as a J-curve)
occurs when there is no limit to population size.
The Logistic curve (also known as an S-curve)
shows the effect of a limiting factor (in this
case the carrying capacity of the environment).
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POPULATION GROWTH STRATEGIES

• There are 2 ways a population can prosper
• Depends on the rate of growth (r)
• Influenced by the carrying capacity (K)

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POPULATION GROWTH STRATEGIES, cont

• r-strategists characterized by exponential
  growth, which results in temporarily large
  populations, followed by sudden crashes in
  population size. Ex. Insects, bacteria, some
  plants
• live in unpredictable and rapidly changing
  environments
• Reproduce quickly when conditions are favorable
• Many offspring small, mature rapidly, no
  parental care
• r rate of growth

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POPULATION GROWTH STRATEGIES, cont

• K-strategists characterized by a high degree of
  specialization. Ex. Trees, whales, tigers, etc.
• Live in stable and predictable environments
• Can compete effectively
• Reproduce late in life
• Few offspring large, mature slowly, often much
  parental care
• K carrying capacity