Organisms and Populations

• Organism and Its Environment

  • Habitat and Niche
    • Habitats provide physical space
    • Ecological niche defines functional role and resource use
  • Major Abiotic Factors
    • Temperature: Varies by biome, affects enzyme kinetics
    • Water: Essential for life, dictates distribution and adaptations
    • Light: Crucial for photosynthesis, photoperiodism in plants/animals
    • Soil: Composition, pH, and percolation determine flora/fauna
  • Responses to Abiotic Factors
    • Regulate: Maintain constant internal environment (homeostasis)
    • Conform: Body temperature/osmotic concentration changes with surroundings
    • Migrate: Temporarily move to a stress-free habitat
    • Suspend: Reduce metabolic activity (e.g., hibernation, aestivation, spores)
  • Adaptations
    • Morphological, physiological, or behavioural traits
    • Examples: Bergmann's rule, Allen's rule, cryptic coloration

• Populations

  • Population Attributes
    • Birth rate (Natality) and Death rate (Mortality)
    • Sex ratio: Proportion of males and females
    • Age pyramids: Expanding, stable, or declining populations
    • Population density: Number of individuals per unit area
  • Population Growth
    • Influenced by food availability, weather, predation, and competition
    • Exponential Growth
      • Equation: $dN/dt = rN$
      • Forms a J-shaped curve
    • Logistic Growth
      • Accounts for Carrying capacity ($K$)
      • Equation: $dN/dt = rN[(K-N)/K]$
      • Forms a Sigmoid (S-shaped) curve
  • Life History Variation
    • Evolution of high reproductive fitness ($r$ and $K$ selection)
    • Breed once (Pacific salmon, bamboo) vs. breed many times (birds, mammals)

• Population Interactions

  • Mutualism ($+,+$)
    • Both species benefit
    • Examples: Lichens (algae + fungi), Mycorrhizae, Pollination
  • Competition ($-,-$)
    • Rivalry for same resources
    • Gause’s Competitive Exclusion Principle
    • Resource partitioning to avoid competition
  • Predation ($+,-$)
    • Predator consumes prey
    • Roles: Energy transfer, prey population control, defense mechanisms (camouflage, toxins)
  • Parasitism ($+,-$)
    • Parasite depends on host for food/shelter
    • Types: Ectoparasites (lice) and Endoparasites (tapeworms), Brood parasitism (cuckoo)
  • Commensalism ($+,0$)
    • One benefits, other is unaffected
    • Examples: Orchid on mango branch, clownfish and sea anemone
  • Amensalism ($-,0$)
    • One is harmed, other is unaffected
    • Example: Allelopathy (Penicillium secreting penicillin to inhibit bacteria)