Population Ecology

1. Population Ecology

2. Definition of Population: • Group of individuals of a single species living in a specific geographic region at the same time

3. Study of populations in relation to environment • Environmental influences on: • population density • age structure • population distribution (dispersion)

4. Births and immigration add individuals to a population. Births Immigration PopuIationsize Emigration Deaths Deaths and emigration remove individuals from a population. • Density is the result of a dynamic interaction of processes that add individuals to a population and those that remove individuals from it • How do these factors • Contribute to Population Size?? • Births • Deaths • Immigration • Emigration

5. Clumped Dispersion • Individuals aggregate in patches • May be influenced by resource availability and behavior

6. Uniform Dispersion • Individuals are evenly distributed • May be influenced by social interactions such as territoriality

7. Random Dispersion • Position of each individual is independent of other individuals (c) Random. Dandelions grow from windblown seeds that land at random and later germinate.

8. How do wildlife biologists quantify populations? Defined Populations -complete counts -incomplete counts -indirect counts Undefined Populations Mark and Recapture

9. Life history traits are products of natural selection • Life history traits are evolutionary outcomes • Reflected in the development, physiology, and behavior of an organism • Three things needed quantify life history • When reproduction begins • How often organism reproduces • How many offspring produced

10. Semelparity: Big Bang • Reproduce a single time and die • putting all available resources into maximizing reproduction at the expense of future life 

11. Iteroparity – Repeated Reproduction • produce offspring repeatedly over time • increased parental care along with enhanced energetic investment per offspring

12. 100 Male Female 80 60 Parents surviving the following winter (%) 40 20 The lower survival rates of kestrels with larger broods indicate that caring for more offspring negatively affects survival of the parents. CONCLUSION 0 Reduced brood size Normal brood size Enlarged brood size “Trade-offs” and Life Histories • Which may lead to trade-offs between survival and reproduction • Organisms have finite resources RESULTS • Kestrels: • Produce a few eggs? • Can invest more into each, ensuring greater survival • Produce many eggs? • Costly but if all survive, fitness is better

13. More is Better? • Some plants produce a large number of small seeds • Ensuring that at least some of them will grow and eventually reproduce

14. Fewer is Better? • Other types of plants produce a moderate number of large seeds • That provide a large store of energy that will help seedlings become established

15. Demography • Study of the vital statistics of a population • And how they change over time • Death rates and birth rates • Zero population growth • Occurs when the birth rate equals the death rate

16. Exponential Population Growth Population increase under idealized conditions No limits on growth • Under these conditions • The rate of reproduction is at its maximum, called the intrinsic rate of increase

17. Example-understanding growth Question: I offer you a job for 1 cent/day and your pay will double every day. You will be hired for 30 days. Will you take my job offer? Answer: If you said YES, you will have made $~21 million dollars for 30 days of work. How is this possible?????

18. Amount of Pay/Day # of Days 1ST DAY OF WORK: 1 cent pay/day 30TH DAY OF WORK: ~10.2 million/day How is this possible?????

19. dN  rmaxN dt Exponential Growth Model *Idealized population in an unlimited environment *Very rapid doubling time; steep J curve *r=N=(b-d)N t r=instrinsic rate of growth

20. 8,000 6,000 Elephant population 4,000 2,000 0 1900 1920 1940 1960 1980 Year Exponential Growth in the Real World • Characteristic of some populations that are rebounding • Cannot be sustained for long in any population

21. Logistic Population Growth • More realistic model of population growth • Carrying capacity (K) • Is the maximum population size the environment can support • In the logistic population growth model • The per capita rate of increase declines as carrying capacity is reached

22. 2,000 dN  1.0N Exponential growth dt 1,500 (K  N) K  1,500 dN  rmax N Logistic growth dt K Population size (N) 1,000 dN 1,500  N  1.0N dt 1,500 500 0 0 5 10 15 Number of generations Logistic Population Growth • Produces a sigmoid (S-shaped) curve Figure 52.12

23. 1,000 800 600 Number of Paramecium/ml 400 200 0 0 5 15 10 Time (days) (a) A Paramecium population in the lab. The growth of Paramecium aurelia in small cultures (black dots) closely approximates logistic growth (red curve) if the experimenter maintains a constant environment. The Logistic Model and Real Populations • The growth of laboratory populations of Paramecium • Fits an S-shaped curve

24. 180 150 120 90 Number of Daphnia/50 ml 60 30 0 160 0 40 60 100 120 140 20 80 Time (days) (b) A Daphnia population in the lab. The growth of a population of Daphnia in a small laboratory culture (black dots) does not correspond well to the logistic model (red curve). This population overshoots the carrying capacity of its artificial environment and then settles down to an approximately stable population size. Logistic Growth and The Real World • Some populations overshoot K • Before settling down to a relatively stable density What type of feedback loop is this?

25. 80 60 40 Number offemales 20 0 1995 2000 1980 1985 1990 1975 Time (years) (c) A song sparrowpopulation in its natural habitat. The population of female song sparrows nesting on Mandarte Island, British Columbia, is periodically reduced by severe winter weather, and population growth is not well described by the logistic model. Logistic Growth and the Real World • Some populations • Fluctuate greatly around K

26. Natural selection (diverse reproductive strategies) a) Relatively few, large offspring (K selected species) b) Many, small offspring (r selected species) (K selected species) (r selected species)

27. Populations Regulated Biotic and Abiotic Factors Two general questions we can ask about regulation of population growth • What environmental factors stop a population from growing? • 2. Why do some populations show radical fluctuations in size over time, while others remain stable?

28. 4.0 10,000 3.8 3.6 Average number of seeds per reproducing individual (log scale) 1,000 3.4 Average clutch size 3.2 3.0 100 2.8 0 0 40 50 60 80 20 30 10 70 0 10 100 Seeds planted per m2 Density of females (a) Plantain. The number of seeds produced by plantain (Plantago major) decreases as density increases. (b) Song sparrow. Clutch size in the song sparrow on Mandarte Island, British Columbia, decreases as density increases and food is in short supply. Competition for Resources • In crowded populations, increasing population density • Intensifies intraspecific competition for resources

29. Many vertebrates and some invertebrates are territorial • Territoriality may limit density

30. Territoriality: Ocean birds • Exhibit territoriality in nesting behavior

31. Health • Population density- • Can influence the health and survival of organisms • In dense populations, pathogens can spread more rapidly

32. 730,000 100,000 Commercial catch (kg) of male crabs (log scale) 10,000 1990 1950 1980 1960 1970 Year Figure 52.19 Fluctuations in Population Size • Extreme fluctuations in population size • Are typically more common in invertebrates than in large mammals

33. Snowshoe hare 160 120 Lynx 9 Lynx population size (thousands) Hare population size (thousands) 80 6 40 3 0 0 1850 1875 1900 1925 Year Population Cycles • Many populations undergo regular boom-and-bust cycles • Influenced by complex interactions between biotic and abiotic factors

34. Human Populations 6 5 4 Human population (billions) 3 2 The Plague 1 0 8000 B.C. 4000 B.C. 3000 B.C. 2000 B.C. 1000 B.C. 1000 A.D. 2000 A.D. 0 Figure 52.22 • No population can grow indefinitely and humans are no exception

35. Global Carrying Capacity • Just how many humans can the biosphere support? • Carrying capacity of earth is unknown…. http://www.youtube.com/watch?v=9_9SutNmfFk http://www.youtube.com/watch?v=UUOEcNomakw&feature=rec-LGOUT-exp_fresh+div-1r-8-HM http://www.youtube.com/watch?v=4B2xOvKFFz4&feature=related

36. Rapid growth Afghanistan Decrease Italy Slow growth United States Male Female Female Male Male Age Age Female 85 85 80–84 80–84 75–79 75–79 70–74 70–74 65–69 65–69 60–64 60–64 55–59 55–59 50–54 50–54 45–49 45–49 40–44 40–44 35–39 35–39 30–34 30–34 25–29 25–29 20–24 20–24 15–19 15–19 10–14 10–14 5–9 5–9 0–4 0–4 8 8 8 6 6 6 4 4 4 2 2 2 0 0 0 2 2 2 4 4 4 6 6 6 8 8 8 Percent of population Percent of population Percent of population Figure 52.25 • Age structure is commonly represented in pyramids

37. 60 80 50 60 40 Infant mortality (deaths per 1,000 births) Life expectancy (years) 40 30 20 20 10 0 0 Developed countries Developed countries Developing countries Developing countries Figure 52.26 Infant Mortality and Life Expectancy • Infant mortality and life expectancy at birth • Vary widely among developed and developing countries but do not capture the wide range of the human condition

38. Search for the Missing Sea Otters Case Study in Population & Community Ecology

39. Sea OttersEnhydra lutris

40. Otter Behavior http://www.youtube.com/watch?v=dQ2Lrnr0gLc http://www.youtube.com/watch?v=YQXKyTWMvpM

41. Population Distribution

43. GROUP QUESTION: 1) What is happening to sea otter populations at several locations in the Aleutian Islands, Alaska? 2) What factors could be contributing to such a rapid change in the size of sea otter populations? Create a list of possible factors.

44. Could the otters simply have migrated from one part of the region to another? To find out, the researchers analyzed populations over a 500-mile-long stretch of the Aleutians from Kiska to Seguam …. By 1993 otter numbers in that whole stretch had been cut by half. Here the geographical scope of the research effort became critical; a smaller region would not have been large enough to reveal the decline. In 1997, they … found that the population decline had worsened, to about 90 percent …. “That told us for sure it was a very large-scale decline, but we were still trying to understand the cause,” Dr. Estes said …. The researchers … ruled out reproductive failure. Their studies enabled them to keep track of how often otters gave birth and how many young survived, and this revealed that reproduction was continuing to re-supply the population. With other possible causes eliminated, … mortality had to be the explanation. In the past, they had seen temporary declines in otter populations because of starvation, pollution or infectious disease. “In all those cases,” Dr. Estes said, “we find lots of bodies. They get weak and tired and come ashore to die.” This time not a single dead otter was found—a clue, he said, that “something really weird was going on.” (Excerpted from Stevens, William K. “Search for missing sea otters turns up a few surprises.” New York Times, January 5, 1999.) Group Question: Read above and eliminate some of the reasons for changes in the relative abundance of sea otters at several locations in the Aleutian Islands, Alaska? What does it have to be?

45. Orca or Killer WhaleOrcinus orca

46. Male vs. Female

47. Orca prey

48. Orca predation behavior https://www.youtube.com/watch?v=ypNg19etJg0 http://www.youtube.com/watch?v=Ks40worW_gQ(hunting sea lions) Orcas & learned hunting behavior? (great white sharks??) : http://www.youtube.com/watch?v=SS6NjdGLVZs&feature=related

49. Group Questions Make a list of the types of information about killer whales you believe the scientists might need to test their hypothesis that increased predation by the whales was the cause of the sea otter decline. Describe two experiments that would allow you to test the hypothesis that increased predation by killer whales was the cause of the sea otter decline. Keep in mind the following key components of any good experiment: a control (something to which to compare the treatment), replication (do it more than once), and consideration of confounding factors (what might cause differences other than what you manipulate in your experiment?).

50. Group question: Interpret the two figures. What do they show? How does this provide evidence that orcas were responsible for the decline in sea otters in Kuluk Bay?