Organisms and Populations

Population attributes - growth, birth rate and death rate, age distribution

  1. Birth rate (or) Natality is the average number of young ones produced by birth/germination/hatching per unit time. (or) it is the number of birth per 1000 persons in a population per year.
  2. Average number of individuals that die per unit time (or) no. of death per 1000 persons in a population per year.
  3. Death rate is represented by survivorship curve made by a plat with x-axis time and y-axis no. of organisms undergoing death will yield 3 types of curve.
  4. Diagonal curve : Eg: Hydra, mice, Convex; Eg: Man, rabbit; Concave : Eg Fish oysters
  5. The major age groups is any population are
    (i) Pre-reproductive / Juvenile / Dependent Phase
    (ii) Reproductive / Adult phase
    (iii) Post-reproductive / Old age phase
  6. If the pre-reproductive population is more than the reproductive and the post reproductive are lesser than then two, then the population is expanding and in future the population size will increase that gives pyramidal graph.
  7. If pre-reproductive = reproductive population, then it is stable populatin (which is in a trend, at present) so the population is future remain unchanged.
  8. If pre-reproductive group < post/reproductive group, it means in future the population size will deplete, called as declining population.
  9. Two popular growth curves are sigmoidal/s-shaped/logistic growth curve with the factor \tt \frac{dN}{dt}=rN\left(\frac{k-N}{k}\right), where \tt \frac{dN}{dt}= rate of change of population size with time; k = carrying capacity; r = intrinsic rate of natural increase; t = time.
  10. J shaped curve/Exponential growth curve contain no stationary phase, Where , = \tt \frac{dN}{dt}=rNand its integral form will be [Nt = N0ert]
  11. J shaped curve with experience crash phase and the population grow well beyond the carrying capacity.

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