Some of the earliest research on keystone species was conducted by Robert T. Paine, who actually coined the term keystone species. For over 25 years Paine and his students removed Pisaster ochraceus, a sea star, from tidal pools on the coast of Washington. Throughout his research, Paine discovered that removal of this predator resulted in

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the right option is; decreased genetic variation  

decreased genetic variation describes the effect of this environmental change.

genetic variation is the naturally occurring genetic diversities or differences between organisms of the same species in a population. genetic variation allows the survival and adaptability of a species when they encounter changing environmental conditions. when an endangered species reduces, it loses genetic variation which may not be restored even if the species rebound and will only be recovered through the gradual collection of mutations over many years.