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 ydciWc

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 m/watch?v=xWm6037u rxs m/watch?v=xWm6037u rxs

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

Video