Correct Option (c)
Assumption 1 is valid. The passage states that a keystone species influences "the flow of energy and materials through ecosystems." Food chains and food webs are the mechanisms through which energy and materials flow in an ecosystem. Therefore, the role of keystone species is integral to the structure and function of these food networks.
Assumption 3 is valid. The University of Washington study detailed in the passage demonstrates that the removal of the keystone species (sea star Pisaster ochraceus) led to significant ecological disruption. Specifically, 28 species of animals and algae disappeared, and the ecosystem eventually became dominated by a single competitor, Mytilus. This severe reduction in biodiversity and simplification of the ecosystem structure indicates a collapse or substantial degradation of the ecosystem.
Incorrect Options:
Assumption 2 is not valid. While the passage uses an aquatic example (sea star in rocky intertidal ecosystems) to illustrate a keystone species, the initial definition provided is general: "A species that exerts an influence out of proportion to its abundance in an ecosystem." The passage does not state or imply that keystone species are exclusively found in aquatic ecosystems; it merely uses one such example. Therefore, restricting keystone species to aquatic ecosystems is an unsupported overgeneralization based on the passage.