Population Ecology

1. Population Ecology Chapter 53 AP Biology

2. Populations • Group of individuals of a single species that live in the same general area • Interact & Interbreed

3. Population Ecology • Study of populations in relation to their environment • Environment influences population density, distribution, age structure, & size

4. Population Density • How do we measure how many individuals there are in a population • Density = # of individuals / area • Sampling Technique is…. • Mark & Recapture Method • N = # marked in 1st catch X total # the 2nd catch ---------------------------------------------------------- # of marked recaptures in 2nd catch • N = Population Size

5. Population Dispersal • Pattern of spacing in a population • Clumped Pattern – in groups, clumps • Most common • Due to food availability • Due to mating and/or social behavior

6. Population Dispersal • Uniform Pattern – even spaced • May result from direct interactions b/w individuals in the population • Due to…. • Competition for food/water • Territoriality

7. Population Dispersal • Random – no strong attraction or repulsion among individuals • Not very common in nature • Position of each individual is independent of other individuals

8. Three Types of Dispersal Reviewed

9. Demography • Study of the factors that affect the growth and decline of populations • Study of vital statistics & how they change over time

10. What factors can change a population’s size? • Adding & removing individuals ……. • Birth • Death • Immigration • Moving INTO a population • Emigration • EXITing a population

11. Survivorship Curves • Graphic representation of the data in a life table

12. Survivorship Curves • What does this tell you about the survival & strategy of a species? • Human • Type I • Hydra • Type II • Dandelion • Type III

13. Reproductive Table • Fertility Schedule • Age-specific summary of the reproductive rates in a population

14. Life History • Traits that affect an organism’s schedule of reproduction & survival • Two Main Types: • Opportunistic • Large # of offspring in 1 reproductive event • Low probability for survival • Little to no parental care • Example: garden weeds • Equilibrial • Smaller # of offspring in 1 reproductive event • More energy in growth & maintenance • More parental care • Higher probability for long-term survival • Example: Large terrestrial vertebrates (elephants)

15. Life History • Three characteristics that affect the # of offspring a female will produce in a lifetime: • Clutch Size - # of offspring/reproductive episode • # of reproductive episodes in a lifetime • Semelparity/Big-bang reproduction – 1 large effort • (Century Plant) • Age at 1st Reproduction • Early Reproduction – less energy for maintenance & growth • Late Reproduction – invests energy in maintenance & growth

16. Population Growth • Change in population…. • (Births + Immigration) – (Deaths + Emigration) • Exponential Model  (j-shaped curve) • Growth under ideal conditions/unlimited resources • Formula = dN ----- = rmaxN dt • Where ….. N = # of individuals r = rate of growth t = time period

17. Exponential Growth • Characteristic of populations introduced to a new environment or rebounding from a catastrophe • J-shaped curve

18. Carrying Capacity • Sets the limit for exponential growth • Maximum number of individuals in a population that an environment can support (with no habitat destruction) • Can change with changes in resources • Represented by “K”

19. Logistic Model of Population Growth • As N approaches K, population growth slows down • Includes the effect of population density on “r”

20. Logistic Model of Growth

21. Life History Traits • K-selection  density dependent • R-selection  density independent; maximizes reproductive success K selection constant mortality r selection

22. Life History Traits • K-selection • Natural selection favors adaptations that will help an organism survive & reproduce with minimal resources • Maximizes population size • r-selection • Favors adaptations that promote rapid reproduction (earlier maturity & increased fecundity) • Fecundity – average # of eggs produced by a female at a given age • Maximizes the “r” (rate of increase) of the population

23. Regulating the Population Size • Limiting Factors • Density-dependent Factors • Food supply • Competition - territoriality • Predators • Habitat/space • toxicity • Density-independent Factors • Environmental Disturbances, such as….. • Natural disasters (hurricane, flood, fire, etc) • Extreme climate changes (early spring frost) • Population Cycle – density-dependent & independent factors often work together to regulate a population’s size

24. Negative Feedback & Population Growth • Negative feedback prevents unlimited growth of a population • What factors can cause negative feedback? • Resource limitations • Territoriality • Predation • Poor health due to overcrowding (disease) • Toxicity • Aggressive behavior among same species

25. Negative Feedback & Population Growth • Plantain --> average # of seeds produced decreases w/ increased sowing density • Song Sparrow  clutch size decreases as density increases • Caused by food shortage

26. Population Dynamics • Due to complex interactions b/w biotic & abiotic factors • Nesting areas have been lost (prairie ponds have dried up or been drained for farming) • Population did not rebound after heavy rains in the 1990’s; • Pintails nest in stubble left after harvesting grain – intense farming has cultivated the “stubble fields” • Nests are move concentrated & easier target for predators

27. Isle Royale, Michigan Study • Moose population is isolated by water • No immigration or emigration • 1973-1983 • Wolf predation • 1995-1996 • Severe winter & food shortage • 75% of population died

28. Predator-Prey Cycles • Lynx  predator • Snowshoe Hare --> prey • 10 Year Cycle • Food shortage & predator-prey interactions

29. Human Population Growth • What factors have caused the exponential growth of the human population?

30. Human Population Growth • No human population can grow indefinitely • Exponential growth is causing…… • Over-consumption of non-renewable resources • Loss of biological species • Environmental degradation

31. History of Human Population Growth • Slow & steady increase until 1650 • Industrial Revolution caused increase • Delayed reproduction decreases population growth rates • Should we use government programs to approach “K” smoothly? • We add 214,000 people to our planet daily • By 2025  @7.8 billion people • Only 500 million in 1650 • In 1996, doubling time was @ 50 years & growth rate was 1.4%

32. Age Structure Diagrams • Relative # of individuals of each age

33. Ecological Footprint • Used to estimate human carrying capacity • Black Dots  bigger ecological footprint than land & resources can support • Blue Dots  smaller ecological footprint

34. Question to Consider • Many people regard the rapid population growth of developing countries as our most serious environmental problem. Others think that the population growth in developed countries, through smaller, is actually a greater threat to the environment. • What kinds of problems result from population growth in… • A) developing countries, and • B) the industrialized world? • Which do you think is the greater threat and why?