NATIONAL QUARTERFINAL STAGE 2026
Tamale SHS (Tamasco): 36
St. Hubert Minor Seminary SHS: 33
Labone SHS: 14
QUESTION
What standard name is given to an organism whose presence and role have a critical, disproportionate effect on the structure and function of its ecosystem?
ANSWER: Keystone species.
EXPLANATION
A keystone species is one whose impact on the structure and functioning of its ecosystem is disproportionately large relative to its own abundance; removing it typically causes drastic, cascading change or collapse of the community, as seen with sea otters controlling sea urchin populations that would otherwise destroy kelp forests.
PRACTICE QUESTIONS
1. Give two examples of keystone species.
ANSWER: Sea otter and the starfish Pisaster.
2. How do sea otters protect kelp forests?
ANSWER: They eat sea urchins, which would otherwise destroy the kelp.
3. What is a trophic cascade?
ANSWER: A chain of effects on lower trophic levels caused by changes at the top of a food web.
4. Who showed the keystone role of a starfish in experiments?
ANSWER: Robert Paine.
5. Which reintroduced predator changed the ecosystem of Yellowstone?
ANSWER: The wolf.
6. How does a keystone species differ from a dominant species?
ANSWER: It has a large effect although its numbers or biomass are small.
7. Why are fig trees keystone species in tropical forests?
ANSWER: They provide fruit for many animals all year round.
8. How do elephants affect their habitat?
ANSWER: They open up the forest and disperse seeds.
9. Why are beavers called ecosystem engineers?
ANSWER: They build dams that create wetlands.
10. What happens to an ecosystem when a keystone species is removed?
ANSWER: Biodiversity falls and the community may collapse.
11. What is a foundation species?
ANSWER: A species that creates the habitat for others, such as corals.
12. Why are keystone species a priority in conservation?
ANSWER: Protecting them protects many other species.