What is frequency of occurence?

Came up in a natural science assesment for cambridge - asks to calculate the frequency of occurence from a table of quadrats and number of species found in each one

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Reply 1

Mr Wednesday

Original post by Hyunsang

Came up in a natural science assesment for cambridge - asks to calculate the frequency of occurence from a table of quadrats and number of species found in each one

Frequency of occurence is how often you find that "thing" (here different types of plants) when looking for it in a set way (here throwing a quadrat on the ground and seeing what's inside its boundaries). Given the tabulated data and the random sampling method, it looks like a sensible starting point is to just average the samples found for X, Y and Z per observation.

That "calculated" bit in the question is a hint, you can't just look at the table and pick the lowest value for a single sample.

(edited 4 years ago)

Reply 2

Hyunsang

Original post by Mr Wednesday

So I add up the number of species found in X Y and Z and divide by 10 for each?

Reply 3

Mr Wednesday

Original post by Hyunsang

So I add up the number of species found in X Y and Z and divide by 10 for each?

Give it a go, see if it produces some sensible numbers .....

Reply 4

Hyunsang

Original post by Mr Wednesday

Give it a go, see if it produces some sensible numbers .....

The answer is 0.7 (C) but i still dont see how i can get that

Reply 5

Mr Wednesday

Original post by Hyunsang

The answer is 0.7 (C) but i still dont see how i can get that

Ah, interesting, it appears there is a "specialist" definition of "frequency of occurence" here.

https://newtonclasses.net/study-the-plant-population-frequency-by-quadrat-method/

It looks to be an average of a binary "yes, I see it at least once in a quadrat" or "no I dont" probability when sampling, not an average population per quadrat.

If it was a simple average, Y is lowest at 5.2, however there are three "zero samples" in the Y column, so that gives frequency of occurence (for that odd definition) of (10-3) / 10 = 0.7.

Reply 6

Emily~3695

From what I can see you look at the number of quadrats where something is counted/where the species is present as this is where something occurs, for species x something occurs in 9/10 quadrats so 0.9, species z something occurs in 8/10 quadrats so 0.8 and species y something occurs in 7/10 quadrats so 0.7 which is the answer, I have no idea if this is right as I’m only in year 11 but hope this helps 😊