Population Ecology

1. Population Ecology

2. Populations • A population is a group of individuals of the same species that live in the same area

3. Population Ecology: Vocabulary • Density: • The number of individuals per unit area/volume • Example: 47 elephants/km2 • Dispersion: • The pattern of spacing among individuals in a population • Clumped • Uniform • Random

5. Environmental conditions are uniform Causes COMPETITION or antagonism between organisms Uniform

6. Clumping • Most common • Reproductive patterns favor clumping • Social behaviors lead to clumping • Optimal density is usually intermediate (medium)

7. No competition No tendency to group/clump Conditions are uniform Rarely happens! Random

8. Factors That Influence Population Size • There are 3 major factors that influence population size: 1. the number of births 2. the number of deaths 3. the number of individuals that enter or leave a population - immigration: individuals entering an existing population - emigration: individuals leaving an existing population

9. Reproductive Episodes • Clutch size: • Number of offspring produced at each reproductive episode • Semelparity • A life history in which an organism spends most of its energy in growth and development, expend their energy in one large reproductive effort, and then die • Many insects, annual plants, salmon, etc.

10. Reproductive Episodes • Iteroparity • A life history pattern in which organisms produce fewer offspring at a time over a span of many seasons • Example: humans, panda bears, etc.

11. Estimating Population Size • The mark-recapture method can be used to estimate the size of a population • Capture, mark, release • Recapture and count • Equation: N = Number marked x Total catch 2nd time Number of marked recaptures

12. Patterns of Population Growth • Exponential Growth: • Occurs in ideal conditions with unlimited resources • J shaped curve • Book example: • 1 bacterium (reproducing every 20 minutes) could produce enough bacteria to form a 1-foot layer over the entire surface of the Earth in a day

13. Patterns of Population Growth • Exponential growth cannot continue indefinitely • It is characteristic of populations who are entering a new environment OR those whose numbers are rebounding from a catastrophic events

14. r- strategists • Grow exponentially when environmental conditions allow; when conditions worsen, population size plummets. • Short life span • Reproduce early in life • Many offspring/large clutch size • Usually small in size • Little or no parental care • Bacteria, some plants, insects

15. Patterns of Population Growth • Logistic Growth: • Pattern of population growth which takes into account the effect of population density on population growth • Occurs when resources become more scarce • Characterized by an S-shaped curve

16. Patterns of Population Growth • Carrying capacity (K): • The maximum number of individuals that a particular environment can support over a long period of time • Determined by such limiting factors as crowding and food resources • Graph levels off at carrying capacity • K-selected populations (equilibrial populations) live near or at the carrying capacity

17. K-strategists • Density stays near carrying capacity. • Large, slow growing organisms • Small population sizes • Long life span; slow maturation • Few young/small clutch size • Reproduce late in life • Parental care • Most large mammals; endangered species

18. Carrying Capacity

19. Boom-and-Bust Cycles

20. Limiting Factors • There are a number of factors that limit the size of populations: • Density-dependent limiting factors • Density-independent limiting factors

21. Density-Dependent Limiting Factors • The effect of density-dependent limiting factors intensifies as the population increases • Intraspecific competition • Food, space, etc. • Predation • Disease (if caused by pathogen/contagious)

22. Density-Independent Limiting Factors • The occurrence and severity of density-independent limiting factors are unrelated to population size • Climate • Disease (if not caused by pathogen/not contagious) • Pollution

23. The Interaction of Limiting Factors • Density-dependent and density-independent limiting factors often work together to regulate the size of a population • Deer in snowy winter • Starve from lack of food (DDLF) • Severity of winter/depth of snow determines access to food (DILF)

24. Survivorship Curves • Type I- live to old age & die (most large mammals) • Type II- constant mortality rate (rodents, lizards, hydra) • Type III- high mortality at young age, but if they survive they live a long life.

25. Age-Structure Diagrams

26. Human Population Growth

27. Human Population Growth • The human population has been increasing exponentially since approximately 1650 • http://www.pbs.org/wgbh/nova/worldbalance/numbers.html

28. Human Population Growth • Implications of exponential human population growth: • Lack of food supplies • Lack of space • Lack of natural resources (metals, fossil fuels, etc) • Lack of sites for waste disposal • Ecologists cannot agree on a carrying capacity for Earth • Are we going to reach carrying capacity through individual choices and/or government programs? OR • Is Earth’s population going to “level off” as a result of mass deaths?