Biology
Biodiversity, interconnectedness, heredity and continuity of life — full Paper 1 + Paper 2 practice External Assessments with marking guides.
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Measuring Biodiversity: Species Richness, Evenness and Simpson's Diversity Index
What Is Biodiversity? Three Levels of Variation
Biodiversity — a contraction of biological diversity — refers to the variety of life on Earth and encompasses all the ways in which living systems differ from one another. The QCAA Biology syllabus requires students to recognise that biodiversity operates simultaneously at three distinct, hierarchical levels: genetic diversity, species diversity, and ecosystem diversity. Each level is measurable, meaningful, and influenced by different ecological and evolutionary processes.
- Genetic diversity describes the range of heritable allelic variation within and between populations of the same species. High genetic diversity equips a population with a broader toolkit of responses to environmental change, disease, and predation. For example, the greater bilby (Macrotis lagotis) populations remaining in isolated refuges across Queensland and the Northern Territory show markedly reduced genetic diversity compared with historical records — a consequence of population fragmentation that increases their vulnerability to disease outbreaks and climatic shifts.
- Species diversity refers to the variety of species within a defined area. It incorporates both how many different species are present (richness) and how evenly those species are distributed across the community (evenness). Species diversity is the level most commonly measured in field surveys and is the primary focus of Simpson's Diversity Index.
- Ecosystem diversity describes the range of different habitat types, ecological communities, and the abiotic and biotic processes that sustain them across a landscape or region. Queensland alone contains an exceptional array of ecosystems — from the wet tropical rainforests of the Daintree, which are listed among the world's oldest continuous rainforests, to the mulga woodlands of the Channel Country, the Great Barrier Reef's coral systems, and the brigalow belt — each harbouring distinct communities of organisms and fulfilling distinct ecosystem functions.
These three levels are interconnected: ecosystem diversity supports species diversity, and species diversity underpins genetic diversity. Conservation strategies that address only one level are rarely sufficient in isolation. Understanding all three levels is therefore fundamental to evaluating community health and designing effective management responses.
Species Richness and Species Evenness: Two Sides of Diversity
When ecologists speak of species diversity in the field, they are almost always referring to two distinct but complementary properties of a community: species richness and species evenness. Students frequently conflate these concepts, yet they can diverge dramatically in real ecosystems, and each tells a different ecological story.
Species richness (S) is simply the total number of different species recorded within a defined sampling area or community. It is a raw count — no weighting is applied for how many individuals of each species are present. Richness is intuitive and easy to compare between sites, but it provides no information about how the organisms are distributed among those species. A sample containing 10 species with 1000 individuals is counted as having a richness of 10, regardless of whether 999 of those individuals belong to a single species.
Relative abundance expresses the proportion of each species' population relative to all individuals recorded in the sample. Formally: relative abundance of species i = (ni / N) × 100%, where ni is the number of individuals of species i and N is the total number of individuals across all species. Relative abundance data can be displayed as bar charts, pie charts, or rank-abundance (Whittaker) plots.
Species evenness (E) measures how similar the relative abundances of species are to one another. A perfectly even community is one in which every species has an identical number of individuals. Evenness is maximised when all species are equally represented and minimised when one or a few species dominate overwhelmingly. Evenness matters because a community with low evenness — even one with high richness — may be functionally fragile, since the ecosystem processes it supports depend disproportionately on dominant species.
| Community | Species | Individuals per species | Richness (S) | Evenness (qualitative) |
|---|---|---|---|---|
| Site A — riparian woodland | 6 | 50, 48, 52, 49, 51, 50 | 6 | High — nearly equal |
| Site B — disturbed paddock margin | 6 | 250, 2, 2, 1, 1, 1 | 6 | Very low — one dominant species |
Both communities above have the same richness (S = 6), yet they are ecologically very different. Site B is clearly dominated by a single species — likely an introduced grass or weed — while Site A represents a balanced, resilient community. This comparison illustrates why richness alone is an insufficient measure of biodiversity.
The Queensland fur seal (*Arctocephalus pusillus doriferus*) is classified using binomial nomenclature. Which component of this name indicates the subspecies?
- Arctocephalus
- pusillus
- doriferus
- Arctocephalus pusillus
Show the worked answer
Answer: C
doriferus is the subspecies epithet; the genus is Arctocephalus and the species epithet is pusillus.
All 20 practice exams
- Exam 1 — Biodiversity measurement: Simpson's Diversity Index, species richness, evenness; Linnaean taxonomy, binomial nomenclature, molecular phylogeny and cladistics; Ecosystem energy flow, trophic levels and efficiency
- Exam 2 — Biodiversity measurement: Simpson's Diversity Index, species richness, evenness, percentage cover — GBR coral bleaching context; Linnaean taxonomy, binomial nomenclature, molecular phylogeny, cladistics; Ecosystem dynamics: energy flow, trophic levels, biogeochemical cycles (carbon, nitrogen, water)
- Exam 3 — Natural selection mechanisms and types — myxomatosis resistance in Australian wild rabbits; Allele frequency change over generations — microevolution and Hardy-Weinberg equilibrium; Biodiversity measures — Simpson's Diversity Index, species richness, evenness
- Exam 4 — Biodiversity measures: Simpson Diversity Index, species richness, evenness; Trophic cascades, mesopredator release, food web stability; Ecological interactions: predation, competition, carrying capacity
- Exam 5 — Cane toad invasion ecology — competitive exclusion, carrying capacity, population growth curves, species distribution; Biodiversity measures — Simpson's Diversity Index, species richness, evenness, percentage cover; Linnaean taxonomy, binomial nomenclature, cladistics and molecular phylogeny
- Exam 6 — Biodiversity measures: species richness, Simpson's Diversity Index, evenness, percentage cover; Linnaean taxonomy, binomial nomenclature, molecular phylogeny and cladistics; Ecosystem energy flow, trophic levels, productivity
- Exam 7 — Sex-linked inheritance and plumage colour in black-throated finch (Poephila cincta); Monohybrid and dihybrid crosses with Punnett square construction and probability calculation; Meiosis as a source of genetic variation — independent assortment and crossing over
- Exam 8 — Ancient Queensland rainforest phylogeny — molecular sequence comparison and cladistics; Linnaean taxonomy and binomial nomenclature; Biodiversity measures: Simpson's Diversity Index, species richness, evenness
- Exam 9 — Genetic drift and Hardy-Weinberg equilibrium disruption in a bottleneck event; Allele frequency calculation and population genetics; Weedy sea dragon conservation genetics (Queensland/Australian context)
- Exam 10 — Nitrogen cycle — nitrification, denitrification, ammonification, nitrogen fixation in sugarcane agricultural and natural wetland contexts; Biodiversity measures — Simpson's Diversity Index, species richness, evenness, percentage cover; Ecosystem energy flow — trophic levels, ecological efficiency, productivity
- Exam 11 — Platypus genome biotechnology — recombinant DNA technology, plasmid vector cloning, venom-related gene, gel electrophoresis verification; DNA structure, semi-conservative replication, transcription, translation; Gene expression regulation, epigenetic mechanisms, transcription factors
- Exam 12 — Koala epigenetics and habitat fragmentation — stress-induced chromatin remodelling and immune gene transcription; DNA structure, semi-conservative replication, transcription and translation; Epigenetic regulation: DNA methylation, histone modification, chromatin remodelling
- Exam 13 — Gondwana macroevolution and vertebrate family diversity across geological eras; Mass extinction events identified from diversity charts; Adaptive radiation in Australian marsupials
- Exam 14 — Freshwater turtle chromosomal non-disjunction — karyotype interpretation, trisomy/monosomy, protein effect and phenotypic consequence; DNA structure, semi-conservative replication, transcription and translation; Gene and chromosomal mutations — types, causes and effects on protein structure and function
- Exam 15 — Parapatric speciation and gene flow in sunflower hybrid zones (southern Queensland); Reproductive isolation mechanisms: pre-zygotic and post-zygotic barriers; Modes of speciation: allopatric, parapatric, sympatric
- Exam 16 — Simpson's Diversity Index (SDI) calculation and interpretation; Energy flow across trophic levels and ecological efficiency; Humpback whale population dynamics and carrying capacity
- Exam 17 — Eastern grey kangaroo disruptive selection — body mass distribution histograms from drought and non-drought years; Types of natural selection: directional, stabilising, disruptive; Allele frequency change and Hardy-Weinberg equilibrium
- Exam 18 — Mutton bird DNA profiling and gel electrophoresis parentage analysis; PCR amplification and biotechnology applications; Molecular phylogeny and cladistics
- Exam 19 — Nitrogen-fixing bacteria mutualism in legume pastures; Biogeochemical nitrogen cycling; Ecosystem interactions and nutrient cycling integration
- Exam 20 — Allopatric speciation and reproductive isolation in Petrogale (rock wallaby) populations of Queensland's Wet Tropics; Molecular divergence timelines and phylogenetic evidence for macroevolution; Loss of gene flow, genetic drift and founder effects in geographically isolated populations
All 20 revision notes
- Measuring Biodiversity: Species Richness, Evenness and Simpson's Diversity Index
- Linnaean Taxonomy, Binomial Nomenclature and Molecular Phylogeny
- Energy Flow, Trophic Transfer Efficiency and Ecological Pyramids
- Biogeochemical Cycles: Water, Carbon and Nitrogen
- Ecological Niche, Interspecific Interactions and Carrying Capacity
- Ecological Succession: Primary, Secondary and Climax Communities
- DNA Double Helix Structure and Semi-Conservative Replication
- Meiosis, Crossing Over and Sources of Genetic Variation
- Transcription, Translation and Regulation of Gene Expression
- Gene Mutations and Chromosomal Abnormalities
- Monohybrid, Dihybrid, Sex-Linked and Polygenic Inheritance
- Recombinant DNA, PCR, Gel Electrophoresis and Cloning
- Natural Selection: The Five-Step Mechanism and Evidence for Evolution
- Types of Natural Selection: Directional, Stabilising and Disruptive
- Hardy-Weinberg Equilibrium and Allele Frequency Analysis
- Mechanisms of Evolution: Genetic Drift, Gene Flow and Mutation
- Speciation: Allopatric, Sympatric and Parapatric Modes
- Patterns of Macroevolution: Divergent, Convergent, Adaptive Radiation and Extinction
- Sampling Techniques and Biodiversity Measures: Percentage Cover and Frequency
- Epigenetic Regulation: Histone Modification, DNA Coiling and Transcription Factors