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
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