Ecologist paul ehrlich likened species in a community to rivets holding together an airplane: airplanes can lose some of their rivets with no ill effects, but may suffer catastrophic failures if one too many are lost. we could extend this analogy to state that some rivets are so crucial that they must be retained for the integrity of the airplane. these "crucial" rivets represent

In the given question, the crucial rivets represent keystone species.

Explanation:

An ecosystem comprises some of the species, which are essential to the survival of the other species in the system, these species are known as the keystone species. The keystone species can be an unassuming plant or a huge predator, and in the absence of a keystone species, the ecosystem may not thrive.  

In an ecosystem, the keystone is regarded as one of the most essential parts. A keystone species refers to an organism, which helps in sustaining the system together. Some of the ecosystems may lose their tendency to amend with the changes in the environment if their keystone species get vanished.  

There are three kinds of keystone species considered by various scientists. These are ecosystem engineers, predators, and mutualists.  

a- multicellular

b-eukaryotic

c-no cell wall

d-heterotrophic

e-autotrophic