9.1-9.5: Natural Ecosystems & Human Activities Notes:

Ecosystems

Key Definitions

• Ecosystem: community of living species (biotic) interacting with non‑living (abiotic) elements (soil, water, rocks).

• Population: group of individuals of the same species in an area.

• Community: all populations of different species in an area.

• Habitat: location within an ecosystem that meets living needs (food, water, shelter, space).

• Niche: unique role of an organism (feeding, shelter, behavior, adaptations).

Biotic Components

• Producers: plants/algae; photosynthesis fixes carbon.

• Consumers:

  • Primary (herbivores).

  • Secondary (carnivores/omnivores).

  • Tertiary/apex (top predators).

• Decomposers: fungi, bacteria, worms recycle nutrients.

Abiotic Components

• Temperature, humidity, water, oxygen, salinity, light, pH, soil minerals, relief, climate, prevailing winds.

Biotic Interactions

• Competition: shortage of resources → aggression.

• Predation: one organism feeds on another.

• Pollination: pollen transfer for reproduction.

• Mutualism: both benefit (e.g., oxpeckers + buffalo).

Photosynthesis

• Word equation: Carbon dioxide + Water → Glucose + Oxygen (with sunlight + chlorophyll).

• Importance: basis of food chains, oxygen supply.

Respiration

• Word equation: Glucose + Oxygen → Carbon dioxide + Water + Energy (ATP).

• Occurs in mitochondria; releases energy for life processes.

Food Chains & Food Webs

• Food chain: linear feeding sequence (producer → herbivore → carnivore → apex → decomposer).

• Food web: interconnected chains showing complexity.

• Trophic levels: 5 levels (producers, primary, secondary, tertiary, decomposers).

• Energy decreases at each level; most stored at producers.

Ecological Pyramids

• Pyramid of numbers: shows number of organisms at each level.

• Pyramid of energy: shows energy flow; widest at producers, narrowest at apex.

Carbon Cycle

• Carbon fixed in plants during photosynthesis.

• Released by respiration at each trophic level.

• Decomposers recycle carbon compounds.

• Combustion adds CO₂ to atmosphere.

Ecosystems Under Threat

Causes of Habitat Loss

• Drainage of wetlands.

• Intensive agriculture: monoculture, pesticides.

• Deforestation: large‑scale forest clearance.

Impacts

• Loss of biodiversity.

• Genetic depletion → reduced adaptability.

• Extinction risk increases.

Deforestation

Causes

• Timber extraction/logging (10 billion trees/year; IKEA largest consumer).

• Subsistence/commercial farming (cattle ranches, palm oil, rice projects).

• Roads/settlements (Amazon highways).

• Rock/mineral extraction (gold mining, oil sands).

Impacts

• Habitat loss → biodiversity decline.

• Soil erosion → desertification (24 billion tonnes topsoil lost annually).

• Climate change: forests store 300 billion tonnes carbon; release 1 billion tonnes CO₂/year.

• Genetic depletion → inbreeding, extinction (orang‑utans, rafflesia).

• Flood/drought cycles due to reduced transpiration.

Managing Forests

Need for Sustainable Management

• Carbon sinks/stores: growing forests absorb CO₂; mature forests store carbon.

• Water cycle: transpiration contributes to rainfall; deforestation reduces moisture → drought.

• Soil erosion prevention: roots stabilize soil; foliage intercepts rainfall.

• Biodiversity: genetic resources for food, medicine (periwinkle → anti‑cancer drug).

• Food/raw materials: subsistence + commercial crops, timber, mining.

• Ecotourism: responsible travel, income for locals, conservation incentive.

Measuring and Managing Biodiversity

Methods for Estimating Biodiversity

• Quadrats: sample plants/slow animals.

• Transects: line sampling across habitat.

• Pooters: collect small insects.

• Pitfall traps: catch ground insects.

• Sampling: random (unbiased) vs systematic (intervals).

Limitations

• Sample size, frequency, human error, representativeness affect validity/reliability.

Management Strategies

• Sustainable harvesting: rubber tapping, Brazil nuts, controlled hunting.

• Sustainable forestry/agroforestry: replanting, certification (SFI).

• Protected areas: national parks, reserves, corridors.

• Biosphere reserves: core, buffer, transition zones.

• Extractive reserves: indigenous management in Amazon.

• Seed banks: preserve genetic diversity (Millennium Seed Bank).

• Zoos/captive breeding: conserve endangered species.

• Ecotourism: supports conservation, local livelihoods.

NOTES DONE BY FARIDA SABET

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