The Piosphere: Sheep Track and Dung Patterns.

The basic ecological unit in arid areas under grazing animals is envisaged as a zone round a watering point and is termed the piosphere (from the Greek "pios" = to drink). A piosphere in which sheep tracks can be distinguished in aerial photographs has been investigated; length, direction and type of track are described; remarkable adherance of the tracks to the near radial (significant deviation of 2.5? to left) indicate navigational skill in sheep. Sheep forage but do not cut visible tracks between the radial tracks. Sheep density can be estimated from dung density since pellets of dung persist for long periods in the arid regions. It is suggested that understanding the piosphere will contribute to management in arid rangelands.