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Population growth curves

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Kader Mullah

population growth curve describes how a population grows in nature and what are the different factors are associated with it.

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PRESENTED BY- MD KADER MULLAH M . Sc 4th semester Roll No. 16/MSB/76 Department of Botany USTM
INTRODUCTION ï‚— Population growth curve is something that shows the pattern of the growth of a population over time i.e., a growth curve is an empirical model of the evolution of a quantity over time. ï‚— Growth curves are widely used in biology for quantities such as population size or biomass , individual body height or biomass. Values for the measured property can be plotted on a graph as a function of time. ï‚— In theory , any kind of organism could take over the Earth just by reproducing.
Continue…..  But in practical, all living organisms need some specific resources such as nutrients and proper environmental conditions to survive and reproduce.  The essential resources are not unlimited, and a population can only reach a size that match the availability of resources in its local environment.
TYPES OF POPULATION GROWTH CURVES There are mainly two types of population growth curves- 1. Exponential growth curve( J-shaped) & 2. Sigmoid growth curve(S-shaped)
EXPONENTIAL GROWTH CURVE ï‚— In this type of growth form, the population grows exponentially, and after attaining the peak value the population may abruptly crash. ï‚— This increase in population is continued till large amount of food materials exist in the habitat. ï‚— After sometime, due to increase in population size the food supply in the habitat becomes limited which ultimately results in decrease in population size.
Continue….  For example, many insect populations show explosive increase in numbers during the rainy season, followed by their disappearance at the end of the season.  The following equation exhibits J-shaped growth: dN/dt = rN where, dN/dt represents rate of change in population. r=biotic potential N= population size
Continue……. Figure: J-shaped growth curve
SIGMOID GROWTH CURVE ï‚— The sigmoid growth curve is also known as Logistics growth curve which is S-shaped. ï‚— When a few organisms are introduced in an area, the population increase is very slow in the beginning i,e., the positive acceleration phase or lag phase. ï‚— In the middle phase the population increase becomes very rapid which is known as logarithmic phase. ï‚— Finally in the last phase the population increase is slowed down i,e. negative acceleration phase.
Continue….  The level beyond which no major increase can occur is referred to as saturation level or carrying capacity which is denoted by K.  In the last phase the new organisms are almost equal to the number of dying individuals and thus there is no more increase in the population size.
Continue….  The J-shaped (sigmoid) growth form is represented by the following equation: dN/dt = rN(K-N/K) =rN(1-N/K) Here, dN/dt is the rate of change in population size. r= biotic potential N= population size (K-N/K) is for environmental resistance.
S-shaped growth curve
CARRYING CAPACITY?  The carrying capacity of a biological species in an environment is the maximum population size of the species that the environment can sustain indefinitely , given the food , habitat , water and other necessities available in the environment.  In population ecology, the carrying capacity is defined as the environment’s maximal load.  Carrying capacity was originally used to determine the number of animals that could graze on a segment of land without destroying it. Later the idea has been expanded to more complex populations.
Population growth curves
Population growth curves
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Population growth curves

  • 1. PRESENTED BY- MD KADER MULLAH M . Sc 4th semester Roll No. 16/MSB/76 Department of Botany USTM
  • 2. INTRODUCTION ï‚— Population growth curve is something that shows the pattern of the growth of a population over time i.e., a growth curve is an empirical model of the evolution of a quantity over time. ï‚— Growth curves are widely used in biology for quantities such as population size or biomass , individual body height or biomass. Values for the measured property can be plotted on a graph as a function of time. ï‚— In theory , any kind of organism could take over the Earth just by reproducing.
  • 3. Continue….. ï‚— But in practical, all living organisms need some specific resources such as nutrients and proper environmental conditions to survive and reproduce. ï‚— The essential resources are not unlimited, and a population can only reach a size that match the availability of resources in its local environment.
  • 4. TYPES OF POPULATION GROWTH CURVES There are mainly two types of population growth curves- 1. Exponential growth curve( J-shaped) & 2. Sigmoid growth curve(S-shaped)
  • 5. EXPONENTIAL GROWTH CURVE ï‚— In this type of growth form, the population grows exponentially, and after attaining the peak value the population may abruptly crash. ï‚— This increase in population is continued till large amount of food materials exist in the habitat. ï‚— After sometime, due to increase in population size the food supply in the habitat becomes limited which ultimately results in decrease in population size.
  • 6. Continue…. ï‚— For example, many insect populations show explosive increase in numbers during the rainy season, followed by their disappearance at the end of the season. ï‚— The following equation exhibits J-shaped growth: dN/dt = rN where, dN/dt represents rate of change in population. r=biotic potential N= population size
  • 8. SIGMOID GROWTH CURVE ï‚— The sigmoid growth curve is also known as Logistics growth curve which is S-shaped. ï‚— When a few organisms are introduced in an area, the population increase is very slow in the beginning i,e., the positive acceleration phase or lag phase. ï‚— In the middle phase the population increase becomes very rapid which is known as logarithmic phase. ï‚— Finally in the last phase the population increase is slowed down i,e. negative acceleration phase.
  • 9. Continue…. ï‚— The level beyond which no major increase can occur is referred to as saturation level or carrying capacity which is denoted by K. ï‚— In the last phase the new organisms are almost equal to the number of dying individuals and thus there is no more increase in the population size.
  • 10. Continue…. ï‚— The J-shaped (sigmoid) growth form is represented by the following equation: dN/dt = rN(K-N/K) =rN(1-N/K) Here, dN/dt is the rate of change in population size. r= biotic potential N= population size (K-N/K) is for environmental resistance.
  • 12. CARRYING CAPACITY? ï‚— The carrying capacity of a biological species in an environment is the maximum population size of the species that the environment can sustain indefinitely , given the food , habitat , water and other necessities available in the environment. ï‚— In population ecology, the carrying capacity is defined as the environment’s maximal load. ï‚— Carrying capacity was originally used to determine the number of animals that could graze on a segment of land without destroying it. Later the idea has been expanded to more complex populations.