Lecture Notes: Organisms and Population

Introduction

• One short video covering important aspects of organisms and population.
• Importance of having textbook (NCERT) and pen ready for note-taking.

Definition of Population

• Population: Group of individuals of the same species in a specific area.
  • Example: Human beings, lotuses in a pond, bacteria in a culture plate.
• Individuals experience birth and death; population is measured in birth rate and death rate.
  • Example Calculation: Birth rate = 8 new lotus plants in a pond of 20 (0.4 per lotus per year).
  • Death rate = 4 fruit flies dying in a population of 40 (0.1 per fruit fly per week).

Population Attributes

• Sex Ratio: Proportion of males to females in a population.
  • Example: 60% females, 40% males.
• Age Distribution and Age Pyramid:
  • Types of Population Growth:
    • Expanding: Broad base of pre-productive age.
    • Stable: Uniform distribution.
    • Declining: Narrow base, fewer pre-productive individuals.

Factors Affecting Population Size

• Dynamic due to food availability, predation, and weather.
• Four Basic Processes:
  • Natality: Birth rate.
  • Mortality: Death rate.
  • Immigration: Individuals entering a habitat.
  • Emigration: Individuals exiting a habitat.
• Population Density Formula:
  • Future Population Density = Current Density + (Birth Rate + Immigration) - (Death Rate + Emigration).

Growth Models

• Exponential Growth (J-shaped curve): Unlimited resources leading to rapid population increase.
  • Formula: (\frac{dN}{dt} = (B - D)N).
  • B - Birth rate, D - Death rate, R - Intrinsic rate of increase.
• Logistic Growth (S-shaped curve): Limited resources with a carrying capacity.
  • Phases: Lag Phase, Acceleration Phase, Deceleration Phase, Asymptote.
  • Formula: (\frac{dN}{dt} = rN\left(\frac{K - N}{K}\right)).

Reproductive Fitness and Strategies

• Darwinian Fitness: High R-value indicates reproductive success.
• Reproductive Strategies:
  • Similparis: One-time breeders (e.g., salmon, bamboo).
  • Iteroparis: Multiple times breeders (e.g., birds, mammals).
• Offspring Production:
  • Many small offspring (e.g., oysters, pelagic fish).
  • Few large offspring (e.g., humans, mammals).

Population Interactions

• Mutualism: Both organisms benefit (e.g., lichen, mycorrhiza).
• Competition: Both are harmed (e.g., flamingos and fishes for zooplankton).
• Predation: One benefits, the other is harmed (e.g., tiger and deer).
• Parasitism: Similar to predation.
• Commensalism: One benefits, the other is unaffected (e.g., barnacles on whales).
• Amensalism: One harmed, the other unaffected.

Predation

• Importance for energy transfer and maintaining prey population balance.
• Exotic Species Control: Example of prickly pear in Australia.
• Biological Control: Use of predators to control pest populations.
• Prey Defenses: Camouflage and poisonous species (e.g., monarch butterfly).

Competition

• Types:
  • Intra and interspecific competition.
  • Competitive Exclusion: Superior species eliminates weaker one (e.g., goats and tortoise).
  • Resource Partitioning: Species divide resources to coexist (e.g., MacArthur's warblers).

Parasitism

• Parasites benefit at the host's expense.
• Special Adaptations: Loss of unnecessary organs, presence of suckers, high reproductive capacity.
• Complex Life Cycles: Involves intermediate hosts (e.g., human liver fluke).

Commensalism

• Examples include orchid on mango trees, barnacles on whales, cattle egrets with grazing cattle.

Mutualism

• Both species benefit.
• Examples: Lichens, mycorrhiza, plant-pollinator relationships.
• Special Cases: Fig-wasp relationship, orchid-bee (sexual deceit).

Conclusion

• Importance of understanding population interactions for ecological balance.
• Encouragement to ask questions and engage with the material for deeper understanding.