Final answer:
Species most vulnerable to extinction are rare due to small geographic ranges or low population densities. Conservation efforts exist but are challenged by habitat loss, pollution, and overfishing, posing significant risks to specific taxa.
Step-by-step explanation:
The species most vulnerable to extinction are those that are relatively rare, either because they have very small geographic ranges or because they exist at low population densities over somewhat larger areas. These species with small ranges are often highly geographically concentrated, and these areas of concentration are not necessarily in regions with the greatest number of species. This pattern applies not only to animals but also to plants and many marine groups.
Furthermore, within groups of organisms, there is a tendency to have more species classified as critically endangered than those considered vulnerable. For example, a greater percentage of bird species are critically endangered compared to mollusk species.
Many vertebrate species are currently facing the threat of extinction, primarily due to habitat loss and pollution. Conservation efforts, such as the Biodiversity Action Plan, have been initiated globally to protect these at-risk species. Despite such efforts, species with slow-growing populations, like whales and certain shark and grouper species, are at significant risk due to factors like hunting and overfishing.