4.1. & 4.2. BIODIVERSITY
BIODIVERSITY: the variety of living things in a habitat / ecosystem
Human impact on biodiversity
Are humans destroying life on earth?
Yes, by processes caused by humans such as: pollution, deforestation & climate change
Measuring biodiversity
1. Species richness
: the total number of species in a particular habitat
- it only considers total number of species – no matter the size or apparent significance
- it does not measure abundance or distribution of each species, just the nº of different species
2. Genetic diversity
: the total number of alleles found within the species
- A habitat is biodiverse if it has a large number of genetically diverse species
- Biodiverse habitats are more likely to survive environmental change.
• Mutation gives rise to new alleles - and a species with many alleles in its population is GENETICALLY DIVERSE
• A genetically diverse species is more likely to be able to survive a sudden change to its environment
→ We calculate the diversity using the... HETEROZYGOSITY INDEX
- If a population has a higher value for the heterozygosity index it is more genetically diverse
3. Simpson’s diversity index
: used to calculate the SPECIES EVENNESS: considers the abundance of each species in a given area
𝑁(𝑁 − 1)
𝐷=
𝛴𝑛(𝑛 − 1)
N = total nº of organisms of all species at a given site
n = total nº of organisms of a particular species
Why is biodiversity important?
1. We rely on other organisms to survive
e.g., air and water are purified by microbes (waste is made non-toxic by species of bacteria and fungi)
e.g., we need plants because... they: cycle all the gases in our atmosphere & start all food chains
: if a species becomes extinct, an entire FOOD WEB is affected
2. Humanity should value all life forms
- that have evolved over millions of years (they are just as valuable as works of art)
Endemism
: A species found in one geographical region and nowhere else, it is called an endemic species
e.g., Islands that separated from land a long time ago tend to have a lot of endemic species
- Australia has a lot of endemic species such as the Koala Bear.
- Madagascar has endemic species like ring tailed lemurs
- Hawaii has endemic species like the salmon bille I'iwi bird.
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• An endemic species is found in one geographical area and no other place
• Each particular habitat has its own particular characteristics
: Biotic and abiotic factors are unique, and these conditions dictate which species became successful in that area.
• If the location is isolated from other areas (e.g. an island) each species in that place evolves in a way unlike any other species.
→ Biodiverse locations usually have a high number of endemic species
4.3. NICHE AND ADAPTATION
What is a niche?
Niche: the role of an organism within its community
- Organisms interact with the abiotic (non-living) and biotic (living) factors in the environment.
- Each species has a specific way of interacting with its environment, and carries out a unique function/role in its habitat. This is called its
niche.
→ No two species occupy exactly the same ecological niche
→ Every species has become adapted over time to carry out its unique niche
Examples
Adaptations
1. Anatomical
: Successful species are well adapted to their niche
→ Anatomical adaptations means it has a unique feature of body shape or body features that increase survival chances
Example
- Diving mammals (whales and seals) have thicker blubber to provide them with heat insulation
: This is important in cold water
: Blubber also has a property that it does not compress under high pressure
2. Physiological
→ A physiological adaptation is a feature of how body systems work such as unique biochemical pathway enzymes used for changes to body
metabolism
: This affects how the body works for increased survival chances.
Example
- Seals have a change in metabolism called the mammalian diving response.
: The seals heart rate drops to prevent drop in scarce oxygen levels.
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3. Behavioral
→ Differences in behavior can also increase survival chances of an organism
Example
- Reptiles orientate themselves to get more sunlight when the air temperature is low
: This gives them sufficient body temperature so they can hunt food and escape from predators
- Courtship rituals are also classified as behavioral adaptations
4.4. NATURAL SELECTION
Natural selection is a term used to describe how some genes are more likely than others to pass to offspring, dictated by environmental
conditions.
- The theory was proposed by Charles Darwin after observations made on a round the world voyage on board HMS Beagle during the 19th
century
- This mechanism allowed Darwin to explain why most individuals of a species are so well adapted to their specific habitat
- It also gave a convincing mechanism to explain how new species arised from existing species.
Natural selection leads to...
Adaptation
• Species become adapted to a particular niche by natural selection:
Variation already exists within any given population (why?)
Individuals born with traits that make them suited to the habitat have more chance of survival
- Those individuals that survive will reproduce to pass on their alleles
• Over time beneficial alleles become common within a species – the species is adapted to its
niche
→ If a species is removed from its niche, it is unlikely to survive
Evolution
→ Evolution is change in allele frequency in a population over time
• Allele frequency is the number of times an allele occurs in a given gene pool (a gene pool is the total
number of alleles that exist in a population)
• Selection pressures are aspects of an environment that determine which organisms are fittest
- The different selection pressures cause them to evolve differently, forming new species over time
(which can’t breed to produce fertile offspring)
- New species can evolve if a section of a population gets geographically isolated
The origin of species
→ Natural selection causes adaptation and evolution
→ It can also lead to formation of new species
- A species is a population of related organisms capable of breeding to produce fertile offspring
Formation of a new species is called speciation
- Normally, speciation requires physical separation of an existing population, so no gene flow occurs
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The geographically isolated populations evolve in different ways – why?
Different random mutations, different selection pressures due to different environmental factors
This leads to reproductive isolation (eventually the individuals are so different from each other that they no longer breed to produce fertile
offspring)
Events in speciation
→ An original population is separated by a barrier (in nature, a geographical barrier)
- This means there can be no gene flow
• Conditions in each place is different, giving rise to different selection pressures
(e.g., presence of different food sources)
• Natural selection leads to adaptation in each place. Mutations may also occur, and
these changes are unique to each population
- After generations, differences in phenotype between the populations increase.
- This leads to reproductive isolation (they no longer mate to produce fertile
offspring) so they become different species.
4.5. HARDY-WEINBERG EQUATIONS
Hardy-Weinberg principle occurs if these conditions are met:
1. No new mutations
2. No immigration or emigartion
3. Mating is random - the alleles all have an equal chance of getting passed on
4. The population is large
5. No natural selection (individuals have an equal chance of passing on their alleles)
Equation nº1
Equation nº2
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