Concept
I always liked the idea of the Wildlife mod both in Civilization V and Civilization VI because having animals roaming around is a great idea. However it was always sad that other than killing them there wasn't much else to do with them, unlike Civilization: Beyond Earth which has a cool system for its aliens. This Game Mode attempts to enhance the experience by giving you three different routes to interact with Wild Animals: Hunting, making Exhibits for leisure, and Protecting them as local fauna.

A World brimming with Life

Wild Animals spawn over time based on the features and terrains present in the map. These Wild Animals are units owned by the Barbarian player so early exploration might be a bit more challenging now. Wild Animals might threaten your improvements or your civilian units, and unlike regular Barbarians when they face a Civilian unit they kill it and heal instead of capturing it! Unlike other Barbarian units, Wild Animals have a limited Lifespan. Wild Animals range from a variety of species, from regular predators to big cats, and then some marine specimens as well. If you play with the Prehistoric Wildlife mod you might encounter some dinosaurs as well.

But don’t worry, some Wild Animals are not aggressive by nature (like Gorillas or Pandas) and will only attack humans if they are attacked. Also, as time goes on, Wild Animals are less dangerous as their Combat Strength doesn’t scale as much as regular units, and with the help of Recon Units -that now receive a combat bonus against Wild Animals- you might prevent damage from being too overwhelming. Wild Animals that have lost 85% of their Health will also stop trying to attack other units out of self-preservation.

Hunting

Defeating Wild Animals provides Bushmeat, which can be consumed at your cities to provide additional Food. This is specially useful early on, and for newly founded cities.

However, Bushmeat, as all meat, decays over time! Not only that but the stock limit is lower than other Strategic Resources (15 at Standard) and it doesn't increase with Barracks or other buildings. So if you want to reap the benefits of hunting you might be better off timing it with your cities. Alternatively, at the discovery of Medieval Faires, you can use the Smokehouses and the Canneries policies to prevent the Bushmeat from decaying, and even to increase the Stock limit.

Animal Exhibits

If you don't want to hunt the Wild Animals for food, there are some alternatives. One of them is capturing them as Exotic Species or instead, allowing you to use them in Animal Exhibits at cities with Entertainment Complexes and Water Parks respectively. This is a great source of Amenities and Tourism, and can even help you gain some Gold and Culture thanks to the interest of your population in them. This can be done after discovering Games & Recreation with the Animal Training policy.

Unlike Bushmeat, these resources do not decay over time, however, the projects expend them. Converting Wild Animal units with the help of Missionaries, Boudicca or units with the ability to capture enemy units grants Exotic Species as well.

Local Fauna Preservation

The other alternative for killing animals for food is to protect them as Local Fauna. To do this, build a Preserve near a Wild Animal unit; doing this instantly transfers the unit to your civilization. Local Fauna may not move or attack, but grants you Faith and Science each turn, as well as Envoys and Diplomatic Favor as you unlock certain Policies and build Sanctuaries, so this is specially useful if you are pursuing a Diplomatic Victory.

However it is important to know that Wild Animals all have a Lifespan of 40 turns (Standard Speed). This amount can be increased by completing the Preserve Stewardship project if you have the mod that enables it. Aside from that, when a protected Local Fauna unit reaches the end of its Lifespan, there is a chance a new generation will be born! This chance depends on the amount of buildings your Preserve holds as well as whether or not you have the Breeding Programs policy card!

Be mindful of your pledge to protect Local Fauna, as enemy units that manage to kill them receive a Poaching bonus against them, making them more susceptible against enemy attacks. Defeating a protected Local Fauna grants a large burst of Gold at the cost of a Favor penalty. Additionally if the Preserve your Local Fauna is protected at is pillaged, the Local Fauna may go Feral again, transferring ownership to the Barbarian player. Protecting Local Fauna is the hardest of the options, but it definitely helps you build your image as a staunch defender of nature!

Into the Future

The late game has also received some new interesting ways to interact with Animals.

• The Animal Rights policy allows you to earn Diplomatic Victory Points when preserving a new Wild Animal unit as Local Fauna (Including units born after the Lifespan of Local Fauna is depleted).
  
• Through the Biome Restoration projects, you can use Exotic Species and Aquatic Species to improve your city’s Appeal and Seasteads as well as gaining some additional Favor.
  
• If you adopt the Wildlife Emancipation policy you can even rescue Exotic Species and Aquatic Species from pillaging Campuses, Entertainment Complexes, Harbors and Water Parks.
  
• If Global Warming reaches levels higher than Phase IV the spawning rate of Wild Animals gets progressively lower.

New Policies

• Fur Trade (Foreign Trade): Combat victories over Wild Animals provide Gold equal to the Combat Strength of the defeated unit.
  
• Ahimsa (Mysticism): Receives +1 Envoy when a new Wild Animal unit is protected as Local Fauna. Obsolete upon the discovery of Environmentalism
  
• Animal Training (Games & Recreation): Defeating Land Wild Animals provides +5 Exotic Species instead of Bushmeat. Obsolete upon the discovery of Colonialism.
  
• Trapping Pits (Military Tradition): Defeating land Wild Animals provides +50% Bushmeat and Exotic Species.
  
• Smokehouses (Medieval Faires): Prevents Bushmeat loss each turn. Obsolete upon the discovery of Urbanization.
  
• Par Force Hunting (Mercenaries): Combat victories over Wild Animals provide Culture equal to the Combat Strength of the defeated unit.
  
• Royal Menageries (Humanism): Owned Local Fauna provides +1 Favor per turn.
  
• Safari Expeditions (Colonialism): Defeating Wild Animals provides +5 Exotic Species / Aquatic Species instead of Bushmeat.
  
• Canneries (Urbanization): Prevents Bushmeat loss each turn. Bushmeat Stock Limit increased by 10.
  
• Whaleships (Capitalism): Defeating water Wild Animals provides +100% Bushmeat and +100% Aquatic Species.
  
• Ex Situ Conservation (Conservation): Receives +10 Exotic Species when establishing National Parks.
  
• Environmental Activism (Environmentalism): Each Local Fauna unit provides +10 Album Sales for Rock Bands.
  
• Breeding Programmes (Environmentalism): Local Fauna units have an 85% chance of being recovered after Lifespan depletion.
  
• Animal Rights (Environamentalism): Receives +1 Diplomatic Victory Points when a new Wild Animal unit as Local Fauna.
  
• Wildlife Emancipation (Global Warming Mitigation): Gain +10 Exotic Species from fully pillaging Entertainment Complexes and Campuses and +10 Aquatic Species when fully pillaging Water Parks and Harbors.

Other Changes
Several other changes were made:

• Wild Animals now receive a combat bonus boost each era to make them remain competitive over time. However this doesn't increase as much after the Industrial era because guns are strong.
  
• Wild Animals have a stronger chance to spawn in owned territory, specially if you have Preserves or National Parks.
  
• Recon units and Naval Ranged units both receive a combat bonus against Wild Animals, this helps Recon units to survive a bit more against the predators and also provides a cool flavor of Hunters and Harpooners.
  
• Since Wild Animals have Lifespan now, their spawn rate has been increased. However if you feel there are too many Animals spawning (or too little) a new slider has been added at the setup screen.
  
• The AI of course doesn't use the projects as well, however they receive additional boosts if they have the resources (and they do get them, even trade them), that mimic the ones received by the projects.
  
• The Temple of Artemis provides Faith from defeating Wild Animals to enhance the "Hunting Wonder" feeling.
  
• The Colosseum receives an additional bonus as well, while the city that has the Colosseum produces an Animal Exhibit, all cities receive +4 Loyalty.
  
• If you have any questions the pedia has all the information.