D4 Flashcards
Selection pressure
- An environmental factor that can influence the success of a population
- Can be abiotic, biotic and anthropogenic
- Can lead to natural selection
Fitness
- An organisms ability to pass on their genes, and have a strong genetic contribution
- Linked to survival, as passing on genes is easier when alive
- Also organism should be adapted to environment
Sexual Selection
- Similar to natural selection, some organisms are more successful at producing offspring
- Related to the ability to attract a mate
Antibiotic resistance
Natural selection where non-resistant bacteria die and therefore resistant bacteria survive and reproduce until whole population becomes resistant.
How did Darwin’s theory lead to a ‘paradigm shift’ in scientific understanding
- Changed the way we viewed evolutionary change
- Before: Lamark’s theory of acquired traits
- Afrer: Darwin’s theory of heritable traits
- Change in evolutionary framework= paradigm shift
What are 3 causes of genetic variation which drive natural selection?
- Mutation
- Meiosis
- Sexual reproduction
What role does carrying capacity play in natural selection?
- Only the more fit/ better adapted organisms survive due to competition if over carrying capacity
- If a population is under carrying capacity, it will not evolve through natural selection
How do abiotic factors impact natural selection
- Can act as a selective pressure
- Extreme abiotic conditions can limit the survivability of a species
- This allows differential success of those with suited adaptations
What is the difference between an acquired and a heritable trait?
- Acquired trait: obtained during lifetime, result of behaviour
- Heritable trait: coded in DNA, passed to offspring, drive evolution
Explain how sexual selection has played a role in the evolution of birds of paradise
- Females are camoflaged, but males have big, bright plumage, as long as they are healthy and have good nutrition
- Males with bright feathers have been sexually selected for as they are more attractive to females
Explain the work of John Edler with guppies in Trinidad and Tobago
- Investigated whether the presence of predators influenced the colouration of guppies
- Bright coloured males- good for getting mates
- Dull coloured- good for camoflage
- He found that the presence of predatory fish resulted in less colouration
Gene pool
All genes and their different alleles present in a population
Allele frequency
- Proportion of total alleles that each individual allele occupies
- Given as a decimal
- Shows how common an allele is
Polymorphic
- many forms- traits that have more than 2 variants
- can be at a phenotypic level as a result of one or multiple genes
- Single nucleotide polymorphism- greater than 2 variants at a base
Directional selection
- One extreme phenotype has an advantage
- Population shifts to that extreme
- Still variation, but all will move closer to the favoured extreme
Stabilising selection
- Natural selection favours the average
- Shortens the continuum, less at either extreme
- Reduced variation and possibility of speciation
Disruptive selection
- Either extreme is favoured over the average
- Each extreme provides a specific advantage, often different niches
- Can be the start of speciation if they stop breeding and occupy different niches
How does geographic isolation impact allele frequency?
- First step to speciation- prevents gene flow
- Evolution can favour one allele in one location, and a different one in another location
- Over time, allele frequency in each location differs
What is neo-Darwinism?
Darwin’s theory of heritable traits + our current understanding of DNA and alleles and how they are inherited
Similarities and differences between artificial and natural selection
- Human interference- active breeding = artificial selection
- If humans only add environmental selective pressure= natural selection
- Both lead to change in allele frequency
Genetic equilibrium
- Opposite of evolution. No change in frequencies over time
- Usually in reference to one trait, therefore one gene
- Attributed to Hardy and Weinberg who created a mathematical model to assess allele frequencies.
What 5 conditions must be met for a population to be in equalibrium, according to Hardy and Weinberg?
- Large population size- too small, if a few die, gene pool shifts— genetic drift
- No immigration or emigration- no new alleles arrive or alleles leave
- No favoured phenotype/ selective pressures- no survival difference between genotypes
- No sexual selection- random mating
- No generation of new alleles by mutation
What do the letters represent in the Hardy-Weinberg equation, and what is the equation?
p+ q= 1
p2+ 2pq + q2= 1
p= dominant allele (A)
q= recessive allele (a)
p2= frequency of 2 dominant alleles (AA)
2pq= frequency of heterozygotes (Aa)
q2= frequency of 2 recessive alleles (aa)
What order do you solve things in a Hardy- Weinberg calculation?
- q2
- q= square root q2
- p= 1-q
- 2pq
- q2
frequency, percentage and number of organisms- Hardy-Weinberg equation
- Frequency= decimal
- Percent= frequency x 100
- Individuals= frequency x pop size
Sustainability
A sustainable ecosystem can fully support itself without outside interferences- not unchanging, but changes slow enough that the organisms can adapt.
Tipping points
The point where an ecosystem can no longer sustain itself and starts to collapse. Often not known until it has been crossed.
How is the Amazon rainforest maintained a long period of sustainability?
- Due to large amounts of plant coverage
- This means it can maintain its own water cycle through transpiration
- How?
1. Plants absorb water from soil
2. Water travels up and out their leaves
3. High transpiration forms clouds (water vapor)
4. When the temperature drops, this turns into rainfall
5. Cycle begins again
What is the threat to the long-term sustainability of the Amazon rainforest?
DEFORESTATION
* The removal of plant life means a decrease in transpiration
* This impacts its own climate cycle
* If we disrupt the water cycle, this disrupts the climate- increased temp, decreased rainfall
* This causes forest fires- further decreases plant life
* When it cannot maintain forest anymore- becomes grassland= TIPPING POINT
* This is already happening in regions of the Amazon
What are the four requirements for an ecosystem to remain sustainable?
- A sufficient supply of energy- enough plants to photosynthesise sunlight and provide for successive trophic levels
- Nutrient recycling- finite nutrients, so decomposers help with cycling of Carbon, Nitrogen and Phosphorous
- Genetic diversity- more likely to withstand smaller changrs, less disruption of food webs and ecosystem diversity
- Response to climate change- human activities causing rapid and severe changes that challenge even resilient ecosystems. Can be combatted by a large tolerance range
What are some challenges to sustainable ecosystems- sufficient supply of energy?
- Loss of producers due to deforestation
- Trophic imbalances- invasive species, extinction of keystone species, eutrophication
What are some challenges to sustainable ecosystems- nutrient recycling?
- Logging and poaching- removal of biomass and nutrients
- Erosion washing away topsoil- removal of nutrients
What are some challenges to sustainable ecosystems- high level of genetic diversity?
- Competition from invasive species- reduces population size and increases inbreeding
What are some challenges to sustainable ecosystems- response to climate change?
- Can occur faster than species can adjust.
What is a mesocosm?
- A small experimental area set up as a working model of an ecosystem
- Can be set up in nature as fieldwork, or created in a lab
- It is common to use sealed containers with the necessities to function as a self-contained sustainable ecosystem
- Can be used to manipulate variables to understand impact
Why is a sealed mesocosm a better model than an open tank?
- Open tanks are not true models of sustainable ecosystems as matter can enter and exit e.g water vapour, O2, CO2
- A sustainable ecosystem should recycle these in a sealed environment, with only sunlight entering through clear sides
What is a Winogradsky column?
- Microbial mesocosm with layers that differ in abiotic environments
- This allows different bacteria to thrive in different layers
- There is more sulfur lower down and more oxygen higher up- this impacts where they can live
- Able to observe the difference between facultative and obligate anaerobes
What is the purpose of the components of a mesocosm?
- Bottom layer of pebbles: drainage tp prevent over moist soil
- Activated charcoal: absorbs extra water, odours and prevents bacterial overgrowth
- Soil: room for growth of roots, provide nutrients including nitrogen and phosphorous
- Plant: photosynthesis- convert sunlight into carbon compounds
- Water: add at the start to create water cycle
What is a keystone species?
- Any type of organism that has a disproportionate effect on the structure of an ecological community
- Disproportionate= larger impact than population size would predict
- Ecosystem collapse is likely if they are removed
What is trophic cascade?
- When the removal of a top predator destabilises the trophic levels below it and disrupts the balance of the ecosystem
- Note: top down population control/ impact
What is soil erosion?
- The loss of upper layer of soil
- Can be due to excess wind and rain
- The topsoil is the most nutrient rich layer so its loss can have large impacts on an ecosystem