paper 2: Populations and Ecosystems Flashcards
define population
individuals of the same species occupying one area at one time that can potentially interbreed
define habitat
an area where an organism lives
define community
all the populations of all the species in one area at one time
define niche
the role an organism plays in the ecosystem and how it interacts with the biotic and abiotic factors
define biotic factor
a living factor which affects the distribution of an organism
define abiotic factor
a non-living factor which affects the distribution of an organism
define carrying capacity
the maximum population size of a species that an ecosystem can support
define ecosystem
consists of the community and the non-living components of its environment
explain why sampling should be carried out at random
to ensure that all data collected is not biased
describe how you would retrieve reliable and representative data when sampling
you must take a large sample
define interspecific competition
competition between different species
define intraspecific competition
competition between the same species
define predation
how the populations of predators and prey affect each other
describe intraspecific competition
- members of the same species compete for the same resources e.g. food
- if population gets too big then intraspecific competition increases so population falls again
- if population gets too small, intraspecific decreases so population size increases again
draw and label a graph showing intraspecific competition
describe interspecific competition
one species will outcompete the other one if they occupy the same niche
draw a graph showing interspecific competition
explain predation
- prey population increase so food source increases for the predator so predator population increases shortly after
- more predators so more prey are killed so prey population decreases
- less prey to eat so predator population decreases because they die of starvation
- less prey eaten so prey population increases and the cycle starts again
draw a graph showing predation
why is there a delay in time between increase prey population and increased predator population
give time for reproduction of predators
why must a sample be random
prevent bias
why must a sample be large
- sample is more representative
- calculate more reliable mean
- allows use of stats test
what are quadrats used for
estimate size of population of a particular species in a certain area
describe the step-by-step method of random sampling with quadrats
- split area into a grid and asign coordinates
- pick coordinates randomly using a random number table
- place quadrat at coordinates and count number of individuals or % cover
- repeat a large number of times and calculate a mean
- multiply this mean by the number of times the quadrat fits ino the area
for sample seaweed with a quadrat, explain which method you would use
% cover
less time consuming than counting individual plants / cannot identify individual plants/ too many individuals
how can you find the correct number of quadrats to use to get representative data
calculate a running mean until the mean stays constant
what are transects used to show
show chnages down an environmental gradient
what is a limitation of using transects
single transect might not go through a representative data
how would you make sure that you have a representative sample of the area when using transects
- select position of transects at random
- use a large number of parallel transects and calculate the mean at each distance
decsribe the step-by-step method of using a transect
- several belt transects are placed at parallel across an area and numbered
- a transect is chosen at random using a random number generator button on a calculator
- a quadrat is placed along the line at regular intervals
- the % cover or number of each species are counted in each quadrat
- this is repeated across a large number of parallel transects and a mean at each interval
what is the mark, release, recapture method used for
used to estimate the sizes of populations of motile organisms
equation for mark, release, recapture
equation for mark, release, recapture
what are the assumptions made with the mark, release, recapture method
- birth rate = death rate
- marking does not influence survival such as increasing chances of predation and is non-toxic
- no immigration/ emmigration
- long enough time for marked individuals to evenly distribute into the population between release and recapture
describe the stages of succession
- starts with colonisation of pioneer species in hostile conditions
- pioneer species change abiotic conditions e.g. from soil/ humus
- environment becomes less hostile and more suitable for new species to colonise
- new species out-compete the pioneer species so pioneer number decrease
- from stage to stage, genetic diversity increases
- eventually a climax community is reached
what does primary siccession start with
bare rock or sand
what does secondary succession start with
soil and some vegetation
what is the ecosystem like in a climax community
- stable populations
- abiotic conditions are constant
- same species are present
explain why species diversity may decrease slightly in a climax community
- trees block light reaching the ground, so less photosynthesis
- only plants which can photosynthesise at low light intensities survive
what is turbidity
a measure of how much solid is in a solution
what piece of equipment measures turbidity
spectrophotometer
how does a spectrophotometer measure turbidity
- light passed through the solution
- absorbance is measured
- the more turbid the solution the more light is absorbed
why is a log scale used when measuring turbidity
when there is a large range of numbers
