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Q97 - Grazer Identity, Diversity, and Nutrient Enrichment in Rock-Pool Food Webs

Theoretical B Real exam question - full text reproduced under IBO's CC BY-NC-SA 4.0 license
Ecology

A rocky shore contains many shallow rock pools dominated by macroalgae and grazing gastropods, comprising primarily Patella ulyssiponensis (P), Littorina littorea (L) and Gibbula umbilicalis (G). The experiment is designed to test the interaction between grazer species and the additive interaction with nutrient enrichment. Pools contained either none, one, two or all three of grazer species at realistic densities (Patella, Littorina and Gibbula). Another complete set of all the manipulation grazer treatments was also established concurrently where nutrient concentrations were enhanced to compare the simultaneous effects of grazer treatments at ambient and enriched nutrient conditions. Gross ecosystem productivity (GEP), number of algal taxa, and the biomass (dry weight) of all algal species were measured.

Figure Q.97, showing gross ecosystem productivity, number of algal taxa, and algal biomass across the different grazer-manipulation treatments (no grazers, single species, pairs, and all three), compared between ambient and nutrient-enriched conditions.

Figure 1. Figure 1.

Using the information and data, determine which of the statements are true or which are false.

A. Gross ecosystem productivity is enhanced by nutrient enrichment and is greater in pools where Littorina is present.
B. The effects of grazer species loss on accumulated algal biomass are regulated by nutrient conditions, grazer identity and grazer diversity.
C. The effects of loss of grazer species on ecosystem functioning depend upon both the diversity and identity of the species present.
D. The presence of all grazers results in lower algal diversity and biomass in both nutrient conditions.
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Question reproduced from IBO 2016, Theoretical Paper B, licensed under CC BY-NC-SA 4.0 - attributed to the International Biology Olympiad. Open the full exam PDF · Community solutions (unofficial)