topic 7: Genetics, populations, evolution and ecosystems Flashcards
How many antigen-determining alleles will be present in a white blood cell
2 = white blood cells are diploid cells
-alleles are present on each chromosome of an homologous pair
-one maternal allele and one paternal allele
notes from the specification
The individuals of a species share the same genes but (usually) different combinations of alleles of these genes. An individual inherits alleles from their parent or parents.
A species exists as one or more populations. There is variation in the phenotypes of organisms in a population, due to genetic and environmental factors. Two forces affect genetic variation in populations: genetic drift and natural selection. Genetic drift can cause changes in allele frequency in small populations. Natural selection occurs when alleles that enhance the fitness of the individuals that carry them rise in frequency. A change in the allele frequency of a population is evolution.
If a population becomes isolated from other populations of the same species, there will be no gene flow between the isolated population and the others. This may lead to the accumulation of genetic differences in the isolated population, compared with the other populations. These differences may ultimately lead to organisms in the isolated population becoming unable to breed and produce fertile offspring with organisms from the other populations. This reproductive isolation means that a new species has evolved.
Populations of different species live in communities. Competition occurs within and between these populations for the means of survival. Within a single community, one population is affected by other populations, the biotic factors, in its environment. Populations within communities are also affected by, and in turn affect, the abiotic (physicochemical) factors in an ecosystem.
genotype vs phenotype
-genotype = genetic constitution of an organism
-phenotype = expression of this genetic constitution and its interaction with the environment
nature of alleles
-alleles can be recessive, dominant or co-dominant
-In a diploid organism, the alleles at a specific locus may be either homozygous or heterozygous.
monohybrid inheritance
-monohybrid inheritance looks at how the alleles for a single gene are passed on from one generation to the next
-when 2 individuals sexually reproduce there is an equal chance of either allele from their homozygous pair making it into their gametes. This means there is an equal chance of the zygote inheriting either allele from their parent
monohybrid diagrams (F1 generation)
One of the genes for the coat colour of horses has the following two alleles:
B, a dominant allele produces a black coat when present
b, a recessive allele produces a chestnut coat when present in a homozygous individual
In this example a heterozygous male is crossed with heterozygous female
Parental phenotype: black coat x black coat
Parental genotype: Bb Bb
Parental gametes: B or b B or b
Ratio of black to chestnut = 3:1 (phenotype)
Genotype ratio = 1:2:1
dihybrid inheritance
-dihybrid inheritance = involves the inheritance of 2 characteristics coded for by 2 different genes located on 2 different chromosomes
genotype + homozygous + heterozygous
What is the genotype: Bb
Explanation: they must be carriers of the round eye allele bc they are able to produce offspring with round eyes (bb)
GG + NN = homozygous dominant
Pure bred homozygous = AA
Mendel
-investigated the inheritance of 2 characteristics of a pea plant at the same tie
-observed flower colour, position, pea colour, pea shape
Producing the F1 generation
Phenotype: Round yellow Wrinkled Green
Genotype: RRYY rryy
Gametes: RY ry
Draw punnet square
Offspring genotype: RrYy
Offspring phenotype: Round yellow
Phenotypic ratio = 1:0
Producing the F2 generation
Phenotype: Round yellow Round yellow
Genotype: RrYy RrYy
Gametes: RY, Ry, rY, ry RY, Ry, rY, ry
Draw Punnet square (4 x 4)
Offspring phenotypes: round + yellow : round + green : wrinkled yellow : wrinkled green
Phenotypic ratio = 9 : 3 : 3 : 1
law of independent assortment
Law of independent assortment = each member of a pair of alleles may combine randomly with their of another pair
co-dominance
-when 2 dominant alleles are expressed in the phenotype (due to a pair of alleles being equally dominant)
Calculating co-dominance
Phenotype: Black Hen White Hen
Genotype: C^B C^B C^W C^W
Gametes: C^B C^W
Offspring genotype = C^B C^W
Offspring phenotype = speckled Hen
Phenotype: speckled speckled
Genotype: C^B C^W C^B C^W
Gametes: C^B C^W C^B C^W
Draw punnet square
Speckled : Black : White
2 : 1 : 1
Phenotype: the observed characteristic due to the genetic constitution of an organism and its interactions with the environment
position of a gene on a particular DNA molecule
locus
homozygous
bb
heterozygous
Bb
true or false = only one pair of alleles can be present in a single gamete
true
what is meant by the term phenotype
the observed characteristic due to the genetic consitution of an organism and its interaction with the environment
Gametes of AaBb genotype
AB, Ab, aB, ab
gametes of aabb
ab
explain 2 reasons why the fruit fly is a useful organism for studyin genetic corsses
1) large sample (400 eggs)
2) short life cycle 7-14 days so can produce many crosses in a short length of time
suggest one reason why observed ratios are often not the same as expected ratios
random fertilisation of gametes
male fruit flies are more likely than female fruit flies to show a phentype produced by a recessive allele carried on the x chromosome. Explain why
-males = one allele for recessive to be shown in phenotype
-females = need 2 recessive alleles to be present in phenotype
explain what is meant by a dominant allele
allele which is always expressed in the phenotype
suggest one reason why farmers would want the calves to be all of the same sex
-females = milk production
-males = meat
-male or female for breeding
explain what causes the sperms of one kind to have 3% more DNA than sperms of the other kind
sperm with more DNA has X chromosome which is larger than Y
in fruit flies the genes for body colour and wing length are linked. Explain what this means
genes are on the same chromosome
use your knowledge of gene linkage to explain these results
-autosomal linkage means that genes on the same chromosome are inherited togethe
-this means that most offspring were GGNN or ggnn
-however due to crossing over some gametes were Gn or gN meaning that some offspring were GgNn or ggNn
give reason for your choice of statistical test
chi squared
categorical data
why are the phenotypic ratios not the same as expected ratios. Give 2 reasons
1) Random fertilisation of gametes
2) crossing over linked genes
sex linkage male genotype =
X^a Y
heterozygous definition
pair of homologous chromosomes carrying 2 different alleles for the same gene
codominance definition
both alleles are equally dominant and expressed in the phenotype
genotype for carriers of CF
what is the probability that 2 carriers of cystic fibrosis would have a girl sufferer
Cc = one dominant and one recessive
cc = recessive = 25%
chance of girl = 50%
25% x 50% = 12.5%
how to know its a monohybrid question
only 2 possible phenotypes
gametes for RRYY
RY
when parental genotype is not homozygous then there are more options than e.g ab for the gametes
sex linkage
-humans have 23 pairs of chromosomes
-22 of these have homologous partners (autosomes)
-23rd pair = sex chromosomes
Any gene carried on the X or Y chromosome is sex linked
female vs male chromosome
XX = female
XY = male
The Y chromosome
Y chromosome is shorter than the X chromosome
This means that homologous chromosomes arent present across the entire length of the X chromosome as Y is shorter (only one homologous pair)
Recessive disorders and genetic disorders are more common as females require 2 recessive alleles on sex chromosome while males require only 1 on the X chromosome to express a recessive phenotype
cannot form typical bivalent
-XY chromosomes are not homologous along the entire length of the chromosome so crossing over doesnt occur. Y is shorter than X chromosome which means a typical bivalent doesn’t form. Chromatids cannot pair up due to short pairing region
typical bivalent
Typical bivalent = cross over of 2 homolgous pairs
Predict the genotypes of offspring of a female who carries the allele for haemophillia and a normal male:
Phenotype: Female carrier Male carrier
Genotype: X^H X^h X^H Y
Gametes: X^H X^h X^h Y
Female normal : male normal : female carrier : male sufferer
1: 1 : 1: 1
autosomal linkage
-refers to the inheritance of genes carried on the same autosome
-the further apart 2 genes are on autosomes the higher the chance of crossing over and therefore genetic variation
Model answer : autosomal linkage
Phenotype: grey body, long wings black body, short wings
Genotype: GgNn ggnn
Gametes: GN, Gn, gN, gn gn
Phenotype: Grey long, grey short, black long, black short
1: 1 : 1 : 1
multiple alleles
Multiple alleles –> where there are more than 2 alleles of which only 2 may be present at the loci of an individuals homologous chromosomes
Any two genes that occur on the same chromosome are said LO be linked.
in a male with AS where would the sex linked mutation be located
non-homologous section of an X chromosome
null vs alternate hypothesis
-Null hypothesis –> there is no relationship between variables (observed and expected results)
-Alternate hypothesis –> there is a relationship between variables
epistasis + pedigree analysis
Peidgree analysis = show the inheritance of a particular phenotype over several generations
Epistasis:
-9:4:3
-one gene affects the expression of another gene to determine some of the phenotype
characteristics of chi-squared test
-large sample size
-discrete categories e.g hair colour
-data is provided as raw count (not percentages)
-comparing experimental with hypotheical results
chi squared equation
Chi squared (X^2) = sum of (observed – expected)^2 / expected results
We square the numbers to make sure there arent any negative values
0.05 = critical value
calculating degrees of freedom
Calculating degrees of freedom = number of categories – 1
do we accept or reject the null hypothesis
If chisquared values are below 0.05 we accept the alternate hypothesis and reject the null hypothesis
If chi-square values are above 0.05 we accept the null hypothesis and reject the alternate hypothesis
A heterozgous pair of rabbits for coat colour and ear length were crossed and the following offspring were produced
calculate observed results and total
total / 9:3:3:1 ratio
calculate expected results
input in equation
find degrees of freedom
look at critical value tables
p and q
-p = dominant
-q = recessive
define population
Population –> group of organisms of the same species occupying a particular space at a particular time that can potentially interbreed
define gene pool
Gene Pool –> all of the alleles of all of the genes of all the indviduals in a population at a given time
Larger gene pool = greater genetic diversity
Small gene pool = increase in recessive mutations + less genetic diversity
e.g in a population of 10,000 people the gene pool is 20,000 alleles for a single gene
2 hardy weinberg equations
-p + q = 1
-p^2 + 2pq + q^2 = 1
what does the hardy weinberg equation tell us
The frequency of dominant and recessive alleles will remain constant in a population from one generation to the next provided certain conditions are met
–> population is large
-no migration in or out of the population
-there are no mutations resulting in new alleles in the population
-mating is taking place randomly within the population
The allele y for blue pigmentation occurs with a frequency of 0.78 in a populatin of clams. Give the frequencies of the genotyypes YY, Yy and yy.
1) p + q = 1
2) p^2 + 2pq + q^2 = 1
3) P + 0.78 = 1
4) p = 0.22
5) (0.22)^2 + 2(0.22x0.78) + (0.78)^2
Yy = 0.0484
YY = 0.3432
Yy = 0.6084
The gene for albinism is known to be a recessive allele. 7ppl in a sample of 10,000 were found to have albino phenotypes. 9993 had skin pigmentation that was normal. Assuming the hardy-weinberg equilibrium what is the allele frequency for the dominant pigmentation allele in this population.
1) p + q = 1
2) p^2 + 2pq + q^2 = 1
3) q^2 = 0.0007
4) q = 0.0265
5) p + 0.0265 = 1 so p = 0.974
Find p2 value
explain the proportions of the two types of clover plant in different parts of the field
-both plants present in low slug density conditions as there is less selection pressure
-however only cyanide plants into high slug density conditions since cyanide can kill slugs so more survive
the inheritance of body colour in fruit flies was investigated. 152 = grey 48 = black
give the genotype of parents and explain
Gg
ratio 3:1
explain why a statistical test should be applied to the data obtained in this investigation
to determine the probability of results being due to chance
what does the hardy weinberg principle predict about the frequency of the t alleles afte another 10 generations
frequency remains the same
suggest 2 factors that scientists should have taken into account when selecting people
age
sex
family history
recreational drugs
explain how resistance to an antibiotic could become widespread in bacterial population following a gene mutation
-frequenct use of antibiotic creates selection pressure
-bacteria with…..
-reproduce and pass on alleles…
-overtime allele freqency increases
-frequency of resistant types increase in subsequent generations
why population size can vary
-effect of abiotic factors
-interactions between organisms (intraspecific = same species) and interspecific (different species), competition and predation
In corn, purple kernels are dominant to yellow. A random sample of 100 kernels is taken from a population in hardy weinberg equilibrium. 9 = yellow and 91 = purple:
-q^2 = 9/100 = 0.09
q = 0.3
P + 0.3 = 1
P = 0.7
A population of cats can be Black (B) or white (b). Given a population of 1,000 cats there are 840 black cats and 160 white cats. Determine the allele frequency:
Q^2 = 0.16
Q = 0.4
P = 0.6
P^2 = 0.36
Bb = 480 cats
BB = 360 cats
-bb = 160 cats
tips for hardy weinberg equations
-find total population
-find recessive allele first
3 factors that affect species survival
-predators
-disease
-competition
causes of genetic variation
-crossing over
-independent segregation
-random fertilisation
-both environmental and genetic factors play into variation
variation
Variation = change in phenotype due to environmental and genetic factors
The primary source of genetic variation is mutation. Meiosis and random fertilisation of gametes during sexual reproduction produce furthe rgenetic variation
Variation helps species survival = allows for survival of the fittest, adapt to the environment and buffer against environmental change
height
Height = controlled by a combination of polygenes and environmental factors
discontinious vs continious variation
Discontinuous variation = organisms fit into limited number of possible values e.g blood group. A characteristic of this variation is usually controlled by a single gene
Skin colour = continious = polygeneic = line graph + bar chart = environmental
selection pressure
Selection pressure –> an environmental factor that determines which individuals live and which individuals die in turn affecting the gene pool
Competition = food, shelter, mates
process of natural selection
-variation due to mutation
-selection pressure
-survival of the fittest
-reproduction
suvival of the fittest
-can camoflague against predators
-better ways to find food
-stronger so are more likely to win mates
reproduction
-those organisms which survive are more likely to reproduce and pass on advantageous alleles to offspring.
-this means that offspring are more likely to survive.
-overtime allele frequency in population increases
environmental influences
Environmental influences = temperature, rainfall, sunlight, soil conditions, pH, food
types of selection pressure
stabilising
directional
disruptive
success criteria for natural selection
-state there is variation in the population due to mutation
-name the characteristic that allows some individuals to survive and why
-survive, reproduce and pass on advantageous alleles to offspring
-overtime frequency of alleles that code for…increases
epistasis
In epistasis the interaction of different loci on the
gene, one gene locus affects the other gene
locus. One gene loci can either mask or suppress
the expression of another gene locus. An example
is two genes in mice that control fur colour.
Genotypes AA or Aa have black bands in their fur,
while genotype aa has solid black fur. Gene B
controls the expression of gene A. Genotypes BB or
Bb will allow expression of gene A, but genotype
bb will not. Mice with genotype bb are all white,
called albino. This idea is illustrated in the
diagram.
recessive vs dominant epistasis
- Recessive epistasis occurs when the presence of
a recessive allele prevents the expression of
another allele at a second locus. Recessive
epistasis gives the ratio of 9:3:4. - Dominant epistasis is when a dominant allele at
one locus completely masks the alleles at a
second locus. Dominant epistasis gives a ratio of
12:3:1.
biotic factors
disease
competition
predators
animals/humans
why is it directional selection
dominant allele= proves advantageous
explain how this might eventually lead to the production of a new species
-reproductively isolated
-different selection pressures
-different adaptations]
-populations become more genetically different
selection
Selection is the process by which individuals that are better adapted to their environment are
more likely to survive and breed. This means that they can pass on their advantageous alleles.
Every living organism is subject to selection determined by the conditions which they are living
in. There are two key types of selection, these are:
stablizing selection
-Stabilizing selection = favour the average
-favours the intermediate phenotype
-usually occurs when environmental conditions are stable
directional selection
Directional selection = favours the extreme phenotype as it has a selective advantage in the population
disruptive selection
-favours both extreme phenotypes
-intermediate allele frequency decreases
-average/intermediate decreases
suggest why the scientists took his sample from the population at random
to avoid bias
so sample is reliable and represetnative
allele =
has a selective advantage
why is it directional selection
one extreme is favoured
conversion to ratio =
X : 1 = simplification
e.g 2.1 : 1
why does LP rapidly increase once selection has been established
LP = dominant allele
-always expressed in the phenotype
lactase persistence is caused by a DNA mutation. This mutation doesnt occur in the gene coding for lactase. Suggest and explain how this mutation causes LP
mutation in promoter gene or transcription factor
lactase gene continues to be transcribed
what term is used to describe populations of different species living in the same habitat
community
explain the advantage of species occupying different niches
there is less competition and less predatation
a student concludes that a decrease in acidity caused an increase in the number of water beetles
evaluation this conclusion
correlation doesnt mean causation
may be due to other abiotic factors e.g pH
variation in number of beetle species
large sample
give 2 conditions necessary for results from mark-release recapture investigations to be valid
-no migration
-large population
-no reproduction
-marking doesnt increase vulnerability to diseases
explain how you would use a quadrat to estimate the number of dandelion plants in a field measuring 100m by 150m
randomly placed quadrats using random number generator
obtain number of dadnelions in a given area
multiply to gives estimate for total field area
explain how different subspecies of giraffe may have become evolved from a common ancestor
-geographical isolation = separate gene pools
-variation due to mutaton
-different selection pressures result in different favourable alleles = pass on advantageus alleles to offspring
-allele frequency changes
-no longer interbreed to produce fertile offspring
allele frequency is affected by
selection pressures
ecosystem
An ecosystem includes all the organisms living in a particular area known as the community as
well as all the non-living elements of that particular environment. The distribution and
abundance of organisms in a habitat is controlled by both biotic (living) factors e.g. predators,
disease and abiotic (non-living factors) such as light levels and temperature. Each species has a
particular role in its habitat called its niche which consists of its biotic and abiotic interactions
with the environment
abiotic factors
- Temperature - each species has a different optimum temperature that it is best able to
survive at, the further away from this the fewer individuals that are able survive. - Light - this is a basic necessity of light, with the rate of photosynthesis increasing as light
intensity increases. - pH - this can have an impact on the action of enzymes with each enzyme having an optimum
pH that it can work at. Where the appropriate pH exists there is a larger proportion of
organisms. - Water and humidity - in instances where water is scarce only small populations of adapted
species will exist. Humidity affects transportation in plants and therefore only those that are
adapted to environments where transpiration is high will survive.
intraspecific comeptition
An example of intraspecific competition is male robins. These maintain a large territory to
support their families, however in winter when food is short they move into other males
territories to obtain enough food to survive.
interspecific competition
Interspecific competition on the other hand is where members of different species compete
with one another for the same resources. This occurs most commonly when different species
occupy the same niche. An example is red and grey squirrels in the UK.
niche
-niche = the role of an organism in its environment
dynamic populations
-dynamic populations = populations vary in size and composition overtime
factors affecting population growth
-limiting factors which can be either biotic or abiotic
-factors change overtime e.g as a population of photosynthetic organisms become larger they will consume mineral ions slowing the growth of the population overtime
-r-strategist species = rapidly growing populations (growth booms and then goes bust)
-k-strategist species = growth in more sustainable manner. Growth follows logarhthmic curve
biotic vs abiotic
Biotic = living features of an ecosystem e.g competition/predatation/disease)
Abiotic = non-living features of an ecosystem e.g sunlight, O2 levels, water
community
Community = all/different of the organisms or all of the species that occupy a specific place at a specific time
carrying capacity
biosphere
Carrying capacity = the population size that can ecosystem is able to support
Biosphere = the regions of the surface and atmosphere of the earth occupied by living organisms
niche
-niche and habitat are not the same
-e.g the niche of a red fox is to be a predator who feeds on small mammals in a forest
-ecological niche = provide scraps of food for decomposers = includes both the animals or plants physical habitate and how it has adapted to life in that habitat
evolution
-evolution = change in the allele frequency in a population –> selection pressures drive evolution
species
-evolution = change in the allele frequency in a population –> selection pressures drive evolution
-species = a group of organisms that can interbreed to produce fertile offspring
speciation
Speciation = events which result in the formation of new species
types of speciation
-sympatric (behavioural isolation)
-allopatric (geographical isolation)
Speciation can be investigated through whether a species produces fertile offspring across generations
formation of new species
For a new species to form the original population needs to be reproductively isolated meaning the gene pool is separated. This could be due to geographical barriers or behavioural separation.
allopatric speciation
-geographical isolation
-It is the most common type of speciation
Allopatric speciation occurs when populations of a species become separated from each other by geographical barriers
The barrier could be natural like a body of water, or a mountain range
It can also be man-made, like a motorway
This creates two populations of the same species who are reproductively separated from each other, and as a result, no genetic exchange can occur between them
If there are sufficient selection pressures acting to change the gene pools (and allele frequencies) within both populations then eventually these populations will diverge and form separate species
The changes in the alleles/genes of each population will affect the phenotypes present in both populations
Over time, the two populations may begin to differ physiologically, behaviourally and morphologically (structurally)
sympatric speciation
-occurs when the original population is behaviourally isolated
-2 populations remain in the same habitate however a mutation has resulted in some of the organisms having different flowering times
-this means that they become reproductively isolated and gene pools separate
-overtime natural selection occurs within each separated populaion which means changes in allele frequency occur
-eventually the two populatons can no longer interbreed to produce fertile offspring
define the term niche
the of an organism within its environment/ecosystem
explain the advanatage of species occupying different niches
less competition and less predetation
these 2 species are thought to have evolved as a result of sympatric speciation
-2 species evolved in the area
-reproductive isolation
-separate gene pools
-cannot interbreed to produce fertile offspring
describe how you would have collected samples t ensure they were representative
-random sampling e.g random calculator
-same size of net
-same size of quadrats
greatest variation =
largest standard deviation
suggest 3 possible limitations of this investigation
-lab guppies may not behaviour in the same way as wild guppies
-transport barrier = no courtship behaviour
-do know if guppies have been used in previous experiments
allopatric speciation strcuture
-different selection pressures = lead to changes in alelele frequency
-variation due to mutation = separate gene pool
describe on way in which scientists could find out whether they are from same species
breed together to see if they produce fertile offspring
give 2 features of a climax community
- same species present over long time
- abiotic factors are constant overtime
- populations stable around carrying capacity
succession occurs in natural ecosystems
-pinoeer species colonise barren and extreme environments and change their environment by forming soil
-environment becomes less hostile
-new species are able to outcompete the pinoeer species
-there is now an increase in bodiversity
-therefore a stable climax community is established
explain how succession results in a wide variety of fish living on coral reefs
-biodiversity increases
-provides more habitats and niches
explain the decrease in gross productivity as the woodland matures
-more competition for light
-less photosynthesis occurs
temperature of the external environment gets rrom their optimum
temperature, the more energy these organisms expend in trying to
maintain their normal body temperature. This leaves less energy
for individual growth and so they mature more slowly and their
reproductive rate slows. The carrying capacity of the population is
therefore reduced.
succession
Succession = the process where an ecosystem changes from simple to complex overtime
A pioneer species is a species that can colonise uninhabited land.
climax community
A climax community is a community that no longer experiences succession.
Explain the process of primary succession.
First, uninhabited land is colonised by a pioneer species.
This species then changes the environment.
This makes it less hostile for other species, enabling them to survive.
Each new species increases the biodiversity, and over time, a stable community forms.
This is called a climax community
genetic drift =
random chance
Genetic drift is when random chance, rather than natural selection, causes a population’s allele frequencies to change.
Genetic drift has a large impact on smaller populations
conservation
Conservation is the active management of an ecosystem to maintain its species and habitats.
Succession is the change in an ecosystem from simple to complex. The end-point of succession is a climax community.
motile + non-motile
Conservation can be used to preserve an ecosystem and prevent other species from entering or growing. This would prevent a climax community from forming.
Motile organisms, like mammals and insects, are able to move.
Non-motile organisms, like plants, are not able to move.
quadrats
Quadrats= investigate non-motile organisms
competitive exclusion principle
The competitive exclusion principle tells us that 2 species cant exactly have the same niche in a habitat and stably coexist
-when grown individually in the lab both species thrive but when they are grown in the same test tube (habitat) with a fixed amount of nutrients both grow poorly
log
Growth and size of human population:
-factors that limit the number of humans = food, physical habitat, disease, predetation
-Log(10) = input normally
-log(e) = In(number)
interspecific vs intraspecific competition
Interspecific competition = different species
Intraspecific competition = same species
calculating change in population size
Change in population size = (B + I) - (D + E)
-b = births
-d = deaths
-I = immigration
-E = emigration
Population change during period / population at start of period x 100 = population size
intraspecific competition
Intraspecific competition:
-occurs between members of the same species
-availability of resources such as food, water, breeding sites determine the maximum size of a population
interspecific competition
The competitive exclusion principle links to interspecific competition
-occurs between members of different species
-one of the species will usually have a competitive advantage = they will increase will the other decreases
-no 2 species occupy the same niche indefinetly
answering a graph question for competition
-After (time) the rise in population is mirrored by the fall in another population
-lack of food/ adverse weather/ new diseases / increase in predators
-one specie has more a chance of finding food etc
-the environment poses as an environment
-explain interspecific competition + carrying capacity
prey and predators
Predators = animals which consume other animals
Prey = animals which are comsumed by predators
The population of prey rarely reaches zero as prey animals are typically adapted to avoid predation
fluctuations in populations
Decrease in population due to fewer prey
Higher number of prey as predator population decreases
More prey so predators increase
Them prey decrease due to more predators
succession
-succession = series of changes that makes an ecosystem more habitable overtime e.g ecosystems are dynamic (always changing) = occurs in barren areas without organic matter
Succession occurs in deserts, volcanic regions post eruptions, rocky shorelines, new land formations
colonisation
Colonisation begins when a pioneer species find their way to an environment and settles, beginning to change the environment
what succession results in
-less hostile abiotic conditions
-greater number of habitats and niches
-increased biodiversity
-more complex food webs
-inceased biomass
pioneer species
-reproduce asexually
-produce a large number of wind dispered seeds
-able to photosynthesis
-able to survive in extreme conditions
making conditions less hostile
-when they die they make soil for the next stage of succession
-stabilise the conditions e,g make sand more secure for next plants
-when they decompose, nutrients released to support the plants
New species are able to outcompete the pioneer species for resources once the conditions have been made suitable for their survival
climax community
Climax community = the development of vegetation in an area overtime which as reached a steady state:
-soil is deep and rich in nutrients to support larger trees and plants
-the community is biodiverse and is able to support a range of wildelife
-community is more stable
common features of succession
-results in an abiotic environment which becomes less hostile
-increased biodiversity more complex food webs and increased biomass overtime
deflected succession
-process which happens during succession to prevent the climax community from being reached
-often cased by human intervention e.g use of lawnmoweres to mow grass to prevent it from becoming a meadow
-farmers will allow their cattle to graze to prevent a climax community being established
proccess of succession
1) pioneer species colonise barren and extreme environments
2) change the envronment by forming soil
3) make the environment less hostile so new species like algae are now able to outcompete pioneer species
4) increase in biodiversity therefore a stable climax community is established
Process of succession:
-pioneer species colonise extreme environment by making it less hostile
-pioneer species change the environment by forming soil
-this makes the environment less hostile to other species like algae and more adaptable
-this increases the level biodiversity as many species present
-the ecosystem eventually stabilises to form a climax community where the species diversity remains fairly constant.
use your knowledge of net producivity to explain why biomass shows little increase after 100 years
-decrease in GPP = increase in respiration
-NPP = GPP - respiration
overall data =
increase in species richness
suggest how the scientists decided that 40 minutes was an appropriate time
-repeat soil sorting for different times and record number of species collected
-too little time = sample not representative
explain why it would not be possible to calculate an index of diversity from the results on the table
no data on the number of indivduals in each species
suggest the benefit of allowing some weeds to grow
provide habitat/niches for insects
weeds = producers in the food chain
sampling techniques to study habitats
random sampling using quadrats
systemic sampling along a belt transect
factors to consider when using quadrats
-size of the quadrat
-number of sample quadrats needed
-position of each quadrat
random sampling
-avoids bias
-ensures data is reliable
choose fields close toegether =
minimise abiotic factors and differences
conservation =
maintenance of an ecosystem in ensuring biodiversity
quadrat practical answer
-divide the field into a grid using 2x tape measures at right angles
-use a random number generator to obtain coordinates
-place quadrat at points and count number of plants
-repeat + calculate mean
-calculate = area field/ area quadrat x mean
