ecosystems

unity and diversity

  • evolution: change in the heritable characteristics of a population via natural selection (darwinism)

  • acquired characteristics: characteristics of individuals that change during their lifetimes

  • lamarckism: theory of evolution that one inherits acquired characteristics, untrue

  • evidence for evolution in base sequences:

    • changes in the base sequence of DNA or RNA and in the amino acid sequences of proteins whenever evolution occurs

    • ex. .covid 19 evolved, with different base sequence changes, and some were more successful than others

    • comparing base sequences of the same gene is different species shows evolutionary differences. more differences→ less closely related species. ex. hox gene family occurs widely in animals, and similarities/differences in Hox genes can explain common/different ancestry

  • selective breeding/agriculture

    • modern breeds of livestock have huge differences from the wild species they closely resemble, same with crop plants

    • artificial selection: selecting and breeding animals/plants most useful to humans

  • homologous structures: features with similar anatomy despite differences in function, such as pentadactyl limbs (5 digits), which most animals have, although the length, thickness and function vary, with some metacarpals and phalanges being lost. the explanation is they were inherited from a common ancestor (tetrapod with pentadactyl limbs), but they evolved after

  • rudimentary organs: organs with no function, such as the appendix, and small pelvis bones in snakes, that are gradually being lost by evolution


  • analogous structures: superficial similarities

  • convergent evolution: analogous structures had different origins but became similar because they perform the same or a similar function

  • bilateral symmetry: bodies with anterior and posterior ends and a need for communication between the two, achieved in vertebrates with a spinal cord and brain, and in vertebrates with a single central nerve cord (analogous)

  • speciation: two populations of a species are split, cannot interbreed (no gene flow between gene pools, usually geographical separation), and have natural selection occur in different ways(differential selection, could be climate, predation, competition, etc.), they will become different. if they are then put together and do not interbreed, speciation has occurred

  • sympatric speciation: same geographical areas, maybe caused by behaviour difference, ex. cichlid fish females only choose male mates that look similar to themselves, when there are blue and yellow cichlid fish, which can cause speciation over time

  • allopatric speciation: different geographical areas

  • adaptations: characteristics that make an individual suited to its environment/way of life

  • adaptive radiation: adaptation to new ecological niches, ex. darwin’s finches

  • sterility of hybrids: ex. mules, horses have 64 chromosomes and donkeys have 62, so a mule has 63 and is therefore almost always sterile.

    • sometimes, even when both parent species have the same number of chromosomes, the offspring can be sterile

    • many species have evolved to prevent hybridisation. ex. animals may check for certain behavioural/physical features in a potential mate

  • polyploid: an organism with more than two sets of homologous chromosomes. consequence of the duplication of chromosomes in a cell without a subsequent cell division, so it is whole-genome duplication.

    • autotetraploid: 4 copies of a single genome, low fertility rate, usually considered same species as diploid although technically not because the features will be very similar. ex. sand rock-cress


    • diploid cross breeding can cause polyploidy

    • if a cell in a sterile hybrid duplicates its chromosomes but does not then divide, it will have 4 sets, and is allotetraploid (4 sets of chromosomes, 2 genomes), can divide by meiosis and overcome fertility problems, must interbreed with other allotetraploids, not either diploid parent species and are therefore a new species


conservation of biodiversity

  • biodiversity can consist of ecosystem diversity, species diversity and genetic diversity within a gene pool

  • estimation of 2-10 million eukaryotic species, difficult to estimate amount of past species or prokaryotic species

  • end of cretaceous period, 66 million years ago, most recent mass extinction due to asteroid crash. all 4 previous mass extinctions were due to volcanic activity and global climate. human activity is predicted to cause the sixth mass extinction, wiping out what is probably the highest biodiversity has ever been

  • anthropogenic species extinction causes:

    • overharvesting of plants, animals and natural resources

    • habitat destruction, loss of natural ecosystems

      • agricultural expansion → loss of forest, grasslands, wetlands, tropics

      • urbanisation

      • exploitation of natural resources

      • mining and smelting → pollution or soil, water and acid rain

      • building dams, ex. the annual flooding of the nile no longer occurs due to dam building

      • drainage or diversion of water → loss of swamps and wetlands

      • leaching fertilisers into water

      • climate change → diff temp, rainfall, etc.

      • ex. loss of the aral sea, between Kazakhstan and Uzbekistan, was the fourth largest lake in the world, but the two major rivers that fed it were diverted, so most of it is now desert, resulting in the extinction of most species there

    • invasive species, which can cause extinction by predation, competition and hybridisation, can be purposeful or accidental

    • pollution (fossil fuels, agriculture, mining, oil extraction, pharmaceuticals)

    • global climate change at a pace too rapid for adaption

    • overpopulation

  • monitoring evidence of a biodiversity crisis:

    • population size of a species

    • range of a species

    • diversity of an ecosystem

    • richness and evenness of biodiversity in an ecosystem

    • area occupied by an ecosystem

    • extent of degradation of an ecosystem

    • number of threatened species within a taxonomic group

    • genetic diversity within a species

  • 75% of the terrestrial environment and 66% of marine environments had been “severely altered” by 1970 as a consequence of human actions

  • strategies to conserve biodiversity:

    • in situ conservation: preserving areas of wilderness

      • through legislation or land purchase

    • rewilding: actively intervening to recover ecosystems to as natural a state of possible

    • ex situ conservation: preserving species outside their natural habitats

    • germplasm: storing living material, such as seeds, tissue samples, eggs and sperm, for a long time for propagation in the future

    • EDGE of Existence project: determining the animal species most in need of conservation: criteria:

      • evolutionarily distinct: does the species have few or no close relatives (small clade)

      • globally endangered: is it in danger of extinction?

      • then targeted for intense conservation efforts