JAMIE CROMARTIE'S STOCKTON POPULATION BIOLOGY WEBSITE

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POPULATION STRUCTURE

Species distributions

Range - geographic area occupied by a particular kind of organism.

Disjunct distribution - range consisting of two or more geographically separated areas (eg. Curly Grass fern, Schizaea pusilla: NJ Pine Barrens, Long Island, Nova Scotia, Newfoundland, AND SOUTH AMERICA!)

Endemic - a species (or genus, family, order, etc.) restricted in its distribution to a specific limited area (eg., a Pine Barrens endemic)

Pupfishes in California
Juniperus californica
Sequoiadendron giganteum

Local distributions are very different from what is often shown on range maps. an example is provided by a study of the habitat requirements of the Least Weasel. Another example is the distribution maps for lorises and pottos, which is compiled based on actual collection records, but also shows range boundaries given by various experts (check the homepage for that site; it is a very good example of conservation-oriented population information.)

Age/size structure

Age class - the members of a population of a given age (eg. two-year olds, three-day olds, etc.)

Year class - the individuals in a population born in a particular year (eg., the 1966 year class, the 1947 year class, etc.)

Size class - the individuals in a population falling within a particular range of measurements (weight, length, diameter, etc.)

Age structure - the proportion of a population in each age or year class, usually represented as a pyramid-shaped bar graph, with the oldest group at the top. See the examples in the practice spreadsheet.

Genetic structure

Five causes of evolution (evolution: any change in gene frequency, [Wilson, E.O. and W. Bossert. 1971. A Primer of Population Biology. Sinauer Associates. Stamford CT. 192pp.])

    mutation pressure
    meiotic drive and a more general account of weirdness among the genes
    gene flow
    natural selection
    genetic drift

The interaction of these forces with the dispersal and dynamics of populations lead to patterns in the distribution of genetic variability across time and space. The following are examples of some studies

Marine zooplankton

Freshwater fishes including applications in salmon conservation

Links to abstracts of study on giant termites

What is a microsatellite?

A Near-extinction Event in Lynx: Do Microsatellite Data Tell the Tale? an example of the limitations of genetic methods.

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