MATERIALS AND METHODS

Study area: The study area is the Thar desert of Rajasthan (22°30’-32°05'N and 68°05’-74°45'E). It covers an area of about 1,91,650 sq. km and spreads over 13 districts of Rajasthan. It includes entire Ganganagar, Hanumangarh, Bikaner, Jaisalmer, Barmer, Jodhpur and Churu districts and part of Nagaur, Ajmer, Pali, Jalore, Jhunjhunun and Sikar districts (Fig. 2). It comes under the Biogeographic Zone 3A-Thar Desert²⁹ which represents a unique ecosystem supporting a rich biodiversity. It is bounded by the Aravali hills in the east, the fertile Indus and Nara valley in the west, the great salt marsh of Kuchchh in the south and the semiarid districts of Haryana and Punjab in the north. It is an extension of the Sahara desert, through Arabian and Persian deserts and continues with the desert portion of Pakisthan on its west³⁰.

Field data collection: The present study was undertaken from October, 2012-September, 2015 during which field survey for Indian desert monitor was carried out in TDR. Population of the species was enumerated through intensive search in different parts of TDR following mostly ‘perambulation’ method^31,32, though ‘belt-transect’ method³³ was followed at selected sites viz. Desert National Park, Jaisalmer and Jorbeer, Bikaner. The GPS points were taken along with habitat and microhabitat information for each encounter of the species that was used in habitat suitability analysis.

Preparation of thematic maps and habitat suitability modelling: Habitat suitability analysis was carried out using GIS-based weighted overlay analysis which is a component of spatial multicriteria evaluation technique and that assigns more importance to some criteria over others^23-28.

Fig. 2:	Map of study area

The most useful application of GIS in this analysis is use of geographically referenced input data for different criteria assignment of percentage influences to those criteria, weights (1-9) to different attributes within each criterion and finally overlay various geo-referenced inputs to derive useful results. The technique allow the user to assign influences and weights to different classes in accordance with their relative importance in terms of suitability for the species that may be derived from knowledge from available literature or piece of information collected on habitat and microhabitat of the species through ground survey.

In this study, different ecological variables such as vegetation, land use/land cover, average annual rainfall, soil, monthly maximum and minimum temperatures along with species occurrence data collected from ground survey were used as inputs. Vegetation map of TDR was prepared from Resource Atlas of Rajasthan as source³⁴, which was geo-referenced and manually digitised with few modifications based on ground survey (Fig. 3a). Land use land cover map of the TDR was prepared from districts planning maps of Rajasthan as source³⁵. Relevant district planning maps (Map No. 056-NA/DP-2000-97, 3849-101D'-01, 7440-103D'-97. 2535-101D'96, 2640-101D'96, 7349-103D'-98, 3800-101D'-01, 2456-101D'96, 019-NA/DP-2000-95, 2281-101D'-95, 3000-101D'-98, 611-105D'-02, 059-NA/DP-2000-97) were scanned, geo-referenced, manually digitised, merged and cut with base map of TDR to prepare the final map (Fig. 3b).

Fig. 3(a-d):	(a) Vegetation of TDR, (b) Land use/ land cover of TDR, (c) Average annual rainfall (in cm) of TDR and (d) Soil types of TDR

Annual rainfall map of TDR was prepared using source map from Roy and Smykatz-Kloss³⁶, which was geo-referenced and manually digitised (Fig. 3c). Other maps viz. soil map, monthly maximum and minimum temperature maps were generated using source maps from Upadhyaya³⁷, which were geo-referenced and digitised (Fig. 3d, Fig. 4a,b). All the maps were geometrically rectified and projected using geographic projection system UTM. The spheroid and datum used were WGS 1984 with UTM zone 42N. The geo-databases for all maps were generated in ArcGIS environment. The GCPs (Ground Control Points) for species sightings were imported on the base map and multiple ring buffers were generated for all the locations (Fig. 4c). All the polygon features were converted into raster with 50 meters pixel size. Finally, all the geo-referenced inputs were overlaid in ArcGIS environment to derive the suitability map (Fig. 4d).

RESULTS AND DISCUSSION

Habitat suitability analysis for any species under geospatial environment is outcome of degree of interactions between biotic and abiotic factors and the species.

Fig. 4(a-d):	(a) Maximum temperature (July in °C) of TDR (b) Minimum temperature (January in °C) of TDR, (c) Location buffer of Indian desert monitor in TDR and (d) Habitat suitability of Indian desert monitor in TDR

In this study, thematic maps for different environmental variables such as vegetation, land use/land cover, average annual rainfall, soil, monthly maximum and minimum temperatures along with species occurrence data collected from ground survey were prepared under geospatial environment and used as independent factors (Table 1, Fig. 3a-d and 4a-c) to produce the final habitat suitability map of Indian desert monitor in TDS. The map (Fig. 4d) showed different potential habitat zones of Indian desert monitor in TDR which are 8.37, 45.55, 38.23, 5.37 and 2.48% as most suitable, moderately high suitable, moderately low suitable, low suitable and unsuitable, respectively (Table 2). This reveals though the species can survive in wider part (most suitable, moderately high suitable, moderately low suitable) of TDR, only a small area of that (8.37%) is best suitable for the species. Of the best suitable area, maximum area falls in Jaisalmer district followed by Bikaner and Barmer districts. These areas are crucial habitats for the species that need immediate conservation attention and should be protected from any kind of habitat degradation or alteration in future in order to save this endangered species in TDR. The study also shows a small part (7.85%) of TDR is either less suitable or unsuitable for the species.

Table 1:	Influences and weightages of different thematic layers used for habitat suitability analysis of Indian desert monitor in TDS

Table 2:	Habitat suitability of Indian desert monitor in TDS

These areas correspond to either hilly terrain at the edge of Aravali mountain range or areas that at present face large scale habitat alternation or degradation due to expanding human settlement and agricultural activities.

In the current study, of the best suitable area for Indian desert monitor, maximum area comes in Western Rajasthan (i.e., Jaisalmer, Bikaner and Barmer districts). In absence of any detailed study on this species, previous studies^10-12 about occasional reporting of the species in TDR supports the finding. The habitat suitability map from this study effectively defines desert monitor’s presence in the study area. Similar findings have also been reported in previous studies^16-23 for other conservation dependent species.

CONCLUSION

Habitat suitability analysis and identification of crucial habitats for Indian desert monitor in TDR can be considered as one of the preliminary conservation initiatives for this endangered species. The study revealed only a small area of TDR as crucial habitats for the species and these areas need to be protected immediately.

SIGNIFICANCE STATEMENT

The study brings into knowledge the crucial habitats of Indian desert monitor lizard in the Thar desert of Rajasthan under geospatial environment. The species is one of the most poorly known and conservation dependent species and lacks any study on its current status. Therefore, the present study is no doubt one of the conservation initiatives in India for this endangered species.

ACKNOWLEDGMENTS

The authors express their sincere thanks to the following personnel and institutions: Sri R.K. Tyagi, Chief Wildlife Warden, Rajasthan for granting permission to carry out this study, University Grants Commission, New Delhi for funding a research project to carry out this study (Project No. 41-77/2012-SR); Sri Anoop K.R., Filed Director, Desert National Park and Sri Surat Singh Poonia assistant Conservator of Forest, Talchhapar Wildlife Sanctuary for their cooperation and logistic support during field surveys, Mr. Tarun Singh, Jaisalmer for assisting in field surveys, Prof. Anubha Kaushik, Dean, USEM, GGSIP University, New Delhi for providing necessary facilities and for her constant encouragement throughout the study.