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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 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. Additional Notes Extract from Wikipedia ~ http://en.wikipedia.org. 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 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. Extract from Wikipedia ~ http://en.wikipedia.org. 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.
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Biodiversity
What is it?
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” (p14 Leveque & 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 (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 , 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.
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 regarded variously as the variety of ecosystems in an area and their interactions or intra-ecosystem variety. The first definition is better.
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 & Spicer (1998)
The definition given defines biodiversity as a scientific concept.
Biodiversity may be considered as a social/political construct.
Biodiversity in the context of measurement and quantification.
Biodiversity in different contextsBiodiversity in different contexts
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: ‘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 one 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” (p7 Lovejoy 1997).
Perceptions of biodiversity 1Perceptions of biodiversity 1
Biodiversity may be considered globally and collectively. Aproximately 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 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 parts of Some examples of measures of parts of biodiversitybiodiversity
Link to Chapter 2Chapter 1 Chapter 1 Biodiversity: what is it?Biodiversity: what is it?
Chapter 2 Chapter 2 ……
I hope that you found chapter 1 informative and that you will enjoy chapter 2.
