Wednesday, 13 April 2016

Changes in Population Size over Time: Modelling Population Growth

NOTE: References to Nelson Grade 12 University Biology Textbook
Population dynamics: The change in a population over time
  • Population is affected by environmental conditions and other regulating factors
  • Because of these species/ environmental conditions, population can change hourly, daily, seasonally, and annually and population may be unpredictable
Population growth rate: the fractional rate at which the number of individuals in a population increases or decreases
  • Refers to the change in a population over a unit period of time
  • Can be calculated as:
(births + immigration) – (deaths + emigration)
Initial population                                                          x100
  • Positive growth rate= increasing population
  • Negative growth rate= decreasing population
  • Growth rate of zero= population is NOT changing
Exponential model of population growth: a pattern of population in which organisms reproduce continuously at a constant rate
  • Humans have the potential for exponential growth
  • Change in population size= number of births – number of deaths
Mathematically…
  • d= “Change in”
  • N= “Population Size”
  • t= “In Time”
  • B= # of births
  • D=# of deaths
Therefore, dN = B – D
                   dt                  ****( first formula on page 601)****
Per capita growth rate(r): the difference between the per capita birth rate and the per capita death rate of a population
  • Per capita birth rate (b) is # of births in the population during specified time period divided by population size:
b= B/N **** SECOND FORMULA ON PAGE 601****
  • Per capita death rate (d) is # of deaths divided by population size:
d= D/N **** UNDER THE TOP ONE ****
Zero population growth (ZPG): a situation in which the death rate and the birth rate are in equilibrium
Carrying Capacity (K): the number of individuals in a population that the environmental resources can support
Logistic model of population growth: a model that describes limited population growth, often due to limited resources or predation
Sigmoid Curve (logistic): an S-shaped curve, typical of population growth that starts slow, accelerates of grows rapidly, and then levels out over time
Additional Information:

  • Mathematical models and graphs help ecologists predict and monitor trends in population
  • Exponential growth and geometric growth models describe population growth when resources are assumed to be unlimited
  • There is an upper limit to the number of individuals that most environments can support. This upper limit is known as the carrying capacity of the population
  • The logistic growth model assumes that the population growth rate cannot be positive when the populations size exceeds its carrying capacity

No comments:

Post a Comment