Unit 2: The Living World: Biodiversity

Ecosystem

A community of living organisms (plants, animals, microbes) interacting with each other and with the nonliving environment (water, air, soil, climate).

Biodiversity

The variety of life at multiple levels (genes, species, ecosystems); supports ecosystem function, stability, and resilience.

Ecosystem services

The benefits people obtain from ecosystems; when ecosystems are damaged, society often must replace these services with costly technology or infrastructure.

Provisioning services

Tangible goods harvested or used from ecosystems (e.g., food, fresh water, timber, medicinal resources, livestock products like fiber, meat, milk).

Regulating services

Natural processes that regulate environmental conditions (e.g., water purification, flood control, climate regulation via carbon storage, erosion control, disease regulation).

Supporting services

Underlying processes that make other services possible (e.g., nutrient cycling, soil formation, primary production/biomass creation, renewing soil fertility).

Cultural services

Nonmaterial benefits from ecosystems (e.g., recreation, aesthetic value, spiritual value, educational value).

Natural pest control

A regulating service in which predators and parasites keep pest populations in balance, reducing pesticide need and helping keep food prices lower.

Pollination

An ecosystem service linked to food production; many flowering plants depend on animal pollinators (insects, birds, bats) to reproduce.

Wetlands

Marshes, swamps, and bogs that often act as natural water filters and also reduce flooding by storing and slowing water.

Trade-off (ecosystem services)

A situation where increasing one benefit (often short-term provisioning like timber/farmland) reduces other services (often long-term regulating/supporting like carbon storage, flood control, soil formation).

Genetic diversity

Variation in DNA within a species (the range of genetic traits in a gene pool); increases the chance some individuals survive disease outbreaks or climate shifts.

Population bottleneck

A large reduction in the size of a single population due to a catastrophic environmental event, leaving a smaller gene pool and reduced genetic diversity.

Minimum viable population size (MVP)

The smallest population size that can persist without facing extinction from random events/natural disasters; linked to inbreeding risk and low genetic diversity after bottlenecks.

Species diversity

The variety of species in an area, commonly described using both species richness and species evenness.

Species richness

The number of different species represented in a community or region.

Species evenness

How evenly individuals are distributed among the species in a community.

Ecosystem diversity

The range of habitats/ecosystems found in a specific area; more ecosystem types can support more species and services.

Specialist species

A species that requires unique resources and/or a specific habitat and often has a limited diet; tends to be lost first with habitat loss.

Generalist species

A species that can live in many environments and often has a varied diet (broad niche).

Keystone species

A species with an ecosystem impact disproportionately large relative to its abundance; removing it can cause major ecosystem shifts and even extinctions of other species.

Indicator species

An organism whose presence, absence, or abundance reflects a specific environmental condition and can indicate ecosystem health.

Island (habitat “island”)

Any suitable habitat patch surrounded by a large area of unsuitable habitat (e.g., a forest fragment surrounded by farmland), not just land surrounded by water.

Theory of island biogeography

A theory explaining that the number of species on an island is determined by a balance between immigration of new species and extinction of existing species, influenced by island size and isolation.

Immigration–extinction balance

In island biogeography, species richness reflects the balance between new species arriving (immigration) and species disappearing (extinction).

Habitat fragmentation

When a habitat is broken into smaller pieces by development, logging, roads, etc., reducing area, increasing isolation, and increasing edge habitat.

Edge effects

Abiotic and biotic changes near habitat boundaries (e.g., more light/wind/temperature swings and easier access for predators/invasive species), often harming interior specialists.

Law of Tolerance

The principle that a species’ existence, abundance, and distribution depend on its tolerance range (minimum, maximum, optimum) for physical and chemical environmental factors.

Adaptation

A biological mechanism by which organisms adjust to new environments or changes in their current environment.

Behavioral adaptation

An adaptation involving actions/behaviors (e.g., instincts, mating behavior, vocalizations).

Physiological adaptation

An adaptation involving internal functioning (e.g., temperature control methods or how food is digested).

Structural adaptation

An adaptation involving physical features (e.g., body coverings or other morphology).

Short-term adaptation (acclimation)

A temporary response to environmental change that is not inherited, does not change DNA, and is not part of evolutionary processes.

Long-term adaptation (evolutionary adaptation)

An adaptation that involves DNA changes over long time periods due to natural selection and evolutionary processes.

Biome

A large ecological region characterized primarily by climate (temperature and precipitation patterns) and typical plant and animal communities adapted to it.

Salinity

Salt concentration in water; a key factor distinguishing freshwater from marine systems and shaping which organisms can survive.

Photic vs. aphotic zones

Photic zone has enough light for photosynthesis; aphotic zone has too little light for photosynthesis, strongly influencing aquatic productivity.

Estuary

A coastal mixing zone where freshwater meets seawater (brackish and variable); highly productive and often serves as nursery habitat while buffering storms.

Eutrophication

Excess nutrients (often nitrogen and phosphorus) trigger algal blooms; when algae die, decomposition consumes dissolved oxygen, creating low-oxygen conditions and potential fish kills.

Disturbance

An event that disrupts ecosystem structure and changes resources or the physical environment (e.g., wildfire, hurricanes, floods, droughts, volcanic eruptions).

Ecological succession

The gradual, orderly change in community composition over time, often after disturbance, involving colonization, establishment, and local extinction.

Pioneer species

Early successional organisms (often generalists) that colonize first; pioneer plants often reproduce quickly and help set conditions for later species.

Facilitation

A succession interaction where one species modifies the environment to better meet the needs of another species.

r- vs. K-strategists

Early succession often features r-strategists (rapid maturity, short-lived, high population size, generalists); later succession tends to include K-strategists (slow maturity, long-lived, lower population size, often specialists).

Primary succession

Succession beginning where no soil is initially present (e.g., new volcanic rock or land exposed by retreating glaciers); soil forms gradually through pioneer activity.

Secondary succession

Succession after a disturbance removes organisms but leaves soil intact (e.g., after fire, storms, abandoned farmland); typically faster than primary succession.

Resistance

How much an ecosystem changes when disturbed (low change = high resistance).

Resilience

How quickly an ecosystem returns to its prior state after a disturbance (faster recovery = higher resilience).

Invasive species

A non-native species that spreads rapidly and causes harm (ecological, economic, or human health); not all introduced species become invasive.

Enemy release

A mechanism for invasive success where predators, parasites, or pathogens from the invader’s native range are absent in the new range, allowing rapid spread.