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Biology · 2022 · 3 marks
CBSE 2022 · Region 2 · Set 1 · Q10
(a) "Some species in an ecosystem exert greater influence in driving major ecosystem services than others." How did Paul Ehrlich explain this concept…
(a)
"Some species in an ecosystem exert greater influence in driving major ecosystem services than others." How did Paul Ehrlich explain this concept in his 'rivet popper hypothesis' ?
OR
(b)(i)
How has the introduction of Nile Perch into Lake Victoria in East Africa had a devastating effect on the indigenous species in the lake ?
(ii)
Name two invasive weed species which have posed a threat to the existence of our native species.
Marking-scheme solution
Paul - Ehrlich compared Airplane with ecosystem, in an airplane (ecosystem) all parts are joined together using thousands of rivets (species), if every passenger travelling in it starts popping a rivet to take home (causing a species to become extinct), it may not affect flight safety (proper functioning of ecosystem) initially, if more and more rivets are removed then the plane becomes dangerously weak over a period of time, loss of rivets on the wings (Key species that drives major ecosystem functions) is a more serious threat to flight
(i)
Extinction of an ecologically unique assemblage of more than $\displaystyle 200$ species of cichlid fish in the lake
(ii)
carrot grass / (Parthenium), Lantana , water hyacinth / (Eichhornia) (or any correct example)
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