Cows and Deer

From here

There's a hobby farmer who lives along the road I sometimes take on my commute to work. He raises cows in his back yard, which is a couple of acres that are fenced in. He feeds them hay and they live in a muddy former pasture. This area receives a lot of rain, and most of the fields around are wet at least part of the year. The cows are heavy, so they kill the root systems of the grasses if they're left in any one place for too long and turn their pasture into mud.

Cows are descended from wild Aurochs, which were animals that survived from the Pleistocene mammoth steppe era. The steppe plants were able to survive heavy browsing and foot traffic of huge animals. The animals were able to mow the foliage down to the ground and move on.

In this area, deer are abundant. (They were actually hunted to extirpation in the 19th century) I have no idea what the population of deer is in this county. Based on statewide estimates, there's probably somewhere around 75,000. The county is 256,000 acres, so that's 3-4 acres per deer. My guess, based on observation, is that there are more deer in the county than the statewide estimates suggest, but I have no idea how many.

We have a herd of deer that live in our woods. Contrary to the stories I've read and heard, the deer wreak very little havoc on the landscape, which makes a lot of sense. They're native to this area. If they wreaked havoc, they would have died out thousands of years ago. At least a dozen deer traverse our property day in and day out, using the same paths much of the time. If they make a path muddy, they switch to a new one. The muddy foot prints collect leaves and moisture and seeds. They're sort of aerating the woods and mixing the top layer of soil, plus their waste is fertilizer that readily breaks down and scatters nutrients and seeds.

So here's the main point: nobody raises or tends to the deer. In fact, people pretend they need to be "culled" so they have an excuse to hunt them, either for food, or because they like to kill animals. If the deer were not hunted or "managed", there would probably be way more of them.

A sort of corollary to that is the selective breeding and management of beef or dairy cows for specific traits, e.g. high milk production, makes them need more human "management". If cows went feral, they'd probably adapt to the local environment. Another one is that the subdivision of land into private parcels might lower the overall productivity of an area.