Populations and ecosystems Flashcards
What is a habitat
a place where a particular population or community live e.g. a lake
What is an environment
the surroundings of an organism, composed of living and non living components
What does abiotic mean
factors that relate to the non living part of the environment e.g. flow of water through a lake
What does biotic mean
factors that relate to the living part of the environment
What is a community
all the populations of different species living in a particular space at the same time
What is a population
a group of organisms belonging to the same species living in a particular place at the same time
What is an ecosystem
the basic unit of ecology, consisting of a community (biotic) of living organisms and their environment (abiotic)
What is a niche
how an organism fits into its environment, the place where it is found and what it does there
What genetic factors cause variation within a species
- mutation
- random segregation of alleles in metaphase in meiosis
- crossing over between chromatids of homologous chromosomes
- random mating of organisms within a species
- random fertilisation
What is mutation
- mutation is a change to the DNA
- mutations can either be a gene mutation or a chromosome mutation
What environmental factors could cause variation
- diet
- disease
- predators
Explain how natural selection causes a change in allele frequency
organisms produce more offspring than are needed to replace the parents.
- most population numbers remain the same, this causes competition for existence
- individuals in a species show variation
- those with advantageous alleles will survive
- these individuals reproduce, passing on their advantageous allele
- this will shift the allele frequency within the gene pool
What are the three types of natural selection
- stabilising selection
- directional selection
- disruptive selection
Define stabilising selection
stabilising selection is the elimination of extreme variations in a population
e.g beetle colour- light and dark beetles may be easy to see but all those in the middle may camouflage well
What is natural selection
the process by which heritable traits become either more or less common in a population due to pressures from the environment
Define directional selection
if an environment changes one extreme form of a trait may be favoured
e.g peppered moth frequency in industrial revolution. darker moths became harder to see so were selected for
Define disruptive selection
both extremes in a trait are selected for but the middle is disadvantageous so is selected against (opposite of stabilising)
e.g salmon male size
large fish can fight off opponents to fertilise eggs, small ones are fast enough to sneak in and fertilise the eggs, medium fish are selected against
Define evolution
is the shift of allele frequency in a gene pool caused by selection pressure
What is speciation
the formation of new species
What is allopatric speciation
- the development of new species due to a physical separation of a species
- population separated by geographical isolation e.g sea, mountain range etc
- isolated populations subjected to different selection pressures.
- natural selection causes a shift in the gene pool, resulting in the two populations being reproductively isolation and therefore a new species has evolved
What is sympatric speciation
-new species formed when there are no physical barriers
reproductive isolation due to:
-behaviour - mates attracted by calls and dances etc
-structure - sex organs incompatible
-gamete mortality
-hybrid inviability- may result in a zygote that cant divide
-hybrid sterility- two species mate to form a hybrid but this cant reptroduce
-polyploidy- failure of separation of chromosomes in meiosis
What is genetic drift
changing of allele frequency due to chance.
e.g forest fire wipes out large proportion of population but at random- not due to an advantage that they have
this has a larger affect on a smaller population
What is the founder effect
organisms that start a new population may not be representative of original population
What factors can affect the population size
abiotic factors:
- climate factors
- lack of shelter
- pollution
biotic factors:
- competition within speciesfor resources e.g light, water, food etc
- competition between species for resources e.g light, water, food etc
- predators
What two methods can be used to estimate a population size
quadrats
for slow moving or non motile organisms,
-divide the area into quadrats, pick a sample of quadrats,
count how many organisms are in the sampled quadrats and multiply up for the total area
mark-release-recapture
capture a population and mark them then release them,
-recapture a sample from the number of marked organisms in the 2nd sample an estimation of the total population can be made
What is succession
the change in structure and species composition of a community over time
What is primary succession
newly formed habitats that have not previously supported a community
What is the pioneer species
the first organism to colonise a new habitat
e.g lichen and algae on bare rock
What is secondary succession
the repopulation at sites that have previously supported a community, usually after a major environmental disturbance e.g forest fire
What is the climax community
when the community reaches and equilibrium with its environment and no further changes occur
