practical: investigating population size

Question 1

what interactions do biologists want to study?

Answer 1

the distribution of species
the abundance of species
interactions between species
interactions between a species and its abiotic environment

Question 2

what piece of equipment is used to measure population size?

Answer 2

a quadrat

Question 3

what size quadrat do we usually use?

Answer 3

50cm x 50cm- 0.25m2

Question 4

how do we measure a population?

Answer 4

place it on the ground
count the number of individuals of our chosen species inside the square

Question 5

how to make data consistent?

Answer 5

count the individuals on the top and left edges only

Question 6

how to measure the abundance using a quadrat?

Answer 6

record:
the total number of an individual species
the total number of different species
the percentage cover

Question 7

how to estimate percentage cover of a quadrat?

Answer 7

count the number of squares with the species
calculate this as a percentage- then multiply by 100
repeat for other species

Question 8

how to find the population of a species?

Answer 8

1) calculate the area of the habitat
2) measure the number of individuals in one quadrat and repeat many times to check out result is reliable- at least 10 quadrats
3) calculate the average number of individuals in a quadrat
4) calculate how any quadrats fit into the total area
5) multiply the result from step 4 by the result from step 3

Question 9

why do we use random sampling?

Answer 9

to make sure our data is valid- we are avoiding choosing areas which may be interesting- bias our result

Question 10

how to take a random sample?

Answer 10

1) lay out 2 tape measures at right angles to make a 10m by 10m set of axes
generate pairs of random numbers between 0-10- these are coordinates
2) use the coordinates to place your quadrat

Question 11

what can affect the distribution of our population?

Answer 11

differences in abiotic conditions such as light intensity or one area may be trampled

Question 12

how can we investigate the distribution of our population?

Answer 12

1) pick 2 contrasting areas and set up a grid in each- use random sampling to take repeated measurements with a quadrat and compare the average results
2) use a transect.

Question 13

what is a transect?

Answer 13

a line across a habitat- placed to pass through a range of abiotic conditions e.g. across a path

Question 14

where is the quadrat placed in terms of the transect?

Answer 14

regular intervals across the transect and used to measure the number or % cover of the species

Question 15

what are the limitations?

Answer 15

can be easy to miss individual organisms when counting in a quadrat, especially if they are covered by another species