Biodiversity
Short for biological diversity, biodiversity is a measure of the variety of life. It can be split up into three different levels of biodiversity: genetic diversity, species diversity, and ecosystem diversity.
Genetic diversity is a measure of the variation within a species. The more differences there are in the genes of a particular population, the greater the genetic diversity.
Species diversity is a measure of the variation of species in a specific area. There are two components that make up species diversity: species evenness and species richness. Species richness is a measure of how many different species there are in a region. Species evenness is a measure of the relative abundance of each species in comparison to one another.
Ecosystem diversity is a measure of the variation of distinct ecosystems/habitats found in a particular area.
Biodiversity is extremely important for the health of an ecosystem; the higher the biodiversity, the greater the ecosystem health.
The health is better because more diverse ecosystems have greater ecosystem resilience, which is the ability of an ecosystem to recover from a disturbance. Population bottlenecks, which greatly reduce the genetic diversity of a population, put the population at significant risk of future damage.
Calculating Species Diversity
It's possible to quantify the species diversity of a community by using the equation to the right; this makes it easy to compare two communities in order to determine which has the greater diversity. The calculated value should be between 0 and 1. The closer it is to 0, the lower the species diversity. The closer it is to 1, the higher the species diversity.
n = total number of organisms of a particular species
N = total number of organisms of all species
Some species are more important than others.
There are a wide range of species that exist within a community, but they do not all have the same impact on the ecosystem. Keystone species have strong effects on communities, effects that are disproportionate based on their number. Like in architecture, if a keystone is removed from an ecosystem, the ecosystem can often collapse. An example of this is otters in kelp forests. Otters eat sea urchins, which eat kelp, which forms the foundation of the ecosystem. When otters are absent, the sea urchins are no longer kept in check and can destroy the ecosystem by decimating the kelp population.
How does this affect islands?
Island biogeography looks at the biodiversity and community ecology on islands. Islands tend to follow very particular trends: the larger an island is, or the closer it is to the mainland, the greater the biodiversity. This is because species tend to colonize islands by coming from other areas. More species are able to swim/fly/travel to an island that is closer when compared to one that is farther away. In addition, specialists are far more common on islands than generalists are, due to the evolutionary pressure from the limited resources on islands.