Unit 2 Notes: Biodiversity, Ecosystem Value, and Species Patterns Across Space

Biodiversity

The variety of life in an area, including variation at multiple biological scales (genetic, species, and ecosystem levels).

Genetic diversity

The variety of genes within a species, including differences among individuals and populations; influences a species’ ability to adapt and persist.

Species diversity

The variety of species in a community, often described using species richness and species evenness.

Species richness

The number of different species present in a community.

Species evenness

How evenly individuals are distributed among the species in a community; low evenness means one/few species dominate.

Keystone species

A species with a disproportionately large effect on ecosystem structure relative to its abundance; removing it can trigger major community changes.

Foundation species

A species that creates or defines a habitat (e.g., kelp in kelp forests, corals in coral reefs); loss can collapse habitat structure.

Ecosystem services

The benefits people obtain from ecosystems; highlights human dependence on ecological processes and functioning ecosystems.

Provisioning services

Ecosystem services that provide physical products, such as food, timber, fresh water, and medicines.

Regulating services

Ecosystem services that regulate ecosystem processes, such as climate regulation (carbon storage), flood control, water purification, and disease regulation.

Cultural services

Nonmaterial ecosystem benefits, such as recreation, tourism, spiritual value, aesthetic value, and education.

Supporting services

Underlying ecological processes that make other services possible, such as nutrient cycling, soil formation, primary production, and habitat provision.

Functional redundancy

When multiple species perform similar ecological roles, so if one declines others can partially compensate, increasing resilience of ecosystem services.

Complementarity

When different species specialize under different conditions (e.g., root depths, flowering times, stress tolerance), stabilizing ecosystem processes across seasons and disturbances.

Island biogeography

A framework predicting species richness on an “island” based on immigration and extinction dynamics, leading to an equilibrium richness.

Habitat island

A patch of suitable habitat surrounded by unsuitable habitat (e.g., a forest fragment in farmland), functionally similar to a true island for many species.

Immigration rate

The rate at which new species colonize an island/fragment; generally decreases as more species are already present.

Extinction rate

The rate at which species already present on an island/fragment disappear; generally increases as more species are present (more competition, smaller populations).

Equilibrium number of species

The balance point in island biogeography where immigration and extinction rates are equal; species composition can still change via turnover.

Species–area relationship (S = cA^z)

A pattern/model showing that larger areas tend to contain more species (S increases with area A), typically not in a linear way due to the exponent z.

Habitat fragmentation

The breaking of a large, continuous habitat into smaller patches, increasing isolation and edges and often raising extinction risk while lowering immigration/gene flow.

Edge effect

Changes in community structure and conditions near habitat boundaries (e.g., more light/wind, altered soil moisture, more invasives/predation), reducing effective interior habitat.

Distance effect

In island biogeography, islands closer to the mainland/source pool have higher immigration rates than far islands due to fewer dispersal barriers.

Size effect

In island biogeography, larger islands tend to have lower extinction rates (larger populations, more habitat types/niches) than small islands.

Wildlife corridor

A connected strip of habitat linking isolated patches, increasing immigration/recolonization and gene flow, though it can also aid spread of disease, invasives, or predators.