Notes towards Biodiversity Chapter 1

Introductory/Titleslide (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 diversityas 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) ~ “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) ~ “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 recombinationin 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) ~ “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) ~ “Organism - A living thing.”

Extract from Wikipedia (2006f) ~ Definitions of species “Typological speciesA 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 speciesA 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 speciesA 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 speciesA 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 speciesA 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.

MicrospeciesSpecies 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), “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 equaltaxonomic 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 ProgramUndated, 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 crisisor 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 inchapter 3.

Additional Notes

Extract from Wikipedia (2006h) ~ 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 cometimpact 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 measurefor 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).