Available at http://planet.uwc.ac.za/nisl/Biodiversity/

Biodiversity: what is it?Biodiversity: what is it?Gwen Raitt

Biodiversity and Conservation

Biology Department

BCB 705:Biodiversity

How do we define ‘biodiversity’?How do we define ‘biodiversity’?

Biodiversity = biotic diversity = biological diversity

Biodiversity may be defined as the number, variety and variability of living organisms at all levels within a region. Three levels of diversity are highlighted:

Genetic diversity

Species or organismal diversity

Ecosystem or ecological diversity – including functional variety and the variety of interactions.

Some definitions specify landscape diversity as well.

Biodiversity = Speciation – Extinction

Section of DNA

How do we define ‘biodiversity’?How do we define ‘biodiversity’?Genetic diversityGenetic diversity

Genetic diversity = “heritable variation within and between populations of organisms” (p. xiii Groombridge 1992).

Within an organism, the following levels of genetic diversity may be recognised:

Nucleotides,

Alleles,

Genes,

Chromosomes.

The primary source of genetic diversity is mutation. Mutation operates at two levels:

Chemical alteration of DNA molecule changing the information;

During replication and/or recombination.

Paired Chromosomes

The individual organism is “the basic unit of the living world” (p. 14 Leveque and Mounolou 2001) hence organismal diversity.

“The species is the basic unit of classification” (p. 9 Heywood and Baste 1995).

The definition of a species is not clear (especially for microorganisms).

Problem - sibling species.

This lack of clarity suggests that organismal diversity is more viable as a level of biodiversity than species diversity.

How do we define ‘biodiversity’?How do we define ‘biodiversity’?Species or organismal diversity (1)Species or organismal diversity (1)

Biodiversity is usually measured in terms of species.

Species diversity ≠ species richness.

Species diversity ≠ taxonomic diversity.

Thus if all the conditions of the species are the same, 2 species belonging to the same genus have a lower taxonomic diversity than 2 species belonging to different families while having the same amount of species diversity.

How do we define ‘biodiversity’?How do we define ‘biodiversity’?Species or organismal diversity (2)Species or organismal diversity (2)

How do we define ‘biodiversity’?How do we define ‘biodiversity’?Ecosystem or ecological diversityEcosystem or ecological diversity

An ecosystem or ecological system is defined as a functioning unit of interacting organisms (plant, animal and microbe = biocoenosis) and their interactions with their physical and chemical environment (biotope) often linked to an area.

Ecosystem diversity is defined as the variety of ecosystems within a bigger landscape and their variability over time.

Ecological diversity is variously regarded as the variety of ecosystems in an area and their interactions or intra-ecosystem variety.

Elements of biodiversityElements of biodiversity

Ecological Diversity

Genetic Diversity

Organismal Diversity

Biomes Kingdoms Bioregions Phyla Landscapes Families Ecosystems Genera Habitats Species Niches Subspecies Populations Populations Populations Individuals Individuals Chromosomes Genes Alleles Nucleotides

Table 1.1: Elements of biodiversity slightly modified from Gaston and Spicer (1998)

The definition given defines biodiversity as a scientific concept.

Biodiversity may also be considered as a social/ political construct.

Biodiversity in the context of measurement and quantification.

Biodiversity in different contextsBiodiversity in different contexts

The term is used in science, the media and parts of the public arena.

Use is linked to the loss of the natural environment and its contents.

In some instances, the word ‘biodiversity’ is regarded as referring not only to the variety of life but also to the value of this life. Bio-diversity is perceived as a value or as having a value. This link to conservation raises some issues:

‘Biodiversity crisis’;

High biodiversity as measured by species richness ≠ high conservation priority;

How does one judge the success of conservation goals and actions?

Biodiversity may be viewed as a source of useful products.

The social/political context of biodiversityThe social/political context of biodiversity

There cannot be a single all-encompassing measure of biodiversity but aspects of biodiversity may be quantified.

The choice of what aspect of biodiversity to measure depends on the purpose the measurement will be used for.

If the chosen aspect of biodiversity is not directly quantifiable, measuring something correlated to the aspect of interest is an option. This is termed a surrogate measure.

Several different ways of looking at biodiversity exist that may be quantified.

Measuring Clams

How do we quantify biodiversity?How do we quantify biodiversity?

Biodiversity may be viewed in the context of evolutionary time.

One could look at the radiation of species or other taxa from a single ancestor.

One could consider the diversity within a selected taxon over time.

One could consider the total number of species that have ever existed.

Biodiversity may be regarded “as a characteristic of natural communities” (p. 7 Lovejoy 1997).

Perceptions of biodiversity 1Perceptions of biodiversity 1

Biodiversity may be considered globally and collectively.

Approximately 1.4—1.8 million species have been described.

How many species are there in total at present?

How much we know about biodiversity depends on location and taxon.

One may look at where biodiversity is concentrated.

The numbers of species tend to increase as one moves toward the equator. Amazon Rainforest

Perceptions of biodiversity 2Perceptions of biodiversity 2

Most measures are concerned with either the genetic or the species level.

Species richness (the number of species) at different scales is frequently used as a measure of biodiversity .

Usually taxon related and/or limited.

Indices.

Shannon-Wiener Index

Biomass

Some examples of measures of aspects of Some examples of measures of aspects of biodiversitybiodiversity

Link to chapter 2Chapter 1 Chapter 1 Biodiversity: what is it?Biodiversity: what is it?

Chapter 2 Chapter 2 The evolution of biodiversityThe evolution of biodiversity

I hope that you found chapter 1 informative and that you will enjoy chapter 2.