Reddit reviews Where the Wild Things Were: Life, Death, and Ecological Wreckage in a Land of Vanishing Predators

I'm still a student, but let me give some small insight on this.

Apex predators can be keystone predators - meaning they exert an unequal influence on the trophic system. If they disappear, the whole system is severely damaged. But that's a different matter (but I recommend a book!)

Let's compare two keystone predators - bears and wolves - and the interactions they might have on deer populations.

Wolves are pack hunters. They directly chase and take down their prey. Because of this, wolves choose some prey over others. A wolf pack might kill a straggler - a weak, older deer, or one with injuries. They might also go for a large prize, maybe a massive buck with a large rack that slows it down (damn you sexual selection!).

The main takeaway is that wolves are killing adults. Wolves aren't likely to select young over full adults - a major advantage of pack hunting is to take down large and difficult-to-catch prey, so they would be squandering that if they targeted the little ones.

Bears, on the other hand, are ambush predators. They sit and they wait for something to encounter it (then they might stalk it). I think most big felids are this way too. Because of this, bears have a lower amount of choice in prey selection. You don't see bears chasing herds of elk across mountain valleys, or working in packs to cut off their unwary prey. They sit, and they wait, and then they maul.

The impact of this is that less experienced prey ends up making the fatal mistake of walking into a grisly (grizzly? har har) death. It's usually young deer that wander a bit too far away from their mothers, or the starving young adult who is going into new territory to find food. Bears usually kill younger prey.

Think about the ecological impacts on a species from these two predation pressures. The death of an old/sick/injured deer is likely to not cause a lot of harm (note that it won't cause a lot of harm - not that it won't influence) to the population. That old deer isn't likely to produce any more children, and the sick or injured one is likely to die soon anyway, and probably wouldn't be selected to mate with. A large buck might be quickly replaced by other rivals following his death, and his children (his investment) are still alive.

The loss of children, on the other hand, has profound effects on population dynamics. A baby deer killed represents a complete loss in investment of the parents, and any possible chance of those genes being spread by that child. Not only has all the work you've put into raising your child go to waste, but all the missed opportunity costs (energy, time, more breeding). No genes will be passed on from all that work. A child will not increase a population via his offspring or his offsprings offspring. A dead elder killed by wolves might not produce any more children - but a dead child will result in the loss of potential offspring that compounds across generations.

The effect of predators on prey is partially determined by what life stage of the prey the predators kill.

If this video fascinates anyone, you might be interested in reading The Wolf's Tooth or Where the Wild Things Were. Both are entertaining, easy to read, and super informative.

Edit: Downvoted for helping others broaden their knowledge on the subject at hand? :(

Where the Wild Things Were is a great book that touches on what happened at Yellowstone, along with other places.

If I may hop in, there is a most excellent book on the critical role top predators play in keeping ecosystems healthy, though it talks more about otters and killer whales than sharks per se:

http://www.amazon.com/Where-Wild-Things-Were-Ecological/dp/1596916249

It has a whole chapter on the deer situation in the Eastern US, though.