Ecosystem

An ecosystem is a community of organisms interacting with each other and with their physical environment.

Components:

Abiotic (non-living):

• Climatic: light, temperature, water, wind.
• Edaphic: soil pH, mineral nutrients.

Biotic (living):

• Producers (autotrophs): plants, algae, cyanobacteria. Fix energy from sunlight (photosynthesis) or chemicals (chemosynthesis).
• Consumers (heterotrophs):
  • Primary (herbivores): cow, grasshopper.
  • Secondary (carnivores feeding on herbivores): frog.
  • Tertiary (top carnivores): tiger, eagle.
• Decomposers / detritivores: bacteria, fungi, earthworms. Break down dead organic matter, recycling nutrients.

FOOD CHAINS

Linear sequence of organisms where each is eaten by the next. Energy flows in one direction (sunlight → producers → consumers → decomposers).

Two types:

1. Grazing food chain (GFC). Starts with living plants.
Example: grass → grasshopper → frog → snake → eagle.

2. Detritus food chain (DFC). Starts with dead organic matter.
Example: dead leaves → fungi → earthworm → bird.

Food web: interconnected food chains. Real ecosystems are webs, not chains.

TROPHIC LEVELS

Each step in a food chain.

• T1: producers
• T2: primary consumers
• T3: secondary consumers
• T4: tertiary consumers
• T5: quaternary consumers (rare — energy too low)

10% rule (Lindeman): only ~10% of energy at one trophic level passes to the next. The rest is lost as heat (respiration), waste, or in undigested form.

This is why:

• Food chains rarely have more than 4-5 trophic levels.
• Top carnivores are few in number (energy bottleneck).
• A vegetarian diet is more "efficient" — eat closer to producers.

ECOLOGICAL PYRAMIDS

Graphical representation of trophic levels.

Pyramid of numbers:

• Usually upright (lots of grass, fewer cows, fewer humans).
• Inverted in tree ecosystems (one tree feeds many insects).

Pyramid of biomass:

• Usually upright (mass of producers > consumers).
• Inverted in aquatic ecosystems (low biomass of phytoplankton at any moment, but high turnover supports many zooplankton).

Pyramid of energy: ALWAYS upright. Energy decreases at each level due to the 10% rule.

ECOSYSTEM PRODUCTIVITY

GPP (Gross Primary Productivity): total organic matter produced by photosynthesis per unit area per unit time.

NPP (Net Primary Productivity): GPP minus respiration loss by plants. This is what's available to consumers.

Earth's annual NPP: ~170 billion tonnes (dry weight). Oceans contribute ~55 billion despite covering 70% of surface — surprisingly low because phytoplankton turnover is fast.

NUTRIENT CYCLES (biogeochemical cycles)

Unlike energy, matter (nutrients) is recycled.

Carbon cycle:

• Atmospheric CO₂ → photosynthesis → organic carbon in producers → consumers/respiration → CO₂ back.
• Long-term: fossil fuels, sedimentary rocks, oceans.
• Anthropogenic disturbance: burning fossil fuels released ancient carbon → climate change.

Nitrogen cycle:

• N₂ in atmosphere (~78%) is unusable by most organisms.
• Nitrogen fixation by Rhizobium (legume nodules), Azotobacter (free-living), cyanobacteria (Anabaena, Nostoc), lightning.
• N₂ → NH₃ → NH₄⁺ (ammonification by decomposers).
• Nitrification: NH₃ → NO₂⁻ (by Nitrosomonas) → NO₃⁻ (by Nitrobacter).
• Plants absorb NO₃⁻; build amino acids/proteins.
• Denitrification: NO₃⁻ → N₂ by Pseudomonas. Returns to atmosphere.

Phosphorus cycle: sedimentary (no atmospheric phase). Phosphate rock → weathering → soil/water → plants → animals → decomposition → soil.

Water cycle: evaporation, condensation, precipitation, runoff, infiltration.

ECOLOGICAL SUCCESSION

Predictable progression of communities over time at a site.

• Primary succession: starts from bare rock or fresh substrate (e.g., after a volcano). First colonizers: lichens.
• Secondary succession: after a disturbance (fire, agriculture abandonment). Faster than primary because soil is intact.

Stages: pioneer → seral communities → climax community (stable, in equilibrium with climate).

Hydrarch succession: in water → ends in forest. Xerarch: in dry/rocky area → ends in forest.

An ecosystem is a community of organisms interacting with each other and with their physical environment.

Components:

Abiotic (non-living):

• Climatic: light, temperature, water, wind.
• Edaphic: soil pH, mineral nutrients.

Biotic (living):

• Producers (autotrophs): plants, algae, cyanobacteria. Fix energy from sunlight (photosynthesis) or chemicals (chemosynthesis).
• Consumers (heterotrophs):
  • Primary (herbivores): cow, grasshopper.
  • Secondary (carnivores feeding on herbivores): frog.
  • Tertiary (top carnivores): tiger, eagle.
• Decomposers / detritivores: bacteria, fungi, earthworms. Break down dead organic matter, recycling nutrients.

FOOD CHAINS

Linear sequence of organisms where each is eaten by the next. Energy flows in one direction (sunlight → producers → consumers → decomposers).

Two types:

1. Grazing food chain (GFC). Starts with living plants.
Example: grass → grasshopper → frog → snake → eagle.

2. Detritus food chain (DFC). Starts with dead organic matter.
Example: dead leaves → fungi → earthworm → bird.

Food web: interconnected food chains. Real ecosystems are webs, not chains.

TROPHIC LEVELS

Each step in a food chain.

• T1: producers
• T2: primary consumers
• T3: secondary consumers
• T4: tertiary consumers
• T5: quaternary consumers (rare — energy too low)

10% rule (Lindeman): only ~10% of energy at one trophic level passes to the next. The rest is lost as heat (respiration), waste, or in undigested form.

This is why:

• Food chains rarely have more than 4-5 trophic levels.
• Top carnivores are few in number (energy bottleneck).
• A vegetarian diet is more "efficient" — eat closer to producers.

ECOLOGICAL PYRAMIDS

Graphical representation of trophic levels.

Pyramid of numbers:

• Usually upright (lots of grass, fewer cows, fewer humans).
• Inverted in tree ecosystems (one tree feeds many insects).

Pyramid of biomass:

• Usually upright (mass of producers > consumers).
• Inverted in aquatic ecosystems (low biomass of phytoplankton at any moment, but high turnover supports many zooplankton).

Pyramid of energy: ALWAYS upright. Energy decreases at each level due to the 10% rule.

ECOSYSTEM PRODUCTIVITY

GPP (Gross Primary Productivity): total organic matter produced by photosynthesis per unit area per unit time.

NPP (Net Primary Productivity): GPP minus respiration loss by plants. This is what's available to consumers.

Earth's annual NPP: ~170 billion tonnes (dry weight). Oceans contribute ~55 billion despite covering 70% of surface — surprisingly low because phytoplankton turnover is fast.

NUTRIENT CYCLES (biogeochemical cycles)

Unlike energy, matter (nutrients) is recycled.

Carbon cycle:

• Atmospheric CO₂ → photosynthesis → organic carbon in producers → consumers/respiration → CO₂ back.
• Long-term: fossil fuels, sedimentary rocks, oceans.
• Anthropogenic disturbance: burning fossil fuels released ancient carbon → climate change.

Nitrogen cycle:

• N₂ in atmosphere (~78%) is unusable by most organisms.
• Nitrogen fixation by Rhizobium (legume nodules), Azotobacter (free-living), cyanobacteria (Anabaena, Nostoc), lightning.
• N₂ → NH₃ → NH₄⁺ (ammonification by decomposers).
• Nitrification: NH₃ → NO₂⁻ (by Nitrosomonas) → NO₃⁻ (by Nitrobacter).
• Plants absorb NO₃⁻; build amino acids/proteins.
• Denitrification: NO₃⁻ → N₂ by Pseudomonas. Returns to atmosphere.

Phosphorus cycle: sedimentary (no atmospheric phase). Phosphate rock → weathering → soil/water → plants → animals → decomposition → soil.

Water cycle: evaporation, condensation, precipitation, runoff, infiltration.

ECOLOGICAL SUCCESSION

Predictable progression of communities over time at a site.

• Primary succession: starts from bare rock or fresh substrate (e.g., after a volcano). First colonizers: lichens.
• Secondary succession: after a disturbance (fire, agriculture abandonment). Faster than primary because soil is intact.

Stages: pioneer → seral communities → climax community (stable, in equilibrium with climate).

Hydrarch succession: in water → ends in forest. Xerarch: in dry/rocky area → ends in forest.

An ecosystem is a community of organisms interacting with each other and with their physical environment.

Components:

Abiotic (non-living):

• Climatic: light, temperature, water, wind.
• Edaphic: soil pH, mineral nutrients.

Biotic (living):

• Producers (autotrophs): plants, algae, cyanobacteria. Fix energy from sunlight (photosynthesis) or chemicals (chemosynthesis).
• Consumers (heterotrophs):
  • Primary (herbivores): cow, grasshopper.
  • Secondary (carnivores feeding on herbivores): frog.
  • Tertiary (top carnivores): tiger, eagle.
• Decomposers / detritivores: bacteria, fungi, earthworms. Break down dead organic matter, recycling nutrients.

FOOD CHAINS

Linear sequence of organisms where each is eaten by the next. Energy flows in one direction (sunlight → producers → consumers → decomposers).

Two types:

1. Grazing food chain (GFC). Starts with living plants.
Example: grass → grasshopper → frog → snake → eagle.

2. Detritus food chain (DFC). Starts with dead organic matter.
Example: dead leaves → fungi → earthworm → bird.

Food web: interconnected food chains. Real ecosystems are webs, not chains.

TROPHIC LEVELS

Each step in a food chain.

• T1: producers
• T2: primary consumers
• T3: secondary consumers
• T4: tertiary consumers
• T5: quaternary consumers (rare — energy too low)

10% rule (Lindeman): only ~10% of energy at one trophic level passes to the next. The rest is lost as heat (respiration), waste, or in undigested form.

This is why:

• Food chains rarely have more than 4-5 trophic levels.
• Top carnivores are few in number (energy bottleneck).
• A vegetarian diet is more "efficient" — eat closer to producers.

ECOLOGICAL PYRAMIDS

Graphical representation of trophic levels.

Pyramid of numbers:

• Usually upright (lots of grass, fewer cows, fewer humans).
• Inverted in tree ecosystems (one tree feeds many insects).

Pyramid of biomass:

• Usually upright (mass of producers > consumers).
• Inverted in aquatic ecosystems (low biomass of phytoplankton at any moment, but high turnover supports many zooplankton).

Pyramid of energy: ALWAYS upright. Energy decreases at each level due to the 10% rule.

ECOSYSTEM PRODUCTIVITY

GPP (Gross Primary Productivity): total organic matter produced by photosynthesis per unit area per unit time.

NPP (Net Primary Productivity): GPP minus respiration loss by plants. This is what's available to consumers.

Earth's annual NPP: ~170 billion tonnes (dry weight). Oceans contribute ~55 billion despite covering 70% of surface — surprisingly low because phytoplankton turnover is fast.

NUTRIENT CYCLES (biogeochemical cycles)

Unlike energy, matter (nutrients) is recycled.

Carbon cycle:

• Atmospheric CO₂ → photosynthesis → organic carbon in producers → consumers/respiration → CO₂ back.
• Long-term: fossil fuels, sedimentary rocks, oceans.
• Anthropogenic disturbance: burning fossil fuels released ancient carbon → climate change.

Nitrogen cycle:

• N₂ in atmosphere (~78%) is unusable by most organisms.
• Nitrogen fixation by Rhizobium (legume nodules), Azotobacter (free-living), cyanobacteria (Anabaena, Nostoc), lightning.
• N₂ → NH₃ → NH₄⁺ (ammonification by decomposers).
• Nitrification: NH₃ → NO₂⁻ (by Nitrosomonas) → NO₃⁻ (by Nitrobacter).
• Plants absorb NO₃⁻; build amino acids/proteins.
• Denitrification: NO₃⁻ → N₂ by Pseudomonas. Returns to atmosphere.

Phosphorus cycle: sedimentary (no atmospheric phase). Phosphate rock → weathering → soil/water → plants → animals → decomposition → soil.

Water cycle: evaporation, condensation, precipitation, runoff, infiltration.

ECOLOGICAL SUCCESSION

Predictable progression of communities over time at a site.

• Primary succession: starts from bare rock or fresh substrate (e.g., after a volcano). First colonizers: lichens.
• Secondary succession: after a disturbance (fire, agriculture abandonment). Faster than primary because soil is intact.

Stages: pioneer → seral communities → climax community (stable, in equilibrium with climate).

Hydrarch succession: in water → ends in forest. Xerarch: in dry/rocky area → ends in forest.