The removal of keystone species will affect,
(a) Producers
(b) Decomposers
(c) Ecosystem
(d) Consumers

Hint: A keystone species can be defined as an organism that helps define an entire ecosystem.If the keystone species were to disappear from the ecosystem, no other species would be able to fill its environmental role. The ecosystem would be forced to radically change, allowing new and possibly invasive species to take over the habitat.

Complete step-by-step answer
Let’s discuss the options and find out the correct answer
- Producers are the organisms that use photosynthesis to capture energy from sunlight, co2 and water to create carbohydrates.The examples of producers are plants, lichens and algae, which convert water, sunlight and carbon dioxide into carbohydrates. So (a) is an incorrect option.
- A decomposer is an organism that decomposes, or breaks down, organic material such as the remains of dead organisms.Examples of them include detritus feeders such as earthworms and sowbugs, as well as some fungi and bacteria.So (b) is an incorrect option.
- A keystone species plays a very important role in maintaining ecosystem and keystone species may be top predators, so the elimination of it will affect the ecosystem but not producers , decomposers or consumers. So the correct option is (c) ecosystem.
- The role of consumers in an ecosystem is to acquire energy by feeding on other organisms and sometimes transfer energy to other consumers.They can get affected and can impact other organisms within the ecosystem. So (d) is an incorrect option.
Hence,the option is C: ecosystem is the correct answer.

Note: Any organism, from plants to fungi, may be a keystone species. They are not always the largest or most abundant species in an ecosystem. However, almost all examples of keystone species are animals that have a huge influence on food webs.