Biological Diversity
What you must understand
Biodiversity has three levels: genetic diversity within a species, species diversity within an ecosystem, and ecosystem diversity. Be able to explain how each level contributes to resilience.
Know how scientists classify organisms: the binomial naming system (genus + species), the hierarchical taxonomic ranks (domain, kingdom, phylum, class, order, family, genus, species), and the use of dichotomous keys. Understand that classification reflects evolutionary relationships, and that molecular evidence (DNA and protein sequences) can revise traditional morphology-based groupings.
Understand adaptations: structural, physiological and behavioural. Relate these to survival in specific environments. Know the concept of selection pressure and how variation within a population interacts with environmental change.
Traps in questions
- "Species diversity" is not the same as "number of individuals"; it combines richness and evenness.
- A dichotomous key must use paired, mutually exclusive characteristics at each step - vague or overlapping features are a common error.
- Scientific names are italicised (or underlined when handwritten); only the genus is capitalised.
- Adaptations must be heritable and improve survival or reproduction; a one-off behaviour is not an adaptation.
Rule of thumb
When asked to compare biodiversity, use the richness + evenness framework: how many different species are present, and how evenly are individuals distributed among them?
Worked example
Two sites each contain 100 individuals. Site A has 10 species with roughly 10 individuals each; Site B has 10 species but 91 individuals of one species. Site A has higher species diversity because evenness is greater, even though richness is equal.