Steps to estimate population with quadrats.
Reveal answer
Random quadrats → count → mean per m² → × total area.
Key words: random · mean
5(a) THE ORGANISM IN THE ENVIRONMENT · RECALL
5.2 Population size using quadrats
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Why place quadrats randomly?
Reveal answer
To avoid bias.
Key words: bias
Why use many quadrats?
Reveal answer
More representative / reliable mean.
Key words: representative
How do you place quadrats randomly?
Reveal answer
Tape measures at right angles → random number coordinates.
Key words: coordinates
What do you measure if plants are hard to count?
Reveal answer
Percentage cover.
Key words: percentage cover
Density in a 0.25 m² quadrat with 5 plants?
Reveal answer
5 ÷ 0.25 = 20 per m².
Key words: 20
What is meant by the term quadrat?
Reveal answer
A square frame of known area used to sample organisms.
Key words: quadrat
What is meant by the term random sampling?
Reveal answer
Choosing sample positions so every position has an equal chance of being chosen.
Key words: random sampling
What is meant by the term population density?
Reveal answer
The number of individuals per unit area.
Key words: population density
What is meant by the term percentage cover?
Reveal answer
The proportion of a quadrat’s area covered by a species, used when individuals cannot be counted.
Key words: percentage cover
Planning the quadrat investigation, Independent. In this investigation? Why it matters?
Reveal answer
In this investigation: Area sampled (for example lawn or field edge). Why it matters: This is the factor being compared.
Key words: Independent
Planning the quadrat investigation, Dependent. In this investigation? Why it matters?
Reveal answer
In this investigation: Number of the chosen species per quadrat. Why it matters: Used to calculate density and population size.
Key words: Dependent
Planning the quadrat investigation, Controlled. In this investigation? Why it matters?
Reveal answer
In this investigation: Quadrat size, number of quadrats, counting rule, date. Why it matters: Differences can then be attributed to the area.
Key words: Controlled
Planning the quadrat investigation, Sampling method. In this investigation? Why it matters?
Reveal answer
In this investigation: Random coordinates from a number generator. Why it matters: Removes selection bias.
Key words: Sampling method
Planning the quadrat investigation, Reliability check. In this investigation? Why it matters?
Reveal answer
In this investigation: Repeat quadrats and look at the range. Why it matters: Shows variation between samples.
Key words: Reliability check
True or false, and why? “Throwing a quadrat over your shoulder is random.”
Reveal answer
False. Throwing is haphazard and can be biased or unsafe. Use coordinates from random numbers.
True or false, and why? “The estimate gives the exact population size.”
Reveal answer
False. It is an estimate from a sample; more quadrats generally give a more representative mean.
True or false, and why? “You only need one quadrat if it looks typical.”
Reveal answer
False. Choosing a “typical” spot is biased, and one sample shows nothing about variation.