As a result many arid-zone species have very broad geographical distributions. Similarly, a number mammal, bird, and reptile species are found over huge areas of Australia. Despite these large geographic distributions, variation through time in environmental conditions means that not all areas are inhabitable at all times.
Severe drought can render areas too low in food or water for occupation.
Experience has taught us that plants and animals with large geographic distributions, and seemingly large population sizes, can be just as prone to extinction as the ones that occur in small numbers in a small area. Many of the mammal and bird species that are now extinct, or declining alarmingly in the arid-zone, formerly had geographic distributions covering more than half of Australia, for example the bilby. It is believed the movements of plants and animals among suitable patches of habitat to avoid harsh and variable environmental conditions is a vital part of the strategy for survival. Seemingly unrelated activities in different parts of the continent, may well be contributing to the decline of species because they degrade critical patches of habitat and break-down the connections between population pockets scattered over the landscape. Planning for conservation needs to take into account that mobile plants and animals move over large areas, and that immobile ones must be catered for on smaller scales.