Micro-organisms (bacteria, archaeas, fungi, protozoa, algae and viruses) occur in all environments and are interrelated with all other life forms. Micro-organisms are largely responsible for maintaining ecosystem function. They are extremely important in biological control mechanisms and in the transformations of food, energy and chemicals, including the mineralization of nutrients. Despite their importance, our understanding of the role and diversity of micro-organisms is very limited largely because of our inability to culture more than a few per cent of them. Molecular techniques being developed should result in the identification of many new micro-organisms. Notwithstanding our limited knowledge it is essential to evaluate the threats to microbial diversity and to attempt to minimize losses. Micro-organisms and microbial diversity risk being lost due to environmental causes such as pollution (by sewage, oil, organic compounds, pesticides and heavy metals), habitat loss (e.g. pH and salinity changes, and flooding), overexploitation (e.g., in agriculture, forestry and fisheries), species introductions and global changes. Micro-organisms that are particularly vulnerable to extinction, be it on a local or global scale, are those with a limited distribution, in specific habitats or those in habitats subject to widespread stress. Accompanying the loss of microbial diversity is the potential for losses of ecosystem function. A number of measures are needed to conserve microbial diversity. It is necessary to improve identification and measurement in terms of taxonomy, genetics and function. Ex situ collections are a means of securing micro-organisms for use and study by man. Where populations are poorly understood in situ conservation in protected habitats is the only option. Systems of indices and bioindicators need to be developed to monitor changes in microbial communities in such habitats. In order to co-ordinate conservation efforts it is essential to develop a global network of information. This can best be done through national and international policies being developed to conserve biological diversity.
Rarefaction, alpha diversity, and statistics