Genetic diversity is an indicator of the degree of variation in the genetic make-up of individuals within a species. The basis of genetic differences is contained in the DNA in the chromosomes of an organism. The chromosomes are responsible for passing on the traits of the parents to the offspring during reproduction. Often, but not always, genetic differences can be seen in the features of the individual animal or plant. One of the best examples is the domestic dog. The great variety of breeds are all part of the same species, all derived from the wild wolf. Thousands of years of breeding by selecting particular traits has resulted in this amazing display of genetic diversity. In humans, we recognize the expression of genetic diversity as differences such as those among races, facial features, and the colour of eyes and hair. Underlying many of these differences are specific differences in the genetic material in the DNA of each person. Genetic diversity is higher in multi-racial communities than in communities of a single race.
Genetic diversity in humans, as in all species, is either reduced, maintained, or increased depending on patterns of breeding over time. Inbreeding among members of the same family tree causes a reduction in genetic diversity. Outbreeding with new families and races causes an increase in genetic diversity.
Genetic diversity is not something you can measure by walking into a forest with a ruler and clipboard in hand. While the concept is based on theoretically measurable differences in DNA, in practice it is impossible to determine the full range of these differences for every species in a particular ecosystem. It is usually necessary to deal in generalities and comparative measures rather than actual measures of specific genetic differences. The factors affecting genetic diversity within a given species are themselves very diverse, ranging from the manner in which plant seeds are fertilized and dispersed to the social behaviour of birds and mammals.
Species diversity is the type of biological diversity that most people would associate with the term. It is simply a count of the number of distinct species in a given ecosystem. This is fairly easy for the larger species of plants and animals but becomes a more difficult and expensive task if we want to count all the smaller and microscopic forms of insects, fungi, and bacteria that live in the trees and the soil. While the species count can give us a lot of useful information it doesn’t tell us about the relative abundance of each species. That requires a count of the population of each species, an even more difficult task than cataloguing the number of species. Even if we knew all the species and their populations, meaningful comparisons within and among different ecosystems are not always easy to make.
Landscape diversity, also known as ecosystem diversity, refers to the variety of distinct ecosystems within a given landscape or geographic area. Some landscapes are very uniform such as the vast stretches of lodgepole pine forest growing back after wildfire. Other landscapes are more varied with a mosaic of different plant associations in close proximity. A more diverse landscape usually supports a higher species diversity across that landscape. Landscape diversity is generally measured in comparative terms rather than numerically. There is no logical way to give an exact measure of the number of distinct ecosystems in a given landscape, or for that matter even to define “landscape” or “ecosystem” with precision.