2. Population Dynamics Population dynamics - the study of the long term changes in population sizes and the factors that cause a change Current focus is on human populations (ageing studies, population booms or declines), but biologists use population dynamics to study competing species and predator-prey relationships as well

3. Examples

6. Population Dynamics 220 year-old discipline Thomas Malthus proposed the 1st equation to characterize human population growth This led to equations for exponential and logistic growth which we will look at later

7. Factors affecting population growth There are 4 factors affecting population growth: 1) Births (natality) 2) Deaths (mortality) 3) Immigration 4) Emigration They can all be put into a neat little equation… N 1 = N 0 + (B – D) + (I – E) If you simply want to look at the change in population from one time interval to the next simply look at: (B – D) + (I – E) N X = population size in generation X

8. Population Dispersion Population Dispersion is how individuals are arranged in their habitat. There are 3 types of population dispersion: 1. Uniform dispersion (usually due to competition between individuals)

9. Population Dispersion Population Dispersion is how individuals are arranged in their habitat. There are 3 types of population dispersion: 2. Clumped dispersion (usually due to uneven distribution of resources)

10. Population Dispersion Population Dispersion is how individuals are arranged in their habitat. There are 3 types of population dispersion: 3. Random dispersion (usually due to an even distribution of resources)

12. Population Density Population Density - a measure of how many individuals of a species are found in a given area Two types of density: 1. Crude density # of individuals divided by the total area 2. Ecological density # of individuals divided by the total useable area D = N/S D = density N = population size S = area

13. Density Sample Questions 1) A backyard measuring 3.0 m by 4.0 m contains 215 dandelions. Determine the population density of the plants. 2) A small field having an area of 1.5 ha contains a pond with a surface area of 0.3 ha and is home to 300 field mice. Calculate their ecological density. 3) Researchers want to relocate some nuisance black bears into a forest in Northern Quebec that is 750 km 2. If each bear requires 40 km 2 of forest to live successfully, how many bears can be successfully relocated here?

14. Population Density Density calculations are done differently if the species being studied is mobile or stationary Quadrat studies are used for non-mobile populations like plants Mark-Recapture studies are used for mobile populations like animals

15. Quadrat Studies Used to study non-mobile populations Quadrat - a small frame of known area that is placed, at random, in a larger ecosystem All of the species in question that are found in that quadrat are counted That number is scaled up according to the ecosystem’s true size More practical than counting every individual in a given ecosystem!

16. Quadrat Studies Estimated Population Density (EPD) (basically a density equation) Total # of sampled individuals Sampled area EPD =

17. Quadrat Study Example 4) Scientists are studying the distribution of Trilliums in a section of Lemoine Point covering 100m by 100m. They place four 1.0m X 1.0m quadrats randomly in this area and count the number of trilliums in each to be 5, 2, 1 and 3 What is the estimated trillium population density? What is the estimated trillium population size? What is one source of error in this method?

18. Mark-Recapture Studies Used for mobile populations Individuals are trapped/captured, marked with a ‘tag’ and returned to the environment A Longworth trap: standard small mammal trap

19. Mark-Recapture Studies Over time, more individuals are trapped/captured in subsequent rounds Every round it’s noted how many individuals are tagged This data can be plugged into an equation to figure out population density

20. Mark-Recapture Study M/N = m/n M = # of individuals marked in first capture N = estimated population size m = # of marked individuals recaptured in 2 nd round n = # of individuals recaptured in 2 nd round

21. Mark-Recapture Example 5) On day one, 20 warblers are captured in mist nets. The birds are then marked with leg bands and released. One week later, the nets are reset and 50 warblers are captured. Of these 50, 10 of them were banded from the week before. Estimate the warbler population size.

22. Transect Studies A transect is a straight line (or rectangle) chosen by researchers and along which they will travel, counting the species being monitored Both mobile and stationary species can be counted this way Size of the transect depends on the species monitored Works best when the expected density is low or when the individuals are very large (eg. Douglas Firs)