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What is biodiversity?

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3.1.1 Biodiversity is the total diversity of living systems and it exists at several levels.

The biodiversity levels are habitat diversity, species diversity, and genetic diversity.

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Biodiversity is the total diversity of living systems. It is not simply a count of species. Biodiversity exists at three interconnected levels, and understanding each level is essential for appreciating why ecosystems function and persist.

Consider the image below from Our World in Data. It shows the distribution of wild land mammal biomass globally. Just ten species account for around 40% of all wild mammal biomass on land. White-tailed deer alone represent 12.3%. Even-hoofed mammals collectively make up 49%.

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This tells us something important: biodiversity is not just about how many species exist (richness), but also about how evenly life is distributed among those species (evenness), and about diversity at the habitat and genetic levels too.

Just ten species make up almost half the weight of all wild mammals on Earth

  1. Look at the Our World in Data article. What does the distribution of wild mammal biomass suggest about species evenness among wild land mammals?

  2. Why is it insufficient to measure biodiversity by simply counting the number of species in an area?

The three levels of biodiversity

Habitat diversity

Habitat diversity refers to the range of different habitats in an ecosystem or biome. Each distinct habitat provides a unique set of abiotic conditions and ecological niches, supporting different communities of organisms.

Case study: Swiss National Park, Engadin

Park - Swiss National Park

The Swiss National Park (170 km², founded 1914) is the oldest national park in the Alps and Central Europe. It spans an altitude range from 1,400 m to 3,174 m. Within this relatively small area, the steep altitudinal gradient creates a remarkable range of distinct habitats:

Habitat type Coverage Characteristics
Coniferous forest 28% Mountain pine, spruce, larch, Swiss stone pine; provides shelter and food for forest species
Alpine grasslands and meadows 21% Rich in flowering plants including edelweiss and Rhaetian poppy; supports marmots, insects, ground-nesting birds
High alpine rock and scree 51% Dolomite rock, scree slopes, permafrost zones; ibex, chamois and specialised plants adapted to extreme conditions

This habitat diversity supports 36 mammal species (including ibex, chamois, red deer, and marmots), around 100 bird species (including golden eagle and bearded vulture), and over 650 vascular plant species. Since 1914, no human intervention has been permitted: fallen trees, avalanches and mudslides are left as natural processes, creating additional microhabitats such as deadwood, scree and tree cavities that further increase habitat diversity.

Contrast this with a monoculture wheat field on the Swiss Plateau. It may cover a comparable area but contains essentially one habitat type, uniform structure, and far fewer ecological niches.

  1. Explain why the altitudinal range of the Swiss National Park (1,400 m to 3,174 m) leads to high habitat diversity.

  2. Identify two specific microhabitats within the Swiss National Park that are created by natural processes and explain why they increase biodiversity.

  3. Suggest why a monoculture wheat field has lower habitat diversity than the Swiss National Park, even if it covers a similar area.

Species diversity