Pere David's deer is a bizarre cervid that went extinct in the wild 1200 years ago. It managed to survive in a single royal hunting garden of China, but this domestic herd was fully eradicated in the 19th by peasants. Thankfully, some deers were brought to Europe; now there are up to 5000 P.D. deers
Population growth of Siberian tiger. According the the last census, now there are approximately 550 tigers. Ungulate density can be improved, but no other reintroductions needs to be made, since no large herbivores like bisons were found there (even if it could be beneficial, boosting tiger density)
The more a horse breed is adapted to its native land, the better is suited for Rewilding efforts. It's very unlikely/ impossible that wild horses/tarpans had a singular ecotype, since each population were adapted to different (a)biotic factors (inclination, temperature, vegetation composition, etc.)
