Populations

Page 521-531

  • Population: a group of individuals of the same species living in the same time, in the same geographical area, and able to interbreed

  • Determining one population from another can be done by considering how likely it is for members of the population to interbreed

  • Populations are dynamic

  • Characteristics that can be used to describe a population:

    • Popoulation density

    • Geographical distribution

    • Max. number of individuals that can be supported by the resources

  • Sampling methods: systematic and random

  • Systematic sampling: lines or grids are set up and measurement/counting occurs at specific, regular intervals

  • Random sampling: randomly chosen zones are chosen, and a specific amount of space is measured there. This is repeated.

  • Random sampling works best for sessile organisms, catch-mark-realease sampling works better for motile organisms

  • Catch-mark-release sampling/lincoln index method: some of a population is captured and marked, then released back into the wild. A secondary sample is then captured, and the ratio of marked to unmarked in the sample is assumed to be the same as in the rest of the population

    Lincoln Index:

  • Carrying capacity: the stabilised number of individuals in a population which the habitat can feasibly support (plateau)

  • Young trees can store energy for years with little to no growth, waiting for old trees to die so they can take a spot in the sunlight

  • Limiting factors:

    • Surface area/capacity

    • Amount of resources such as food

    • Build-up of waste products su ch as CO2 and excrement

    • Predation

    • Disease

  • Density-dependent factors: limiting factors that depend on population density, such as the spread of disease

  • Positive feedback: when something increases the population and the result leads to more growth, i.e rapid reproduction

    • Example: during childbirth, a chemical is released that causes more contractions

  • Negative feedback: spread of disease, threat of predation, competition for resources - keeps populations from growing out of hand

    Sigmoid population growth

  • Reasons for phase 1- exponential growth:

    • Plentiful resources

    • Little to no competition

    • Good abiotic factors (no climate change)

    • Little to no risk of predation or disease

  • Reasons for phase 2- transitional period:

    • Increasing competition for resources

    • Predators attracted

    • Higher risk of disease

Class work 1:

  • Communities: a group of populations that are living and interacting together

  • Species: can produce fertile offspring by interbreeding

  • Ecosystem: a community and an abiotic environment

Understanding populations:

  • Population density: N= (mean # per quadrat) * (total area) / area of each quadrat

  • Percentage frequency: (number of organisms)/(total number of squares) * 100

Class work 2:

Lincoln index/capture-mark-recapture method

  • Sample size and size of recaptured individuals in the 2nd sample can influence the estimate

Allelopath