Biodiversity (Genetic, Population, Species, Habitat)

Biodiversity is a contemporary term which has several subcategories. In general, the term applies to the relative amount of biological elements existing within a given area. The accompanying image illustrates the complexity and importance of biodiversity at different levels from the genetic to the landscape scale, noting how biodiversity influences and helps define the structural, functional and compositional nature of our environment.

Genetic biodiversity refers to the total number of genotypes available within a given population. For example, whooping cranes were driven to the brink of extinction; at one point the total global population stood at 14 individuals. Today, the population has returned to a more comfortable level. Still, the current population is limited to the genetic material which was contained within those 14 birds, and it will take eons and many, many generations for genetic diversity to build up again. Populations with low genetic biodiversity may be more susceptible to certain diseases given the limited amount of genetic resistance potentially available. A "genetic bottleneck" refers to the loss of valuable survival traits from a population that has shrunk to a low level and then re-expanded.

Population biodiversity refers to the total amount of populations a given species has, worldwide. For instance, Pacific salmon are anadromous, meaning that they are born in freshwater, spend their adult life in the ocean, and then return to the fresh water from whence they originally came to reproduce and then expire. These fish rarely stray to other river systems, migrating in distinct populations from river to sea and then back to the same river. While the total number of pink salmon may be "healthy", given the number of fish surviving in Alaska, population biodiversity may suffer if several rivers in southern British Columbia suddenly experience the loss of the runs of these fish.

Species biodiversity is the total number of species found within a given area. In natural systems, as an example, species biodiversity is considered quite high in the tropical regions of the world, while the number may be quite moderate in temperate zones. In the woodlands of Pennsylvania, for instance, it is not uncommon to count on one hand the total number of tree species within an acre of land. In the tropics, the number of tree species found within an acre of land may be over 250.

Habitat or ecological biodiversity refers to the number of different habitats or ecotypes found within a given region. In the Pacific Northwest, industrial forestry has reduced entire landscapes to monocultural tree plantations with a simple, homogeneous forest structure. On the other hand, in the region's natural systems there exists a much higher level of ecological diversity, given the various natural processes (e.g., wind, fire, flooding, disease, succession, competition) which create a mosaic of habitat types.