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Feeding relationships

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Question 14

The diagram shows an aquatic food web in a freshwater pond. An aquatic food web diagram. At the bottom is 'phytoplankton' (producer). Arrows point from 'phytoplankton' to three primary consumers: 'zooplankton', 'water snail', and 'tadpole'. From 'zooplankton', an arrow points to the secondary consumer 'dragonfly nymph'. From 'tadpole', an arrow points to the secondary consumer 'diving beetle'. From 'water snail', two arrows point upwards: one to 'dragonfly nymph' and one to 'diving beetle'. At the top, a single tertiary consumer 'perch' has arrows pointing to it from both 'dragonfly nymph' and 'diving beetle'.

a.

Use the food web diagram to determine each of the following:

  1. The number of trophic levels in this food web.
  2. The total number of distinct food chains.
  3. The number of different species that act as predators.
  4. The total number of different consumer species.
[4]
b.

A student used a 1 m21\text{ m}^21 m2 quadrat to sample the population density of water snails in two different zones of the pond: Zone A (shallow water near the shore) and Zone B (deep water in the center). The table shows the student's results:

QuadratZone A (snails per m2)Zone B (snails per m2)11452117315441285186 \begin{array}{|c|c|c|}\hline \textbf{Quadrat} & \textbf{Zone A (snails per m}^2\textbf{)} & \textbf{Zone B (snails per m}^2\textbf{)} \\ \hline 1 & 14 & 5 \\ \hline 2 & 11 & 7 \\ \hline 3 & 15 & 4 \\ \hline 4 & 12 & 8 \\ \hline 5 & 18 & 6 \\ \hline \end{array} Quadrat12345​Zone A (snails per m2)1411151218​Zone B (snails per m2)57486​​

Calculate the mean density of water snails in Zone A and Zone B.

[2]
c.

State which zone has a higher density of water snails, and suggest two ecological reasons (abiotic or biotic factors) for this difference.

[3]

Feeding relationships Questions

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