Describe the exponential growth model of a diagram along with a curve.and Describe the logistic growth model of population along with a suitable curve. Why is this curve more realistic?
Answers
Answer:
Solution :
Population Growth Form: The graphic pattern obtained when a population growth is plotted against time is called population growth form or model. There are two types namely: Exponential J-shaped and Logistic or S-shaped.
J-shaped or Exponential Growth Form: At any point of time, population size does not reach the equilibrium.
J-shaped growth form has three phases
a. Establishment or Initial phase- Lag phase: There is a slow rise in population as the initial size of the population is very small.
b. Log phase: Population size increases rapidly
c. Crash phase: A point is reached where the population size declines suddenly due to mass scale deaths. This occurs when the food chains are short or excess of human interference. It occurs in many insect populations. They show an explosive increase in the number during the rainy season but almost disappear during the end of the season.
Population Growth Form: The graphic pattern obtained when a population growth is plotted against time is called population growth form or model. There are two types namely: Exponential J-shaped and Logistic or S-shaped.
Logistic or S-shaped growth Form: It has three phases. It is also called logistic growth or Verhulet-Pearl Logistic growth .
a. Lag phase: In this phase, there is a slow increase in population size.
b. Log Phase: After a population size reaches a take off stage, their period starts. It continues until environmental resistance comes into play.
c. Deceleration Phase: growth rate slows down in this phase. This phase leads to equilibrium phase when the population size reaches the point of carrying capacity of an area.
dNdtdNdt=rN(K−N/K)=rN(1−N/K)=rN(K−N/K)=rN(1−N/K)
d= rate of change
N = number of existing individuals
T =Time
dNdtdNdt= Rate of change in population size
r=intrinsic rate of natural increase
k−Nor1−(K/N)k−Nor1−(K/N)=environmental resistance wuth K being the carrying capacity of the area.
No species in nature has at its disposal unlimited resources to permit exponential growth. Resources will always be limited and organisms need to compete and only the fittest survive. Hence Exponential growth model is realistic in nature.