Question

Answer the following questions:

• • [(i)] Describe the Species-Area relationship as observed by Alexander von Humboldt, for a wide variety of taxa in nature.
  • [(ii)] Draw the graph showing Species-Area relationship for \( S = CA^Z \). What is the significance of ‘\( Z \)’ in Species-Area relationship?
  OR
• • [(i)] Describe the logistic population growth curve with the help of a suitable graphical representation.
  • [(ii)] Write the equation of Verhulst-Pearl logistic growth curve and explain what ‘\( K \)’ and ‘\( r \)’ suggest in the given equation.

Hint:

Species richness grows with area in a predictable manner. Logistic growth is more applicable in nature than exponential due to resource limitations.

Answer 1

1. • [(i)] Alexander von Humboldt observed that species richness increases with increasing area, but not linearly. Initially, the increase is rapid, then slows down. This pattern holds for different types of organisms in various habitats.
   • [(ii)] The mathematical expression is: S = C A^Z where:
     • S = species richness
     • A = area
     • C = constant
     • Z = slope of the curve on a log scale
     The value of Z typically ranges from 0.1 to 0.2 for smaller areas and 0.6 to 1.2 for large areas like continents. Z represents the rate at which species richness increases with area.
2. • [(i)] Logistic growth is more realistic as it considers environmental resistance. The curve has three phases:
     • Lag phase: slow growth.
     • Exponential phase: rapid growth.
     • Stationary phase: population stabilises due to limited resources.
     The curve is S-shaped.
   • [(ii)] The Verhulst-Pearl equation is: dN/dt = r N ((K - N)/K) where:
     • N = population size
     • r = intrinsic rate of natural increase
     • K = carrying capacity
     • dN/dt = rate of change in population
     Here, K represents the maximum population size that the environment can sustain. r indicates the population's potential for growth.