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145 Cards in this Set
- Front
- Back
What is a population? |
A group of individuals of the same species that occupy a particular area at a particular time (same time) and have the potential to interbreed |
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How many populations make up one species? |
One or many. Many if the species live in different areas. One group in one country and one in another - they are the same species but as they live in different areas they are different populations |
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What is a gene pool? |
All the alleles of all the genes of all the individuals that make up one population |
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How do you calculate the number of alleles in a population? |
Each individual will possess 2 alleles per gene ( pair of homologous chromosomes - same genes. One maternal and one paternal allele) . No of genes in individual × 2 = alleles in individual. This × no. Of individuals in the population |
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What is alleic frequency? |
The frequency of a particular allele in a gene pool ( how many times it occurs in the gene pool) |
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What is the alleic frequency of a beneficial allele like? |
High as it is beneficial. Individuals who possess have greater reproductive success so pass it on more and numbers increase. Also more likely to survive |
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What is the hardy-weinberg principle? |
An equation from which we can calculate frequencies of alleles , genotypes and phenotypes for one particular gene in a population |
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Under what conditions does the hardy-weinberg principle work? |
Large population- no genetic drift, mating is random , no selection pressures , no mutations of the allele , no allele flow in or out - migration - so the population is isolated |
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Why doesnt the principle work without these conditions? |
The principle works on the basis that allele frequencies remain constant from one gen to another but if these conditions are not met this is not the case e.g - natural selection may occur which changes alleic frequencies over time |
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How does migration effect alleic frequencies? |
When individuals leave or enter they take alleles with them or introduce them |
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How does having a small population effect alleic frequency? |
Genetic drift could occur which means allele frequencies change a lot very quickly |
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How does non-random mating effect alleic frequencies? |
Not all genetic combos have the possibility of mating so variation is reduced. Specific combos may pick specific combos - reducing variation |
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How do selection pressures effect alleic frequencies? |
Specific allele may be favoured as more suited to conditions - more likely to be passed on so frequency increases through generations. It is not constant |
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How can mutations effect alleic frequencies? |
Mutation of the allele may produce a new allele so equation would no longer work |
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What is p in the hardy weingberg equation? |
The frequency of the dominant allele |
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What is q? |
The frequency of the recessive allele |
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Why is p+q=1 ? |
If you express the frequencies as fractions/decimals of total alleles for this gene they will add to 1 as no other alleles are possible |
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Why does p^2 + 2pq + q^2 = 1 ? |
Only possible geneotypes for a gene are homo dom , homo recessive and hetereozygous so if we expressed these genotypes as a fraction of the total geneotypes it would equal to 1 ( for a gene with only 2 alleles) |
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What is p^2 ? |
Homo dom |
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What is q^2 ? |
Homo recessive |
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What is 2pq ? Why is it x2 ? |
Hetereo Could be aA or Aa , depends which allele is on paternal /maternal chromosome |
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What terms would give the frequency of the dominant phenotype? |
P^2 + 2pq as dom allele always expressed over recessive |
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Which terms give the frequency of the recessive phenotype? |
Q^2 |
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Why is the hardy weinberg principle used if these conditions for it to work can never be met? |
Calculation used as an estimate Used to see if these conditions are not met in a population. Compare one gen to another and if frequencies one of these conditions has not been met so you could consider that a selection pressure may be present etc |
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What causes genetic diversity in a population? |
Mutations of alleles to create new ones Meiosis creates unique gametes due to segregation and crossing over and random fertilisation means any allele combo is possible |
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What causes phenotype diversity in a population? |
Genetic diversity and environmental factors affecting how alleles are expressed |
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What do we call phenotype diversity that is only controlled by genes and not the environment? How can it be presented? |
Discontinuous variation and can be represented on a bar chart as it is discrete. Allele decides whether you have one phenotype or the other - no intemediates resulting from the environment |
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What is an example of the environment affecting phenotypes? |
Having genes to grow tall but not receiving correct diet for this so your growth is limited (There is also epigenetics) |
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What phenotypes so a continuous variation? How can they be represented? |
Controlled by multiple genes and the environment. Displayed on normal distribution as arent discrete , can take any value really Normally height and mass |
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What allows natural selection and evolution to occur? |
Genetic diversity / phenotype diversity as wide range means one will be suited to the selection pressures and will have a better chance of survival |
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What happens to the gene pool when natural selection occurs? |
Alleic frequency of the favourable allele increases as individual has better chance of survival and reproductive success and so produces more offspring and offspring survive too as they possess the allele |
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What are common selection pressures? How may an individual be able to survive in them (suited to them)? |
Harsh environment , predators , disease and inter/intra specific competition. Longer fur for cold weather , can hide from predators e.g colour , better features for competing and getting resources than other individuals of the species e.g size and strength. May be less susceptible to a disease |
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How does natural selection lead to evolution? |
Many generations of favouring the allele and the alleic frequency increases so much that virtually every individual has the allele and is suited to the environment - entire species has evolved to be adapted to the selection pressures so the selection pressure no longer exists. Less favourable alles die out as only certain population size can be supported and those better adapted will survive |
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Why do population sizes not increase exponentially? |
Death rate is very high due to individuals being out competed , selected against etc and the habitat can only support a specific size so all animal populations are constantly competing for resources |
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Why is variation maintained in populations even if it means they may be less suited? |
Incase selection pressures change again so population has a chance of having a new favourable allele and surviving by adapting. Without variation they may all die out because they will all be selected against |
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What are the 3 types of natural selection? |
Stabilising directional and disruptive |
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When do these types of selection occur? |
Stabilising when selection pressures havent changed for a long time Directional when selection pressure suddenly changes Disruptive when selection pressure changes and favours both extremes or selection constantly changing and favours both extremes in different cases e.g season changes |
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Stabilising selection is an example of how... |
Evolution due to natural selection occurs |
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Over time what can disruptive selection lead to? Why? |
Speciation as the two seperate extremes will reprodiuctively isolate themselves from eachother due to differences and eventually so much genetic change may have occured that they can no longer interbreed |
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What has to happen for speciation to occur? |
One population splits into two and are reproductively isolated. Over time genetic changes e.g. mutations and natural selection if the environments are different so eventually can no longer interbreed and are considered to be seperate species |
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What is allopatric speciation? |
Populations are reproductively isolated because of geographical barrier. Selection pressures are different either side so natural selection is different. Resulting alleic frequencies are different and mutations. Eventually become so different they can no longer interbreed and are considered to be seperate species |
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What is sympatric speciation? |
Not geographically isolated. In the same area but are reproductively isolated due to mutation which changes mating season /chromosome number or are carrying out non-random mating etc.over time genetic differences accumulate due to further mutations etc that they can no longer interbreed and are considered to be two species |
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What is genetic drift? |
When alleic frequencies are altered due to chance and not because of differential survival |
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Where does genetic drift have an effect and can cause evolution? |
In small populations. Increasing allele frequency due to reproduction has a massive change on overall allele frequency as it is a greater proportion of all the alleles present. Therefore evolution and speciation occurs much quickly in small populations due to this. A mutated allele will be quickly passed on and result in evolution. Chance has greater influence in smaller samples ( think random sampling) |
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Define genotype. |
The genetic constitution of an organism. All the alleles that an organism possesses - determines phenotype |
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Define phenotype. |
Observable or biochemical characteristics of an organism. Is a result of the expression of the genotype and environmental influence |
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What does it mean if a gene has multiple alleles? |
More than 2 forms of a gene exist |
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How do you produce a pure breed ? (Is homozygous dominant for one gene) |
Keep breeding together ones with desirable phenotype until only produce the desirable phenotype |
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What is the F1 generation? What does it produce? What can be concluded? |
Crossing pure breeds for one gene but have different alleles All heterozygous produced Phenotype tells you the dominant allele |
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What is the F2 generation? What ratios are always given for monohybrid crosses? |
2 F1s crossed - both are hetereozygous 3:1 dom to recessive but one is homo dom one is home recessive and 2 are hetereo |
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Why does a larger sample size of cross results result in a ratio closer to predicted ratio? |
Larger sample = less effects of chance (anomaly influence) If its smaller more statistical error occurs , each event of fertilisation of gametes is independent to the last so any combo can form based on probability |
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Rules for a genetic cross : |
Give a key Use letter where capital and lower case look different Show parents genotypes and phenotypes Show gametes produced via meiosis , encircle them Label male and female in punnett square State genotype and phenotype of possible offspring |
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How do you produce an F1 generation for dihybrid ?? |
Both pure breeds and one must be pure dom for both characteristics and the other must be pure recessive for both characteristics |
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What is the expected ratio of an F2 gen for dihybrid? |
9:3:3:1 |
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What should you consider if phenotype ratios deviate from expected? |
Some kind of abnormal inheritance such as linkage , codominance , multiple alleles, epistasis, mutations , crossing over Or due to chance (as fertilisation is random and small sample sizes are effected by chance - or natural selection) - find out using chi-squared |
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If you have two pure breeds for a gene with codominant alleles what will their offspring be like? |
All have phenotype which results from codominance |
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How do you represent codominant alleles with symbols? |
Letter for gene and superscript for allele (different letter)as capitals and not for different alleles cannot be used as represent dominance /recessiveness |
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Why do males suffer more from sex linked conditions? |
As Y is smaller than X no equivalent loci . Only one recessive sex linked gene required on X for expression. Need 2 in females as have XX |
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What parent do males inherit sex linked genes from? What about females? |
Mother (must be a carrier) as its on X chromosome Daughter has to get it from mother and father (dad must have it and mother must be a carrier)- if dad has it daughter will be a carrier |
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What symbols do you use to represent sex linked genes? |
X and Y with superscripts of lower and upper case from dom and recessive. But Y wont have one as no equivalent loci |
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What is autosomal linkage?what does this entail for inheritance? |
Where 2 genes are found on the same chromosome. Less gamete combos as certain alleles stick together as whole chromosomes go into gametes. Can only be changed by crossing over which is rare |
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How does autosomal linkage simplify dihybrid ratios? |
For f2 gen its 3:1 not 9:3:3:1 as less gametes possible |
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What conditions must be met for chi-squared to be used? |
Sample size over 20 Catergoric data Compares experimental raw data to theoretical raw data |
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Formula to calculate chi-squared? |
Sum of (O-E )^2 / E |
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How do you calculate degrees of freedom? |
Number of classes - 1 |
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What will be recessive/dominant for multiple alleles? |
Can have a hierachy of dominance or show co-dominance |
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What causes animals to have different fur colours all over? |
Sex linked gene for fur colour. X chromosomes in the fur cells of females can deactivate. Alleles are codominant so 3 colours can be produced for fur |
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What are the features of a climax community? |
Same species stay for a long time Abiotic factors are constant Population sizes are constant and at the carrying capacity |
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If it says give the frequency of allele/genotype how should you express it? |
As a decimal. Only percentage if asked and it will ask for actual number |
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Define community |
All the populations of the different species living and interacting in th3 same place at the same time (within an ecosystem) |
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Define ecosystem. |
All the living (biotic) and non-living (abiotic) components of a particular area |
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What is an ecological niche? |
The unique role of an organism of a species in an ecosystem/its habitat. It includes all the abiotic and biotic adaptations and intereactions aswell as its behaviour and where it lives (habitat) |
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Can two different species share a niche? Why? What is this known as? |
No as this would lead to interspecific competition eventually leading to the species better adapted to the niche outcompeteing the other and leading to its exitinction. Two species may appear to have the same niche but slight behavioural differences mean they dont This is called the competitive exclusion principle |
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What two things occur in an ecosystem (unit 5)? |
Flow of energy via the foodchain Cycling of nutrients |
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How should you plot a graph of population size vs time if it increases exponentially like bacteria growth? |
Use a log graph - turns into a straight line with a sensible scale and we can see any changes in population growth |
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What is the carrying capacity? |
The maximum population size of a species that an ecosystem can support - cannot get any larger than this. This size is maintained over a period of time |
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What determines the carrying capacity? |
Abiotic and biotic factors of the ecosystem and how the organism is adapted to them/their availability |
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How can abiotic factors effect the carrying capacity? |
They can become limiting factors for the growth of a population once a certain size is reached as their isnt enough resources to increase any further as current population is using all the resources Also if abiotic factors change with season change population size may decrease as less resources to support - less adapted individuals die. Not at optimum point |
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Define abiotic factors. Examples? |
The non-living components of an ecosysten. Temperature , light availability , pH and water |
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Why do different abiotic factors effect different species differently? |
They have different ecological niche - adapted in a different way |
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How does temperature effect population size? |
Each species has an optimum temp (part of niche) , when at the optimum population size is greatest as its better adapted - more chance of survival. If not optimum size decreases as less adapted - migt be less resources too , limiting factor E.g enzyme function too slow/denatured which effects metabolic rate and growth and reproduction and warm-blooded mammals have to use energy to maintain optimum body temp - less energy for growth and reproduction if using most of it to maintain |
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How does light availability effect population size? |
Needed for photosynthesis. More = more photo so more growth of plants and reproduction and more energy available to other organisms for growth and reproduction so population size increase |
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How does pH effect population size? |
Effects enzyme function. Each species has an optimum pH. If optimum = larger population |
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How does water effect population size? |
Needed for survival so if scarce small population as limiting resources - only those adapted survive and carrying capacity is low (more xerophytes) |
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What happens to population size if abiotic changes are too extreme? |
None can survive so go extinct |
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Define biotic factors. Examples? |
The living components of an ecosystem. Competition , predation ,disease , food (if it is other populations- the food chain) |
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What is the difference between intraspecific and interspecific competition? |
Intra - within a species Inter- between species |
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How does the availability of resources effect the amount of competition? |
Less resources = more competition |
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Why predators and preys evolved over time to be better at this? |
Individuals with characteristics that made them better were more likely to survive. Predator get prey and prey not get eaten so pass on this characteristic to the next gen increasing allele frequency as it is favourable Selection pressure is created by this cycle |
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How do the populations of predator and prey change over time? |
Fluctuate. But follow each other pattern |
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Explain why this occurs. |
Predators eat prey and increase in population size and reduce the prey population which results in less food resources - limiting factor so predator population decreases as intrapspecific competition occurs. With fewer predators prey population can grow as less are eaten and then the process repeats |
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Why may the predator prey fluctuations be less severe in reality? |
Eat a range of food so dont effect eachother as much |
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What is a habitat? |
The place where an organism lives. (Has specific conditions and other organisms present) |
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How many habitats are within an ecosystem? |
Many |
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What are microhabitats? |
Habitats within habitats that have spefic microclimates (usually for small organisms) |
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Why does population size fluctuate around the carrying capacity? |
Size increases when resources plentiful but this means more resources are required so only those best adapted survive and size decreases until theres resources available and size increases again (similar to predator-prey) |
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Why are different organisms found in different habitats? |
Adapted to different biotic and abiotic factors - have different niches |
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What 4 factors determine whether the human population increases or decreases? |
The balance between birth rate death rate immigration and emigration (migration only applies to individual populations not the whole world) |
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What graphs are used to predict how human populations will change in the future? Why? |
Population pyramids (age vs population percent with males on left and females on right) Depends on number of child bearing aged females |
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What does the population pyramid for an increasing population look like? |
Larger number of young people due to high birth rate which outweighs death rate |
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What does the population pyramid look like for a decreasing population? |
Low birth rate so narrow base |
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How does a human population change when it develops economically? |
Originally high birth and death but as conditions improve death decreases and then birth decreasing until both are low but the population is much larger |
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How can individuals of a population prevent other individuals from receiving resources? |
Grow and block them out such as covering a pond surface or trees growing tall |
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Why is it difficult to conclude population size changes are due to competition? |
Sizes are affected by abiotic factors too (also predators) Correlation does not always mean causation There may be a time lag in data |
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Why is it difficult to obtain reliable data on natural populations? |
All the individuals cannot be counted. We must rely on samples |
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Why cant quadrats be used for motile species? When are they used? |
Motile species will move away and too quickly to be measured Can use quadrats for plants and non-motile species as they wont |
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What method do we use to measure the abundance of motile species? |
Mark release recapture technique |
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How does MRR work? |
Sample caught counted marked and released. Time is given for dispersion. Second cample caught number counted but also number already marked are counted too |
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What is the equation to work out population size of a species when you have used MRR? |
First sample size × second sample size ÷ number marked in second sample |
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What assumptions does MRR rely on? |
Mark used is not rubbed off after dispersion Marking does not effect survival of species e.g predation and also not toxic to it No deaths or births occur changing population size No migration changingpopulation size Dispersion time is sufficient for complete and even dispersion Equation relies on the fact that ratio of marked to unmarked in second sample is same as marked to unmarked in all population |
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How is random sampling with quadrats carried out? |
Select a study area and lay out two long tape measures at right angles at the edge of the study area Use a computer to generate a large number (large number of samples- more representative as effects of chance are less) of coordinates (not bias as no human involvement) . Place qudrat at each point using tape measures to find it look at abundance / number of species in quadrat and record results |
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What is systematic sampling? What is it used for? |
Looking at gradual changes over an area (e.g. along a line of succession) Use a belt transect by setting up a line or tape on the floor for the area you want to observe. Quadrat put next to it and moved along at regular intervals and samples are taken |
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What are the two ways abundance in quadrats is measured? |
Frequency and percentage cover |
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What is percentage cover? When do we use it? Pro and con? |
Estimate of percentage that a species in a quadrat covers. Used when they are difficult to count individually or in a high abundance. This makes it quicker to collect samples but is difficult when the plant is in overlapping layers |
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What is frequency? When do we use it? |
Count number of squares of the quadrat the species appears. Divide this by total squares to get a percentage (likelihood it appears). Used also when hard to count individually. |
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What can you do if you just want the abundance of species and number of species? |
Count them individually in the quadrat |
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What are the two different types of quadrat? |
Point and frame |
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How can a pilot study be used to decide which quadrat to use? |
Carry out same study with different sizes and then plot a graph of no. Of species counted/abundance against size and where the graph begins to level off is the size you should use as any larger size will give the same result but be more time consuming |
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What other 2 factors effect which size qudrat is used? |
Size of the organisms Where distribution is not even using a large number of small quadrats is more representative than a small number of large ones |
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What do you need to balance when using quadrats in a study? |
Representative results and how long the study will take If there is a high species diversity more samples need to be taken so it is representative |
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If the assumptions of MRR are not met how do you explain their effects on the population estimate? |
See how they numerically change the equation and think about proportions |
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What is it called when an ecosystem (biotic and abiotic) changes over time? |
Succession |
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What is the difference between primary and secondary succession? |
Primary - occurs on land that has been newly formed or exposed , nothing has ever lived there before. No soil present Secondary - organisms have leaved there before but have been cleared such as by humans of a fire. Soil is present due to these previous organisms |
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What is the process of primary succession? |
A pioneer species colonises the new land which has harsh abiotic conditions as there is no soil or water present so only pioneer species which are adapted are able to grow. The presence of the pioneer species changes the abiotic conditions making them less hostile e.g. when they die they are broken down to produce soil that contains nutrients and can hold water (more the thicker it gets). New organisms can now grow as the abiotic factors are more suited to them. They out compete the pioneer species. These then die making abiotic factors less harsh again as provide more nutrients and soil. More species can grow and outcompete old ones as they are more suited. The ecosystem becomes more diverse , biodiversity increases as species diversity increases and it reaches a climax community - no more change |
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What is the difference in the process of secondary succession compared to primary? |
Soil already present so pioneer species is different |
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Define climax community. |
The organisms which make up the final stage of ecological succession (ecosystem supports largest and most diverse community) |
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What determines the climax community and the dominant species of it? |
Abiotic factors of the resulting ecosystem after succession - dominant is one most adapted , suited niche |
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What features of an organism would make it a suitable pioneer species? |
Tolerance to extreme conditions - harsh abiotic factors Can fix nitrogen as no nutrients available as no soil Asexual reproduction or rapid production of wind dispersed seeds and spores so population increases rapidly and widely Can photosynthesis so are not dependent on others that are not present |
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What else apart from breakdown of dead remains can produce soil? |
The weathering of the base rock by the pioneer species |
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How does succession of plants lead to animals been able to live in the ecosystem too? |
Provides food sources and habitats for them |
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Which occurs quicker, primary or secondary? |
Secondary as soil already present so plants can grow and migration into cleared area occurs |
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What is polymorphism? |
A species has seperate distinct forms that occur in the same breeding population - they are the same species still. E.g. the peppered moth |
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Define speciation. |
The evolution of a new species from an existing species |
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Give examples of selection pressures which are not environmental? |
Predation disease and competition - better suited to withstand these = greater survival and reproductive success |
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What is the purpose of overproduction of offspring? |
Creates too many individuals for the available resources so intraspecific competition occurs Best suited survive - causing natural selection Also compensates for high death rates to keep population size constant |
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What does dynamic mean? |
Constantly changing |
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What else does soil do apart from providing nutrients ? |
Holds water for plants |
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What is a climax community? |
Community is constant and unchanging over a long period of time. Species in equilibrium. No new species and no species being outcompeted. Large biodiversity |
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Why is biodiversity greater in mid-succession than in the climax community? |
The dominant species out competes |
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How does succession effect biomass of a community? |
Increases it as species diversity increases (number of individuals is greater) |
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What determines the dominant species of a community? |
The abiotic factors - the dominant species is best adapted to these |
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What is one way of conserving habitats (and species within them) in a community? |
Managing succession - preventing changes in the community so habitats remain and the species are not out-competed |
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Examples of how succession can be managed? |
Burning heather and having sheep graze (if these are stopped secondary succession occurs) |
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Define conservation. |
Maintaining ecosystems and the species and habitats within them. Make best use of resources whilst preserving at the same time |
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What are the reasons for conservation? |
Ethical - respect for other living things , animals should coexist along side us Economic - organisms can provide us with resources which could be valuable Aesthetics Personal - maintain our life support system |