30 Sep Biodiversity in IB ESS: Diversity, Food Webs and Conservation
Biodiversity in IB ESS connects ecology, conservation and human decisions. It includes variation within species, between species and among ecosystems or habitats. Counting species is useful, but it does not capture every aspect of biodiversity.
Three levels of biodiversity
- Genetic diversity: variation in genetic information within a species or population.
- Species diversity: the variety of species and their relative abundance in a community.
- Habitat or ecosystem diversity: the variety of habitats or ecosystems in a wider area.
These levels are connected, but they are not interchangeable. Species richness is the number of species recorded. Evenness describes how individuals are distributed among those species. Two communities with the same richness can have different diversity if one is dominated by a single species.
The Convention on Biological Diversity introduction explains genetic, species and ecosystem dimensions. Avoid treating a single count as a complete assessment of ecosystem health.
Food webs and keystone species
Food webs represent feeding relationships. Changes in one population can affect others, but the response depends on the species’ role and the wider system. A keystone species has a disproportionately large influence relative to its abundance.
For example, sea otters consume sea urchins, which can graze kelp. NOAA describes how sea otters help maintain kelp habitats through this interaction. Reducing a keystone species can cause major changes; it does not follow that removing any keystone species always makes every part of an ecosystem collapse.
Diversity and resilience
Biodiversity can support functions and responses to environmental change, but high diversity is not immunity to drought, disease or climate change. Species composition, functional roles, connectivity and the severity of disturbance also matter. See the CBD review of forest biodiversity and resilience.
Explain threats accurately
Habitat loss and fragmentation, overexploitation, invasive species, pollution and climate change can affect biodiversity. Distinguish the mechanism in each case rather than listing threats without explanation.
For example, excess nitrogen and phosphorus from fertilizer or manure can enrich water and contribute to eutrophication. Pesticides can harm organisms through toxic effects; they should not all be described as sources of nitrate and phosphate. The EPA explanation of nutrient sources helps separate these processes.
Evaluate conservation strategies
Protected areas, habitat restoration, sustainable harvesting and invasive-species management need suitable design and implementation. Assess monitoring, enforcement, ecological connectivity, funding and the effects on local communities. A protected-area boundary alone does not guarantee a conservation outcome.
Original practice: richness and evenness
This is an original exercise, not an official IB question or a graded answer. Two sampled communities each contain four species. In one, individuals are distributed fairly evenly; in the other, most belong to one species. Explain why equal richness does not imply equal diversity. What sampling limitations would you check before comparing them?
Read the fieldwork methods guide and management strategies guide to connect biodiversity evidence to decisions.
Practise with individual ESS support
In Marija’s online IB ESS SL and HL lessons, you can work on concepts, data interpretation and clear explanations. Request a free 20-minute trial lesson to discuss your priorities. For IA work, the investigation and submitted writing remain your own.
Course reference: Official IB ESS guide, first assessment 2026 and IB course updates. Reviewed 7 October 2026.
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