EFFECTS OF IRRIGATION AGRICULTURE TO THE DESERT RODENTS

This paper deals with ecological relationship between rodent species composition and changing land use pattern in the canal command areas of Rajasthan desert having 60, 40, 30 and 10 years of intensive irrigation. Major canal systems in Sri Ganganagar District of Rajasthan State (India) are Gang Canal (1927-28), Bhakhara Canal (1951-52) and Indira Gandhi Canal (1956-57). Irrigated cropping is practiced in about 80 % of the area for varying periods. The remaining area is a typical desert having sandy plains and alkaline patches. Species composition and trap index revealed that the small mammal population was highest in 10 year old irrigation cropping systems and minimum in the 60 year old irrigated fields. Two mesic species of rodents viz., Rattus meltada pallidior and Mus musculus bactrianus were found to inhabit 60, 40 and 30 years old irrigation cropping systems, whereas, two xeric rodent species viz., Meriones hurrianae and Gerbillus gleadowi were found only in 10 years old irrigation systems. This showed that the xeric rodents are being replaced by mesic species after about 30 years of intensive irrigation cropping system. Besides these two mesic species, Rattus rattus and Tatera indica were also trapped from sugarcane and cotton fields during winter season. The fields had an irrigation intensity of 30, 40 and 60 years. The 10 year old irrigation areas also harboured R. meltada and M. musculus in sugarcane fields whereas in gram fields cultivated on the sandy plains true desertic species like M. hurrianae, G. gleadowi and Rattus gleadowi were noticed in winter season. The areas with 30 and 10 years old irrigation recorded occurrence of Suncus stoliczkanus also which is rarely found in the desert ecosystem. Similarly during summer season, R. meltada pallidior predominantly occurred in 60, 40 and 10 years old irrigation system. Besides this T. indica was also trapped in the crop fields with 60 and 10 year old irrigation intensities. Suncus murinus, the shrew also inhabited the crop fields with 60 and 30 year of irrigation status. Changes in land use pattern due to intensive irrigation through canal systems had resulted in << atavism >> in the habitat as shown by presence of two common domestic mammals, M. musculus and S. murinus in the crop fields with 30 or more years of irrigation practice.