Last update: March 2012
Contact: Thorsten Galert
I. Scientific aspects
Biological diversity, or in short biodiversity (see module Biodiversity), has been defined by the leading Convention on Biological Diversity (CBD) (see module Convention on Biological Diversity (CBD)) as "... the variability among living organisms from all sources including, inter alia, terrestrial, marine and other aquatic ecosystems and the ecological complexes of which they are part; this includes diversity within species, between species and of ecosystems." From a biological perspective, biodiversity thus encompasses more than the mere diversity of species: it also includes varietal diversity (e.g. of agricultural crops), so-called genetic resources (see module Genetic Resources) and the variety of ecological processes.
The term "biodiversity" thus covers biological diversity on three levels:
- the diversity of species (plants, animals, microbes, fungi),
- the variety of genetic information carried by living organisms,
- the variety of ecosystems or habitats.
Biodiversity, as the diversity of all living things, is to be distinguished from geodiversity (see module Geodiversity), although they are interdependent in many ways.
Assessment of biological diversity
Biodiversity is often understood as the number of different species (see module "Species"). In order to measure biodiversity not only in terms of quantity, qualitative aspects of biological diversity in a particular area or region are being included in the form of the following parameters:
species density, frequency distribution of species, rarity, functional diversity and ecosystem services, diversity in terms of species relationships, endangered species, non-indigenous species, and value for human beings.
These parameters (see module Parameters to Assess Biological Diversity) can be used to set priorities for the selection of areas to be protected by conversation measures.
Numbers of species
Estimates on the number of different species (see module Species) range from 5 to 30 million species of animals, plants and micro-organisms . The Millennium Ecosystem Assessment (see module Millennium Ecosystem Assessment), based on all species that have so far been identified, estimates the total number of species (see module Numbers of Species) on Earth at 13.6 million.
Distribution of biological diversity
Biodiversity hotspots are areas that feature a particularly high density of species and ecosystems which are, at the same time, especially endangered. In general, species density increases from the poles to the equator: the largest diversity can be found in the tropics and subtropics, with the tropical rain forests being the richest ecosystems in the world. The deep-sea floor, which remains to a large extent unexplored, is also home to myriad animal species and micro-organisms. Within the marine ecosystems, tropical coral reefs account for the largest diversity of species.
The following map (Fig. 1) (see module Map of the Global Distribution of Species Richness of Vascular Plants) shows the distribution of vascular plant species on Earth. Due to several correlations, it can be assumed that a similar distribution applies to animal species. However, a comparable map of the distribution of fauna has not been created yet.
Ecosystems services and functions
Ecosystem services are services provided by nature or ecosystems, which are useful to human beings (see below: "Economic aspects of biodiversity"). They include, for instance, the provision of freshwater through precipitation and soil filtration, carbon sequestration in vegetable biomass, pollination of plants by insect colonies and climate regulation, but also primary production of plants that are of use to human beings. According to the Millennium Ecosystem Assessment (see module Millennium Ecosystem Assessment), ecosystem services (see module Ecosystem Services) can be broken down into four categories: supporting, provisioning, regulating and cultural services.
The decimation of ecosystems by human activities may have serious impacts on the balance of an ecosystem, which in turn may affect human well-being. For example, satellite pictures have shown that coastal areas in the tropics with intact mangrove forests were much less affected by the 2004 tsunami disaster in Southeast Asia than areas where the forests had been cut down.
As it is difficult to determine accurate numbers of species and to precisely quantify diversity (e.g. of ecosystems), the assessment of biodiversity loss (see module Biodiversity Loss) is a very challenging task. However, it is a fact that biodiversity is threatened at the global level; this is e.g. reflected in the destruction of ecosystems (such as rain forests or coral reefs) or in the threat of extinction of species (such as the panda or the Przewalski's horse). The Millennium Ecosystem Assessment (see module Millennium Ecosystem Assessment) identifies five key drivers of biodiversity loss: 1. habitat change, 2. climate change, 3. invasive alien species (see module Biodiversity Loss Due to Invasive Alien Species), 4. overexploitation of species (e.g. overfishing), and 5. pollution, including overfertilisation. As a response to the increasing loss of biodiversity, the Convention on Biological Diversity (CBD) (see module Convention on Biological Diversity (CBD)) was adopted at the United Nations Conference on Environment and Development (UNCED) in Rio de Janeiro in 1992 . 190 contracting parties, including Germany, had signed up to this international nature conservation agreement by 2007.