b6
distribution
where an organism is found in a habitat eg. a part of a field
abundance
how many individuals you find in an area eg. population size
can be estimated by counting the no. of individuals ( or working out the percentage cover) in samples taken. Then these results need scaling up for the total area
both would be to time consuming to measure the no. of individuals and distribution of every species in the area you are investigating. so instead you take samples
measure how common an organisms in 2 sample areas and compare them
study how the distribution changes across an area
pooters
jars that have rubber bungs sealing the top and 2 tubes stuck through the bung
if you suck on the shorter tube, and put the end of the longer tube over an insect it will be sucked into the jar
for your first sample crawl around for a few minutes sucking up as many insects as you can eg. from a base of a tree. Then count the no you have collected
do this in your second sample area, compare what you find
spend same amount of time sampling in each area , and choose sample areas of similar sizes
pitfall traps
steep-sided containers that are sunk in a hole in the ground ( the top is partly open
leave the trap overnight in your first sample area, insects that come along and fall into the container and cant get out gain so you can count them
then set up one in your second sample area and compare what you find
nets
sweep nets
nets lined with strong cloth for collecting insects, spiders ect from long grass
stand still in your first sample and sweep the net once from left to right through grass. Then quickly sweep net up and turn insects out into a container to count them
repeat the sweep in your second sample area and compare the no of organisms you find
pond net
net used for collecting insects water snails from ponds and rivers
to use one , stand in your first sample and sweep the net along the the bottom of the pond and turn the net out into a white tray with a bit of water in to count the organisms you have caught
then sweep your pond net in your second sample area and compare what you find
quadrat
a square frame enclosing a known area, to compare how common an organism is in 2 sample areas are
place a 1m squared quadrat on the ground at a random point within the first sample areaeg. divide the area into a grid and use a random no. generator to pick co-ordinates
count all the organisms your interested in within the quadrat
repeat steps 1 and 2 lots of time ( the larger the sample size the better)
repeat all steps in second sample area
FINALLY compare the 2 means
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capture recapture
capture a sample of the population and mark the animals in a harmless way
release them back into the environment
recapture another sample of the population, count how many of this sample are marked
estimate population size = no in first sample x no in second sample divided by no. in second sample previously marked
population sizes work out the mean no. of organisms per quadrat, them multiply mean by total area of the habitat
you have to make a no. of assumptions when using this method, these include no change in population sizes between the samples( births and deathS) and the marking hasnt affected individuals chance of survival( eg, making more visible to predators)