The keystone for this ecosystem appears to be the various amounts of flowers (including grasses). If they were removed, the beaver's only food source would disappear, the insects only food source would disappear, and the food sources available for the other species consuming the flowers/grasses would dwindle and become more specific. With the beaver's food being gone, it will slowly start to die off because it has no sustenance, and then the bald eagle's and coyote's food source would also decrease. Also, the insects would start to die off, as their only food source will be gone they will have no way to survive. With insects also gone along with flowers/grasses, the meadow vole and frogs would also have no food source, and same for the bats. With all of those now having no food source, they too would start to die off, and then consequently, the highest predators would die of no food source. Because the loss of that one species causing the entire food web to crash, it can easily be determined that it is the keystone species in this ecosystem.
One of the predator-prey relationship exhibited in this park is the coyote and white tail deer. Coyotes are the only predator in Cuyahoga that eat deer, so they play a vital role in making sure the populations of the deer don't increase too drastically. The problem is, however, that coyote have many other available food sources that are easier to catch and eat, and they more than often choose to go after those organisms instead, leaving the deer population unchecked. Without the coyote being a predator to the deer, the deer population would sky rocket and drastically decrease the plant life, the food source for most things in the park, and cause major issues.
Another example of predation occurring in the park is the Great Blue Heron preying up bullfrogs. Even though there are a few predators in the park, Great Blue Herons are the only ones that actually eat frogs. As is the case with most predators, these Herons serve as the only direct limitation to the bullfrog population because without the consumption of the frogs, insect population would decrease and cause a wave of negative effects to ripple through the food web. Because insects are eating a large portion of the grass/flowers, it would cause a short lived increase in plant life if insects were decreased too much. The increase in the keystone species would cause a massive amount of organisms to experience a large population growth, which would then turn around and over-consume the keystone species and cause a devastating effect, overall doing exactly the opposite of what increasing it did.