POPULATION ECOLOGY

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POPULATION ECOLOGY
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ECOLOGY

• Study of living organisms as groups
• Interactions between living organisms
  (predator-prey, parasitism etc)
• Interactions between organisms and their
  environments
• Study of patterns of distribution and abundance
  of organisms

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Biotic factors

• Biotic factors living organisms affecting
  others
• Producers, consumers, detrivores, decomposers,
  parasite, host, predator, competitor, herbivore,
  symbiont and pathogen.

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Abiotic factors

• Non-living factors (chemical and physical)
• Temperature, light, soil, water, oxygen

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Populations

• Groups of individuals of the same species living
  in the same geographic area
• Population ecologists study distribution,
  density, rate of growth, demographics (old/young,
  male/female)
• Data and models used in population genetics and
  evolution

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Communities

• All the populations in a given area
• Interactions and change over time are major focus
  of studies
• Ecological succession Change in communities
  over time, especially after a natural or man made
  disruption

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Primary succession

• Establishment and change in communities in a
  completely new environment

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Secondary succession

• Occurs after a major disturbance ( fire, flood)

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Ecosystem

• An ecosystem (or ecological system) is a
  collection of communities of organisms and the
  environment in which they live.
• Ecosystems can vary greatly in size. Some
  examples of small ecosystems are tidal pools or
  the stomach of an individual cow.
• Larger ecosystems might encompass lakes,
  agricultural fields, or stands of forests.
• Ecologists often invent boundaries for
  ecosystems.

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Biomes

• Groups of ecosystems found in specific regions.
• Characteristics are usually determined by abiotic
  factors

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Habitat

• Can be defined as the complete environmental
  requirements of an organism for survival food,
  water, cover, space, and arrangement

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Range

• Geographical area where a population is found

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Niche

• The role of an organism in the community
• Specialists can only survive in specific
  environments
• Eg Koala, Panda bear

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• Generalists have large ranges because are not
  fussy
• Eg rats, cockroaches and humans

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Trophic structure

• Describes the feeding relationships in an
  ecosystem or community.
• Describes the abundance organisms in niches and
  the of flow of energy

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Food webs
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14.1 Characteristics of Populations
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Population Density

• Population Density (D)total number of
  individuals (N) divided by the area occupied by
  the population (A)
• Eg If 480 moose live in a 600 hectare region of
  Algonquin park, then the population density is
• DN/A
• 480 moose/600 ha
• 0.8 moose/ha

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• Crude density the number of individuals per
  unit of space or volume
• Ecological density the number of individuals per
  unit of area or volume that is actually used by
  the individuals.
• Eg the moose in Algonquin park do not use the
  open lakes. If the 600 ha of the park includes
  70 ha of open lake then the ecological density
  would be 0.9 moose/ha.
• (D480 moose/ (600-70) ha

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Patterns of dispersion

• Clumped dispersion dense groups in parts of
  habitat best suited for survival
• Uniform dispersion even distribution
• Random dispersion habitat is uniform, little
  competition with other species

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Measuring Populations

• Methods for estimating population sizes depend on
  the organism being studied (range, mobility)
• Populations are dynamic so scientists rely on
  sampling techniques to estimate the size of
  populations
• Some sampling techniques are direct (quadrant,
  tagging), other are indirect (number or tracks,
  nesting sites)

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Quadrat sampling
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• Quadrat sampling is usually carried out when the
  area under study is fairly uniform, very large,
  and or there is limited time available.
• Large numbers of samples are taken from different
  positions within the habitat.

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• A quadrat frame is placed on the ground and the
  animals, and/ or plants inside it counted,
  measured, or collected, depending on what the
  survey is for.
• This is done many times at different points
  within the habitat to give a large number of
  different samples.

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Mark- Recapture Method

• Used for wild animals
• Marking techniques are designed not to harm the
  individuals being caught
• Timing must be chosen carefully to ensure
  accuracy of numbers.

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• Assumptions
• Every organism in a population has an equal
  chance of being caught
• During the time between initial marking and
  recapture, the proportion of marked to unmarked
  remains constant
• Population size does not change (increase or
  decrease) during the study