11.4 Biodiversity and ecosystem services

Biodiversity covers the variety of life at three levels: species, genetic, and ecosystem. Together, these levels support ecosystem stability and resilience, allowing natural systems to adapt to disturbances and keep ecological processes running.

Ecosystem services are the benefits that humans get from functioning ecosystems. They fall into four categories: provisioning, regulating, supporting, and cultural. Understanding how biodiversity underpins these services is central to sustainable resource management.

Types of Biodiversity

Species Diversity

Species diversity refers to the variety of different species within a given area. It has two components: species richness (the total number of species present) and species evenness (how evenly individuals are distributed among those species). An area could have high richness but low evenness if one species dominates while dozens of others are rare.

• Higher species diversity is generally linked to more complex and stable ecosystems
• Tropical rainforests are a classic example, hosting an estimated 50% of all terrestrial species on just ~6% of Earth's land surface
• Coral reefs are another hotspot, sometimes called "the rainforests of the sea" for their extraordinary diversity of fish, corals, and invertebrates

Genetic Diversity

Genetic diversity is the variety of genes within a species or population. This variation is what natural selection acts on, giving populations the raw material to adapt when environmental conditions shift.

• When genetic diversity drops, populations become more vulnerable to diseases and environmental stressors because fewer individuals carry traits that might help them survive new challenges
• Crop varieties illustrate this well: thousands of distinct varieties of rice and wheat exist worldwide, each adapted to different climates, soils, and pest pressures. Relying on just a few varieties increases the risk of widespread crop failure
• The Irish Potato Famine (1845–1852) is a stark historical example. Heavy dependence on a single potato variety with low genetic diversity left the entire crop susceptible to blight

Ecosystem Diversity

Ecosystem diversity refers to the variety of habitats, biological communities, and ecological processes within a region. It spans both terrestrial ecosystems (forests, grasslands, deserts) and aquatic ecosystems (lakes, rivers, oceans, coral reefs).

• Maintaining ecosystem diversity preserves the range of ecological functions and services a region can provide
• The Great Barrier Reef system, for instance, contains coral reefs, seagrass beds, and mangrove forests, each supporting different species and performing different ecological roles
• The Amazon basin combines multiple forest types, river systems, and wetlands into one of the most ecologically diverse regions on Earth

Ecosystem Services

Provisioning Services

Provisioning services are the tangible products humans obtain directly from ecosystems.

• Food: crops, livestock, wild-caught fish (global fisheries supply roughly 3.3 billion people with nearly 20% of their animal protein)
• Fresh water: filtered and stored by watersheds and aquifers
• Raw materials: timber for construction, fibers like cotton and wool for textiles
• Medicinal resources: many pharmaceuticals originate from plant or animal compounds. Around 25% of modern medicines are derived from rainforest plants

Regulating Services

Regulating services are benefits that come from ecosystems controlling natural processes.

• Climate regulation: forests and oceans act as carbon sinks. The world's forests absorb roughly 2.6 billion tonnes of $CO_2$ per year
• Water purification: wetlands filter sediments, nutrients, and pollutants from water before it reaches rivers and groundwater
• Flood control: floodplains and wetlands absorb excess water, reducing downstream flood damage
• Pollination: insects like bees and butterflies pollinate roughly 75% of the world's leading food crops

Supporting Services

Supporting services are the underlying processes that make all other ecosystem services possible. Without them, provisioning, regulating, and cultural services would collapse.

• Nutrient cycling: decomposers break down dead organic matter, releasing nitrogen, phosphorus, and other nutrients back into the soil for plant uptake
• Soil formation: the slow weathering of rock combined with biological activity builds the soil that agriculture depends on
• Primary production: photosynthesis by plants and algae converts sunlight into chemical energy, forming the base of nearly every food web on Earth

Cultural Services

Cultural services are the non-material benefits people draw from ecosystems.

• Recreation: hiking, birdwatching, snorkeling, and other outdoor activities that depend on healthy ecosystems
• Aesthetic value: scenic landscapes that influence where people live, travel, and find meaning
• Spiritual and religious significance: sacred groves, rivers, and mountains hold deep importance for many indigenous and religious communities worldwide
• Education and science: natural ecosystems serve as living laboratories for research and environmental education

Biodiversity and Ecosystem Stability

Ecosystem Resilience

Ecosystem resilience is the ability of an ecosystem to absorb disturbances and recover without shifting into a fundamentally different state. Biodiversity strengthens resilience through two key mechanisms:

• Functional redundancy: when multiple species perform similar ecological roles, the loss of one species doesn't eliminate that function entirely. Other species can compensate and keep the ecosystem running.
• Response diversity: different species respond to the same environmental change in different ways. This variety increases the odds that at least some species will survive and maintain ecosystem processes under new conditions.

A diverse forest with many tree species, for example, is far more resilient to a pest outbreak than a monoculture plantation. If a beetle targets one tree species, the remaining species continue to provide canopy cover, habitat, and carbon storage.

Keystone Species

A keystone species has a disproportionately large effect on ecosystem structure and function relative to its abundance. Removing a keystone species triggers cascading changes throughout the community.

• Sea otters prey on sea urchins, keeping urchin populations in check. Without otters, sea urchin numbers explode and they overgraze kelp forests, transforming productive kelp ecosystems into barren "urchin barrens."
• Gray wolves in Yellowstone regulate elk populations. When wolves were reintroduced in 1995, elk stopped overbrowsing willows and aspens along riverbanks. Vegetation recovered, streambanks stabilized, and even river channel patterns shifted.
• African elephants knock down trees and create clearings, maintaining a mosaic of forest and grassland habitats. They also disperse seeds across large distances through their dung.

These examples show that protecting biodiversity isn't just about saving individual species. It's about preserving the relationships and interactions that keep entire ecosystems functioning.