Ecology and Ecosystems

🟢 Lite — Quick Review (1h–1d)

Rapid summary for last-minute revision before your exam.

Ecology and Ecosystems — Quick Facts

Key Definitions:

• Ecology: The scientific study of interactions among organisms and their environment
• Ecosystem: A community of living organisms interacting with each other and their physical environment
• Habitat: The natural home or environment of an organism
• Niche: The role and position a species has within an ecosystem
• Population: A group of organisms of the same species living in the same area
• Community: All populations of different species living and interacting in an area

Levels of Ecological Organisation (smallest to largest): Organism → Population → Community → Ecosystem → Biome → Biosphere

Key Ecological Relationships:

Relationship	Description	Example
Predation	One organism kills and eats another	Lion eating zebra
Competition	Organisms vie for same resource	Two plants competing for sunlight
Parasitism	One benefits, one harmed	Tapeworm in human intestine
Mutualism	Both organisms benefit	Bee and flowering plant
Commensalism	One benefits, one unaffected	Barnacle on whale

⚡ Exam Tip (NABTEB): Remember: “mutualism” = MUTUAL benefit; “commensalism” = COMMENSAL (sharing the table, one benefits); “parasitism” = PARASITE benefits at HOST’s expense.

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🟡 Standard — Regular Study (2d–2mo)

For students who want genuine understanding.

Ecology and Ecosystems — Study Guide

The Ecosystem: Structure and Function

An ecosystem consists of two main components:

Biotic Factors (Living):

• Producers (autotrophs): Green plants, algae — make food via photosynthesis
• Consumers (heterotrophs): Animals that eat other organisms
  • Primary consumers: Herbivores
  • Secondary consumers: Carnivores eating herbivores
  • Tertiary consumers: Top predators
• Decomposers: Bacteria, fungi — break down dead organic matter

Abiotic Factors (Non-living):

• Light intensity
• Temperature
• Water availability
• Soil composition
• pH levels
• Wind speed
• Atmospheric gases (CO₂, O₂)

Energy Flow Through Ecosystems:

Energy flows in ONE DIRECTION only: Sun → Producers → Primary Consumers → Secondary Consumers → Tertiary Consumers → Decomposers

The 10% Rule: Only about 10% of energy is passed from one trophic level to the next. The remaining 90% is lost as heat during metabolism, movement, and other life processes.

Food Chains and Food Webs:

Food Chain: A linear sequence showing energy flow from producer to consumer

• Grass → Grasshopper → Frog → Snake → Hawk

Food Web: Interconnected food chains showing multiple feeding relationships

• More realistic representation of nature
• Shows that organisms usually eat multiple species

Ecological Pyramids:

Three types of ecological pyramids:

1. Pyramid of Numbers: Number of organisms at each trophic level

   • Usually pyramid-shaped (many producers, few top predators)
   • Can be inverted (one tree → many insects → few birds)

2. Pyramid of Biomass: Total dry weight of organisms

   • Usually pyramid-shaped
   • Measured in g/m²

3. Pyramid of Energy: Energy content at each level

   • ALWAYS pyramid-shaped (energy decreases at each level)
   • Most accurate representation

Biogeochemical Cycles:

The Water Cycle:

• Evaporation from water bodies → transpiration from plants → condensation → precipitation → runoff/infiltration → evaporation

The Carbon Cycle:

• Photosynthesis absorbs CO₂
• Respiration releases CO₂
• Decomposition releases CO₂
• Combustion (burning fossil fuels) releases CO₂
• Formation of limestone (long-term carbon storage)

The Nitrogen Cycle:

1. Nitrogen fixation: Atmospheric N₂ → NH₃ (by Rhizobium bacteria in legume root nodules)
2. Nitrification: NH₃ → NO₂⁻ → NO₃⁻ (by nitrifying bacteria)
3. Assimilation: Plants absorb NO₃⁻
4. Ammonification: Dead organisms → NH₃ (by decomposers)
5. Denitrification: NO₃⁻ → N₂ (by denitrifying bacteria)

Population Dynamics:

Population Growth Curves:

• Exponential growth: J-shaped curve (when resources unlimited)
• Logistic growth: S-shaped curve (resources become limited, growth slows)
• Carrying capacity (K): Maximum population size an environment can sustain

Factors Affecting Population Size:

• Birth rate (natality)
• Death rate (mortality)
• Immigration
• Emigration

Human Population Growth:

• Currently over 8 billion globally
• Growth rate: approximately 1% per year
• Nigeria: one of the fastest-growing populations (estimated 200+ million)

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🔴 Extended — Deep Study (3mo+)

Comprehensive theory for serious preparation.

Ecology and Ecosystems — Comprehensive Notes

Ecological Relationships in Depth

Predation:

Predators control prey populations and prevent overgrazing. Predator-prey population cycles follow predictable patterns — when prey increases, predators increase, then prey decreases, then predators decrease.

Biological Control: Using natural predators to control pest populations. Examples:

• Ladybird beetles controlling aphids
• Nile crocodiles controlling fish populations
• Parasitic wasps controlling caterpillar pests

Competition:

Intraspecific competition: Between members of the SAME species

• Competition for food, territory, mates
• Strongest competitors survive and reproduce

Interspecific competition: Between DIFFERENT species

• Gause’s Competitive Exclusion Principle: Two species competing for identical resources cannot coexist indefinitely
• One will outcompete the other (competitive exclusion)

Resource Partitioning: Species divide resources to reduce competition:

• Different feeding times (nocturnal vs. diurnal)
• Different food sources
• Different habitats within same area

Symbiotic Relationships:

Mutualism (+/+):

• Mycorrhizae: Fungi + plant roots (fungi provide minerals, plant provides carbohydrates)
• Lichens: Fungi + algae/cyanobacteria
• Pollination: Insects/birds get nectar, plants get pollen distributed
• Nitrogen fixation: Rhizobium bacteria in legume root nodules

Parasitism (+/-):

• Endoparasites: Live inside host (tapeworm, malaria parasite Plasmodium)
• Ectoparasites: Live on host surface (tick, leech, lice)
• Brood parasitism: Cuckoo bird lays eggs in other birds’ nests

Commensalism (+/0):

• Epiphytes growing on trees (orchids on mango trees)
• Barnacles on whales
• Remora fish attached to sharks

Succession:

Primary Succession: Formation of soil where no soil existed previously

• Pioneer species (lichens, mosses) → Soil formation → Grasses → Shrubs → Climax community
• Takes hundreds to thousands of years

Secondary Succession: Soil already exists after disturbance

• Fire, farming, deforestation → Pioneer species → Grasses → Shrubs → Climax community
• Faster than primary succession

Climax Community: Stable, self-perpetuating end stage of succession. In Nigeria/West Africa: tropical rainforest climax.

Biomes:

Major Biomes of the World:

• Tropical rainforest
• Temperate forest
• Boreal forest (taiga)
• Temperate grassland
• Tundra
• Desert
• Savanna

African Biomes:

• Tropical rainforest: Congo Basin, West Africa — highest biodiversity
• Savanna: Most of Nigeria — grasslands with scattered trees
• Desert: Sahara (north), Namib/Kalahari (south)
• Montane: Ethiopian Highlands

Nigerian Ecology:

Nigeria’s ecosystems include:

• Mangrove swamps (coastal Niger Delta)
• Tropical rainforest (southern Nigeria)
• Guinea savanna (central Nigeria)
• Sudan savanna (northern Nigeria)
• Sahel at extreme north

Threats to Nigerian Ecosystems:

1. Deforestation: Estimated 3.5% annual loss of forest cover
2. Desertification: Advancement of Sahara into northern Nigeria
3. Oil pollution: Niger Delta oil spills affecting mangroves
4. Overgrazing: Exposes soil to erosion
5. Hunting: Bushmeat trade threatening wildlife
6. Climate change: Altering rainfall patterns

Conservation in Nigeria:

Protected Areas:

• Yankari Game Reserve (Bauchi)
• Gashaka-Gumti National Park (Taraba)
• Okomu Forest Reserve (Edo)
• Cross River National Park (Cross River)
• Chad Basin National Park (Borno)

Conservation Strategies:

• In-situ conservation: Protecting species in natural habitats
• Ex-situ conservation: Protecting species outside habitats (zoos, seed banks)
• Wildlife conservation laws in Nigeria
• Reforestation programmes

Pollution and Environment:

Water Pollution:

• Sources: Industrial discharge, agricultural runoff (fertilisers, pesticides), sewage
• Eutrophication: Excess nutrients cause algal bloom → oxygen depletion → fish death
• Thermal pollution: Power plant cooling water raises water temperature

Air Pollution:

• Greenhouse gases: CO₂, CH₄, N₂O → global warming
• Ozone layer depletion: CFCs
• Acid rain: SO₂, NOₓ from industries

Global Warming Consequences:

• Rising sea levels (threatens coastal cities)
• More extreme weather events
• Species migration and extinction
• Agricultural disruption
• Water scarcity

Carbon Footprint Reduction:

• Afforestation and reforestation
• Renewable energy adoption
• Energy efficiency
• Sustainable transportation

⚡ NABTEB Exam Pattern: NABTEB frequently asks:

• Drawing and interpreting ecological pyramids
• The 10% energy transfer rule with calculations
• Identifying ecosystem components
• Nitrogen cycle with bacterial roles
• Differences between food chains and food webs
• Conservation challenges in Nigeria

Expect calculation questions: “If producers have 10,000 kJ energy, how much is available to secondary consumers?” Answer: 10% of 10% of 10,000 = 100 kJ

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