Biology · Lesson 17

Ecology: who eats whom

JAMBWAECNECO

What the syllabus asks

JAMB: ecosystem, food chains and webs, energy flow, nutrient cycling, ecological factors, population, adaptations, pollution, conservation

WAEC: ecology — concepts (environment, biosphere, habitat, population, community, ecosystem, niche), ecological factors (abiotic: climatic, edaphic, topographic; biotic), measuring instruments, food chains and food webs, trophic levels, ecological pyramids, energy flow, nutrient cycles (carbon, nitrogen, water), ecological relationships (predation, parasitism, mutualism, commensalism, competition),…

NECO: ecology — concepts (environment, biosphere, habitat, population, community, ecosystem, niche), ecological factors (abiotic: climatic, edaphic, topographic; biotic), measuring instruments, food chains and food webs, trophic levels, ecological pyramids, energy flow, nutrient cycles (carbon, nitrogen, water), ecological relationships (predation, parasitism, mutualism, commensalism, competition),…

What you will learn

Define the main ecological terms and levels of organisation.
Describe abiotic and biotic factors and the instruments used to measure them.
Construct and interpret food chains, food webs and ecological pyramids.
Explain energy flow and calculate energy transfer efficiency.
Describe the carbon, nitrogen and water cycles.
Describe ecological relationships and estimate population size.
Describe Nigerian biomes and adaptations, succession, pollution and conservation.

Key points

Ecology studies organisms and their environment; levels: organism, population, community, ecosystem, biome, biosphere.
Habitat = where an organism lives; niche = its role.
Abiotic factors: climatic, edaphic, topographic; instruments: rain gauge, hygrometer, anemometer, Secchi disc, pH meter.
Food chains run producer → primary → secondary → tertiary consumer; arrows show energy flow; food webs are more stable.
Pyramids of numbers and biomass can be inverted; the pyramid of energy is always upright.
Only about 10% of energy passes to the next level; losses through respiration (heat), waste and uneaten parts.
Carbon cycle: photosynthesis removes CO₂; respiration, decay and combustion return it; excess CO₂ causes global warming.
Nitrogen cycle: fixation (Rhizobium, lightning, Haber), decay, nitrification (Nitrosomonas, Nitrobacter), denitrification.
Relationships: mutualism (+/+), commensalism (+/0), parasitism and predation (+/−), competition (−/−).
Population estimates: quadrat (mean × area) and Lincoln index (N₁ × N₂/M); sigmoid growth to carrying capacity.
Nigerian biomes from mangrove to Sahel with adaptations; succession from pioneers (lichens) to climax.
Pollution (air, water, land, noise) and conservation (parks, laws, afforestation, sustainable use).

Start here: What ecology studies

Walk through the Okomu forest in Edo State, the savanna of Yankari, a mangrove swamp near Calabar, or even a school compound, and you see living things everywhere depending on one another: grass feeding goats, goats feeding people, dung beetles rolling dung, birds nesting in trees, fungi rotting fallen logs. Ecology is the study of these relationships between organisms and their environment.

Ecology: the scientific study of the interactions of organisms with one another and with their physical (non-living) environment.

Levels of organisation

Organism (individual): a single living thing, e.g. one tilapia.
Population: all members of one species in an area at one time, e.g. all the tilapia in Kainji Lake.
Community: all the populations of different species living together in an area, e.g. the fish, frogs, water lilies, algae and bacteria of the lake.
Ecosystem: the community plus its non-living environment (water, light, temperature, minerals), all interacting as a unit.
Biome: a large region with a characteristic climate and vegetation, e.g. tropical rainforest, savanna.
Biosphere: all the parts of the Earth (land, water, air) where life exists.

Habitat and niche

The habitat is the place where an organism lives: its "address". The niche is its role or "profession": what it eats, what eats it, when it is active and how it affects other species. Two species can share a habitat but not the same niche for long: one would out-compete the other. For example, cattle egrets and cows share the same field, but the egret feeds on insects disturbed by the cow, while the cow eats grass.

Types of habitat

Terrestrial habitats (land): forests, grasslands, deserts, farms. Aquatic habitats: freshwater (rivers, lakes, ponds), marine (the sea) and estuarine/brackish (where rivers meet the sea, as in the Niger Delta mangroves).

Worked example 17.1

Classify each as population, community or ecosystem: (a) all the weaver birds in a village; (b) all the plants, animals and microbes in a pond; (c) a pond with its water, mud, light and all its organisms.

(a) One species only: population.
(b) Many species, living things only: community.
(c) Living plus non-living: ecosystem.

(a) population (b) community (c) ecosystem

⚠️ Common mistake: confusing habitat (where an organism lives) with niche (its role).

Try it yourself. What is the difference between a community and an ecosystem?

Show solution

An ecosystem includes the non-living (abiotic) environment as well as the community.

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Practice questions

1. Organisms that make their own food are called

producers
consumers
decomposers
scavengers

Show answer

A: producers
Green plants are producers.

2. In the food chain grass → grasshopper → toad → snake, the toad is a

primary consumer
producer
tertiary consumer
secondary consumer

Show answer

D: secondary consumer
Grasshopper eats grass (primary), toad eats grasshopper (secondary).

3. The relationship between a tapeworm and man is

mutualism
saprophytism
parasitism
commensalism

Show answer

C: parasitism
The tapeworm benefits; man is harmed.

4. Mangrove swamps in the Niger Delta are characterised by plants with

spines instead of leaves
breathing roots (pneumatophores)
thick waxy cuticles to reduce water loss
deep tap roots

Show answer

B: breathing roots (pneumatophores)
The mud is waterlogged and low in oxygen; pneumatophores grow up to take in air.

5. Which instrument measures relative humidity?

Hygrometer
Anemometer
Rain gauge
Barometer

Show answer

A: Hygrometer
Hygrometer = humidity; anemometer = wind speed; barometer = pressure.

Key words

Ecology: Study of the relationships between organisms and their environment.
Habitat: The natural home of an organism.
Population: All organisms of the same species living in an area at the same time.
Community: All the populations of different species living and interacting in an area.
Ecosystem: A community together with its non-living environment, functioning as a unit.
Niche: The role of an organism in its ecosystem, including what it eats, where it lives and how it interacts.
Biosphere: All parts of the Earth where life exists.
Abiotic factor: A non-living factor of the environment, e.g. temperature, light, soil.
Biotic factor: A living factor, e.g. predators, competitors, parasites.
Producer: An organism that makes its own food, usually by photosynthesis.
Consumer: An organism that feeds on other organisms.
Decomposer: An organism that breaks down dead matter and returns nutrients to the environment.

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