Ecology & Ecosystems is a core part of A-Level Biology. Revise the key concepts and common mistakes below, then lock them in with the free games.
Key concepts
Primary successionStarts on bare rock with no soil — e.g. after a volcanic eruption
Secondary successionStarts where soil already exists — e.g. after fire or clearance
Pioneer speciesFirst colonisers — tolerant of harsh conditions, often lichens
Climax communityStable end-point of succession — e.g. oak woodland in UK
Interspecific competitionCompetition between different species for the same resource
Intraspecific competitionCompetition within one species — drives natural selection
Exponential growthUnlimited resources — population doubles repeatedly
Logistic growthS-shaped curve — slows as resources run low
Carrying capacity (K)Maximum population the environment can support sustainably
Density-dependent factorEffect changes with population density (e.g. food, disease)
Predator-prey cycleLagged oscillations — prey peak first, then predators
Lincoln indexN = (M × C) / R for mark-release-recapture
PopulationAll members of one species in a given area at a given time
CommunityAll the populations living and interacting in an area
Common mistakes to avoid
Questions where students often pick the tempting wrong answer — make sure you know the right one:
Why is interspecific competition between similar species important?✗ Competition only happens between predators and their prey. ✓ Two species cannot occupy exactly the same niche indefinitely — competition often leads to displacement or niche divergence.
What does the carrying capacity (K) of an environment represent?✗ The starting population size ✓ The maximum population the environment can sustain
Which is a density-dependent factor on population growth?✗ A volcano eruption ✓ Spread of an infectious disease
What does a gene code for?✗ A gene codes for a specific physical feature like eye colour directly. ✓ Typically a polypeptide (protein) — through transcription to mRNA and translation by ribosomes.
What does it mean for an allele to be 'dominant'?✗ A dominant allele is the most common allele in a population. ✓ It is expressed in the phenotype when at least one copy is present (in a heterozygote).
Practise Ecology & Ecosystems — free games
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