This is actually a problem caused by success. When Zoo A has repeated breeding success with Species X, it will pass young stock on to Zoo B and Zoo C, perhaps receiving their surplus stocks of Species Y and Species Z in return, all transfers being mediated by studbook holders and associations as appropriate.
This is a great advance on the situation 50 years ago when animals imported from the wild were much more easily available, and many were kept singly or in pairs, with distinctly patchy breeding results in consequence.
The conditions which caused this process to happen will continue to operate, so zoo managers will have to make deliberate decisions to avoid increasing uniformity. Fortunately there are several ways to do this. Conway's bullfrog solution* (if I may call it that) is better exhibits to display the animals and to educate visitors. An alternative is more specialisation, for example Gerald Durrell decided that his small zoo on the island of Jersey should concentrate on small endangered species from islands, such as lemurs, Mauritius pink pigeons and Caribbean iguanas, as well as having a few more popular species: obviously zoos that are relatively close together need to specialise differently, but that is not a problem if they are associated like Antwerp & Planckendael or Regents Park & Whipsnade, or if other factors such as amount of space or climate are different. Publicity is important too, zoos can now communicate directly with the pubic via social media, without needing to interest journalists in stories - which is not to say that mass media don't matter, but zoos can have more say in the agenda: in the UK in the past few years, TV series on the animals and keepers at ZSL, Edinburgh & HWP, and in particular Chester, have all gone beyond the lions, tigers and meerkats to show keepers working with wolverines, frogs and insects.
* I first read Conway's splendid article 'How to exhibit a bullfrog: a bed-time story for zoo men' in International Zoo Yearbook Volume 13 (1973). A copy is available on Zoolex https://www.zoolex.org/media/uploads/2018/07/30/conway_how_to_exhibit_a_bullfrog.pdf
This is a great advance on the situation 50 years ago when animals imported from the wild were much more easily available, and many were kept singly or in pairs, with distinctly patchy breeding results in consequence.
The conditions which caused this process to happen will continue to operate, so zoo managers will have to make deliberate decisions to avoid increasing uniformity. Fortunately there are several ways to do this. Conway's bullfrog solution* (if I may call it that) is better exhibits to display the animals and to educate visitors. An alternative is more specialisation, for example Gerald Durrell decided that his small zoo on the island of Jersey should concentrate on small endangered species from islands, such as lemurs, Mauritius pink pigeons and Caribbean iguanas, as well as having a few more popular species: obviously zoos that are relatively close together need to specialise differently, but that is not a problem if they are associated like Antwerp & Planckendael or Regents Park & Whipsnade, or if other factors such as amount of space or climate are different. Publicity is important too, zoos can now communicate directly with the pubic via social media, without needing to interest journalists in stories - which is not to say that mass media don't matter, but zoos can have more say in the agenda: in the UK in the past few years, TV series on the animals and keepers at ZSL, Edinburgh & HWP, and in particular Chester, have all gone beyond the lions, tigers and meerkats to show keepers working with wolverines, frogs and insects.
* I first read Conway's splendid article 'How to exhibit a bullfrog: a bed-time story for zoo men' in International Zoo Yearbook Volume 13 (1973). A copy is available on Zoolex https://www.zoolex.org/media/uploads/2018/07/30/conway_how_to_exhibit_a_bullfrog.pdf