As evidence we see the abnormal capacity of the human brain and the highly developed capacity for association, where the processing of olfactory stimuli in other species normally occurs. It becomes reduced to a subjective venture in humans, where in viable species it is much more limited to the objective. By viable, I refer to species that do not need to impose their world views upon nature to the disproportionate extent humans do in order to survive. Add to this species that are ill suited community participants within an ecosystem to such an extent that they critically compromise the long term viability of that ecosystem, will go extinct as the communities they occupy collapse. Some examples of species destroying ecosystems are the antelope and sheep of the American west, which literally ate their habitat out of existence once humans had exterminated the Grizzly bears from the region.
Energy efficiency is a relative term, grounded in the mineral and water regime of the habitat.
The greater the diversity of plant species, the wider the spectrum of mineral nutrients that will be 'easily' assimilated, the more mechanisms there will be to store or acquire moisture and the greater the potential for the system to withstand environmental catastrophe. The more nutrients available to an ecosystem, the more efficiently it can produce biomass. The more biomass a system can produce the more animal life it can sustain. Climax ecosystems have evolved to compensate for this by actually decreasing in total biodiversity. In that way, limiting their biomass production rates, they avoid being eaten to oblivion.