Application of GIS to investigate the use of space in coral reef fish: a comparison of territorial behaviour in two Red Sea butterflyfishes

The space use of two coral‐feeding Red Sea butterflyfish species (Chaetodon austriacus and C. trifascialis) was studied at three sites in the Gulf of Aqaba to determine the extent of intraspecific territoriality. Individuals or pairs were observed in shallow water (<5 m). Their locations were recorded on maps of each study reef. The Animal Movement Analysis Extension (AMAE) in ArcView was used to plot territory borders and compute territory size for each species. Chaetodon austriacus, a generalist corallivore that exploited evenly distributed food resources, maintained small exclusive pair territories with clearly defined territory boundaries. In contrast, C. trifascialis, a specialist corallivore that exploited patchily distributed food resources, demonstrated considerable variation in territorial behaviour that ranged from the defence of small exclusive solitary territories to the shared use of a large home range. Comparisons of territory area estimates showed that 95% kernel probability density function territory boundaries matched intuitive territory boundaries and, unlike the minimum convex polygon area, did not contain obvious areas that were not used by individuals or pairs. We show that comparing different territory size measures can be very useful in describing subtle differences in territorial behaviour between species and studies. For this purpose, GIS is an ideal technology with which to carry out such analyses quickly and easily.