Notes towards Biodiversity Chapter 1
Introductory/Title Slide (1)
Welcome to the Biodiversity Course of the National Information Society Learnership
Ecological Informatics. We will start this course by looking at what ‘biodiversity’ is.
My name is Gwen Raitt. I will be presenting this chapter.
I hope you enjoy the course. Please let me know about any problems or issues that you
have with this course. The email address is available from the side bar.
How do we define ‘biodiversity’?
Biodiversity is a synonym for biotic or biological diversity. Biodiversity may be defined
as the number, variety and variability of living organisms at all levels within a region
(Groombridge 1992, Dobson 1996, Yeld 1997, Anderson 1999, Wikipedia Contributors
2006a). Three levels of diversity are highlighted: genetic diversity, species or
organismal diversity and ecosystem or ecological diversity – including functional variety
and the variety of interactions (Yeld 1997, Gaston & Spicer 1998, Anderson 1999,
Wikipedia Contributors 2006a). Some definitions specify landscape diversity as well
(see Gaston 1996a and Gaston & Spicer 1998). Biodiversity equals the difference
between speciation and extinction (Miller 2002). Speciation refers to the evolutionary
development of new species while extinction refers to the loss of existing species
(Wikipedia Contributors 2006c, g). This definition considers biodiversity from the
perspective of organismal diversity.
How do we define ‘biodiversity’? Genetic diversity
Genetic diversity may be described as the heritable variation within and between
populations of organisms (Groombridge 1992). Within an organism, the following levels
of genetic diversity may be recognized: nucleotides (the building blocks of DNA and
RNA), alleles (variations within a gene), genes (codes for other molecules) and
chromosomes (macromolecule containing genes in eukaryotic cells (Groombridge 1992,
Wikipedia Contributors 2006b)) (Groombridge 1992, Gaston & Spicer 1998).
The primary source of genetic diversity is mutation (Lévêque and Mounolou 2001).
Mutation operates at two levels. The first is chemical alteration of the DNA molecule
changing the information. Cells have repair systems that catch most of these changes and
correct them (Groombridge 1992, Lévêque and Mounolou 2001, Wikipedia Contributors
2006f). The second level is during replication and/or recombination during mitosis or
meiosis (Groombridge 1992, Lévêque and Mounolou 2001). Recombination results in
new combinations of genes (Groombridge 1992) and is thus a secondary source of
genetic diversity.
How do we define ‘biodiversity’? Species or organismal diversity (1)
The individual organism is “the basic unit of the living world” (p14 Lévêque &
Mounolou 2001) hence organismal diversity. “The species is the basic unit of
classification” (p9 Heywood & Baste 1995). The definition of a species is not clear
(particularly with regard to microorganisms (Pietra 2002)) and is therefore debated
(Groombridge 1992, Bisby 1995, Heywood & Baste 1995, Wikipedia Contributors
2006h). Further problems recognizing species are presented by sibling species (Pietra
2002). Sibling species cannot be distinguished morphologically (Clark & Charest 1987)
but show significant differences at a molecular level (Stork 1997). This lack of clarity
suggests that organismal diversity is more viable as a level of biodiversity than species
diversity.
The pictures show South African examples of species. The beetle is a toktokkie (Genus
Psammodes), the spider is a horned baboon spider (Family Theraphosidae) and the plant
is blombos, Metalasia muricata.
How do we define ‘biodiversity’? Species or organismal diversity (2)
Biodiversity is usually measured in terms of species (Groombridge 1992).
Species diversity ≠ species richness. Species diversity may be defined as the variety
(number) of species and their relative abundance and distribution in a region (World
Resources Institute 1989) where species richness only considers the variety of species in
a region (Biosociety 2006).
Species diversity ≠ taxonomic diversity. Taxonomic or taxic (Bisby 1995) diversity
refers to the diversity of taxa higher in the hierarchy than the species (Groombridge 1992,
Pietra 2002). Thus if all the conditions of the species are the same, two species belonging
to the same genus have a lower taxonomic diversity than two species belonging to
different families while having the same amount of species diversity.
The pictures show some more South African examples of species. The frog is known as
the clicking stream frog (Strongylopus grayii), the bird is a black eagle (Aquila
verreauxii) and the antelope is a klipspringer (Oreotragus oreotragus).
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) (Wikipedia Contributors 2006e) often
linked to an area (Mooney et al. 1995).
Ecosystem diversity is defined as the variety of ecosystems within a bigger landscape and
their variability over time (Lévêque & Mounolou 2001, FAO 2004).
Ecological diversity is regarded variously as the variety of ecosystems in an area and
their interactions (Lévêque & Mounolou 2001, LEAF Program 2006, Draper 2002) or
intra-ecosystem variety (SustainableAg.net 2001). The first definition is better.
Elements of biodiversity
This table shows the elements of biodiversity linked to the highlighted categories of
biodiversity.
Biodiversity in different contexts (Gaston 1996a)
The definition given earlier defines biodiversity as a scientific concept.
Biodiversity may be considered as a social/political construct or in the context of
measurement and quantification (Gaston 1996a).
The Social/Political Context of Biodiversity
The term biodiversity is used in science, the media and parts of the public arena (Gaston
1996a). Use of the term is linked to the loss of the natural environment and its contents
(Gaston 1996a). 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 (Gaston 1996a). This link to conservation raises some issues:
‘Biodiversity crisis’ The present loss of biodiversity is considered a crisis or extinction
crisis (Groombridge 1992, Gaston & Spicer 1998). Some say that we are facing or in the
midst of the sixth mass extinction caused by humanity (Groombridge 1992, Eldredge
2001, Miller 2002, Wikipedia Contributors 2006d). High biodiversity as measured by
species richness ≠ high conservation priority. Other considerations such as level of
threat, origins of species (a high biodiversity may result from the introduction of alien
species) and contribution to a broad conservation goal need to be taken into account when
determining conservation priority (Gaston 1996a). How does one judge the success of
conservation goals and actions? What aspects of biodiversity should conservation
concentrate on? What is the purpose of conservation (Gaston 1996a)?
Biodiversity may be viewed as a source of useful products. This view has been useful in
promoting conservation of biodiversity (Lévêque & Mounolou 2001, Pietra 2002) and is
considered as part of Chapter 2.
How do we quantify biodiversity?
There cannot be one all-encompassing measure of biodiversity but aspects of biodiversity
may be quantified (Gaston 1996a, Gaston & Spicer 1998, Wikipedia Contributors 2006a).
The complexity of the concept of biodiversity is irreducible (Gaston 1996a). The choice
of what aspect of biodiversity to measure depends on the purpose the measurement will
be used for (Gaston 1996a, Lévêque & Mounolou 2001, Wikipedia Contributors 2006a).
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
(Gaston & Spicer 1998). An example of a surrogate measure is the use of fossil family
diversity as a surrogate for fossil species diversity. Species richness may be a surrogate
measure (Gaston & Spicer 1998). 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 (Lovejoy 1997). One
could look at the radiation of species or other taxa from a single ancestor (Lovejoy 1997).
One could consider the diversity within a selected taxon over time (Anderson 1999). One
could consider the total number of species that have ever existed. It is estimated that
90—99.9% of species that have ever existed are extinct (Gaston & Spicer 1998, Miller
2002). Biodiversity may be regarded “as a characteristic of natural communities” (p7
Lovejoy 1997). This usually looks at categories of species not the total biodiversity, e.g.
the number of plant species in a community.
Perceptions of biodiversity 2
Biodiversity may be considered globally and collectively (Lovejoy 1997).
Approximately 1.4—1.8 million species have been described (Dobson 1996, Lovejoy
1997). How many species are there in total at present? Estimates of the total number of
species on this planet go up to 111,5 million species (Gaston & Spicer 1998). Working
estimates range from 12.5—14 million species (Groombridge 1992, Bisby 1995). How
much we know about biodiversity depends on location and taxon. For example, more is
known about the insect fauna in Britain than in Australia. In Australia, vertebrates are
better known than insects (Lovejoy 1997). One may look at where biodiversity is
concentrated – the ‘hotspots’ (Lovejoy 1997). The numbers of species tend to increase as
one moves toward the equator (Lovejoy 1997).
Some examples of measures of parts of biodiversity
Most measures are concerned with either the genetic or species level (Gaston 1996a).
Species richness (the number of species) in an area is a frequently used measure of
biodiversity (Gaston 1996b, Lévêque & Mounolou 2001). This is usually taxon related
and/or limited, e.g. the number of plant and/or animal species without considering
microbes. Indices may be based on models of diversity. The Shannon-Wiener Index is a
commonly used diversity index (Wikipedia Contributors 2006a). Shannon-Wiener Index
= Shannon Index = Shannon-Weaver Index. The Shannon Index is a non-parametric
index of species diversity used to compare the biodiversity of different areas (Southwood
& Henderson 2000, Wikipedia Contributors 2006a. Biomass measures productivity. In
plants, it may be limited to above ground biomass (Chapman 1976).
Last slide
I hope that you found chapter 1 informative and that you will enjoy chapter 2.