Know your flagship, keystone, priority and indicator species

A flagship species is a species selected to act as an ambassador, icon or symbol for a defined habitat, issue, campaign or environmental cause.
By focusing on, and achieving conservation of that species, the status of many other species which share its habitat – or are vulnerable to the same threats - may also be improved.
Flagship species are usually relatively large, and considered to be 'charismatic' in western cultures.
Flagship species may or may not be keystone species and may or may not be good indicators of biological process.

The terms “flagship” and “keystone” have generally consistent definitions across the conservation community, however “priority species” is a WWF term, and is solely for the purposes of planning and simple communication.
For WWF, a “priority species” may be either a flagship or a keystone species and is chosen to represent an ecoregion or region.
A “priority species” is reflective of a key threat across that ecoregion - such that conservation of the species will contribute significantly to a broader threat mitigation outcome. It is often crucial to the economic and/or spiritual wellbeing of peoples within that ecoregion.

A keystone species is a species that plays an essential role in the structure, functioning or productivity of a habitat or ecosystem at a defined level (habitat, soil, seed dispersal, etc).
Disappearance of such species may lead to significant ecosystem change or dysfunction which may have knock on effects on a broader scale. Examples include the elephant's role in maintaining habitat structure, and bats and insects in pollination.
By focussing on keystone species, conservation actions for that species may help to preserve the structure and function of a wide range of habitats which are linked with that species during its life cycle.

An indicator species is a species or group of species chosen as an indicator of, or proxy for, the state of an ecosystem or of a certain process within that ecosystem.
Examples include crayfish as indicators of freshwater quality; corals as indicators of marine processes such as siltation, seawater rise and sea temperature fluctuation; peregrine falcons as an indicator of pesticide loads; or native plants as indicators for the presence and impact of alien species.