Keystone species is that species whose presence and number in the ecosystem plays an important role in balancing the ecosystem and without them, the other species would be affected directly and indirectly.
A dominant predator is considered to be a keystone species because the removal of that predator allow their prey to explode in numbers which will decrease the overall biodiversity of the area. Prairie dogs, otters, bison are the examples of keystone species. So the correct answer is B. Key stone species.
pupils dilate. fight or flight is self explanatory... you either stay and fight or run away...when being attacked your body releases adrenaline, blood pressure and heart rate increase, or you could run away.. pupils dilating is NOT included.