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TOPIC 5 EVOLUTION AND BIODIVERSITY - Coggle Diagram
TOPIC 5 EVOLUTION AND BIODIVERSITY
evolution
evolution
Evolution is the cumulative change in the heritable characteristic of a population (i.e. biological change over time)
These characteristics are encoded by genes and transferred between generations as alleles
theories of evolution
Lamarck
Proposed that species change via habitual use and disuse
A giraffe stretches it neck to reach leaves in tall trees
The giraffe’s neck becomes extended from constant us
The giraffe’s offspring inherit its long neck
This theory has been rejected because these acquired traits
do not have a genetic basis (and thus cannot be inherited)
Darwin (and Wallace)
Proposed that species change via natural selection
A giraffe with a longer neck can reach leaves in tall trees
The giraffe will get enough food to survive and reproduce
The giraffe has more offspring (that inherit a long neck)
mechanisms of change
There are three main mechanisms by which genetic variation
within a population is maintained:
Mutations – changes to the gene sequence
Sexual reproduction – new gene combinations
Gene flow – immigration and emigration
There are two mechanisms by which population variety can
be altered (decrease biodiversity):
Random chance (genetic drift)
Directed intervention (natural or artificial selection)
The impact of a change is greater if the population is small
(this may occur via population bottlenecks or founder effect)
speciation
If populations become isolated, the level of genetic divergence
gradually increases the longer the populations remain separated
Continuous variation across a geographical range of related
populations matches this concept of gradual divergence
Speciation will occur when populations diverge to the extent that
they can no longer interbreed and produce fertile, viable offspring
evidence for evolution
fossil record
A fossil is the preserved remain or trace of a past organism
The totality of all fossils is called the fossil record
Law of Fossil Succession
The fossil record shows that changes have occurred in organisms and these changes have occurred in a consistent sequence of development (the law of fossil succession)
Transitional Fossils
Transitional fossils represent intermediary forms within the
evolution of a genus and demonstrate species connections
selective breeding
Selective breeding involves the mating of animals with
desired characteristics (it is a form of artificial selection)
As human intervention drives selection, changes will occur
over fewer generations as phenotype extremes are promoted
molecular evidence
Closely related species share a greater degree of similarity in
their DNA and protein sequences (due to common ancestry)
If a particular gene has a stable mutation rate, the time of
evolutionary divergence can be estimated (‘molecular clock’)
vestigial structures
Some species show the presence of functionless or reduced
remnants of organs that were once present in ancestors
comparative anatomy
Homologous structures are anatomical features that share a
common basic structure despite having distinct functions
e.g. pentadactyl limb
The rapid diversification of an anatomical feature is a result
of adaptive radiation (organisms adapt to different niches)
comparative embryology
Comparing embryonic development in animals demonstrates
similarities that suggest a common evolutionary pathway
biogeography
Biogeography is the distribution of species across an area
Related species will usually be found in close proximity
Exceptions may be explained via continental drift
natural selection
The process of natural selection occurs in response to certain conditions:
There is genetic (inheritable) variation within a population (caused by mutations, meiosis and sexual reproduction)
There is competition for survival (species tend to produce more offspring than the environment can support)
Environmental selection pressures give rise to differential rates of reproduction
Organisms with beneficial traits are likely to survive and reproduce, while those less well adapted produce less offspring
Over generations, these beneficial traits become more common (evolution = a change in allele frequency in a gene pool)
selection pressures
Examples of environmental selection pressures include:
Predator / prey dynamics
Abiotic factors (e.g. climate)
Nutrient supply (food source)
Diseases / pathogens
Available resources (e.g. light)
Space requirements (habitat)
adaptations
Adaptations are traits that make an individual suited to its environment and way of life
Adaptations can be structural, behavioural, physiological, biochemical or developmental
Populations will evolve different adaptations according to environmental conditions
The functional position of an organism in the environment is its ecological niche
When members of a species occupy a variety of different ecological niches, it will lead to the rapid diversification of the original ancestral line (this is called adaptive radiation)
examples of evolution
bacteria has antibiotic resistance
peppered moth (industrial revolution)
classification
binomial nomenclature
The binomial system of naming is a globally recognised
classification scheme developed at a series of congresses
It was first proposed by Carl Linnaeus in 1735
According to the binomial system, every organism has a
two-part scientific name:
Genus is written first and is capitalised (e.g. Homo)
Species follows in lower case (e.g. Homo sapiens)
hierarchy of taxa
Taxonomy is the science of classifying organisms based
on shared characteristics (or taxa)
More taxa shared = more closely related organisms
Kingdom, Phylum, Class, Order, Family, Genus, Species
dichotomous key
A dichotomous key involves sequentially dividing organisms into two categories until every organism is individually identified
domains of life
All living organisms are classified into one of three domains:
Eukarya (all eukaryotic organisms)
Archaea (prokaryotic extremophiles)
Eubacteria (common pathogenic bacteria)
Originally, the two prokaryotic domains (Archaea and Eubacteria)
were considered part of a single kingdom (Monera)
However, biochemical differences prompted a reclassification
natural classification
Natural classification involves grouping organisms according to
common ancestry rather than by common characteristics
This allows for species to be identified by their evolutionary
pathways and enables the prediction of traits within a group
A disadvantage of natural classification is that taxonomists may
need to reclassify groups if new phylogenetic evidence emerges
Gorillas and chimps were included in a Homininae sub-family
The figwort family was reclassified based on cladistics data
cladistics
clades
Cladistics involve classifying organisms into groups of species (clades)
A clade consists of a single common ancestor and all descendants
Cladograms are tree diagrams where each branch point represent the splitting of two new species groups from a common ancestral species
Each branch point (node) represents a speciation event
The more nodes between groups, the less related the groups are
structural evidence
historically, cladograms have been constructed based on structural characteristics, however this is not always a reliable method for establishing evolutionary connections
Related species may have distinctive (homologous) features
Unrelated species may have similar (analogous) features
molecular evidence
Cladograms are now being generated via a comparison of
biochemical evidence (i.e. DNA or amino acid sequences)
Related species will have sequences with more similarities
Amino acid sequences will accumulate differences at a
slower rate to DNA sequences (due to degeneracy)
if a sequence accumulates mutations at a constant rate, the time of divergence can be calculated based on the number of mutations between the two species (molecular clock)
biodiversity
plant phyla
Bryophyta (e.g. liverworts and mosses)
• No vascularisation (lacks xylem / phloem)
• Reproduce via spores released by stalks
• No ‘true’ leaves, roots or stems
Coniferophyta (e.g. conifers)
• Have vascularisation (xylem and phloem)
• Reproduce via seeds (found in cones)
• Narrow leaves with a thick, waxy cuticle
Filicinophyta (e.g. ferns)
• Have vascularisation (xylem and phloem)
• Reproduce via spores in sporangia
• Have large fronds divided into leaflets
Angiospermophyta (e.g. flowering plants)
• Have vascularisation (xylem and phloem)
• Reproduce via seeds (found in fruits)
• Have flowers as reproductive organs
invertebrate phyla
Porifera (e.g. sponges)
• Have an asymmetrical body plan
• Have no mouth or anus (have pores)
• May have spicules for structural support
Annelida (e.g. earthworms and leeches)
• Possess bilateral symmetry
• Have a separate mouth and anus
• Body composed of ringed segments
Cnidaria (e.g. jellyfish and anemones)
• Possess radial symmetry
• Have a mouth but no anus (single opening)
• Has tentacles and stinging cells (cnidocytes)
Platyhelmintha (e.g. flatworms, tapeworms)
• Possess bilateral symmetry
• Have a mouth but no anus (single opening)
• Has a flattened body (increases SA:Vol ratio)
Arthropoda (e.g. insects, spiders, crustaceans)
• Possess bilateral symmetry
• Have a separate mouth and anus
• Have jointed appendages and exoskeleton
vertebrate classes
Phylum Chordata (i.e. vertebrates)
• Possess bilateral symmetry
• Have a separate mouth and anus
• Have a notochord (may form a backbone)
reptiles
• Covered in scales (made of keratin)
• Have internal fertilisation (lays soft eggs)
• Breathe via lungs and are ectothermic
birds
• Covered in feathers (made of keratin)
• Have internal fertilisation (lays hard eggs)
• Breathe via lungs and are endothermic
fish
• Covered in scales (bony plates of skin)
• Reproduce via external fertilisation
• Breathe through gills and are ectothermic
amphibians
• Have a moist skin (permeable to gases)
• Reproduce via external fertilisation
• Breathe through skin and are ectothermic
mammals
• Covered in skin (and keratin hair follicles)
• Have internal fertilisation (and lactation)
• Breathe via lungs and are endothermic