populations + variation Flashcards
population
group of organisms of the same species occupying the same area at the same time
Allopatric speciation
Occurs when there is geographical isolation
Means they face different selection pressures
Variation due to mutations
Different alleles are advantageous
Individuals with those alleles more likely to survive and reproduce
Leads to change in allele frequency
Happens overtime till populations can no longer breed with reproductive success
Sympatric speciation
Occurs when there is no geographical isolation
Mutations cause variation
Reproductive isolation occurs as changes in alleles and phenotypes prevent breeding
Could be due to differences in mating seasons, changes to reproductive organs
Becomes separate species when can no longer interbreed and produce fertile offspring
Genetic drift
Individuals in a population show differences in their genotypes
By CHANCE the allele for one genotype is passed on more than others
So number of individuals with this allele increases
Changes in allele frequency could lead to speciation
bigger impact in smaller populations
- in larger, chance variations even out
Natural selection
Mutations create new alleles of a gene
If this gene is beneficial, organisms survived and passes it on
Individuals with this beneficial allele more likely to survive and reproduce
Increases allele frequency of beneficial allele
what is the result of natural selection?
species that are better adapted to their environment
anatomical - structural features
eg blubber
behavioural - way it acts
eg playing dead
physiological - processes within body
eg hibernation
what is a gene pool?
all the alleles of all the genes in a population at a given time
what is allele frequency?
how often an allele occurs in a population (gene pool)
what is a population?
group of organisms of the same species occupying a particular area at a particular time
sources of genetic variation
differences in base sequences between organisms of the same species, due to:
mutations
random fertilisation
meiosis
- independent segregation
- crossing over
= new alleles (can be beneficial or not)
why do individuals show variation?
due to genetic and environmental factors
eg mutation or different selection pressures
differences caused by genetic variation passed on
- inherited in DNA
environmental not
how do new species arise from existing?
when they become reproductively separated
can’t breed to create fertile offspring
stabilising selection
individuals with characteristics towards middle of range more likely to survive and reproduce
- alleles selected for
occurs when environment isn’t changing - reduces range of phenotypes
- preserves characteristics
eg human birth weights
those with mid weights more likely to survive, range smaller
directional selection
individuals with alleles for extreme characteristics more likely to survive and reproduce
- alleles at one extreme selected for
could be in response to environmental changes
- results in change in allele frequency
eg antibiotic resistance
those with resistance allele survive, passed on, increased number with resistance allele
disruptive selection
individuals with alleles for extreme phenotypes at either end of range more like to survive and reproduce
- extreme alleles selected for
- average phenotypes selected against (decrease in frequency)
when environment favours more than one phenotype
- result in change in allele frequency
- increase in frequency of extremes
what is evolution?
a change in allele frequency overtime
organisms become better adapted
occurs by
- natural selection
- genetic drift (chance)
what has created variety of species?
evolutionary change and speciation
populations divided over many years, into many different species
what is the Hardy Weinberg principle used to calculate?
predicts frequency of
alleles, genotypes and phenotypes
hardy-weinberg equations for allele frequency
p + q = 1
p = frequency of one allele
q = frequency of other
hardy-weinberg principle for genotype and phenotype frequency
p2 + 2pq + q2 = 1
p2 = homozygous dominant (PP)
2qp = heterozygous (Pp)
q2 = homozygous ressesive (pp)
assumptions of hardy Weinberg
accurate prediction needs:
no selection
no mutations
no migration
random mating
large population
what is a niche?
the role of a species in its habitat
including its biotic (eg what it eats)
and abiotic (carbon dioxide it breathes out)
interactions
adaptations in an ecosystem
adaptations = features that increase an organisms chance of survival
- adapted to biotic and abiotic factors
- anatomical - structural features
- behavioural - how it acts
- physiological - internal processes
adaptations allow a species to have its own niche
adaptations to abiotic conditions
webbed feet
- walk on land and swim in water
blubber
- for warmth, live where there is lots of food
hibernation
- over rate of metabolism over winter
- conserve energy in coldest months
adaptations to biotic conditions
mating calls
- attract mate of same species
- more successful mating
killing competition for resources
- bacteria producing antibiotics
adaptations to food sources
- rocks to open shellfish, more access to food
why do environmental factors limit population size?
result in differential survival and reproduction
create selection pressures
- some individuals better adapted, so survive
what is carrying capacity?
maximum stable population size of a species that an ecosystem can support
affected by biotic and abiotic factors
how do abiotic factors affect population size? (carrying capacity)
light
water
space
temperature
when these are ideal, organisms can survive and reproduce more successfully
eg ideal temperature, less energy used maintaining it
cant reproduce as well in unideal surroundings
how do biotic factors affect population size? (carrying capacity)
interspecific competition
intraspecific competition
predation
how does interspecific competition affect population size?
- competition between organisms of different species
- for same resources eg food
- means resources for both species reduced
- lower population sizes for both, less energy for growth and reproduction
- if one is better adapted, it will be outcompeted, can’t exist alongside other species, no resources
how does intraspecific competition affect population size?
- competition between organisms of same species
- for same resources eg food
- population increases when resources plentiful
- but then more organisms competing for sam space and food
- resources become limiting, population begins to decline
- smaler population so less completion for food, better for growth and reproduction
- population grows again
how does predation affect population size?
where an organism kills and eats another
population sizes between predators and prey interlinked - changes in one affect the other
- as prey population increases, more food for predators
- so predator population grows
- but means more prey is eaten
- so prey population falls
- means there’s less food for predators so their population decreases
(prey can then increase again)
how do you investigate population size of non-motile organisms?
quadrats and transects
quadrats used to calculate
- species frequency, how often species is found
- percentage cover, count squares with more than 50%, out of all the 100, quicker than counting all species
transects used to find out how plants are distributed across an area
- quadrats placed at set intervals along transect
- calculate species frequency or percentage cover
how do you investigate population size of motile organisms?
mark release recapture
- capture sample
- mark them (eg paint)
- release
- wait time
- recapture from same population
- count how many of second sample are marked
- use equations to estimate population size
total size =
no. in 1st sample X no. in 2nd sample
over
no. of marked in 2nd sample
asume
- markings haven’t affected chance of survival
- no significant changes in population size eg migration or deaths
- marked sample had enough time to mix back in with population
how to chose a sample
chose small area within area being investigated (less time consuming)
divide area in grid and use random number generator to select coordinates
avoids bias
how do you investigate effects of environmental factors on species distrubution?
create transect
- tape measure
place quadrat along transect
- at set intervals, eg every 2m
count squares in quadrat containing species
- calculate percentage cover
also record environmental factor in each quadrat eg pH
(use digital probe to measure pH)
repeat along transect
safety issues during fieldwork
suitable clothing and footwear
suitable time of day eg tides
ethical issues during fieldwork
damage vegetation and soils
impact animal species
should be planned to have smallest impact possible
eg don’t walk on species
what is succession?
the process by which an ecosystem changes over time
describe primary succession
happens of newly formed land
no soil or organic matter
- pioneer species colonise land
have to survive hostile abiotic conditions eg no soil - pioneer species change abiotic conditions
die and decompose to create soil - this makes conditions less hostile
eg has soil to retain water - new species can grow
can abiotic conditions more by dying and decomposing, more suitable to more species - soil becomes deeper and richer with minerals, can retain more water
larger species can grow
reaches climax community
describe secondary succession
happens on land cleared of all species
but soil remains
happens same as primary but starts at later stage as soil already present
pioneer species may be larger shrubs than in primary as conditions are less hostile
at each stage better adapted species more in and outcompete older ones
ecosystem becomes more complex
reaches climax community
what is a climax community?
where ecosystem is supporting largest and most complex community it can
in a steady state
different ecosystems have different climax communities
what is conservation?
protection and management of ecosystems
aims to protect species and habitats
managing succession in conservation
preventing succession allows ecosystems to be preserved
- stops climax community being reached
plagioclimax - climax community when succession is stopped arificially
(eg due to human activity)
animals allowed to graze on land
- keeps vegetation low
- stops larger plants establishing in area
managed fires it
- after fire secondary succession happens
- preserves pioneer species
- burnt again for other species can grow back
other methods of conservation (not succession management)
protected areas
eg national parks
- protect animals from hunting and habitats from urbanisation
fishing quotas
- limits on amount of fishing
- keep it sustainable
endangered species bred in captivity
seedbanks incase species become extinct
defining a species
observable characteristics
differences in DNA/RNA
differences in proteins
ability to reproduce and given fertile offspring
causes of change to allele frequency
natural selection
speciation (geographical isolation)
genetic drift
how does differential reproductive access affect allele frequency
those who reproduce pass alleles on
those with beneficial alleles more likely to survive and reproduce
therefore increases allele frequnecy of beneficial allele
causes of differential survival and reproduction
predation
competition
disease
(selection pressures)
causes of reproductive separation
become separate gene pool with no gene flow between
seasonal - different mating seasons
mechanical - changes to reproductive parts, cant breed
behavioural - courtship changes
how does succession result in variety of organisms?
increases biodiversity
environment less hostile for more species
more food and habitats available overtime
