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During an ecological study of a lake, a group of students recorded the following observations.

During an ecological study of a lake, a group of students recorded the following observations.
(i) Planktonic crustaceans feed on planktonic algae;
(ii) Small fish feed on planktonic crustaceans, worms and insect larvae;
(iii) Worms feed on insect larvae;
(iv) A bird species feeds on small fish, planktonic crustaceans, worms and large fish;
(v) Insect larvae feed on planktonic algae;
(vi) Large fish feed on small fish.
(a) From this record of observations, construct a food web.
(b) From the food web, isolate and write down a food chain that ends with:-
(i) Bird species as a secondary consumer.
(ii) Large fish as a tertiary consumer.
(c) The biomass of the producers in the lake was found to be greater than that of primary consumers. Explain this observation.
(d) Using the food web, identify three pairs of organisms that compete for food in the lake and for each case, name the food being competed for.
(e) (i) State three ways by which human beings may interfere with this lake ecosystem.
(i) Explain how each of the ways stated in (e) (i) above may affect life in the lake.

Answers

(b) (i) Bird species as a secondary consumer.
Planktonic algae ?Planktonic crustaceans ?Bird species;
(ii) Large fish as a tertiary consumer.
Planktonic algae ? Planktonic crustaceans ?Small fish ? Large fish;
Planktonic algae ? Insect larvae ?Small fish ?Large fish;
(c) Energy is lost as it passes from the producers up the trophic levels; Producers require greater biomass to compensate for the energy losses in order to support consumers depending on it;
(d) Bird species and small fish; compete for planktonic crustaceans;
Bird species and small fish; compete for worms;Bird species and large fish; compete for small fish;Small fish and worms; compete for insect larvae;Planktonic crustaceans and insect larvae; compete for planktonic algae;
(e) (i) Pollution of water;Overfishing;Introduction of new fish species into the lake;Biological control of mosquitoes;
(ii) Pollution caused by toxic chemical substances may kill organisms in the lake;Overfishing depletes some species of fish inceasing the numbers of another species of organism;Newly introduced fish may clear the other species or increase competition in the lake;Biological control of mosquitoes may lead to clearance of insect larvae which is food to other organisms;

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sharon kalunda answered the question on September 16, 2019 at 05:32

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