Too small or just right?
One of the most common criticisms one sees about zoos is that the cages/enclosures/cages are too small and that the animals have much more space in the wild. This is both right and wrong.
Animals in the wild DO have more space, no-one can deny it but it is no holiday camp out there in the wild. Animals can not go just where they want to they are confined within a (usually) invisible barrier. They are in their territory!
The size of a territory is determined by a variety of factors the most pressing one being the availability of food. The less food available the bigger the territory needs to be to aquire it. Plenty of food and the territory can be quite small. Life would be easy in the wild if all the animals got on well but they don't. There is almost constant competion for territory. Animals have to fight tooth and claw to defend what they do have and fight again to aquire more in times of shortage.
Territory under threat
Territory is almost constantly under threat. Animals breed. Young are forced out into the big wild world to cope on their own...to steal territory from someone older or weaker than themselves. Mankind takes more of the wild for farmland or to build a reservoir perhaps and animals are forced out to fight and compete for limited resources. It is a cruel world. Fighting often leads to injury, infection and slow lingering death. Wildlife magazines and movies very rarely show the sick and injured, it would not be too popular if it did.
In many cases fighting does not occur. Territories are claimed by displays, noisy calls and dances. The result though is the same. The animal is left stressed and with nowhere to go.
Territory is also determined by species, by climate, by food type, mate availibity and a variety of other factors.
Within a zoo environment the need for vast open spaces to hunt or gather food is unnecessary. The food is brought to the animal...safely. It doesn't have to worry where the next meal is coming from. There will (in a good zoo) always be enough food to eat, a dry place to sleep, shade, water, somewhere to hide, to climb, to dig, and a mate when natural urges emerge.
Black and rufous giant elephant-shrew
Cages/Enclosures in zoos need to consider the species they hold. They need not imitate the wild but often do, to a degree, to keep the visitors more than the animals happy.
Flight distances need to be considered. This is the distance between you and the animal at which they feel most comfortable. Flight distances are explained very well here. Though this deals with cattle the principle is the same.
There needs to be Environmental Enrichment as keeping the animals mind healthy is just as important as the body.