Biol4 - Ecology - Estimating Populations + Definitions

Question 0

Describe how you could estimate the number of non moving organisms in an area (7)

Answer 0

~using a random number generator
~obtain co-ordinates
~place quadrats at coordinates obtained
~ensure sufficient number of quadrats to obtain a representative sample
~count number of organisms in each quadrat
~calculate the average number from these numbers
~multiply by the area of the field

Question 1

Define population (1)

Answer 1

All the organisms of one species in a habitat at one time

Question 2

Estimating percentage cover of a plant in an area (7)

Answer 2

~use quadrats
~randomly placed in a field etc
~estimate percentage of area covered by plant in each quadrat
~using a technique e.g. Subdivide quadrat to small squares and count any square more than half covered
~Add all the percentage cover estimates up and divide them by how many quadrats you have used
~multiply the mean % cover by the area of the field
~this is the estimated percentage cover for the field/area

Question 3

How do you use mark-release-recapture technique to estimate population size (7)

Answer 3

~choose a suitable trap
~place traps randomly
~capture a sample of organisms, count them and mark them unobtrusively (so theyre not hunted more)
~release them and allow sufficient time to mix in with the rest of the population
~capture a second sample with the same method
~count the number in the second sample and those that are marked
~can calculate estimated population using this formula: (image)

                    N# 1st sample x N# 2nd sample  Population = ----------------------------------------
                      Total N# marked in 2nd sample

Question 4

Assumptions for mark-release-recapture to be valid (5)

Answer 4

~no significant immigration or births
~organisms do not become trap happy or trap shy
~organisms mix completely with parent population
~mark doesnt affect survival chances
~sufficiently large sample is taken each time

Question 5

Define the term biosphere (1)

Answer 5

The life-supporting layer of land, air and water that surrounds the earth

Question 6

Define the term community (1)

Answer 6

All the populations of all the organisms living and interacting in particular habitat at the same time

Question 7

Define the term habitat (1)

Answer 7

Is the place/environment where a community of organisms lives

Question 8

Define the term microhabitat (1)

Answer 8

Smaller units within each habitat with their own microclimate (eg the mud at the bottom of a stream may be a microhabitat for a blood worm)

Question 9

Define the term abundance (1)

Answer 9

The number of individuals of a species in a given space

Question 10

Explain what is meant by a transect? (1)

Answer 10

A transect is a line across a habitat

Question 10

Explain what is meant by niche (2)

Answer 10

~set of conditions (in a habitat) that an organism requires (to survive, reproduce and maintain viable population)
~the role of a species in an environment

Question 11

Why sample at random? (3)

Answer 11

~avoid bias
~so data is representative
~allows use of statistical test