How would the removal of humans change the wildlife?

Question

Suppose all the humans in Britain suddenly disappeared. This gives the animals -- wild, domesticated and feral, free roam. What would the wildlife look like 300 years later? The starting conditions are as follows. . . .

Environment: Temperate climate -- plentiful rain and occasional snow. Temperature between 0-25 C$^\circ$ depending on the season. The environment consists of farmland, patches of forestry, (abandoned) cities and towns, patches of maintained woodland (national parks), and some unmanaged wilderness (think the moors of Scotland).

Herbivores: Large numbers of domestic cows, pigs, sheep, chickens and horses. Largest wild herbivore is the red deer. Various smaller breeds of deer exist. Various small omnivores, including mice, rats and hedgehogs.

Carnivores: Large wild predators are conspicuously absent. Largest potential predator is some sort of large dog. Smaller predators include badgers, foxes, hawks, stoats, owls, herons and house cats.

So how is the biosphere thrown out of wack over the next few centuries?

Answer 1

Every single square inch of Britain/the UK is a managed landscape. Even our 'wilderness' areas such as the Scottish Highlands and the North York Moors only have the vegetation they do because people go to a hell of a lot of effort to keep it that way.

So once people are gone all sorts of habitats from the South Downs grasslands to upland blanket bogs are going to revert to forest. The UK will become wildwood again, as it was after the Ice Age. But with some exotic species such as Leylandii and Douglas fir mixed in with the native trees.

Meanwhile, all the flat bits near the sea where people's houses are constantly being flooded (Somerset Levels, Norfolk Broads) finally get their way and revert back to swamp, reed beds and/or salt marsh.

The wildlife which likes forests will do well. Wildlife which needs more open landscapes will do very badly. Since red foxes already occupy the small canine niche, feral dogs will fill the niche occupied by wolves and coyotes in other countries. The UK already has feral wild boar which are forest animals, so those will do well. They'll likely crossbreed with whatever pig breeds manage to survive the loss of humans.

Pretty much all dairy cattle are history. They are too specialised to fit human needs, and don't have good survival prospects in the wild. Beef cattle are a better bet. After a few generations they will resemble wild Chillingham cattle in behaviour. Perhaps they'll go all the way and produce a new aurochs - true forest cattle.

Pet cats go feral at the drop of a hat, so they won't have much problem adapting. They already interbreed with the Scottish Wildcat, so that species will likely continue to decline as it gets swamped by kitty cat genes.

I'd recommend Derek Yalden's History of British Mammals as a resource to see what the UK was like with less human influence.

Meanwhile... birds. Migratory birds which rely on agricultural land (geese grazing on pasture for instance) will do badly. Birds which like wetlands or forests will find an empty Britain to be a great place. Tops of skyscrapers and every window ledge will become seabird and pigeon colonies. The gulls will, of course, take an initial population hit as there are no longer landfill sites to scavenge from or ploughs to follow and pick up worms (though many UK soils are so impoverished the latter no longer happens). Once they've gone back to catching fish they will recover.

Answer 2

After 300 years, you may find some surprises without human intervention.

Big(ger) Cats. There's a big push to reintroduce the Eurasian Lynx in England. While it isn't legal to keep them, it is quite possible that there are a group of people with a secret population. There's also been mysterious, albeit unsubstantiated, sightings of large black cats in recent years. Add to that your ordinary, everyday, house cat & special breeds. A Maine Coon can be about 18 pounds. It would take just one of extraordinary size, that's enthusiastic about breeding, to up the size of a house cat. With all the deer around, and mid-size prey, it would make sense for them to get a little bigger and take advantage of all that food. As quickly as they breed, I would not be at all surprised to see a 20-50 pound cat derived from formerly domesticated cats in 300 years.

Thick Woodland Aside from the moors, vegetation and trees will take over, even in highly urbanized areas.

Adapt or die Most sheep, which are bred not to shed and rely on shearing will die or be unable to breed because of their coats. Cows are not built for the woodland, so most of those will stick to open field areas, as will most horses. Most cows will die. Pigs are highly adaptable and grow wild fairly quickly, so there would be a good population of those. In fact, I would say one of the most dangerous things to any human who happens to wander about in this new/old land is going to be pigs. They weigh several hundred pounds. Regular feral pigs, as linked there, are not too agressive, but the longer they spend out, generationally, the more territorial and likely to attack that they get. Pigs, also, are omnivores and will eat anything. After 300 years, these will be the most dangerous things in the woodlands. Chickens, might survive, but would have to be less conspicuous in plumage, to survive things like hawks.

Herds You're going to see herds of horses and deer on the moors and sometimes the woodlands. They will move with the seasons.

Foxes There will be an abundance of these. They will likely fight and kill formerly domesticated cats, of which there will be plenty because of the large starting population. They will also feast on little animals and are great opportunists when it comes to caresses. They will compete with hawks and stoats.

Wild dogs I believe wild dogs will start to revert to wolf-like behavior, and they will work in packs. Besides the wild pigs, they will be very, very dangerous. Wolves weigh from 40-175 pounds, a pretty wide range. But their strength is in packing up. A pack would be able to take down the weakest of the large herbivores and will likely be the apex predator for the island.

Addendum to Pigs: If you stick to the human trails, pigs aren't aggressive--but if you wander about the woods, it's going to be slow going. Most humans won't fight through the undergrowth, so there's going to be things called "pig trails." These are basically pathways that have been created by the egress of pigs. If humans are going to be coming back and experiencing this land, it's pretty likely that they will take the easiest route in the over grown woodland. That's going to be a pig trail, which means that they will likely be running into pigs. There will be general wildlife trails throughout the woods (kind of like a public road) but there will also be "private roads" left by pigs. We humans can't see the no trespassing warnings left by scent, so...

Answer 3

Humans have a symbiotic relationship with domesticated animals. If we were suddenly gone their numbers would plummet. Some would find ways to survive but not nearly as many as today.

Our conservation efforts are mostly to offset the impact of other human activity. So most of those issues resolve themselves. All the oil tankers in transit eventually run aground and some cause spills that no one does anything about. That's bad but it's a big planet. Similar disasters pop up w from many sources from nuclear reactors melting down (depending on design) to air planes crashing and starting fires.

Fish populations explode as their primary predator (us) vanishes. Alternate predators explode in population until a new balance is reached.

Farmland goes native. Roads grow weeds. Even the nice part of town starts to look like the wrong side of the tracks.

Eventually all we built is in ruins and the wild animals just keep doing what they've always done. In 300 years you won't see them change much. Some may be dead. Humans aren't required for extinction.

Those that survive may find an open niche to fill. That won't change much in 300 years but after a few billion years of evolution we may have planet of the kitty cats. Most everything of us will be gone by then. Our technology would have vanished with us. Maybe some fossils and some space probes survive. But sadly, the entertaining laser pointers would be gone.