1. Population Ecology

2. What is a Population? Population - A group of individuals of the same species that live together and interbreed Populations: o Share resources o Are influenced by the same environmental factors o Breed with one another

3. Density and Distribution Two important characteristics of a population are the density, and spacing of individuals

4. Population Density Population Density – Number of individuals per unit or area of volume Examples: o Number of oak tree’s per acre o Number of deer per square mile o Number of plankton per liter of water

5. Measuring population density One of the most popular method of calculating population density is the mark- recapture method Here’s how it is done…

6. Steps to the Mark-Recapture Method 1.Boundaries are set for the study 2.Traps are set out to capture animals 3.Animals are marked with tags, dies, collars, or bands, then released 4.Traps are set again at a later date 5.Recaptured animals are used to estimate population density of an area

7. Formula Number of Recaptures in Second Catch Total number in Second Catch Number Marked in First Catch Total Population (N) Number Marked in First Catch X Total number in second catch Number of Recaptures in Second Catch

8. Example Scientists capture 50 rabbits, and put ear tags on them Two weeks later, 100 rabbits are captured o 10 of these rabbits were recaptures from the first capture

9. Formula Number of Recaptures in Second Catch Total number in Second Catch Number Marked in First Catch Total Population (N) The estimated population would be 500 rabbits

10. Number Marked in First Catch X Total number in second catch Number of Recaptures in Second Catch

11. Other Methods Scientists will sometimes use indexes for population size, by counting things such as: o Number of Nests o Number of Burrows o Tracks o Droppings

12. Dispersion Population Dispersion – The pattern of spacing among individuals within the geographic boundaries of the population Three main types of population Dispersion: o Clumped o Uniform o Random

13. Clumped Clumped Dispersion – When individuals are grouped into patches Why would they be clumped? o Food Sources for animals o Soil Conditions for plants This is the most common type of dispersion

14. Uniform Uniform Dispersion – When individuals are evenly spaced

15. Random Random Dispersion – Unpredictable distribution of individuals The most rare of the three types of dispersion

16. Demography Demography – The study of the vital statistics that affect population size Some Demographic Variables: o Birth Rate o Mortality Rate o Immigration Rates o Emigration Rates

17. Life Tables Life Tables – An age-specific summary of the survival pattern of a population Life Tables Show: o Probability of surviving a particular age o Life expectancy o Fertility at each age

19. Uses of Life Tables Originally created for life insurance agencies Biologists use them to study population dynamics See if mortality rates increase due to environmental factors See at what age a species is most fertile

20. Survivorship Curves Survivorship Curves – A plot of the proportion or numbers in a cohort still alive at each age There are 3 types of survivorship curves o I o II o III

22. Type I Little mortality at early ages Mortality rate increases as the organisms get older An example of this is with humans We have few offspring, but give them great care

24. Type III This curve shows high mortality rates during the early stages of life The line flattens out once the organisms reach a ‘critical age’ of survival This is for animals that produces many offspring, but little to no care for them o Example – plants, clams, fish

26. Type II This is a constant death rate This falls in-between I and III type curves Examples here are squirrels, lizards

28. Population Growth Biotic Potential – the maximum growth rate of a population under ideal conditions, and unlimited resources (no restrictions) Factors affecting biotic potential: Age of Reproductive Maturity Clutch Size Frequency of Reproduction Reproductive Lifetime Survivorship of offspring to reproductive maturity

29. Carrying Capacity The maximum number of individuals of a population that can be sustained in a particular habitat o How many rainbow trout could this creek support? o How many wolves can survive in Isle Royale National Park?

30. Limiting Factors Limiting factors are things that prevent populations from reaching their biotic potential (2 types) Density-Dependent Factors Density-Independent Factors

31. Density-Dependent Factors Factors whose effects become more intense as the pop. density becomes greater Examples: o Resource Competition (Food, Space, Sunlight, O 2 ) o Toxic Levels of Waste (CO 2 levels)

32. Density-Independent Factors Factors that are not effected by pop. density Examples: o Natural Disasters o Climate extremes o Pollution

33. Population Formulas Population Growth Formula: r = reproductive rate N = population size

34. Growth Patterns There are 2 types of pop. Growth patterns: Exponential – Occurs when growth rate is above zero Logistical – When limiting factors restrict size of population