Biodiversity and Evolution

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  • Created by: Buffya
  • Created on: 01-06-13 01:05


A species is a group of individual organisms that have similarites in appearance, anatomy, physiology, biochemistry and genetics, whose members are free to interbreed and produce fertile offspring.

A habitat is the place where an organism lives.

Biodiversity is the variety of life - the range of living organisms to be found. It can be considered by the range of habitats, the differences between species and the genetic variation between individuals.

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Random sampling is studying a small area of a habitat assuming it contains a representative set of species which can be applied to the whole habitat. It can be random by using random coordinates or taking samples at regular intervals

You can measure the abundance of plants using a quadrat. This is a square frame which defines the size of the sample. The abundance can be measured by percentage cover or the ACFOR scale. 

Plants can also be measured using a transect which is a line taken across the habitat. A line transect is when the plants touching the line are recorded. A continuous belt transect is when a quadrat is placed by the line.

Animals can be measured by sweep netting, pitfall traps, Tullgren funnel, light traps and collecting from trees. 

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Simpson's Index of Biodiversity

Species richness is the number of species in a habitat. It can be measure using a qualitative technique. 

Species evenness is the abundance of individuals in each species. It has to be measured using qualitative tests that measure the frequency of plants and the density of animals.

The Simpson's index of biodiversity measures both species richness and evenness. 

D = 1 - [E(n/N)2]

A high value indicates a diverse habitat with many species and organisms. A small change will have a small effect.

A low value indicates that a few species dominate the habitat. A small change will have a big disturbance.

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Biological classification is the process of sorting living things into groups. Natural classification does this by grouping things according to how closely related they are. It reflects the evolutionary distance between species.

Taxonomy is the study of the principles behind classification.

Phylogeny is the study of the evolutionary relationship between organisms. The more closely related they are, the more recently in the past they share a common ancestor. This is the basis for classification. Humans and gorillas are monophyletic - they belong to the same phylogenetic group.

The current system of classification is Domain, Kingdom, Phylum, Class, Order, Family, Genus, Species.

The binomial system uses two names to identify each species. The genus name (has a capital first letter) and the species name.

A dichotomous key uses a series of questions with two alternative answers to help you identify a specimen.

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Five kingdoms

Plants are autotrophic organisms - they make their own food by photosynthesis. They are eukaryotic multicellular organisms that have a cellulose cell wall.

Fungi are saprotrophic, which means they cause decay on organic substances. They are eukaryotic and have chitin cell walls. They consist of a mycelium which has hyphae.

Animals are heterotrophic, eukaryotic organisms. They are multicellular and able to move around. They produce fertilised eggs which forms a blastula.

Prokaryotes have no nucleus and a single loop of DNA. They also have no membrane-bound organells and respire on cell surface membranes, not mitochondria.

Protoctists are organisms that do not belong to any of the above 4 groups. They are eukaryotic but can be single-celled or multi-celled. They show features of both plant cells and animal cells.

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Three domains

Classification systems were based originally on observable features but now molecular evidence is being used to clarify relationships between organisms.

A protein called cytochrome c is used in the process of respiration, but it is not identical in all species. The sequence of amino acids in cytochrome c can be identified. If the sequences are the same, the species are more closely related. The more differences found between the sequences, the less closely related the two species.

Comparison of DNA sequences provides a way to classify species. The more similar the sequence, the closer related the two species.

Carl Woese suggested the three-domain classification. This is based on RNA. The Prokaryotae kingdom is split into the Archaebacteria which have many similarities to Eukaryotes - similar RNA polymerase, membrane and flagellum structure and have proteins on DNA. The Eubacteria are fundamentally different in those areas.

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Variation and adaptation

Variation is the presence of variety - the difference between individuals

Variation within species can be continous and discontinous. Continuous variation is when there is a full range of intermediate phenotypes between two extremes. Discontinous variation is variation in which there are discrete groups of phenotypes with no or very few individuals in between them.

There are two causes of variation. Genetic variation is the differences between the genes and the combination of genes and alleles. There are also environmental causes of variation which can be linked to genetic variation.

An adaptation is a feature that enhances survival and long-term reproductive success. There are behavioural (earthworm contracting), biochemical (enzymes), and anatomical (structural - flagella).

Xerophytic plants are adapted to living in very dry conditions. Their behavioural adaptations include opening stomata at night or rolling leaves. Biochemical adaptations is the mechanism by which a plant can open or close their stomata. Anatomical adaptations may be the size of roots and leaves.

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Natural selection

Darwin made four observations:

  • offspring generally appear similar to their parents
  • no two individuals are identical
  • organisms have the ability to produce large numbers of offspring
  • populations in nature tend to remain fairly stable in size

Natural selection is the selection by the environment on particular individuals that show certain variations. These individuals will survive to reproduce and pass on their varations.

Speciation is the formation of a new species from a pre-existing one. This is often a long, slow accumulation of changes. There must be a reproductive barrier so that some members become so different they can no longer interbreed.

Geographical separation will prevent interbreeding so speciation is likely to occur. This is known as allopatric speciation. A reproductive barrier may arise due to a physical or behavioural change which is known as sympatric speciation.

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Darwin studied the fossils of brachiopods which appeared to change slowly over time, which could be used to date rocks. There were also similarites between species found today and fossil species e.g. Armadillos and Glyptodonts. The evolution of the modern horse can be seen as well as the evolution of humans. However fossil evidence is incomplete and show only the hard parts of the organism.

Cytochrome c and DNA sequence can also support evolution.

Variation, adaptation and selection is part of evolution. An individual varies which can be by mutation. The environment applies selection pressures and those with an advantage in variations will survive and pass on their characteristic. The next generation will become better suited to their environment - adaptation.

Pests and microorganisms have evolved to resist pesticide and drugs. They survive these chemicals and when eaten by predators can pass it up the food chain. Another problem is that medical researchers have to develop new and effective drugs.

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Extinction is when a species ceases to exist. Human activity is causing harm to other species, extinction which leads to loss of biodiversity.

We have a need to conserve biodiversity. Economic reasons are that we can use organisms structure and adaptations to help technology. Ecological reasons are that certain organisms are needed in natural ecosystems e.g. photosynthesis to remove CO2. Ethical reasons are that animals have a right to survive and live the way they have adapted. Aesthetic reasons are that natural systems are important for human health. There is also a huge potential for future drugs and vaccines in organisms.

The gene pool is the sum total and variety of all the genes in a population or species at a given time. A smaller gene pool leads to less genetic variation and decreases the ability to evolve. Agriculture has caused a monoculture of plants which is genetic erosion.

Climate change may cause change in habitats. Domesticated animal and plants may be wiped out by a disease as they have a smaller gene pool. Diseases may also migrate.

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Conservation in situ and ex situ

Conservation in situ means conserving a species in its normal environment. Advantages are that all the conditions they require are already present. They are adapted to that environment and should be able to survive and breed successfully. It also permanently protects biodiversity, ecosystems and heritage. Disadvantages are that people may continue to hunt protected animals, illegal harvesting and tourists may leave litter.

Conservation ex situ means conserving an endangered species by activities that take place outside its normal environment. Repopulation may be possible. However, if a species has been made extinct there must be a reason such as lack of food. Captive-bred individuals may be unable to find food or avoid predators. They may not be accepted by other members of the species. Also, there is limited space which limits the number of individuals, restricting genetic diversity.

Botanical gardens are involved in the conservation of species. Seeds can be stored easily, plants can be bred asexually and captive-bred individuals can be replanted in the wild. Disadvantages are that they may not be genetically diverse, may breed clones and can't be stored for a long time.

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International cooperation

The Convention on Internation Trade of Endangered species aims to:

  • regulate and monitor international trade in selected species
  • ensure international trade doesn't affect wild populations
  • ensure that trade in wild plants is prohibited for commercial purposes
  • ensure that trade in less endangered species are allowed, subject to permit

The Rio Convention on Biodiversity has aims to:

  • conserve biodiversity
  • sustainable use of its components
  • appropriate shared access to genetic resources
  • sharing and transfer of scientific knowledge

Environmental Impact Assessment is a means of assessing the likely significant environmental impact of a devolopment. On a local level it involves the size of development, environmental sensitivity and types of impact expected. It is taken into account with making a planning decision.

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