Population growth


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Population growth

  1. 1. Chapter 52 Population Ecology p.1151-1156, 1158-1168 Chapter 53 Community Ecology p.1176-1181 Population Growth
  2. 2. Terms Population Habitat Geographic range
  3. 3. Characteristics of Population Density Dispersion
  4. 4. Density Number of individuals per unit area or volume D = N / A N = population size A = area
  5. 5. Types of Density Crude density: number of individuals in the total area of the habitat Ecological density: number of individuals in the area actually used by the individuals In the equation D=N/A, the value for area is the only difference Example: Moose live in 600 ha of Algonquin Park. However, 70 ha is open lake which is not utilized by the moose.
  6. 6. Dispersion Distribution pattern of a population 3 types: Clumped Random uniform
  7. 7. Dispersion http://www.bio.miami.edu/dana/pix/dispersion.jpg
  8. 8. Dispersion
  9. 9. Dispersion Clumped Random Uniform Description Resource distribution Resource abundance Interaction between individuals Example
  10. 10. Studying Populations Survey: a count Sampling: taking a measurement from a portion of the population and applying it to the whole Tracking: monitoring / following an individual organism
  11. 11. Sampling Methods Transect Quadrat Mark-Recapture
  12. 12. Transect Method A line placed across a community of organisms, usually in a form of a string between 2 markers. Subsequent transects are arranged equal distances from each other. 3 types of transects: Point Continuous belt
  13. 13. Transect Method: Point Sampling The string is marked off at equal intervals to indicate where a count is to be taken.
  14. 14. Transect Method: Continuous Sampling Whole area along the line is counted
  15. 15. Transect Method: Belt Sampling A form of quadrat sample
  16. 16. Transect Method Used to determine information on the distribution of a species Useful when there are environmental gradients that change the distribution and density patterns in a sampled area
  17. 17. Quadrat Method
  18. 18. The math: ratios What you want to know: Size of total population (N) What you already know: size of geographic area (A) What you will determine by sampling: Individuals in sampled area (N1) size of sampled area (A1) N/A = N1/A1
  19. 19. Sample Question: Quadrat Ragweed plants occupy a field measuring 100 m x 100 m. A student places three 2.0 m x 2.0 m quadrats in the field. Estimate the population density and size if she finds 18, 11 and 24 ragweed plants in the three quadrats.
  20. 20. Mark-Recapture Method
  21. 21. The math: ratios What you want to know: Size of total population (N) What you know from the first capture: Number of marked individuals (M1) in a population What you know from the second capture: Number of marked individuals (M2) Total number of individuals in capture (N2) M1/N = M2/N2
  22. 22. Sample Question: Mark-Recapture Wildlife researchers surveyed an area of wetlands where 80 ducks were captured in traps, marked with permanent metal bands, and then released. Two weeks later, 100 ducks were captured. Of the ducks recaptured, 12 were marked. Estimate the total size of the duck population.
  23. 23. Sampling Summary Quadrat Transect Mark- recapture Description Method Types of populations Calculations
  24. 24. Transect Activity Birds of Prey in Ontario
  25. 25. Quadrat Simulation: Sunflower seeds population 1. Obtain materials to make a quadrat of a known size. Use a ruler to calculate the total area of your quadrat. 2. Obtain a measuring tape and go outside to measure the total geographical area. 3. Toss your quadrat randomly into the area. 4. Count and record the number of individuals in the quadrat. 5. Repeat in 9 more locations making sure the quadrats are all in different areas. 6. Calculate density and estimate population size. 7. Compare to actual population size.
  26. 26. Mark-Recapture Simulation: Marshmallow population 1. Take a bag containing a marshmallow population. 2. Without looking, take up a small handful of marshmallows. Record the number of individuals taken. 3. Using a toothpick, mark those individuals by poking a hole through them. 4. Return them to the bag and mix them thoroughly. 5. Take out another small handful of marshmallows. 6. Record the total number taken and the number of marked individuals. 7. Calculate density and estimate population size. 8. Compare to actual population size by counting all marshmallows in the bag.
  27. 27. Activity: Mark-Recapture Survey Design of the school population  In teams, you will design a mark-recapture method to estimate the total number of individuals in the school  Obtain approval for your design before carrying it out  The objective is to be the team with the most accurate population count based on the data collected Your group will hand in: Lab protocol in formal language (recall the 3 P’s: past tense, passive voice, paragraph form) A set of data with relevant calculations
  28. 28. Demography Study of the changes in the characteristics of a population Life history: all the traits that affect an organisms reproduction and survival
  29. 29. LifeTable Summarizes demographic characteristics of a population Method: monitor a cohort until they die Cohort: a group of individuals of similar ages Originally developed by insurance companies to measure human mortality rates Adapted by ecologist
  30. 30. Survivorship Curves
  31. 31. Survivorship Curves
  32. 32. Survivorship Curves
  33. 33. Survivorship Curves
  34. 34. Trends?
  35. 35. Survivorship Characteristics Type I Type II Type III Mortality Gestation period Parental care Organism size Examples
  36. 36. Fecundity Potential for a species to produce offspring Average number of offspring produced by a female over her lifetime
  37. 37. Activity In your groups, brainstorm factors that may affect fecundity. Determine whether the factors will increase or decrease fecundity.
  38. 38. Factors Affecting Fecundity Age of sexual maturity Maximum reproductive age Length of gestation period Number of offspring per gestation period Seahorse giving birth: http://www.youtube.com/watch? v=uKrkXXaRMUI&feature=player_embedded Amount of parental care Sex ratio (number males vs females)
  39. 39. Measuring Population Change Immigration Emigration Natality (birth rate) Mortality (death rate) Change in population size (ΔN) = (B+I) – (D+E)
  40. 40. Sample Question: Population Change The growth rate for a population of 90 field mice in 6 months is 429%. If the number of births was 342, the number of deaths was 43, and there was no emigration, calculate the number of mice that migrated into the area.
  41. 41. Population Growth Models Exponential Logistic (sigmoid)
  42. 42. Exponential Growth Model A growth pattern exhibited by organisms reproducing at a constant rate Unrestricted growth
  43. 43. Exponential Growth Model Biotic potential (r): highest possible growth rate for a population Intrinsic rate of increase (rmax): Rate at which a population naturally grows when no external factors are acting on it Highest possible growth rate under ideal conditions (i.e. unlimited resources, no predation or disease) Intrinsic factors affecting rmax are the same as those affecting fecundity
  44. 44. Rmax and body mass Relationship between the maximum intrinsic rate of natural increase (rmax ) and adult female body mass for a representative sample of 58 primate species. Humans (arrowed) have a relatively low, but not extreme, value relative to body size (data from Ross, 1988).
  45. 45. Logistic Growth Model A model that describes limited population growth, often due to limited resources or predation Restricted growth due to environmental resistance resulting in leveling off of growth
  46. 46. Logistic Growth Model Carrying capacity (K): number of individuals in a population that the environmental resources can support When population reaches carrying capacity, growth rate is zero (N = K, r = 0) Zero population growth (ZPG): when r = 0
  47. 47. Logistic Growth Curve
  48. 48. Comparing growth curves
  49. 49. Factors affecting population growth 2 classes of factors: Density-independent Density-dependent Activity: Brainstorm examples of each type of factor
  50. 50. Density-Independent Factors http://nupge.ca/sites/new.nupge.ca//files/images/2011/forest-fire_FL.jpg
  51. 51. Density-Independent Factors http://therivermanagementblog.files.wordpress.com/2013/01/dsc03951.jpg
  52. 52. Density-Independent Factors Natural disturbances: fire, flood, earthquake Climate change / temperature fluctuations
  53. 53. Density-Dependent Factors Competition: food, space, mate Predation Disease Allee effect
  54. 54. Competition an interaction in which 2 or more populations lose access to resources 2 classes: Interspecific: between members of different species Intraspecific: between members of the same species
  55. 55. Interspecific Competition Interference competition: individuals of one species harm individuals of another species directly Example: lions chase hyenas from their kill Exploitative competition: individuals of one species has superior ability to gather the same resource as another species Example: birds and ant in desert both eat seeds Example: fast growing seedlings create shade, reducing the survival of ground-cover plants
  56. 56. Resource Partitioning A means of dealing with competition by using different resources within a habitat
  57. 57. Resource Partitioning Example
  58. 58. Predation population cycles: alternating periods of large and small population sizes sinusoidal growth: wavelike oscillating growth pattern, typical of predator-prey interactions
  59. 59. Disease Density increases spreading of disease Example:White-nose syndrome in hibernating little brown bats. White fungus appears around bat’s snout and body. Resulting in high mortality and rapid decline in numbers.
  60. 60. Disease
  61. 61. Allee Effect When the population density is too low, a population cannot survive or fails to reproduce enough to offset mortality, increases the risk of extinction Example: great auk, passenger pigeon minimum viable population size: the smallest population size that is likely to survive
  62. 62. Defense Mechanisms Camouflage Mimicry Chemical defense Behavioural defense Structural defense
  63. 63. Camouflage A type of protective coloration where organism mimics the patterns of its environment
  64. 64. Mimicry A type of protective coloration where organisms resemble another Batesian: palatable or harmless species mimics an unpalatable or poisonous one Mullerian: unpalatable species that share a common predator look the same Mimic octopus: http://www.youtube.com/watch?v=t- LTWFnGmeg
  65. 65. Chemical Defense An organism releases noxious odours or concentrates poisons in its body to make itself chemically unattractive Noxious chemicals: Skunk Bombardier beetle (http://www.youtube.com/watch?v=35Swo8OWMgo) Poisons Monarch butterflies Malaysian ants (explode)
  66. 66. Behavioural Defense Passive: hiding, freezing, playing dead Active: fleeing, herding, mobbing, using distraction Bird mobbing: http://www.youtube.com/watch? v=ppy2iiOt6YU
  67. 67. Structural Defense An external armour that is hard or thorny Hard – tortoise Thorny – porcupine, prickly pear cactus Porcupine: http://www.youtube.com/watch? v=acXEj0M3Tkc
  68. 68. Classify these defense mechanisms  Sea cucumber spills its guts http://www.youtube.com/watch?v=wXf_YodWw40  Hagfish slime attack http://www.youtube.com/watch?v=lZq4Dme7wi4 http://www.youtube.com/watch?v=Bb2EOP3ohnE  Blood squirting regal horned lizard http://www.youtube.com/watch?v=gEl6TXrkZnk  Pistol shrimp sonic stun gun http://www.youtube.com/watch?v=XC6I8iPiHT8 http://www.youtube.com/watch?v=KkY_mSwboMQ
  69. 69. Symbiosis Species having a physically close ecological association with each other Mutualism boxer crab & sea anemone: (3:00-3:25) http://www.youtube.com/watch?v=fBgDrAjDPqw Ants and acacia tree: http://www.youtube.com/watch? v=Xm2qdxVVRm4 Commensalism Clown fish & sea anemone: http://www.youtube.com/watch?v=fkzUziLiiDM Parasitism
  70. 70. Summary of Interactions Interaction Relationship Effect Example Competition -/- Predation +/- Herbivory +/- Parasitism +/- Mutualism +/+ Commensalism +/0