Measuring Populations
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Measuring Populations
description
Measuring Populations. Introduction. If you had one male and one female elephant in the wild They would reproduce every so often and have a baby elephant That would increase the population Over a short time the elephants would have a much larger population. Introduction. - PowerPoint PPT Presentation
Transcript of Measuring Populations
Measuring Populations
Introduction
• If you had one male and one female elephant in the wild
• They would reproduce every so often and have a baby elephant
• That would increase the population
• Over a short time the elephants would have a much larger population
Introduction
• The elephants could grow to 19 million elephants in just 750 years
• So why isn’t the world overrun by elephants?
• There are factors that keep populations around the same size
Population Growth Rate
• The growth rate is the amount that a population changes over a set time
• The growth rate could be positive– This would mean more
organisms
• The growth rate could be negative– This would mean less
organisms
Population Growth Rate
• To have a positive growth rate, there would have to be…– More individuals that are born
than die– More individuals that
immigrate than emigrate
• To have a negative growth rate there would have to be…– More individuals that die than
are born– More individuals that emigrate
than immigrate
Population Growth Rate
• Many organisms cannot emigrate or immigrate
• Plants, Fungi, animals that are separated by a boundary
• If you are going to have to worry about organisms that emigrate or immigrate, you will be specifically told
Population Size
• We know that researchers often use samples when working with populations
• These sample sizes are often 1000
• It allows us to compare one population to a different population
Population Size
• If talking about births in a year we would put it in terms of 1000
• A researcher could say there are 52 births of 1000 in a year
• This would mean that for every 1000 organisms there are 52 born every year
Population Size
• The same could be said for death rate
• Researchers could have a death rate of 43 of 1000 per year
• This would mean for every 1000 organisms there would be 43 that die every year
Population Size
• To actually figure out how many organisms would be in the population during the next year we would follow a simple formula
• (Birth Rate – Death rate) x Population = Estimated Population Change
Example
Workspace • Grab a partner and lets try an example
• For the Amare Fish of Owdijtown there is a birth rate of 100 of 1000
• For the Amare Fish of Owdijtown there is a death rate of 50 of 1000
• The population of Amare Fish in Owdij Lake is currently 1000
• What is the estimated population change next year?
The Exponential Model
• As long as a birth rate is larger than the death rate, there should be an increase in growth
• One type of increase in growth is exponential growth
• This means that the population grows very rapidly
The Exponential Model
• In exponential growth the rapid growth has no restrictions from the environment
• Bacteria often show this• Their need for resources
is so small and their new environment is often so large that they have no limit to their resources
http://www.youtube.com/watch?v=gEwzDydciWc
The Exponential Model
The Logistic Model
• The logistic model shows a population that grows but then has a limiting factor
• A limiting factor is something that halts a populations growth
• Space, amount of food and amount of water are good examples of limiting factors
The Logistic Model
• In the logistic model there is rapid growth until the growth reaches a limiting factor
• When the population hits the limiting factor, it stops growing
• The population remains fairly consistent after reaching the limiting factor
The Logistic Model
Population Regulation
• The factors that regulate population size can be affected by density
• This breaks up the regulating factors for a population to…– Density dependent– Density independent
Population Regulation
• Density dependent factors depend upon how many organisms are packed into a local area
• Factors such as resources, territory and availability of mates all depend on how many organisms are in an area
Population Regulation
• Density independent factors regulate the population without having to do with density
• Things like weather, floods and fires
• It does not matter how many organisms are in an area if there is a fire
Population Fluctuations• Populations can depend
upon the amount of food, water and habitat
• What is another way that populations can be affected?
• Predator and prey relationships are also very important
Population Fluctuations
• There is a very famous study of Snowshoe Hares and Lynx
• These two have a very classic predator prey relationship
• The Lynx hunts and kills the snowshoe hare
Video
• http://www.youtube.com/watch?v=xWm6037urxs
Population Fluctuations
• After seventy years of observations, a very interesting trend arouse
• It was noticed that every year there was an increase in hares, there was an increase in Lynx shortly after
• This is because there was more energy to have more babies
Population Fluctuations
• Every year there was a decrease in hares, there was a decrease in Lynx shortly after
• This is because there was not enough energy to have a lot of babies
Population Fluctuations
• It also works in reverse, if the level of Lynx goes down, then the level of hare goes up shortly after
• If the numbers of Lynx goes up, the level of hare goes down shortly after
Predator Prey Dynamics
• On an island off Lake Superior a study was done that illustrates predator and prey relationships
• This island was relatively isolated and had no major land mammals
• During a hard winter in the early part of the century a group of Moose crossed the ice and started a population
Predator Prey Dynamics
• Ecologists noted their arrival and started recording their populations
• In 1949, a similar event happened with a small pack of wolves
• Because of the isolation and the lack of other large mammals, this was an ideal system
Predator Prey Dynamics
• Ecologists noted that every year there was a rise in the moose population, there was a rise in the wolf population right after
• Ecologists also noted that every year there was a dip in the moose population, there was a dip in the wolf population right after
Predator Prey Dynamics• The moose population and
the wolf population are regulated by environmental resistance
• More wolves means it is harder for the moose to survive (Environmental Resistance)
• Too many moose and there will not be enough food (Environmental Resistance)
• Not enough moose and the wolves will die (Environmental Resistance)
Predator Prey Dynamics
• In the winter of 1996 there was a very severe snowfall and in the summer there was an infestation of ticks
• This caused a sharp decrease in the moose population
• It also caused kept the wolf population low for a long time
