Sampling Biologists often want to find out what organisms are present in an environment / what these organism do /where these organisms go etc… Often it isn’t feasible to identify all the organisms present, so instead samples can be taken Samples look at a small section, allowing us to predict what the whole is like – e.g. would couldn’t feasibly measure the height of every blade of grass, but we could look at a small sample grass and get an idea of what all the rest may be like
Sampling Techniques How can we sample organisms / areas? Tagging – e.g. a few whales can be tagged and tracked, to give us an idea of where their migration routes are
Sampling Techniques How can we sample organisms / areas? Pitfall traps – e.g. a small trap can be set to collect a range of organisms within an area
Sampling Techniques How can we sample organisms / areas? Quadrat – e.g. a quadrat is thrown in an area, and the number of organisms within the quadrant are counted to give an estimate for a much larger area
Quadrat A quadrat is randomly placed in different locations, and the organisms within the quadrat are counted so an average can be taken (the more samples, the more accurate this method is) If the field is 1000m 2 then 1000 quadrats could fit (a quadrat is 1m 2 ) If the field is 5000m 2 then 5000 quadratscould fit (a quadrat is 1m 2 )
Sampling Techniques Sampling is a good way to estimate population size – although is not 100% accurate, if done properly it can give good estimates and is very time efficient! Your task in pairs is to sample how many daisies there are in 2 different parts of the field (open field & around tree) How can you sample to find if more daises grow in the open field or around the trees ?
Sampling Questions Sampling is a good way to estimate population size – although is not 100% accurate, if done properly it can give good estimates and is very time efficient! Do More Daisies grow in the open or under trees? How many times will you have to do it? How are you going to sample your daisies? How will you choose which part to sample? How will you record your results? How long do you think it will take? What do you think you will find out? How will you make it safe?
Sampling Questions Using the quadrat you need to randomly throw it within the sample area, and count the number of daisies within that area This needs to be repeated 3 times, and an average calculated for each area of sampling – design a results table to collect your results…
Results Record your sampling results within the table Area 1 – open field Area 2 – around tree Area Number of daises Sample 1Sample 2Sample 3Sample Average Open Field Around Trees
Findings Using your averages, work out the daisy population size in the open field and around the trees Remember – the quadrant is 1m 2 in area, and the field size is 100m 2 in the open field and 10m 2 around trees For example: - If your average daisies in the open field was 20, then a population estimate would be 20 x 100 = 2000 daisies If your average daisies under the tree was 3, then a population estimate would be 3 x 10 = 30 daisies
Analysis Can you suggest reasons why the population sizes are different? The daisies need a variety of conditions to survive, including light – around the trees light is less abundant than out in the open field, so less daisies are able to grow there There may also be less nutrients / water available allowing less daisies to grow in this area
Moving Quadrats are usually used for plants, but they can also be used to estimate some animal population sizes (as long as these only move a little)!