Diagrams D, E and F are illustrations of tools used for ecological studies. Study them and answer questions (a) to (c). (a)(i) Identify diagrams D, E and F....

Answer Details

(a)(i) Identity of the diagrams

• D = Sweep net (hand net) - a long-handled net with a mesh bag.
• E = Pooter (insect aspirator) - a jar carrying two tubes through its lid.
• F = Quadrat - a square frame of side 1 m divided into smaller squares.

(a)(ii) Names of the parts I to VIII

(a)(iii) One function each of I, III, IV, V and VII

• I (handle): provides a grip so the net can be held and swung to sweep up organisms.
• III (mouth tube): it is sucked to create a partial vacuum inside the jar, drawing the insect in through the inlet tube.
• IV (gauze): prevents the insect and debris from being sucked out of the jar into the collector's mouth.
• V (collecting jar): receives and holds the trapped insects for observation.
• VII (frame): marks out a fixed, known area (1 m by 1 m) within which organisms are counted.

(b) One use each of D, E and F

• D (sweep net): catching small, fast-moving animals such as flying insects (or aquatic organisms when swept through water).
• E (pooter): picking up small, delicate insects and other tiny arthropods from the ground or vegetation without harming them.
• F (quadrat): sampling to estimate the population density or percentage cover of plants and slow-moving/sessile animals in a habitat.

(c) Brief description of how each tool is used

D - Sweep net: The net is swung to and fro (or in a figure-of-eight) through vegetation, air or water while walking along a chosen line. Small animals are trapped in the mesh bag (II); the mouth of the bag is then closed and the catch is transferred into a container for counting and identification.

E - Pooter: The inlet tube (VI) is held close to or directly over the insect. The collector sucks sharply through the mouth tube (III); the suction draws the insect through the inlet tube into the jar (V). The gauze (IV) over the mouth tube keeps the insect inside the jar and stops it entering the mouth. The trapped insect is then examined or preserved.

F - Quadrat: The frame is thrown or placed at random points on the ground. At each placing, the organisms rooted or resting inside the frame are counted (or their cover estimated using the grid squares VIII). Several random placings are made and averaged. The area sampled is

\[ A_q = 1\,\text{m} \times 1\,\text{m} = 1\,\text{m}^2 \]

If \(N\) organisms are counted over \(n\) quadrats, the mean number per quadrat is \(\dfrac{N}{n}\), and since each quadrat covers \(1\,\text{m}^2\) the population density is

\[ \text{Density} = \frac{N}{n}\ \text{organisms per } \text{m}^2 \]

Multiplying this density by the total area \(A\) of the habitat gives an estimate of the whole population:

\[ \text{Estimated population} = \frac{N}{n} \times A \]