A nature reserve.
should brakes be kept in a good condition
In its natural habitat the frog populations are kept small by natural predation, specific parasites and a harsh living condition. Without these the frogs can spread very rapidly.
what natural occurrence kept the indus balley supplied with plenty of water
It kept out invader's.
The area of Union Bay Natural Area is 202,342.82112 square meters.
The area of Tandy Hills Natural Area is 647,497.027584 square meters.
The area of Tideman Johnson Natural Area is 31,120.325888256004 square meters.
The area of Johnson Run Natural Area is 874,120.9872384 square meters.
The area of Sielbeck Forest Natural Area is 1,558,039.7226240002 square meters.
The area of Pinnacle Natural Area Preserve is 2,881,361.7727488 square meters.
As long as they are getting as much natural lightas they want, and the area they are kept in is cool/well ventilated/clean/plenty of space, then no - they will not get sick.
Messy area/area where pigs are kept