Pocket Notes — Organisms and Populations
Levels of ecology
Organism → Population → Community → Ecosystem → Biome → Biosphere.
Definitions
- Habitat — where an organism lives.
- Niche — role / job of the organism.
- Population — group of individuals, same species, same area, interbreeding.
Coping with abiotic stress (4 strategies)
- Regulate — homeostasis (mammals, birds).
- Conform — change with environment.
- Migrate — move (Siberian cranes → Bharatpur).
- Suspend — dormancy:
- Hibernation = winter dormancy.
- Aestivation = summer dormancy.
- Diapause = paused development.
Population growth formulas
- Exponential: dN/dt = rN → J-shaped.
- Logistic: dN/dt = rN(K − N)/K → S-shaped.
- K = carrying capacity.
- r = intrinsic rate of increase.
Age pyramid shapes
| Shape | Meaning |
|---|
| Pyramid (wide base) | Expanding |
| Bell | Stable |
| Urn (narrow base) | Declining |
Species interactions summary (memorise signs)
| Interaction | A | B |
|---|
| Mutualism | + | + |
| Competition | − | − |
| Predation | + | − |
| Parasitism | + | − |
| Commensalism | + | 0 |
| Amensalism | − | 0 |
Classic examples
- Mutualism: lichen (alga + fungus); mycorrhiza; fig-fig wasp.
- Sexual deceit: Ophrys orchid mimics female bee.
- Commensalism: orchid on mango tree; barnacles on whale; cattle egret & grazing cattle.
- Predation: lion & deer.
- Parasitism: Cuscuta (parasitic plant); ticks, lice; brood parasitism — cuckoo lays eggs in crow's nest.
- Amensalism: Penicillium releasing penicillin.
Predator role
- Controls prey populations.
- Maintains diversity (keystone species: sea star Pisaster).
- Plants defense: thorns (Acacia), chemicals (cardiac glycosides in Calotropis).
Two key ecology principles
- Gause's Competitive Exclusion: two species with identical niche → one wins.
- Resource Partitioning (MacArthur's warblers) — coexistence by using different niche parts.
Adaptation examples (quick recall)
- Kangaroo rat — no water needed, concentrates urine.
- Cactus & desert plants — CAM, thick cuticle, sunken stomata.
- Whale blubber — cold insulation.
- Allen's rule — cold mammals have shorter appendages.
- High-altitude humans — more RBCs, deeper breathing.
Study-quotient
- Ecology's central question: why does an organism live where it lives?
- Populations characterised by density, natality, mortality, age structure, sex ratio.
Pocket Notes — Organisms and Populations
Levels of ecology
Organism → Population → Community → Ecosystem → Biome → Biosphere.
Definitions
- Habitat — where an organism lives.
- Niche — role / job of the organism.
- Population — group of individuals, same species, same area, interbreeding.
Coping with abiotic stress (4 strategies)
- Regulate — homeostasis (mammals, birds).
- Conform — change with environment.
- Migrate — move (Siberian cranes → Bharatpur).
- Suspend — dormancy:
- Hibernation = winter dormancy.
- Aestivation = summer dormancy.
- Diapause = paused development.
Population growth formulas
- Exponential: dN/dt = rN → J-shaped.
- Logistic: dN/dt = rN(K − N)/K → S-shaped.
- K = carrying capacity.
- r = intrinsic rate of increase.
Age pyramid shapes
| Shape | Meaning |
|---|
| Pyramid (wide base) | Expanding |
| Bell | Stable |
| Urn (narrow base) | Declining |
Species interactions summary (memorise signs)
| Interaction | A | B |
|---|
| Mutualism | + | + |
| Competition | − | − |
| Predation | + | − |
| Parasitism | + | − |
| Commensalism | + | 0 |
| Amensalism | − | 0 |
Classic examples
- Mutualism: lichen (alga + fungus); mycorrhiza; fig-fig wasp.
- Sexual deceit: Ophrys orchid mimics female bee.
- Commensalism: orchid on mango tree; barnacles on whale; cattle egret & grazing cattle.
- Predation: lion & deer.
- Parasitism: Cuscuta (parasitic plant); ticks, lice; brood parasitism — cuckoo lays eggs in crow's nest.
- Amensalism: Penicillium releasing penicillin.
Predator role
- Controls prey populations.
- Maintains diversity (keystone species: sea star Pisaster).
- Plants defense: thorns (Acacia), chemicals (cardiac glycosides in Calotropis).
Two key ecology principles
- Gause's Competitive Exclusion: two species with identical niche → one wins.
- Resource Partitioning (MacArthur's warblers) — coexistence by using different niche parts.
Adaptation examples (quick recall)
- Kangaroo rat — no water needed, concentrates urine.
- Cactus & desert plants — CAM, thick cuticle, sunken stomata.
- Whale blubber — cold insulation.
- Allen's rule — cold mammals have shorter appendages.
- High-altitude humans — more RBCs, deeper breathing.
Study-quotient
- Ecology's central question: why does an organism live where it lives?
- Populations characterised by density, natality, mortality, age structure, sex ratio.