Chapter 53: Population Ecology

1. Chapter 53: Population Ecology

2. Essential Knowledge • 2.a.1 – All living systems require constant input of free energy (53.3 & 53.4). • 2.d.1 – All biological systems from cells and organisms to populations, communities, and ecosystems are affected by complex biotic and abiotic interactions involving exchange of matter and free energy (53.1 – 53.5). • 4.a.5 – Communities are composed of populations of organisms that interact in complex ways (53.1-53.3, 53.5 & 53.6).

3. Population Ecology • Study of the factors that affect population size and composition. • Population: • Def: Individuals of a single species that occupy the same geographic area • Ex: Humans living in Indianapolis, IN

4. Important Characteristics 1. Density 2. Dispersion

5. Density • Number of individuals per unit area or volume. • Ex: • Diatoms - 5 million/m3 • Trees - 5,000/km2 • Deer - 4/km2

6. Dispersion • Pattern of spacing among individuals. • Types: 1. Clumped 2. Uniform/Even 3. Random

8. Clumped Dispersion • May result form a patchy environment. • May increase chances for survival. • Ex: • Schooling behavior • Flocks of birds

9. Uniform Dispersion • Often the result of antagonistic interactions between individuals. • Known as even or regular dispersion • Ex: • Territories • Spacing between desert plants

10. Random Dispersion • Often the result of the absence of strong attractions or repulsions between individuals. • Not a common pattern.

11. Demography • The study of the vital statistics that affect population size. • Ex: Birth and Death rates • Factors of Demography: • Age structure of population • Birth and death rates • Generation time • Sex ratio and reproductive behavior

12. Life Tables • Mortality summary for a cohort of individuals. • First developed from life insurance studies. • What do they show us? • Mortality rate per year • Life span of the organism • Fecundity (birth rate)

14. Survivorship Curve • Plot of the numbers of a cohort still alive over time. • Curve Types: • Type I • Type II • Type III

15. Type I • Low early deaths. • High late deaths. • Ex: • Humans • Other large mammals

16. Type II • Constant death rate. • Ex: • Annual plants • Many invertebrates

17. Type III • High early deaths. • Low late deaths. • Ex: • Trees • Oysters

18. Comment • Curve type may change between young and adults. • Ex: Nestlings - Type III Adult Birds- Type II

19. Life History Strategies 1. "r" or Opportunistic species 2. "k" or Equilibrial species

20. "r" Species • Increase fitness by producing as many offspring as possible. • Do this by: • Early maturation • Many reproductive events • Many offspring

21. Result • Maximize reproduction so that at least a few offspring survive to the next generation. • Most offspring die (Type III curve).

22. "k" Species • Increase fitness by having most offspring survive. • Do this by: • High parental care • Late maturation • Few reproduction events • Few offspring.

23. Result • Maximize survivorship of each offspring. • Few offspring, but most survive (Type I curve).

24. What is the strategy? • For a weed? • For an endangered species? • For Garden Pests?

25. Population Growth • DN/Dt = b - d • Where: • N= population size • t = time • b = birth rate • d = death rate

26. Rate of Increase • r = difference between birth rate and death rate. • r = b - d

27. Equation with “r”: • DN/Dt = rN • N = population size • t = time • r = rate of increase

28. From Calculus • The equation DN/Dt= rNbecomes: • dN/dt = rmax N • rmax= intrinsic rate of increase

29. Exponential Growth • dN/dt = rmax N • Characteristic of "r" species. • Produces a “J-shaped” growth curve. • Only holds for ideal conditions and unlimited resources.

31. Logistic Growth • dN/dt = rmax N K-N K • K = carrying capacity • Result of logistic growth? • “S-shaped” growth curve • Characteristic of “k” species • Common when resources are limited

33. Comment • K is not a constant value. • Populations often oscillate around “K” as the environment changes.

35. Additional Comments • Populations often overshoot “K”, then drop back to or below “K”. • AP Exam rarely asks you to work the equations, but you should be able to give them.

36. Regulation of Population Size 1. Density- Dependent Factors 2. Density- Independent Factors

37. Density-Dependent • Affect is related to N • As N increases, mortality increases • Ex: Food, nesting space, disease

39. Density-Independent • Affect is not related to N • Mortality not related to population size • Ex: Weather and climate

40. Population Cycles • Cyclic changes in N over time • Often seen in predator/prey cycles • Ex: Snowshoe Hare – Lynx • Causes? • Density dependent factors • Chemical cycles • Saturation strategy to confuse predators

42. Age Structure Diagrams • Show the percent of a population in different age categories • Method to get data similar to a Life Table, but at one point in time

44. Importance • Can be used to predict future population growth trends, especially for long lived species.

45. Exponential Growth • Produces age structures that are a triangle or pyramid shape Logistic Growth • Produces age structures that have even sizes between most age categories

46. Declining Populations • Produce age structures with a narrow base and wider middles

47. Summary • Identify the difference between population density and dispersion. • Recognize the types of dispersion patterns and the interactions that lead to them. • Identify the types of survivorship curves. • Recognize the characteristics of "r" and "k" life history strategies. • Identify the types of population growth models. • Identify factors that regulate population size. • Recognize how age-structure diagrams relate to population growth.