Introduction
By G. Nel.
Environmental (biotic and abiotic) as well as anthropological factors determine the presence or absence of a species in a specific area. One or more of these factors can change over a short or long period of time. Environmental changes include aspects such as yearly rainfall, floods and droughts and can normally not be managed. Management have to adapt to these changes. Anthropological changes include aspects such as agricultural practises (deforestation, overgrazing etc.) and international borders of countries that artificially divide distribution ranges or migration routes. Most of these changes can be managed. Changes of environmental and anthropological factors can have a positive or negative effect on a species and might even alter the distribution patterns of a species.
It is necessary to determine the magnitude of changes, if any, because it may determine management actions to be implemented and therefore have financial or other ecological implications. For instance habitat, local climatic conditions, veld condition, freedom of movements etc. have changed over the past fifty years on most game farms situated in South Africa. These aspects induced a change in the carrying capacity, which on its turn induced a change in the amount of animals and species to be kept on the property. This alters the functioning of the natural systems.