Problem
Most zoos do not operate in isolation, but rely on the guidance of zoological associations to establish "best practices" for animal care, conservation, and safety. This includes standards and recommendations for exhibit spaces. In North America, the "gold standard" of accreditation is the Association of Zoos and Aquariums (AZA).
Know that they recommend geographic or bioclimatic exhibit layouts vs. taxonomic groupings. This is because the manner in which animals are exhibited is a reflection of their underlying philosophy: Does the institute adhere to modern, progressive methods of animal care? The AZA believes that "understanding, engaging, and committing to the advancement of standards, practices, related policies and philosophies constitutes 'modern zoological practices and philosophies.'" These best practices and philosophies define excellence in the profession and are what distinguish AZA-accredited institutions from other institutions that have animals for guests to see and appreciate.
To the AZA (and to many others), geographically or bioclimatic layouts reflect a more modern philosophy of care, though it is difficult and expensive to overhaul and/or move an exhibit. This can leave zoos in a difficult situation: How might they reflect a modern, progressive philosophy of care while also working within their budgetary constraints?