Table 1.

Examples of naturally occurring, unintentional and deliberately created human made factors that may promote isolation

	Natural isolating factors	Human activity with incidental effects	Artificial and deliberate methods
Physical barriers	Sea, large rivers and lakes, mountains and hills, desert and barren or poor terrain	Buildings, roads, railways	Insecticide, drainage
Vegetation	Unsuitable habitat type, excessive shade, no shelter	Large monospecies plantations	Land use change e. g. clearing and planting
Distance	Between suitable habitats, to nearest host	Sparse human presence, no farm animals, no plumbing or irrigation	Zones with no host, no natural or human-made breeding sites etc.
Time	Seasonal events, flood, animal bird migration	Crops, animal movement	Time limited or interrupted water supplies
Temperature	Seasonal changes, latitude, altitude
Competition	Neighbouring habitat zones favour a competitor		Promotion of benign competitor or predator