Unit 5: Ecology and Environment

Chapter 1: Organisms and Populations

Population Attributes

  • Density: Number of individuals per unit area.
  • Sex Ratio: Ratio of males to females.
  • Natality: Birth rate.
  • Mortality: Death rate.
  • Age Distribution: Proportion of individuals in different age groups.

Population Growth Models

  • Exponential Growth (J-shaped curve):
    • Occurs with unlimited resources.
    • Equation: dN/dt = rN
  • Logistic Growth (S-shaped curve):
    • Occurs with limited resources.
    • Considers carrying capacity (K).
    • Equation: dN/dt = rN * ((K - N) / K)

Age Pyramids

  • Graphical representation of age distribution.
  • Shapes indicate growth status:
    • Expanding: Triangular pyramid.
    • Stable: Bell-shaped pyramid.
    • Declining: Urn-shaped pyramid.

Population Interactions

Interaction Species A Species B Example
Mutualism + + Lichens, Mycorrhiza
Competition - - Gause's Principle
Predation + - Lion and Deer
Parasitism + - Lice, Tapeworm
Commensalism + 0 Orchid on Mango Tree
Amensalism - 0 Penicillium and Bacteria

Mutualism (+/+)

  • Both species benefit.
  • Examples:
    • Lichens: Fungus + Algae
    • Mycorrhiza: Fungi + Plant Roots
    • Pollination: Plant + Pollinator

Competition (-/-)

  • Both species are harmed.
  • Gause's Competitive Exclusion Principle: Two species competing for the same limited resources cannot coexist indefinitely.
  • Resource Partitioning: A way to avoid competition.

Predation & Parasitism (+/-)

  • Predation: Predator kills and eats prey.
  • Parasitism: Parasite lives on/in a host, causing harm.
    • Ectoparasites: On the surface (e.g., lice).
    • Endoparasites: Inside the body (e.g., tapeworm).
    • Brood Parasitism: (e.g., Cuckoo and Crow).

Commensalism (+/0) & Amensalism (-/0)

  • Commensalism: One benefits, the other is unaffected.
    • Example: Orchid on a mango tree.
  • Amensalism: One is harmed, the other is unaffected.
    • Example: Penicillium inhibiting bacterial growth.