17 & 18 - SPECIES DIVERSITY & RICHNESS (2)

Community

A group of interacting plants and animals inhabiting a given area.

Ecosystem

The community plus the habitat (non-living environment).

Species Richness

The number of species present in a community.

Species Evenness

The relative abundance of species in a community (also known as equitability).

Vertical Stratification

The layering of different levels within a community or ecosystem that affects light and species composition.

Ecotone

A physical and biological transitional habitat between two ecosystems.

Edge Effects

Distinct ecological conditions and higher species richness in ecotones compared to either bordering ecosystem.

Shannon Diversity Index

A measure that includes both species richness and evenness in a single index.

Species-Time Hypothesis

The hypothesis that communities diversify with age and that temperate regions are less species-rich than tropical regions because they are younger.

Species-Area Hypothesis

The proposal that larger areas contain more species because they can support larger populations and a greater range of habitats.

Species-Energy Hypothesis

The hypothesis that available energy determines species richness and influences productivity.

Natural Enemies Hypothesis

The theory that the action of natural enemies reduces prey density and competition, allowing more species to coexist.

Keystone Species

A species that has a disproportionately large effect on its environment relative to its abundance.

Extinction

The permanent loss of a species from the environment.

Mass Extinction

Widespread and rapid decrease in the biodiversity on Earth, typically resulting in the loss of a large number of species.

Lazarus Taxa

Groups that vanish during mass extinctions and then reappear later.

Invasive Species

Species that are introduced to an area where they are not native and can cause harm to the local ecosystem.

Latitudinal Species Richness Gradient

The phenomenon where the number of species generally increases from polar to tropical regions.

Importance Value

A measure of the relative significance of a species in a community based on its abundance and distribution.