Notes towards Biodiversity Chapter 1
Introductory/Title slide (1)
Welcome to the Biodiversity Course of the National Information Society Learnership in
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 that you enjoy the
course.
Please let the course convener know about any problems or issues that you have with this
course.
The pictures show Namaqua rock mouse (Aethomys namaquensis) pollination of a Protea
species and the king protea (Protea cynaroides).
How do we define ‘biodiversity’?
Biodiversity is a synonym for biotic or biological diversity. It 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 and Spicer 1998, Anderson 1999,
Wikipedia Contributors 2006a). Some definitions specify landscape diversity as well
(see Gaston 1996a and Gaston and 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 2006b, c). This definition
considers biodiversity from the perspective of organismal diversity.
Additional Notes
Extract from Wikipedia (2006b) ~ http://en.wikipedia.org/wiki/. “Modes of speciation.
Allopatric (geographic)
During allopatric speciation, a population splits into two geographically isolated
allopatric populations (for example, by habitat fragmentation or emigration). The isolated
populations then undergo genotypic and/or phenotypic divergence as they (a) become
subjected to dissimilar selective pressures or (b) they independently undergo genetic drift.
When the populations come back into contact, they have evolved such that they are
reproductively isolated and are no longer capable of exchanging genes.
Parapatric (somewhat Geographic)
In parapatric speciation, the zones of two diverging populations are separate but do
overlap. There is only partial separation afforded by geography, so individuals of each
species may come in contact or cross the barrier from time to time, but reduced fitness of
the heterozygote leads to selection for behaviours or mechanisms which prevent breeding
between the two species.
Sympatric (non Geographic)
In sympatric speciation, species diverge while inhabiting the same place (sympatric).
Examples of sympatric speciation are found in insects which become dependent on
different host plants in the same area. Increased ploidy levels, i.e. polyploidy, is a
mechanism often attributed to causing some speciation events in sympatry. It should be
noted that not all polyploids are completely reproductively isolated from their parental
plants, so an increase in chromosome number may not result in the complete cessation of
gene flow between the incipient polyploids and their parental diploids.”
Extract from Wikipedia (2006c) ~ http://en.wikipedia.org/wiki/. “In biology and
ecology, extinction is the ceasing of existence of a species or group of taxa. The moment
of extinction is generally considered to be the death of the last individual of that species.
Extinction is usually a natural phenomenon; it is estimated that more than 99.9% of all
species that have ever lived are now extinct. Through evolution, new species are created
by speciation — where new organisms arise and thrive when they are able to find and
exploit an ecological niche — and species become extinct when they are no longer able
to survive in changing conditions or against superior competition. A typical species
becomes extinct within 10 million years of its first appearance, although some species
survive virtually unchanged for hundreds of millions of years.”
How do we define ‘biodiversity’? Genetic diversity
Genetic diversity may be described as the “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 (the building blocks
of DNA and RNA), alleles (variations within a gene), genes (codes for other molecules)
and chromosomes (macromolecules containing genes in eukaryotic cells (Groombridge
1992, Wikipedia Contributors 2006d)) (Groombridge 1992, Gaston and Spicer 1998).
The primary source of genetic diversity is mutation (Lévêque and Mounolou 2001).
Mutation operates at two levels. The first is the 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
2006e). The second level is mistakes made during replication and/or recombination in
the processes of 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.
Additional Notes
Extract from Wikipedia (2006e) ~ http://en.wikipedia.org/wiki/. “In biology, mutations
are changes to the genetic material (usually DNA or RNA). Mutations can be caused by
copying errors in the genetic material during cell division and by exposure to radiation,
chemicals, or viruses, or can occur deliberately under cellular control during processes
such as meiosis or hypermutation. In multicellular organisms, mutations can be
subdivided into germline mutations, which can be passed on to progeny and somatic
mutations, which cannot be transmitted to progeny. Mutations, when accidental, often
lead to the malfunction or death of a cell and can cause cancer. Mutations are considered
the driving force of evolution, where less favorable (or deleterious) mutations are
removed from the gene pool by natural selection, while more favorable (beneficial or
advantageous) ones tend to accumulate. Neutral mutations are defined as mutations
whose effects do not influence the fitness of either the species or the individuals who
make up the species. These can accumulate over time. Contrary to tales of science fiction,
the overwhelming majority of mutations have no significant effect, since DNA repair is
able to revert most changes before they become permanent mutations, and many
organisms have mechanisms for eliminating otherwise permanently mutated somatic
cells.”
How do we define ‘biodiversity’? Species or organismal diversity (1)
The individual organism is “the basic unit of the living world” (p. 14 Lévêque 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 (particularly with regard to microorganisms) and is
therefore debated (Groombridge 1992, Bisby 1995, Heywood and Baste 1995, Pietra
2002, Wikipedia Contributors 2006f). Further problems recognising species are
presented by sibling (or cryptic) species (Pietra 2002). Sibling species cannot be
distinguished morphologically (Clark and Charest 1987) but show significant differences
at the 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.
Additional Notes
Extract from the glossary of Environment Canada (2006) ~
http://www.ec.gc.ca/water/en/info/gloss/e_gloss.htm. “Organism - A living thing.”
Extract from Wikipedia (2006f) ~ http://en.wikipedia.org/wiki/. Definitions of species
“Typological species A group of organisms in which individuals are members of the
species if they sufficiently conform to certain fixed properties. The clusters of variations
or phenotypes within specimens (ie: longer and shorter tails) would differentiate the
species. This method was used as a ‘classical’ method of determining species, such as
with Linnaeus early in evolutionary theory. However, we now know that different
phenotypes do not always constitute different species (e.g.: a 4-winged Drosophila born
to a 2-winged mother is not a different species). Species named in this manner are called
morphospecies.
Morphological species A population or group of populations that differs morphologically
from other populations. For example, we can distinguish between a chicken and a duck
because they have different shaped bills and the duck has webbed feet. Species have been
defined in this way since well before the beginning of recorded history. This species
concept is much criticised because more recent genetic data reveal that genetically
distinct populations may look very similar and, contrarily, large morphological
differences sometimes exist between very closely-related populations. Nonetheless, most
species known have been described solely from morphology.
Biological / Isolation species A set of actually or potentially interbreeding populations.
This is generally the most useful formulation for scientists working with living examples
of the higher taxa like mammals, fish, and birds, but meaningless for organisms that do
not reproduce sexually. It does not distinguish between the theoretical possibility of
interbreeding and the actual likelihood of gene flow between populations and is thus
impractical in instances of allopatric (geographically isolated) populations. The results of
breeding experiments done in artificial conditions may or may not reflect what would
happen if the same organisms encountered each other in the wild, making it difficult to
gauge whether or not the results of such experiments are meaningful in reference to
natural populations.
Mate-recognition species A group of organisms that are known to recognise one another
as potential mates. Like the isolation species concept above, it applies only to organisms
that reproduce sexually. Unlike the isolation species concept, it focuses specifically on
pre-mating reproductive isolation.
Phylogenetic / Evolutionary / Darwinian species A group of organisms that shares an
ancestor; a lineage that maintains its integrity with respect to other lineages through both
time and space. At some point in the progress of such a group, members may diverge
from one another: when such a divergence becomes sufficiently clear, the two
populations are regarded as separate species.
Microspecies Species that reproduce without meiosis or mitosis so that each generation
is genetically identical to the previous generation. See also apomixis.”
Extract from Glossary for Biological Systematics (1987),
http://www.csupomona.edu/~jcclark/classes/bio406/glossary.html. “Sibling species species that are not morphologically distinguishable.”
Sibling species show significant differences at a molecular level (Stork 1997).
How do we define ‘biodiversity’? Species or organismal diversity (2)
Biodiversity is usually measured in terms of species (Groombridge 1992).
Species diversity does not equal species richness. Species diversity may be defined as
the variety (number) of species and their relative abundance and distribution in a region
(WRI 1992) where species richness only considers the variety of species in a region
(Biosociety undated).
Species diversity does not equal taxonomic diversity. Taxonomic (or taxic) diversity
refers to the diversity of taxa higher in the classification hierarchy than the species. 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 (Groombridge 1992, Bisby 1995, Pietra
2002).
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 2006g) and is
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 and Mounolou 2001, FAO 2004).
Ecological diversity is variously regarded as the variety of ecosystems in an area and
their interactions (Lévêque and Mounolou 2001, LEAF Program Undated, Draper 2002)
or intra-ecosystem variety (SustainableAg.net 2001).
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
also 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. 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. The ‘biodiversity
crisis’ - the present loss of biodiversity is considered a crisis or extinction crisis
(Groombridge 1992, Gaston and Spicer 1998). Some say that we are facing or in the
midst of the sixth mass extinction and that this mass extinction is caused by humanity
(Groombridge 1992, Eldredge 2001, Miller 2002, Wikipedia Contributors 2006h). High
biodiversity as measured by species richness does not equal 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 the conservation of biodiversity (Lévêque and Mounolou 2001, Pietra 2002)
and is considered in chapter 3.
Additional Notes
Extract from Wikipedia (2006h) ~ http://en.wikipedia.org/wiki/. Extinction events
“The classical ‘Big Five’ mass extinctions identified by Raup and Sepkoski (1982) are
widely agreed upon as some of the most significant: End Ordovician, Late Devonian, End
Permian, End Triassic, and End Cretaceous.
These and a selection of other extinction events are highlighted below:
488 million years ago — a series of mass extinctions at the Cambrian-Ordovician
transition (the Cambrian-Ordovician extinction events) eliminated many brachiopods and
conodonts and severely reduced the number of trilobite species.
444 million years ago — at the Ordovician-Silurian transition two Ordovician-Silurian
extinction events occurred, probably as the result of a period of glaciation. Marine
habitats changed drastically as sea levels decreased, causing the first die-off, and then
another occurred between 500 thousand to a million years later when sea levels rose
rapidly. It has been suggested that a gamma ray burst may have triggered this extinction.
360 million years ago — near the Devonian-Carboniferous transition (the Late Devonian
extinction) a prolonged series of extinctions led to the elimination of about 70% of all
species. This was not a sudden event, with the period of decline lasting perhaps as long as
20 million years. However, there is evidence for a series of extinction pulses within this
period.
251 million years ago — at the Permian-Triassic transition (the Permian-Triassic
extinction event) about 95% of all marine species went extinct. This catastrophe was
Earth's worst mass extinction, killing 53% of marine families, 84% of marine genera, and
an estimated 70% of land species (including plants, insects, and vertebrate animals.)
200 million years ago — at the Triassic-Jurassic transition (the Triassic-Jurassic
extinction event) about 20% of all marine families as well as most non-dinosaurian
archosaurs, most therapsids, and the last of the large amphibians were eliminated.
65 million years ago — at the Cretaceous-Paleogene transition (the Cretaceous-Tertiary
extinction event) about 50% of all species became extinct (including all non-avian
dinosaurs). This extinction is widely believed to have resulted from an asteroid or comet
impact event.
Present day — the Holocene extinction event. A 1998 survey by the American Museum
of Natural History found that 70% of biologists view the present era as part of a mass
extinction event ,the fastest to have ever occurred. Some, such as E. O. Wilson of
Harvard University, predict that man's destruction of the biosphere could cause the
extinction of one-half of all species in the next 100 years. Research and conservation
efforts, such as the IUCN's annual ‘Red List’ of threatened species, all point to an
ongoing period of enhanced extinction, though some offer much lower rates and hence
longer time scales before the onset of catastrophic damage. The extinction of many
megafauna near the end of the most recent ice age is also sometimes considered a part of
the Holocene extinction event.”
How do we quantify biodiversity?
There cannot be a single all-encompassing measure of biodiversity but aspects of
biodiversity may be quantified (Gaston 1996a, Gaston and 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 and 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 and 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 for biodiversity (Gaston and 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 and Spicer 1998, Miller
2002).
Biodiversity may be regarded “as a characteristic of natural communities” (p. 7 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 about 111.5 million species (Gaston and Spicer 1998).
Working estimates range from 12.5—14 million species (Groombridge 1992, Bisby
1995). How much we know about biodiversity depends on both location and taxon, e.g.
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 aspects of biodiversity
Most measures are concerned with either the genetic or the species level (Gaston 1996a).
Species richness (the number of species) at different scales is a frequently used measure
of biodiversity (Gaston 1996b, Lévêque and 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). The Shannon-Wiener Index is also
known as the Shannon Index or the Shannon-Weaver Index. The Shannon Index is a
non-parametric index of species diversity used to compare the biodiversity of different
areas (Southwood and Henderson 2000, Wikipedia Contributors 2006a).
Biomass measures productivity – a different aspect of biodiversity. In plants, it may be
limited to the above ground biomass (Chapman 1976).
Additional Notes
Measures of diversity using species richness from Southwood and Henderson (2000)
(p463). Alpha diversity (α diversity) is the species richness within a community or
habitat. Beta diversity (β diversity) measures “the rate and extent of change in species”
composition along a gradient between habitats. Gamma diversity (γ diversity) is the
species richness “of a range of habitats in” a given area, which comprises “the α diversity
of the habitats” combined “with the extent of the β diversity between them.”
Last slide
I hope that you found chapter 1 informative and that you will enjoy chapter 2. The
picture shows a springbuck (Antidorcas marsupialis).