3. Biodiversity and Its Importance

Biodiversity is the variety of life. It has three levels:

• Genetic diversity — variation in DNA within a species; allows adaptation to change.
• Species diversity — the number and relative abundance of different species in an area.
• Ecosystem diversity — the variety of different habitats and ecosystems on Earth.

Why biodiversity matters — ecosystem services:
Biodiversity is not just aesthetically valuable; ecosystems provide services humans depend on:

• Provisioning: food, fresh water, timber, medicines (about 40% of pharmaceuticals come from wild species).
• Regulating: climate regulation, flood control, water purification, crop pollination, disease control.
• Supporting: nutrient cycling, soil formation, oxygen production.
• Cultural: recreation, ecotourism, spiritual value.

Keystone species: a species whose impact on its ecosystem is disproportionately large relative to its abundance. Removing a keystone species collapses the ecosystem. Classic example: sea otters eat sea urchins; without otters, urchins explode and destroy kelp forests.

Indicator species: sensitive organisms whose health signals the condition of an ecosystem. Frogs (permeable skin) and lichens are classic indicators of pollution.

Threats to biodiversity — the "HIPPO" framework:

• Habitat destruction — the leading threat (deforestation, wetland draining, urban sprawl).
• Invasive species — non-native organisms that outcompete locals (kudzu vine, zebra mussels, cane toads).
• Pollution — toxins, nutrient runoff, plastic.
• Population (human) growth — more people = more resource demand.
• Overexploitation — overhunting, overfishing, poaching.

Species richness vs. evenness:

• Richness = how many species are present.
• Evenness = how evenly individuals are distributed among species.

An ecosystem with 5 species each with 20% of individuals has higher diversity than one with 5 species where 95% are one species.