The Varieties of Life on Earth

  • Created by: sikemi__
  • Created on: 22-05-21 15:33

What is biodiversity?

  • The variety of life, in all its many manifestations. It encompasses all forms, levels and combinations of natural variation and thus serves as a broad unifying concept (Gaston & Spicer, 2004)
  • Can look at diversity within/between species and of ecosystems
    • Genetic diversity - the ultimate source of all diversity, rested in DNA
    • Species diversity (taxonomic diversity) - most focus in biodiversity research is done at this level
    • Ecosystem diversity - the variety of different types of landscapes withina. region, country, continent or even the world
  • Biodiversity in its simplest form is all life on Earth.
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Context - why is it important?

  • Contemporary rates of extinction are an estimated 1000 to 10,000 times that of the background rate of biological and fossil extinction.
  • Whilst extinction is normal, we are speeding it up.
  • It is estimated that one in four species is at risk of extinction. The May 2019 UN report stated that the current declines in biodiversity is unprecedented and species extinction rates are accelerating.
  • The UN Sustainable Development Goals 14 and 15 focus on life below water and life on land respectively.
  • For almost all of the four main species (birds, fish, mammals, reptiles and amphibians), it is habitat degradation that is leading to species declines, followed by exploitation. 
  • For fish, exploitation is the leading cause of species decline. Climate change will arguably become more of a major cause of species decline. 
  • However, it is difficult to set climate change apart from habitat degradation (although habitat degradation is often linked to human impacts). 
  • Other drivers of species decline include invasive species and disease and pollution.
  • Idea of planetary boundaries (Steffen et al, 2015)
    • An attempt to identify safe operating spaces within which humanity and different parts of the Eath's system are operating with normality
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How do we measure biodiversity?

  • Species richness
  • Positives - measurable, databases exist e.g. IUCN Red List of Threatened Species
  • Negatives - just one measure of biodviersity, problems surrounding defining a species (also, are they all equivalent? in terms of what?), problem with sysnonyms as one species might have multiple names so be double/triple counted
  • Estimated to be between 3.5 and 111.5 million living species (uncertainty), Mora et al (2011) estimated 8.7 million
    • Uncertainties lie in taxonomic groups e.g. viruses, bacteria, fungi, protozoans, mites, insects. Also habitats and biomes e.g. soils, tropical biomes, deep-ocean benthos.
    • Mora et al (2011) estimate that 86%. of existing species on Earth and 91% of species in the sea are yet to be described.
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What is a species?

  • Definition is needed to begin to count how many there are and how many are endangered/extinct
  • Definitions depend on whether you are looking at species alive today or those in the fossil record or those based on their DNA
  • Three concepts: biological species concept (defines a species taxon as a group of organisms that can successfully interbreed and produce fertile offspring), evolutioonary species concept (a single lineage of ancestor-descendant populations of organisms which maintains its identity from other such lineages [in space and time] and which has its own evolutionary tendencies and historical fate” (Wiley, 1981)) and phylogenetics (what the DNA record has to tell us about how species are related and what makes them different).
  • Problems  - when looking at the evolutionary species concept, the fossil record isn't good at preserving the range of species that have ever lived. Also, within some species there is hybridisation - a problem as different species names are given to each of the slightly different morphotypes which are distinct but may not occur as different ecological communities.
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Biological species concept

  • Formulated by Swedish naturalist Carl Linnaeus (1707-1778): created our modern taxonomic hierarchy (genus, family, order…kingdoms)
  • Later refined and developed by Ernst Mayr (1904-2005) who looked at formulating this via a distinct reproductive group where a population of organisms which naturally mate in the wild and produce viable offspring that can also reproduce are part of one group
  • It is possible to have interbreeding between species e.g. mule from a donkey and a horse but these hybrids are sterile. Therefore, mules aren't species, they are hybrids.
  • The Biological Species Concept is perhaps the most commonly used definition of a species but it is not universally applicable.
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Evolutionary species concept

  • Organisms which have direct ancestor-descendant relationships, i.e. shared evolutionary history
  • Inferred from morphological similarities (size/shape) of fossils
  • New species occur when an evolutionary line divides into more than two new lineages
  • Problems…
    • Precise evolutionary history of fossils is impossible to know.
    • There is divergence over geological time as continents move away from each other (specimens might be lost after death and they may not be well preserved into the fossil record).
    • Not all fossils have yet been found
    • Only some areas of the world are good fossil bearing environments (fossils are more likely to form due to death at sea, bones are scavenged on land)
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  • Allows us to look at the evolution of animals such as dogs (Canidae) and see how they are related to each other (and to what degree).
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Biodiversity when we only think of species richnes

  • Easily understood
  • Practical for conservation
  • Many record already exist


  • Overly simplistic
  • Problems with taxonomic synonoyms
  • Are all species equivalent?
  • What about higher levels of ecological organisation such as ecosystems, habitats and landscapes?
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Biodiversity when we think of MORE than species ri

  • Biodiversity is much more than species richness
  • It can be broken down into 
    • Genetic, i.e. within species
      • Populations, individuals, chromosomes, genes, nucleotides.
    • Organisational or taxonomic diversity
      • Domains or kingdoms, phyla, families, genera, species, subspecies, populations, individuals.
    • Ecosystems
      • Biomes, bioregions, landscapes, ecosystems, habitats, niches, populations.
  • It can also be looked at in other ways...
    • Presence/absence - Sample plots (quadrats) to count species presence.
    • Abundance - How common is a species within a quadrat? E.g. percentage cover.
    • Frequency - In how many quadrats does it occur?
    • Rarity - To what extent are species threatened with extinction.
    • Endemism - Whether a species is restricted in its geographical location (need to consider the scale of that location).
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