1. POPULATION DYNAMICS

2. Population Dynamics and the Sea Otter The population dynamics of the sea otter have helped us to better understand the ecological importance of this keystone species. Sea otter – almost extinct in 1900’s, caused a population explosion of sea urchins because nothing to keep pop. In check Kelp beds lost, decrease in diversity When sea otters made a comeback, deforested kelp areas recovered

3. Population Dynamics and the Sea Otter

4. Population Dynamics Population dynamics is the change in population structure due to environmental stress and changes in environmental conditions.

5. Population Dynamics Four ways in which population structure changes: –Size (# of individuals) –Density (# of individuals in a certain space) –Dispersion (spatial patterns) –Age distribution

6. Dispersion – Spatial Patterns

7. Population Size Population change = (births + immigration) – (deaths + emigration) –Immigration – organisms moving into a population –Emigration – organisms leaving pop.

8. Population Size To determine percent growth rate: =[(CBR-CDR) + (IR-ER)] *100 CBR crude birth rate = #births/1000 CDR crude death rate = #deaths/1000 IR Immigration rate = #immigrating/1000 ER emigration rate = #emigrating/1000

9. Population Size Biotic Potential – a population’s growth potential Intrinsic Rate of Increase (r) – rate at which a population would increase with unlimited resources –Ex. One single female housefly could give rise to 5.6 trillion flies in 13 months with no controls on the pop.

10. Population Size ….but, as we know, in nature there are always limits to population growth. –Environmental resistance are all the factors that limit population growth

11. Population Size Together the biotic potential and environmental resistance determine carrying capacity (K)

12. Population Size Carrying capacity (K) -- # of individuals of a given species that can be sustained indefinitely in a given space (area or volume)

13. Population Size Exponential Growth – a population that has few resource limitations; growth starts out slowly, but gets faster and faster (j-shaped growth curve)

14. Exponential Growth

15. Logistic Growth Involves exponential growth, with a steady decrease in population growth as it encounters environmental resistance, approaching carrying capacity and leveling off Sigmoid growth curve

16. Logistic Growth

17. In reality, populations fluctuate slightly above and below the carrying capacity

18. Population Size – Doubling Time How long it takes for the population to double = 70/ % growth rate –Ex. In 2002, world pop. Grew by 1.28%…..so 70/1.28=54.7 (so world pop. Should double in approx. 55 yrs.

19. What if carrying capacity is exceeded? This happens when a pop. Uses up its resource base and temporarily overshoots carrying capacity Occurs because of reproductive time lag: period needed for birth rate to fall and death rate to rise Pop. Would then suffer a crash or dieback

20. Example of Overshoot 26 Reindeer were introduced to an island off of Alaska in 1910 1935 – pop.= 2,000 (no predators and plentiful resources) By 1950, the pop. Crashed with only 8 reindeer remaining

21. Factors Affecting Carrying Capacity Competition within and between species Immigration and emigration Natural and human caused catastrophes Seasonal changes in resource availability

22. What About Human Pop. Carrying Capacity? Currently growing at an exponential rate Humans can be affected by overshooting carrying capacity –Ex. Potato famine in 1845 (Ireland) 1 million people died and 3 million emigrated

23. Population Density Density-independent population controls:affect pop. Size regardless of density Examples: floods, fires, hurricanes, unseasonable weather, habitat destruction, pesticide spraying

24. Population Density Density-dependent population controls:have a greater affect as population increases Examples:competition, predation, parasitism, disease

25. Population Density Human Example: Bubonic Plague (bacterium usually found in rodents) spread like wildfire through cities of Europe in 14 th century killing 25 million people

26. Revisiting Predator-Prey Relationship

27. Top-down control hypothesis: the predator population keeps the prey population in check …but is this really true?

28. Revisiting Predator-Prey Relationship Research shows that the snowshoe hare pop. Has a similar cycle even when lynx aren’t present Bottom-up control hypothesis: the hare population overshoots its carrying capacity, and then crashes, so in reality the hare pop. Controls the lynx pop.

29. Revisiting Predator-Prey Relationship It has been found that both of these hypotheses are not mutually exclusive, they exist in different ecosystems

30. Reproductive Patterns Asexual Reproduction: all offspring are clones or identical copies

31. Reproductive Patterns Sexual Reproduction: half of genetic material coming from each parent; 97% of known organisms Risks:females only ones producing offspring, chance of genetic errors, mating may spread disease, injury

32. Reproductive Patterns If sex is so risky, why do so many organisms reproduce this way? –Greater genetic diversity, so more likely to survive environmental change –Males can help provide for offspring, increasing chances for survival

33. Reproductive Patterns Two different patterns: r-selected species K-selected species

34. Reproductive Patterns r-selected species or opportunists: reproduce early and put most of their energy into reproducing Called opportunists because can rapidly colonize a new habitat or colonize after a disturbance; usually boom and bust cycles

35. Characteristics of r- selected species Little or no parental care Early reproductive age Many offspring at once Short lived

36. Characteristics of r- selected species examples

37. K-selected species or competitors Tend to do well in competitive conditions when population size is near carrying capacity (K) Thrive best when environmental conditions are stable

38. K-selected species or competitors Characteristics: –Develop inside mothers –Reproduce late in life –Mature slowly –Parental care –Fewer offspring –*prone to extinction due to these char.

39. K-selected species or competitors

41. Survivorship Curves Shows the # of survivors of each age group

42. Survivorship Curves Type I:late loss curves (humans, typical K-selected species) –High survivorship (parental care) until a certain age, then a high mortality

43. Survivorship Curves Type II – constant loss curve (songbirds, lizards) –Fairly constant mortality rate in all age classes

44. Survivorship Curves Type III:early loss curves (r- selected species, fish, insects) –High juvenile mortality rate

45. Conservation Biology A multidisciplinary science to take action to preserve species and ecosystems 3 principles: –Biodiversity is necessary to life on earth –Humans should not cause or hasten ecological damage including extinction –Best way to preserve biodiversity is to protect intact ecosystems

46. Conservation Biology

47. How humans have altered natural ecosystems: –Fragmenting and degrading habitat

48. How humans have altered natural ecosystems: –Simplifying natural ecosystems (monocultures)

49. Conservation Biology –Using, wasting, or destroying a percentage of earth’s primary productivity

50. Conservation Biology Genetic resistance of some pest and bacteria pops. Due to overuse of pesticides and antibiotics

51. Conservation Biology Eliminating some predators

52. Conservation Biology Deliberately or accidentally introducing nonnative species

53. Conservation Biology Overharvesting renewable resources

54. Conservation Biology Interfering with the normal chemical cycling and energy flows in ecosystems

55. Conservation Biology So… what can we do? –Learn about processes and adaptations by which nature sustains itself –Mimic lessons from nature