What affects their distribution and how can we investigate it?

Organisms and their environment

B2.4

In groups LIST what your main needs will be as the following organisms:A dandelionAn actual lionA Burmese pythonMould on some cheeseA beeAn oak treeTuberculosis bacteria

What do you need to survive?

Physical factors may affect the distribution of organisms, including:TemperatureAmount of lightAvailability of:

Oxygen Carbon dioxideWaterNutrients

Write these into your notes with a different example and organism for each one.

Organisms need resources!

Define the following terms in as few words as possible, then find them for these numbers:

2 4 9 3 5 2 4 2 5MeanMode MedianRange

A quick maths reminderMean: 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: 2 2 2 3 4 4 5 5 9)

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?

Counting daisies

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 many did you count?

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:

Is your estimate the same?

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.

Quadrats: Top Tips

How do you think the abundance of bluebells changes depending on how deep into this woodland you go?

Finding a trend

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?

Bluebell abundance in woodlandDistance into woodland (m)

% cover of bluebells

Transect 1 Transect 2 Transect 3 Mean cover

1 15 20 18 182 26 30 31 293 43 38 37 394 45 50 46 475 54 50 56 536 61 64 58 617 67 60 64 648 63 68 72 689 68 65 71 68

10 70 68 71 70

Click to reveal…

Graph of results

Click to

reveal…

Because we have quantitative results we can specifically say how the trend develops – it starts at 18% for 1m, 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!

Quant vs. Qual again…

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 percentagesampling along a transect to find a trend

What have we learned?