7 Populations Flashcards
gene pool
all the alleles of all genes of all the individuals in a population at a given time
allelic frequency
the number of times an allele occurs within the gene pool
population
a group of organisms of the same species that occupies a particular space at a particular time and that can potentially interbreed
the hardy-weinberg principle
provides a mathematical equation that can be used to calculate the frequencies of the alleles of a particular gene in a population
makes the assumption that the proportion of dominant and recessive alleles of any gene in a population remains the same from one generation to the next this can be the case provided that five conditions are met
species
exist as one or more populations
a group of individuals that have a common ancestry and so share the same genes by different alleles and are capable of breeding with one another to produce fertile offspring
hady-weinberg principle conditions
- no mutations arise
- the population is isolated, that is, there is no flow of alleles into or out of the population
- there is no selection, that is, all alleles are equally likely to be passed to the next generation
- the population is large
- mating within the population is random
hardy-weinberg equations
p + q = 1.0
probability of dominant allele= p
probability of recessive allele= q
p^2 + 2pq + q^2 = 1.0
what do genetic variations arise as a result of?
mutations
meiosis
random fertilisation of gametes
mutations
these sudden changes to genes and chromosomes may, or may not, be passed on to the next generation
mutations are a main source of variation
meisosis
this special form of nuclear division produces new combinations of alleles and the offspring are therefore different from parents
which gamete fuses with which at fertilisation is a random process further adding to the variety of offspring two parents can produce
variation due to environmental influences
environment exerts influence on all organisms
these influences affect the way the organism’s genes are expressed
An example is two plants that possess the same alleles for the flower colour. However an environmental factor of one plant growing in a soil that lacks a certain mineral may mean the pigment in one will not develop so will have a slightly different flower colour. If a large enough sample is taken out of this trait then a normal distribution will be shown
selection pressures
environmental factors hat limit the population of a species
predation, disease and competition
determine the frequency of all alleles within the gene pool
process of evolution by means of natural selection depends upon what factors
- organisms produce more offspring than can be supported by the available supply of food, light, space, etc
- there is genetic variety within the populations of all species
- a variety of phenotypes that selection operates against
role of over-production of offspring in natural selection
where there are too many offspring for the available resources, there is competition amongst individuals (intraspecific competition) for the limited resources available
those individuals in a population best suited to prevailing conditions will be more likely to survive
these individuals will be more likely to breed and so pass on their more favourable allele combinations to the next generation, which will therefore have a diff allele freq from the previous one
role of variation in natural selection
the larger a population is, and the more genetically varied the individuals within it, the greater the chance that one or more individuals will have the combination of alleles that lead to a phenotype which is advantageous in the struggle for survival
these individuals are therefore more likely to breed and pass their allele combinations on
variations therefore provides the potential for a population to evolve and adapt to new circumstances
types of selection
stabilising
directional
disruptive
stabilising selection
preserves the average phenotype of a population by favouring average individuals
selection against extreme phenotypes
occurs where the environmental conditions are constant over long periods of time
directional selection
changes the phenotypes of a population by favouring phenotypes that vary in one direction from the mean of the population
selection for one extreme phenotype
occurs when the environmental conditions change and the phenotypes best suited to the new conditions are more likely to survive.
disruptive selection
favours individuals with extreme phenotypes rather than those with phenotypes around the mean of the population
occurs when an environmental factor such as temp takes two or more distinct forms
speciation
the evolution of new species from existing ones
how are new species formed
reproductive separation followed by genetic change due to natural selection
within a species thee are one or more populations
although individuals tend to breed only with others in the same population, they are nevertheless capable of breeding with individuals in other populations
if a population becomes separated in some way from other populations and undergoes different mutations- it will become genetically different from the other populations,
each of the populations will experience diff selection pressures as the environment of each will be slightly diff
natural selection will lead to changes in the allelic frequencies of each population
diff phenotypes each combination of alleles produces will be subject to selection pressure that will lead to each population becoming adapted to its local environment. adaptive radiation. results in changes to the allele freq of each pop
if pops were no longer physically separated, they would be unable to interbreed successfully
each pop would now be a diff species each with it sown gene pool
genetic drift
something that can take place in small populations.
this is because the relatively few members of a small population possess a smaller variety of alleles than the members of a large population.
their genetic diversity is less
as these few individuals breed, the genetic diversity of the population is restricted to those few alleles in the original population.
as there are only a small number of diff alleles, there is not an equal chance of each being passed on.
those that are passed on will quickly affect the whole population as their freq is high.
any mutation to one of these alleles that is selectively favoured will also more quickly affect the whole population because its freq will be high.
the effects of genetic drift will be greater and the pop will change relatively rapidly, making it more likely to develop into a separate species.
in large pops the effect of a mutant allele will be diluted as its freq is far less in the larger gene pool.
the effects of genetic drift are likely to be less, and development into a new species is likely to be slower
two forms of speciation
allopatric
sympatric
allopatric speciation
allopatric means diff countries and describes the form of speciation where two populations become geographically separated
geographical separation may br the result of any physical barrier between two pops which prevents them from interbreeding
these barriers include oceans, rivers, mountain ranges and deserts
if environmental conditions either side of the barrier vary, then natural selection will influence the two populations differently and each will evolve leading to adaptations to their local conditions
these changes may take many hundreds or thousands of generations, but ultimately lead to reproductive separation and the formation of separate species
sympatric separation
sympatric means same country and describes the form of speciation that results within a population in the same area leading to them becoming reproductively separated
ecology
the study of the inter-relationships between organisms and their environment
the environment includes both living (biotic) and non living (abiotic) factors
ecosystems
are dynamic systems made up of a community and all the non living factors of its environment
2 major processes:
-the flow of energy through the system
-the cycling of elements within the system
community
all the populations of diff species living and interacting in a particular place at the same time
habitat
the place where an organism normally lives and is characterised by physical conditions and the other types of organisms present
niche
describes how an organism fits into the environment
refers to where and organism lives and what it does there
includes all the biotic and abiotic conditions to which an organism is adapted in order to survive, reproduce and maintain a viable population
abiotic factors
- temp
- light
- pH
- water and humidity
temp- abiotic factor
each species has a diff optimum temp at which it is best able to survive
the further away from this, the fewer individuals in a population are able to survive and the smaller is the population that can be supported
light- abiotic factor
rate of photosynthesis inc as light intensity inc
the greater the rate of PS, the faster plants grow and the more spores or seeds they produce
pH- abiotic factor
affects the action of enzymes
each enzyme has an optimum pH at which it operates most efficiently
water and humidity- abiotic factor
where water is scarce, populations are small and consist only of species that are well adapted to living in dry conditions
humidity affects transpiration rates in plants and the evaporation of water from the bodies of animals
intraspecific competition
occurs when individuals of the same species compete with one another for resources such as food, water, breeding sites etc
interspecific competition
occurs when individuals of diff species compete for resources such as food, light, water etc
one species will normally have a competitive advantage over the other
the pop of this species will gradually inc in size while the pop of the other will diminish
competitive exclusion principle
states that where two species are competing for limited resources, the one that uses these resources most efficiently will ultimately eliminate the other
predation
occurs when one organism is consumed by another
in nature, the area over which the population can travel is far greater (than a lab) and the variety of the environment is much more diverse
some of the prey can escape predation as the fewer there are the harder they are to find and catch
so, although the prey pop falls to a low level, it rarely becomes extinct
effect of predator-prey relationship on population size
predators eat prey, thereby reducing the pop of prey.
with fewer prey available the predators are in greater competition with each other for the prey that are left.
the predator pop is reduced as some individuals are unable to obtain enough prey for their survival or to reproduce.
with fewer predators left, fewer prey are eaten and so more survive and are able to reproduce.
the prey population therefore inc.
with more prey now available as food, the predator population in turn increases
sampling techniques used in the study of habitats
- random sampling using frame quadrate or point quadrats
- systematic sampling along a belt transact
quadrats
two types
-point quadrat
-frame quadrat
factors to consider when using quadrats:
-size of quad to use
-number of sample quads to record within the area
-position of each quad within the study area
point quadrat
consists of a horizontal bar supported by two legs. at set intervals along the horizontal bar are ten holes, through each of which a long pin may be dropped. each species the pin touches is recorded.
frame quadrat
a square frame divided by string or wire into equally sized subdivisions. placed in diff locations within the area being studied. abundance of each species within the quadrat is then recorded
sampling at random
important to avoid bias in collecting data. avoiding bias ensures that the data obtained is reliable.
- lay out two long tape measures at right angles, along two sides of the study area
- obtain a series of coordinates by using random numbers taken from a table or generated by a computer
- place a quadrat at the intersection of each pair of coordinates and record the species within it
systematic sampling along belt transects
sometimes more informative to measure the abundance and distribution of a species in a systematic rather than a random manner.
this is important where some form of gradual change in the communities of plants and animals takes place
a belt transect can be made by stretching a string or tape across the ground in a straight line
a frame quadrat is laid down along side the line and the species within it recorded
it is moved its own length along the line and the process is repeated
measuring abundance
abundance is the number of individuals of a species within a given area
for species that don’t move around, it can be measured in several ways, depending on the size of the species being counted and the habitat:
- frequency: the likelihood of a particular species occurring in a quadrat
-percentage cover: an estimate of the area within a quadrat that a particular species covers.
mark-release-recapture techniques
useful for measuring abundance of motile organisms
known number of animals are caught, marked in some way, and then released back into the community
some time later, a given number of individuals is collected randomly and the number of marked individuals is recorded
estimated population size= (total number of individuals in the first sample x total number of individuals in second sample) / (number of marked individuals recaptured)
mark-release-recapture techniques assumptions
- the proportion of marked to unmarked individuals in the second sample is the same as the proportion of marked to unmarked individuals in the pop as a whole
- the marked individuals released from the first sample distribute themselves evenly amongst the remainder of the population and have sufficient time to do so
- the population has a definite boundary so that there is no immigration into or emigration out of the population
- there are few, if any deaths and births within the population
- the method of marking is not toxic to the individual
- the mark or label is not lost or rubbed off during the investigation
succession
Ecosystems are very dynamic, for instance succession is the change of one community of
organisms into the other. Primary succession occurs when area previously devoid of life is
colonised by communities of organisms, for example after the eruption of a volcano which lead
to formation of a rock surface. The area is first colonised by the pioneer species such as lichens
which are adapted to survive in such harsh conditions. As organisms die, they are decomposed
by microorganisms thus adding humus, this in turn leads to formation of soil which makes the
environment more suitable for more complex organisms. Over time, the soil becomes richer in
minerals thus enabling larger plants such as shrubs to survive. Eventually, a climax community
is established which is the final stage of succession, a self-sustaining and stable community of
organisms.
Secondary succession occurs in a previously colonised area in which an existing community has
been cleared. This type of succession can occur after events such as forest fires. As a soil layer
is already present, succession begins at a later stage.
pioneer species
organisms that colonise inhospitable environments- first stage of succession
make up a pioneer community and often have features that suit the to colonisation
pioneer species features suited to colonisation
- asexual reproduction
- production of vast quantities of wind-dispersed seeds or spores
- rapid germination of seeds
- ability to photosynthesise
- ability to fix nitrogen from the atmosphere
- tolerance to extreme conditions
during succession what common features emerge
- the non living environment becomes less hostile
- a greater number and variety of habitats and niches
- increased biodiversity
- more complex foodwebs
- increased biomass
conservation
the management of the earth’s natural resources by humans in such a way that max use of them can be made in the future
this involves the active intervention of humans and so is a dynamic process
main reasons for conservation
- personal
- ethical
- economic
- cultural and aesthetic
