2. CHAPTER 9 Population Dynamics, Carrying Capacity and Conservation Biology

3. I. Population Dynamics A. Characteristics of a population 1. Size - number of individuals 2. Density - number of individuals per space 3. Age Distribution – portions of individuals of each age

4. 4. Dispersion – spatial patterns of organisms Clumped Elephants ** MOST COMMON SPATIAL PATTERN IN NATURE (GO TO THE RESOURCES) Random (dandelions) Uniform (creosote bush)

5. B. 4 Factors that govern population size Births + Emigration - Immigration + Deaths Deaths -

6. C. Terms Related to Populations 1. Zero Population Growth Lost = Gains 2. Biotic Potential Populations Capacity for growth

7. 3. Intrinsic Rate of Increase (r) Rate at which a population would grow with unlimited resources Populations with a high “r”… Reproduce early in life Short generation times Can reproduce many times Have many offspring each time they reproduce

8. 4. Environmental Resistance All factors acting jointly to limit the growth of a population Together biotic potential and environmental resistance determine…

9. 5. Carrying Capacity “k” -Number of individuals of a given species that can be sustained in a given space indefinitely

10. 6. Minimum Viable Population (MVP) Fewest number of members of a species needed to insure the species survives If a population declines below MVP… - Certain individuals may not be able to find a mate -Interbreeding occurs (weak or mutant offspring) -Genetic diversity may be too low to adapt to environmental changes

11. II. POPULATION GROWTH Growth occurs in two ways… A. Exponential: Population with few or no resource limitations. Starts slow and increases “J-shaped curve” Population size (N) Time (t)

12. Population size (N) K B. Logistic: Exponential at first… Slowing as the population encounters environmental resistance “S- shaped curve”

13. 2.01.5 1.0.5 Number of sheep (millions) 180018251850187519001925

14. What if Population Size Exceeds “k” -A population may use up resources and overshoot the “k” -Overshoot occurs due to… Reproductive Lag Time Period needed for the birth rate to fall and the death rate to rise in response to overconsumption

15. - This lag can cause Dieback or Crash -Occurs unless the excess individuals… Switch to new resources Move to an area with more favorable conditions

16. Reindeer in Alaska Fig. 9.6, p. 201 2,000 1,500 Number of reindeer 19101920193019401950 Year 1,000 500

17. Humans are not exempt from carrying capacity diebacks and crashes… -Easter Island -Potato Famine -Ireland (1845)

19. September 23, 2008 According to current calculations, humanity’s first Earth Overshoot Day was December 31, 1986. By 1995 it was more than a month earlier, arriving on November 21. Ten years later it was six weeks earlier than in 1995, occurring on October 2, 2005. Humanity’s use of nature (in terms of natural resources and services) went from using slightly more than half of planet Earth’s biocapacity in 1961 to the equivalent of 1.4 planet Earths in 2008.

20. SHOW EASTER ISLAND.flv

21. The earth’s carrying capacity has been extended by…

22. III. Factors that Affect Carrying Capacity Competition Immigration and Emigration Catastrophic Events Seasonal Fluctuations

23. POPULATION SIZE Growth factors (biotic potential) Favorable light Favorable temperature Favorable chemical environment (optimal level of critical nutrients) Abiotic Biotic High reproductive rate Generalized niche Adequate food supply Suitable habitat Ability to compete for resources Ability to hide from or defend against predators Ability to resist diseases and parasites Ability to migrate and live in other habitats Ability to adapt to environmental change Decrease factors (environmental resistance) Too much or too little light Temperature too high or too low Unfavorable chemical environment (too much or too little of critical nutrients) Abiotic Biotic Low reproductive rate Specialized niche Inadequate food supply Unsuitable or destroyed habitat Too many competitors Insufficient ability to hide from or defend against predators Inability to resist diseases and parasites Inability to migrate and live in other habitats Inability to adapt to environmental change

24. IV. Population Density And Population Growth A. Density-Independent Population Controls: Affect a population size regardless of the density Flood, hurricanes, drought, fire, habitat destruction, pesticide spraying

25. B. Density-Dependent Population Controls: Greater effect as density increases Competition, predation, parasitism and disease

26. C. Natural Population Curves 1. Stable: Fluctuates slightly above and below the “k” 2. Irruptive: Population explodes and crashes back to a lower level 3. Irregular: Changes irregularly for unknown reasons 4. Cyclic: Sharp increases followed by crashes in a regular pattern

27. Number of individuals Time 2. Irruptive 1. Stable 4. Cyclic 3. Irregular

28. The Lynx-Hare Cycle Population size (thousands)Population size (thousands) 160160 140140 120120 100100 8080 6060 4040 2020 0 18451845 18551855 18651865 18751875 18851885 18951895 19051905 19151915 19251925 19351935 YearYear Hare Lynx

29. 1. Top-Down Hypothesis -Possible explanation for the 10-year population cycles of Hare and Lynx -Lynx preying on hares reduce their population -Shortage of hares reduces the lynx population -Lower # of Lynxes, hares increase -Lynx pop. Increases due to greater food supply V. Predation and Population Control

30. VIDEO

31. 2. Bottom-Up Control *Second possible reason for hare decline Based on study where hare numbers decreased on island w/o lynx members Believed that population crashes may be a result of decreases in primary producers

32. The Lynx-Hare Cycle Population size (thousands)Population size (thousands) 160160 140140 120120 100100 8080 6060 4040 2020 0 18451845 18551855 18651865 18751875 18851885 18951895 19051905 19151915 19251925 19351935 YearYear Hare Lynx

33. VI. REPRODUCTION AND SURVIVAL A. Types of reproduction: -Asexual: Creates a genetic clone Common in simple organism -Sexual: Create offspring by union of gametes Costly/risky to organisms Done by 97% of known organisms

34. B. Reproduction Patterns 1. Opportunists: (r-selected species) -Reproduce early and put most of their energy into it -Large litters -Reach reproductive age early -Short generation times Little or no care to the offspring -Reproduce quickly when a disturbance opens up a new niche -Often get displaced by a more competitive species

35. r-Selected Species cockroachdandelion Many small offspring Little or no parental care and protection of offspring Early reproductive age Most offspring die before reaching reproductive age Small adults Adapted to unstable climate and environmental conditions High population growth rate (r) Population size fluctuates wildly above and below carrying capacity (K) Generalist niche Low ability to compete Early successional species

36. 2. Competitor or (k-Selected Species) -Put little energy into reproduction -Reproduce late in life -Few offspring -Long generations -Put energy into protection and nurturing -Display log growth -Thrive best in constant environments *Availability of habitat determines the population size

37. Fewer, larger offspring High parental care and protection of offspring Later reproductive age Most offspring survive to reproductive age Larger adults Adapted to stable climate and environmental conditions Lower population growth rate (r) Population size fairly stable and usually close to carrying capacity (K) Specialist niche High ability to compete Late successional species elephantsaguaro K-Selected Species

38. C. Survivorship Curves Shows the number of survivors at each age group of a particular species Late Loss: k-selected species, reduced juvenile mortality Ex: Humans and elephants Early Loss: r-selected species, high juvenile mortality Constant Loss: face mortality at all ages Songbirds, lizards, small mammals

39. Percentage surviving (log scale ) 100 10 1 0 Age

41. VII. CONSERVATION BIOLOGY Sustaining wildlife populations Goals: Investigate human impacts on biodiversity Develop practical approaches to maintain biodiversity Key Topics: Endangered species management Wildlife reserves Ecological Restoration Ecological Economics Environmental Ethics

42. 3 Principles of Conservation Biology Biodiversity is necessary to all life and should not be reduced by human actions Humans should not hasten extinction The best way to preserve biodiversity is to protect intact ecosystems and provide habitat