Biodiversity, Ecosystem Services, and Population Dynamics: Key Concepts and Theories

Biodiversity

The variety of life in an ecosystem, measured at three levels: genetic, species, and ecosystem diversity.

Genetic diversity

The variety of genes within a population of a single species; increases resilience to disease and environmental change.

Species diversity

The number of different species in an ecosystem (richness) and the relative abundance of each species (evenness).

Ecosystem diversity

The variety of habitats, communities, and ecological processes within a region.

Species richness

The total number of different species present in an ecosystem.

Species evenness

How equally abundant the different species are in an ecosystem.

Bottleneck event

A sudden environmental disturbance that drastically reduces population size, leading to a loss of genetic diversity.

Inbreeding depression

Reduced biological fitness in a population due to breeding between closely related individuals; common in small populations (e.g., Florida panther).

Ecosystem resilience

The ability of an ecosystem to recover its structure and function after a disturbance; increases with higher biodiversity.

Provisioning services

Ecosystem services that provide tangible products: food, water, timber, fiber, medicine (e.g., fish, lumber, berries).

Regulating services

Ecosystem services that moderate natural processes: climate regulation, flood control, water purification, pollination (e.g., trees storing CO₂).

Supporting services

Fundamental ecosystem processes that support other services: nutrient cycling, soil formation, primary production (e.g., wetlands filtering water).

Cultural services

Non-material benefits: recreation, aesthetic enjoyment, spiritual enrichment, educational value (e.g., national park tourism).

Island biogeography theory

Predicts species richness on islands based on island size and distance from the mainland.

Larger islands support more species because...

They have greater habitat diversity, more niches, larger populations (lower extinction), and higher genetic diversity.

Islands closer to the mainland support more species because...

Easier colonization (higher immigration rates) and more frequent gene flow.

Habitat island

A patch of natural habitat surrounded by human-altered landscape (e.g., a national park surrounded by farmland).

Adaptive radiation

Rapid evolution of a single ancestor into multiple species to fill different ecological niches (e.g., Galápagos finches).

Ecological range of tolerance

The range of an environmental variable (e.g., temperature, pH) within which a species can survive.

Optimal range (tolerance)

The subrange where organisms thrive, grow, and reproduce most successfully.

Zone of physiological stress

Range where organisms survive but experience reduced growth, reproduction, or activity.

Zone of intolerance

Range where environmental conditions cause death (e.g., thermal shock, suffocation).

Natural disruptions

Events like hurricanes, wildfires, droughts, or volcanic eruptions that alter ecosystem structure/function.

Periodic disruptions

Occur at regular intervals (e.g., seasonal floods).

Episodic disruptions

Occur irregularly (e.g., hurricanes, wildfires).

Random disruptions

Unpredictable events (e.g., asteroid impacts, earthquakes).

Adaptation

A heritable trait that increases an organism's fitness (ability to survive and reproduce) in a specific environment.

Natural selection

The process by which individuals with advantageous adaptations survive and pass those traits to offspring, leading to evolutionary change.

Selective pressure

An environmental factor that drives natural selection (e.g., predation, drought, temperature).

Pace of evolution

Faster in species with short lifespans and high reproduction (e.g., bacteria); slower in long-lived species (e.g., elephants).

Ecological succession

The predictable sequence of changes in species composition in a community over time.

Primary succession

Succession on bare rock with no soil (e.g., after volcanic eruption or glacial retreat); starts with lichens/mosses.

Secondary succession

Succession in areas with existing soil but after a disturbance (e.g., fire, logging); starts with grasses/weeds.

Pioneer species

First colonizers in succession; fast-growing, sun-tolerant, wind-dispersed (e.g., lichens, grasses, aspen).

Climax community

Stable, mature community at the end of succession; dominated by slow-growing, shade-tolerant species (e.g., oaks, maples).

Exponential growth

Population growth under unlimited resources; J-shaped curve; formula: p(t)=p0e^rt.

Logistic growth

Population growth limited by carrying capacity; S-shaped curve; levels off at K.

Carrying capacity (K)

Maximum population size an environment can sustain indefinitely.

Intrinsic rate of increase (r)

Per capita growth rate: r=b−d (birth rate minus death rate).

r-selected species

High r, short lifespan, many offspring, little parental care, opportunistic (e.g., mosquitoes, weeds).

K-selected species

Low r, long lifespan, few offspring, high parental care, competitive near K (e.g., elephants, humans, whales).

Can population models produce negative values?

No—both exponential and logistic models yield positive values only if p0>0, reflecting biological reality.

Why is logistic growth more realistic?

It incorporates carrying capacity (K), reflecting real-world limits like food, space, and disease.