Population Dynamics

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Population Dynamics
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Population Dynamics

• Different communities vary in the number of
  populations they contain.

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Population Dynamics

• Different communities vary in the number of
  populations they contain.
• The number of populations in a community
  corresponds to the species richness of a
  community.

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Population Dynamics

• Different communities vary in the number of
  populations they contain.
• The number of populations in a community
  corresponds to the species richness of a
  community.
• Factors that affect the number of species in an
  area include

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Population Dynamics

• Different communities vary in the number of
  populations they contain.
• The number of populations in a community
  corresponds to the species richness of a
  community.
• Factors that affect the number of species in an
  area include
• Physical size of the area

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Population Dynamics

• Different communities vary in the number of
  populations they contain.
• The number of populations in a community
  corresponds to the species richness of a
  community.
• Factors that affect the number of species in an
  area include
• Physical size of the area
• Latitude

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Population Dynamics

• Any population can be characterised in terms of
  several attributes, including
• Abundance
• Distribution
• Age structure of population
• Rate of growth

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Population Dynamics

• Abundance is defined as the number of individuals
  of a given species per unit area.

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Population Dynamics

• Abundance is defined as the number of individuals
  of a given species per unit area.
• Total counts or sampling are used to assess
  population abundance.

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Population Dynamics

• Distribution of a population identifies how
  members of a population are spread over space.

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Population Dynamics
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Population Dynamics

• Distribution of a population identifies how
  members of a population are spread over space.
• In a population, individual members vary in their
  ages and life spans. The age structure of a
  population identifies the proportion of its
  members that are

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Population Dynamics

• In a population, individual members vary in their
  ages and life spans. The age structure of a
  population identifies the proportion of its
  members that are
• At pre-reproductive age (too young to reproduce)

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Population Dynamics

• In a population, individual members vary in their
  ages and life spans. The age structure of a
  population identifies the proportion of its
  members that are
• At pre-reproductive age (too young to reproduce)
• At reproductive age

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Population Dynamics

• In a population, individual members vary in their
  ages and life spans. The age structure of a
  population identifies the proportion of its
  members that are
• At pre-reproductive age (too young to reproduce)
• At reproductive age
• At post-reproductive age (no longer able to
  reproduce)

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Population Dynamics

• In a population, individual members vary in their
  ages and life spans. The age structure of a
  population identifies the proportion of its
  members that are
• At pre-reproductive age (too young to reproduce)
• At reproductive age
• At post-reproductive age (no longer able to
  reproduce)
• The shape of the plot of the age structure of a
  population indicates its reproductive capacity.

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Age-sex structure graphs
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Sampling Populations

• It is difficult to know exactly the size of a
  particular population, so there are some sampling
  techniques used
• Quadrats
• Transects
• Mark-recapture

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Quadrats
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Quadrats

• Quadrats are square areas of known size and are
  often sub-divided into smaller units.

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Quadrats

• Quadrats are square areas of known size and are
  often sub-divided into smaller units.
• They are used to estimate the abundance of
  plants, of sessile (immobile) animals and slow
  moving animals.

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Quadrats

• Quadrats are square areas of known size and are
  often sub-divided into smaller units.
• They are used to estimate the abundance of
  plants, of sessile (immobile) animals and slow
  moving animals.
• It is useless for fast moving animals that will
  not wait around to be sampled.

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Quadrats
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Transect lines
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Transect lines

• A transect line is a strip laid across the area
  to be studied.

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Transect lines

• A transect line is a strip laid across the area
  to be studied.
• It is useful in identifying changes in vegetation
  with changes in the environment.

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Mark-recapture technique
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Mark-recapture technique

• This technique is used on animals

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Mark-recapture technique

• This technique is used on animals
• It involves collecting a sample of the animal
  population being studied by trapping them.

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Mark-recapture technique

• This technique is used on animals
• It involves collecting a sample of the animal
  population being studied by trapping them.
• The trapped animals are marked in some way and
  are then released.

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Mark-recapture technique

• This technique is used on animals
• It involves collecting a sample of the animal
  population being studied by trapping them.
• The trapped animals are marked in some way and
  are then released.
• Later, another sample of the population is
  trapped.

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Mark-recapture technique
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Variables affecting population size

• Variables that influence population size include

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Variables affecting population size

• Variables that influence population size include
• Birth rate
• Death rate
• Migration rate

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Variables affecting population size

• The growth rate is positive when population size
  increases

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Variables affecting population size

• The growth rate is positive when population size
  increases
• The growth rate is negative when population size
  decreases.

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Variables affecting population size

• The growth rate is positive when population size
  increases
• The growth rate is negative when population size
  decreases.
• When birth rate and death rate are equal the
  population is said to have zero population
  growth.

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Variables affecting population size

• A population is defined as being open or closed
  depending on whether or not migration can occur.

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Variables affecting population size

• A population is defined as being open or closed
  depending on whether or not migration can occur.
• Migration into or out of closed populations is
  nil, unlike open populations.

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Population Dynamics

• Population size of one species is affected by
  population size of another species in the
  community.

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Population Dynamics

• Population size of one species is affected by
  population size of another species in the
  community.
• Populations of some species are short lived and
  produce very large numbers of offspring
  (r-selected).

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Population Dynamics

• Population size of one species is affected by
  population size of another species in the
  community.
• Populations of some species are short lived and
  produce very large numbers of offspring
  (r-selected).
• Populations of other species produce small
  numbers of offspring at less frequent intervals
  (k-selected).

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The End