How humans influence biodiversity, with examples in a range of different context — AQA A-Level Environmental Science

This topic examines the multifaceted pathways through which human activities alter species richness, genetic variability, and ecosystem dynamics across terrestrial, freshwater, and marine biomes. Students investigate both direct impacts, such as habitat fragmentation and overexploitation, and indirect drivers, including anthropogenic climate change and biological invasions.

Understanding these relationships forms the cornerstone of environmental management, linking basic ecology to conservation biology, statutory habitat designations, and landscape-scale restoration schemes. Evaluating these mechanisms enables students to assess real-world trade-offs between socio-economic resource extraction and the preservation of biosphere stability.

• →Habitat fragmentation creates isolated patches, increases the ratio of edge-to-interior habitat, limits gene flow, and makes metapopulations vulnerable to inbreeding depression and local extinction.
• →Plagioclimax communities (such as chalk downland, heather moorland, and coppiced woodland) represent deflated successional stages maintained by human intervention, which often support unique or higher biodiversity than the natural climax community.
• →Overexploitation occurs when harvesting exceeds maximum sustainable yield (MSY), depleting reproductive stock and disrupting food webs via trophic cascades.
• →Invasive non-native species (INNS) disrupt endemic taxa through competitive exclusion, disease transmission, niche displacement, and hybridisation.
• →Anthropogenic abiotic changes, including ocean acidification, agrochemical eutrophication, and acid deposition, alter chemical niches beyond the physiological tolerances of vulnerable organisms.

• Defines direct exploitation as human removal or killing of organisms rather than indirect habitat change
• Explains over-exploitation as harvesting a resource faster than the population can replace it
• Explains deliberate eradication as intentional removal of a target species
• Gives a named example for each route and states how the population is reduced
• Links reduced population size to a consequent fall in biodiversity

• 💡Label each example clearly as over-exploitation or deliberate eradication
• 💡Use examples from more than one context, such as marine, terrestrial and plant harvesting
• 💡State the mechanism of decline for each example rather than only naming the species
• 💡Use precise ecological terminology rather than colloquial language: say 'competitive exclusion', 'abiotic niche alteration', and 'trophic cascade' rather than 'animals fighting for food' or 'upsetting nature'.
• 💡Always reference both components of biodiversity when evaluating habitats: species richness (number of distinct taxa) and species evenness (relative equitability of abundances).
• 💡Include specific, named case studies in open-ended answers, detailing the location, human activity, target species, and ecological outcome (e.g. Rodondo Island rewilding, Dartmoor moorland burning, or Dodd Wood red squirrel reserves).

• Confuses direct exploitation with habitat destruction; keep removal of organisms separate from indirect habitat change
• Gives an example without naming the mechanism; state whether it is over-harvesting or deliberate eradication
• Assumes a reduced population has no further effect; explain the added vulnerability of small populations
• Misconception: All human intervention inevitably degrades biodiversity. Correction: Human-maintained plagioclimax habitats (e.g. coppicing, grazing) arrest succession and often harbor higher microhabitat heterogeneity and rare species compared to climax high forest.
• Misconception: Habitat degradation is synonymous with total habitat loss. Correction: Degradation involves reduced habitat quality (e.g., pollution, edge effects, invasive species) while the physical area remains, whereas habitat loss is the complete removal of the biophysical environment.
• Misconception: Introducing a natural predator to control an invasive species always restores native biodiversity. Correction: Biological control agents can become invasive themselves if they are generalists, preying on non-target native species and exacerbating biodiversity loss.

1. 1Week 1 (Days 1-3): Review the core drivers of anthropogenic biodiversity loss (HIPPO framework: Habitat destruction, Invasive species, Pollution, Population, Overharvesting) and link each to a specific UK and global ecosystem.
2. 2Week 1 (Days 4-7): Analyse positive human interventions, focusing on plagioclimax management (coppicing, rotational heather burning, conservation grazing) and rewilding methodologies.
3. 3Week 2 (Days 8-10): Practice quantitative calculation questions involving Simpson's Index, Lincoln Index mark-release-recapture data, and population growth curves from real AQA past papers.
4. 4Week 2 (Days 11-14): Complete timed 9-mark and 25-mark evaluative essays comparing differing conservation and land-use strategies, self-assessing against official AQA mark schemes.

• 📋Data analysis and mathematical questions: Calculating and interpreting changes in Simpson's Index of Diversity before and after anthropogenic disturbance.
• 📋Extended response (6 to 9 marks): Explaining the ecological mechanisms of habitat fragmentation or the consequences of introducing non-native species.
• 📋Evaluative synoptic essays (25 marks): Critically assessing whether human activities can be managed to maintain both economic exploitation and native biodiversity.