Species Diversity, Populations & Communities

Species Diversity

The number and variety of life forms present in a biological community.

Species

A group of living organisms consisting of similar individuals capable of interbreeding and producing fertile offspring.

Diversity

The state of being diverse; the variability of species within a particular habitat or ecosystem.

Species Richness

A measure of the number of different species within a given area.

Species Evenness

A measure of the relative abundance of the different species within a given area.

Ecological Niche

The role, function, or “job” of a species in its ecosystem (its "profession").

Ecological Habitat

The physical place or environment where a species lives (its "address").

Generalist Species

Species with broad niches that can tolerate a wide range of environmental conditions (e.g., cockroaches, humans).

Specialist Species

Species with narrow niches that thrive only in specific habitats (e.g., giant panda, koala).

Keystone Species

A species that has a disproportionately large impact on its ecosystem relative to its abundance (e.g., sea otters, wolves).

Indicator Species

Species that serve as biological monitors of environmental health (e.g., amphibians for pollution, lichens for air quality).

Foundation Species

Species that play a major role in shaping ecosystems by creating or enhancing habitats (e.g., coral, mangroves).

Invasive Species

Non-native species introduced to a new habitat that can outcompete natives and disrupt the ecosystem (e.g., kudzu vine, zebra mussels).

Native Species

Species that naturally occur in a specific region and are part of the natural ecological balance (e.g., Philippine eagle).

Population

All members of the same species living in the same area.

Community

Populations of all different organisms that live and interact in the same area.

Uniform Distribution

A population dispersion pattern where individuals are evenly spaced due to acute competition for resources.

Random Distribution

A rare dispersion pattern where individuals are spread unpredictably, found in uniform environments.

Clump Distribution

The most common dispersion pattern where individuals are found grouped together in patches.

Population Density

The number of individuals in a population per unit area (calculated as # of individuals ÷ unit of space).

Mutualism

A symbiotic relationship that is beneficial to both species involved.

Commensalism

A relationship that is beneficial to one species and neutral to the other.

Parasitism

A relationship where one organism (parasite) benefits by deriving nutrients from a host, which is harmed.

Predation

An interaction where a predator kills and eats a prey organism.

Competition

An interaction that occurs when organisms use the same limited resources, harming both parties.

Neutralism

An interaction where two species occupy the same niche but have no effect on each other.

Ecological Succession

The natural, gradual changes in the types of species that live in an area; the gradual replacement of one plant community by another.

Primary Succession

Succession that begins in an area without soil and where no community has lived before (e.g., on bare rock).

Secondary Succession

The process of re-stabilization that follows a disturbance in an area where life has formed an ecosystem and soil remains.

Pioneer Species

The first species to colonize a barren area in primary succession (e.g., lichens).

Climax Community

A mature, stable community that is the final stage of ecological succession.

Extinction

The reduction of a species to such low abundance that it no longer interacts significantly with other species.

Causes of Extinction

Taking for profit, hunting/trapping, overharvesting, introduced species, destruction of habitat, and pollution.

Invasive Species

Non-native species that infest an area, reduce biodiversity, and degrade ecosystem health.

Forest Pests & Disease

Exotic pests and pathogens that can have a profound effect on forests (e.g., Dutch elm disease).