What affects their distribution and how can we investigate it? B2.4

In groups consider what your main needs will be as the following organisms: A dandelion An actual lion A Burmese python Mould on some cheese A bee An oak tree Tuberculosis bacteria

Physical factors may affect the distribution of organisms, including: Temperature Amount of light Availability of: Oxygen Carbon dioxide Water Nutrients Write these into your notes with a different example and organism for each one.

Organisms will be found in locations where the physical factors from the last slide suit them. Different organisms are adapted to survive in different environments, so they don’t all compete for the same resources. The particular set of conditions that an organism is suited to is called its ‘niche’.

Define the following terms in as few words as possible, then find them for these numbers: Mean Mode Median Range Mean: add up all the numbers and then divide by the number of numbers (answer: 36/9 = 4) Mode: the value that occurs most often (answer: 2) Median: the "middle" value in the list of numbers when they are arranged in numerical order (answer: ) Range: the difference between the largest and smallest values (answer: 9 – 2 = 7)

There are two main kinds of data that we can gather for the daisies in this field: Qualitative: ‘there are lots of daisies in the field’ Quantitative: ‘there are 5087 daisies in the field’ Quantitative data gives a specific measure for your subject, but qualitative data only gives a rough idea. Quantitative data is usually more useful… …why do you think this is?

How did you estimate the number of daisies? Did you try to count them all? Or did you use another method? We need a quantitative estimate for the number of daisies – it doesn’t have to be perfect but it should be as close as possible to the real number. Write your first estimate down, then try again, seeing if this will help…

How did you use the grid to estimate the number of daisies? Did it help? There are 78 daisies If you were asked to count the number of daisies in the school field, it would be impractical to count each one. How could you use the grid method to get an accurate, reproducible estimate? Make a rough plan. Use your plan to make an estimate for the next field:

There were 103 daisies in the field. How close were you? Your plan should have involved the following steps: Select at least three quadrats and count how many daisies are in each (eg 4, 8, 3) Add them to get a total and divide by the number of samples to find the mean number of daisies per quadrat ( = /3 = 5 daisies per quadrat) Multiply the mean by the number of quadrats that would fit into the field to get your estimated total number of daisies. (5 x 20 = 100 daisies estimated in the field)

They only work for immobile/slow moving populations. The more data you collect, the more reproducible your result…the more samples the better! Quadrats should be placed randomly to avoid bias. If you don’t know the exact size of your field you can estimate the percentage cover by seeing what percentage of each quadrat contains the organism and calculating the mean.

How do you think the abundance of bluebells changes depending on how deep into this woodland you go? By placing one quadrat each metre along a straight line you can find the % cover for different distances. This is called ‘sampling along a transect’. This can be used to show a trend – what would you do with the results on the following slide?

Distance into woodland (m) % cover of bluebells Transect 1Transect 2Transect 3Mean cover Click to reveal…

Click to reveal…

Because we have quantitative results we can specifically say how the trend develops – it starts at 18% for 1 m, increases rapidly to 61% for 6m but levels out at 68% for 8m. If we’d only had qualitative results we’d only be able to say ‘there are more bluebells the further in you go’ – not much good! You must include references to data when describing trends!

Physical factors may affect the distribution of organisms, including: water, light, nutrients, oxygen, carbon dioxide and temperature Quantitative data on the distribution of organisms can be obtained by: random sampling with quadrats to estimate a number or percentage sampling along a transect to find a trend