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Biodiversity: what is it?
Gwen Raitt
Biodiversity and
Conservation
Biology
Department
Available at http://planet.uwc.ac.za/nisl/Biodiversity/
BCB 705:
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:
Section

Genetic diversity
of DNA

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
How do we define ‘biodiversity’?
Genetic 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:

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Nucleotides,
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Alleles,
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Genes,

Chromosomes.
Paired
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.
How do we define ‘biodiversity’?
Species or organismal diversity (1)

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).

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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’?
Species or organismal diversity (2)

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’?
Ecosystem 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 biodiversity
Table 1.1: Elements of biodiversity slightly modified from Gaston
and Spicer (1998)
Ecological
Diversity
Biomes
Bioregions
Landscapes
Ecosystems
Habitats
Niches
Populations
Genetic
Diversity
Populations
Individuals
Chromosomes
Genes
Alleles
Nucleotides
Organismal
Diversity
Kingdoms
Phyla
Families
Genera
Species
Subspecies
Populations
Individuals
Biodiversity in different contexts

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.
The social/political context of biodiversity

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. Biodiversity is perceived as a value or as having a value. This link to
conservation raises some issues:


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‘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.
How do we quantify biodiversity?

There cannot be a single allencompassing 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. Measuring Clams

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.
Perceptions of biodiversity 1

Biodiversity may be viewed in the context of evolutionary time.

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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 2

Biodiversity may be considered
globally and collectively.

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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
Some examples of measures of aspects of
biodiversity

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 .

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Indices.

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Usually taxon related and/or limited.
Shannon-Wiener Index
Biomass
Chapter 1 Biodiversity: what is it?
Chapter
The evolution2of biodiversity
Link
to2 chapter
I hope that you found chapter 1 informative and that you will
enjoy chapter 2.