Silverback Gorillas

How can Silverbacks get so big and strong by eating just green plants?

For the same reason that Elephants, Hippos, and Rhinos grow so large they spend most of their time eating.

WS

Green plants cannot provide the protein to put that kind of muscle on a gorilla. I heard a Silverback Gorilla has the strength to flip over a minivan.

I don't see many Rhinos on Natgeo Wild. Are they nearly extinct?

Mountain gorilla (Gorilla beringei beringei):
This subspecies consumes parts of at least 142 plant species and only 3 types of fruit (there is hardly any fruit available due to the high altitude. About 86% of their diet is leaves, shoots, and stems, 7% is roots, 3% is flowers, 2% is fruit, and 2% ants, snails, and grubsion
For info on the Rhino situation check out Poaching Wars in the Africa Big Five section, lots of channels, and Blogs no longer report Rhino sightings

WS

Why do Silverback Gorillas eventually get taken down by their first-born? Such ingratitude toward the one who raised and protected him.

Gratitude is a human emotion that we put on animals, it doesn't apply to wildlife. The reason the son takes over is because male animals are hard wired to pass on their genes to the next generation its their prime aim in life. The easiest way a young silver back can do that is to take over the group from his father. Otherwise he has to go off, and either take over another group, or attract females to him. So if his father Is getting older and weaker then that is his easiest route to pass not only his genes, but also his fathers genes on. In most wildlife group behaviour the offspring are forced out when they reach sexual maturity like the sub adult males in Lion prides, or in the Leopards case the mother will force her daughters out first because she knows her daughter will become a competitor for males attention and her territory. Its just the way nature works Dura

WS

Females are by nature faithful and monogamous. They're mothering and nurturing. They would be want to see their daughters get a mate. The female's brain is just wired differently. They're not like males.