Why would either zoo want to give up the most important species of all?! I hope both continue to have polar bears, even if it is the only species overlap
It is kind of a complicated issue. Of course, they want each zoo to be as complete and attractive as possible. At the same time, they don't want them to appear almost identical, as this wouldn't motivate people to actually visit both of them. In a way it is both a dream and a nightmare for a zoo administration to be in charge of two large/very large zoos. There is far more potential, but it is also far more complicated.
In the past, Berlin Tierpark has been stripped of some of its most expensive but also most attractive and popular animals (apes, seals, pygmy hippos...). They have all the space and natural landscapes you'd need to create one of the finest zoos on the globe, but they lack(ed) funding (this started to change but then Covid-19 kicked in) and haven't been independent since Berlin Zoo took them over. Returning some of the lost attractions will be a project for decades rather than years.
Meanwhile, Berlin Zoo never as much as thought of giving up just one of the 4 groups of apes for instance. Some of the generous donors even made very clear they would never accept that. On the other hand, space is limited, while standards are ever increasing.
Personally, I think the newly developed concept seems the best/most logical compromise:
-Berlin Zoo gets to keep the most popular species and builds attractive, state of the art enclosures for them. They also stick with the classic systematic approach: So children asking to see "the" monkeys, elephants, lions, penguins, crocodiles etc will virtually always find them very quickly and easily (and usually there will be even more than they probably looked for). So this would be very satisfying for average visitors.
-Berlin Tierpark, however, develops a new profile with geo zones and naturalistic landscapes with large groups/herds and large/huge (often mixed species) exhibits, thus justifying the huge space. For instance, the Africa zone will include many of the most spectacular animals like elephants, (hopefully rhinos), giraffes, buffalos, zebras and common antelopes and also some rarely seen species like gerenuks or honey badgers/ratels. And Himalaya will be set on an actual hill and display far, far more than "just" snow leopards and red pandas.
One advantage of these complementary concepts is that it will allow visitors to develop a more complex and comprehensive view on nature. And on a more pragmatic level, it also makes more allowance for some redundancy: Berlin Zoo exhibits polar bears close to other carnivores and close to mentally associated animals like seals and penguins. Berlin Tierpark, however, embeds them in a North American area with moose, wood bisons etc. (They will handle this similarly, when Berlin Tierpark gets orangs and seals again) And they are flexible to have a breeding couple/group at the one zoo and a bachelor group at the other one.
