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  1. 1. Populations
  2. 2. Population• Group of individuals of the same species occupying a common geographical area (a species is an interbreeding group of organisms that produces fertile offspring). – Same species, same place, same time!
  3. 3. Factors affecting Population• G.1.1 Outline the factors that affect the distribution of plant species, including temperature, water, light, soil pH, salinity and mineral nutrients.• G.1.2 Explain the factors that affect the distribution of animal species, including temperature, water, breeding sites, food supply and territory.
  4. 4. Population Dynamics• Natality – offspring are produced and added to the population (birth)• Mortality – individuals die and are lost from the population (death)• Immigration – individuals move into the area from somewhere else and add to the population• Emigration – individuals move out of the area and are lost from the population
  5. 5. Population Dynamics∀∆ = N + I – M – E• In closed populations: ∆ = N – M• In English: Change = Births + Newcomers – Deaths – Exiters
  6. 6. Populations5.3.2: Draw a graph showing the sigmoid (S-shaped) population growth curve.5.3.3: Explain reasons for the exponential growth phase, the plateau phase and the transitional phase between these two phases.
  7. 7. Exponential Phase• Population increases exponentially because the natality rate is higher than the mortality rate.• This is because there is an abundance of food, and disease and predators are rare.
  8. 8. Transitional Phase• Difference between natality and mortality rates are not as great, but natality is still higher so population continues to grow, but at a slower rate.• Food is no longer as abundant due to the increase in the population size. May also be increase predation and disease.
  9. 9. Plateau Phase• Natality and mortality are equal so the population size stays constant.• Limiting Factors (5.3.4): – shortage of food or other resources – increase in predators – more diseases or parasites• If a population is limited, then it has reached its carrying capacity
  10. 10. Other Population Curves Growth curve for bacteria bacteria # time• Boom and bust
  11. 11. Factors Limiting the Growth of Natural Populations• All populations have a limit for exponential growth  biotic potential (intrinsic rate of increase), r, under perfect conditions• Dependent on - # offspring/birth, capacity for survival, procreation rate, maturity• Since population is mainly affected by B-D, the factors that limit growth either  birth rate or  death rate• Abiotic factors – blizzards, hurricanes, floods (weather) – density independent regulation (death rate is independent of the population)• Biotic factors – predators, competitors, parasites – density dependent regulation (the proportion of individuals that die will depend on the size of the population – the birth rate and death rate are affected by the size of the population)
  12. 12. Survivorship Patterns (r- and K-)• r- (small letter, small creatures)• K- (large letter, large creatures)
  13. 13. r- selected• r-selected populations (small letter – small creatures)• variable, unpredictable climate  ability to adapt• density independent factors  mortality• lots of offspring• high juvenile mortality• population below carrying capacity• low level of competition• early development, reproduction, small body size, high reproductive capacity, reproduce only one, many offspring• short life-span (less than one year)• little/no parental care
  14. 14. K- selected• K-selected populations (capital letter – large creatures)• offspring’s survival depends on ability to obtain limited resources – produce a few highly competitive offspring (many young die if climate changes drastically)• fairly constant/predictable offspring• density-dependent mortality• low juvenile mortality• fairly constant population – at/near carrying capacity• high levels of competition• slow development, greater competitive ability, large body size, delayed & repeated reproduction, fewer, larger offspring• life-span longer