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Population
a group of individuals of the same species that inhibit a given area
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characteristics of a population include:
- - density
- - proportion of individuals of various ages and stages
- - spacing of individuals
- - birth, death, and movement of individuals
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and individual organism has a unitary nature, meaning-->
form, development, growth, and longevity (the zygote grows into a genetically unique organism)
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in modular organisms-->
the zygote develops into a unit of construction that then produces futher, similar modules (common in plants)
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genet
genetic individual arising from a zygote
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ramets
- modules produced asexually by the genet
- -ramets may be physically linked to the parent or separate
- -ramets are clones or exact copies of the parent genet (corals or sponges)
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distribution
- describes the population's spatial location
- - influenced by the occurrence of suitable environmental conditions
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geographic range
the area of a population that encompasses all individuals of a species
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the distribution of a population defines its spatial location:
- individuals are not distributed evenly throughout the geographic range of a population
- individuals can only occupy areas that can meet their requirements
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local or subpopulations
- due to environmental heterogeneity, populations are divided into these
- a metapopulation is a collection of local subpopulations
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abundance
is the number of individuals in the population and defines its size
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population density
the number of individuals per unit area or per unit volume
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population distribution pattern--random
an individual's position is independent of other
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population distribution pattern--uniform
results from negative interaction among individuals
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population distribution pattern--clumped
results from patchy resources, social groupings, ramet dynamics
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population size formula
population size=density x area
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sampling methods for plants and sessile animals
- - counting the organism in a subsample (quadrats)
- - abundance estimates may be skewed by a clumped spatial distribution
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capture-recapture or mark-recapture methods
- based on trapping, marking, and releasing a known number of marked animals (M) into the population (N)
- sometime later, the same population of sampled and the ratio of marked (R) to sampled (n) individuals in the second sample represents the ratio for the entrire population
- N/M = n/R
- Lincoln Index or Petersen index of relative population size
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indices of abundance
counts of individuals based on vocalizations, scat, tracks, or other signs
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age structure
- proportion of individuals in different age classes
- determined by aging its members
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life history
the length of time that an individual remains in each stage (short-lived vs. long lived organisms)
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dispersal
the movement of individuals in space; directly influences their local density
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emigration
when an individual moves OUT of a subpopulation
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immigration
when an individual moves INTO a subpopulation
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passive dispersal
- gravity, wind, water, animals
- disperal distance depends on the agents of dispersal
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active dispersal
- mobile animals
- often the dispersing individals are seeking vacant habitat to occupy
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migration
- a round trip movement made by an animal
- can be daily, seasonal, short or long range
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range expansion
- can be associated with temporal changes in environmental conditions
- (ex. shift in tree population--retreating glaciers--more room for tree expansion)
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range expansion
can result for populations that have been introduced to a region where they did not previously exist
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