Chapter 25: Ecosystem

Ecology: Study of relationship of animals to their environment. Term coined by Ernst Haeckel (1866).

Ecosystem: A major unit of ecology. System involving interaction of organisms with their environment.

Population: Group of interbreeding individuals of same species in same area.

Community: All populations within an ecosystem.

Biosphere: Thin layer of earth where all living things live.

Habitat: Actual place where an organism lives.

Niche: Basic role of an organism in community (Profession). Coined by Charles Elton.

Autecology vs Synecology: Autecology is study of single population; Synecology is study of different communities.

Biotic Components:

• Producers: Green photosynthetic plants (Autotrophs).
• Consumers: Animals (Heterotrophs). Primary, Secondary, Tertiary.
• Decomposers: Fungi and Bacteria (Saprotrophs). Recycle nutrients.

Abiotic Components: Atmosphere (Air), Hydrosphere (Water), Lithosphere (Soil/Earth).

Food Chain: Series of steps of eating and being eaten (e.g., Grass -> Caterpillar -> Blue Bird -> Eagle).

Food Web: Combination of many food chains. Complex network of trophic levels. Keeps ecosystem balance.

Trophic Levels: Feeding levels (T1: Producers, T2: Primary Consumers, etc.).

Energy Flow: Unidirectional. 1% solar energy trapped by plants (Gross Primary Production). Net Primary Production = Gross - Respiration. 10% energy transfer rule between trophic levels.

Change in community structure over time.

• Primary Succession: Starts on bare area (Rock/Sand). Hydrosphere (Water), Xerosere (Dry land).
• Secondary Succession: Re-establishment after disturbance (e.g., fire, cutting). Faster than primary.

Stages of Succession (Xerosere):

1. Crustose Lichen Stage
2. Foliose Lichen Stage
3. Moss Stage
4. Herbaceous Stage
5. Shrub Stage
6. Climax Forest (Stable community)

• Predation: Predator kills and eats Prey. Regulates population size (e.g., Cat & Mouse).
• Parasitism: Parasite feeds on Host. Ectoparasites (outside) and Endoparasites (inside).
• Symbiosis: Close association.
  • Mutualism: Both benefit (e.g., Mycorrhiza - Fungi/Root; Root Nodules - Bacteria/Legume; Lichens - Algae/Fungi).
  • Commensalism: One benefits, other unaffected (e.g., Shark and Remora).
• Grazing: Animals feed on grass. Moderate grazing helps grassland; overgrazing causes erosion.

Circulation of Nitrogen. Steps:

1. Ammonification: Decomposition of protein to Ammonia by bacteria/fungi.
2. Nitrification: Nitrifying bacteria oxidize Ammonia to Nitrates.
3. Assimilation: Plants absorb Nitrates/Ammonium to make proteins.

Depletion: Leaching, Soil erosion, Denitrification (release of N2). Remedies: N-fixing bacteria, Fertilizers.