Food Analysis of Indian Gerbil (Tatera indica, Hardwicke, 1807) in Pothwar, Pakistan

Diets are significantly important to ascertain evolution, approaches of life history and ecological niche of the animals. Thus, the information on the food of animals is fundamentally important for many ecological studies (Kronfeld and Dayan, 1998). It is also necessary for the conservation of the species, concerns on the introduction of game animals and for nature conservation (Cole et al., 1995), and developing biological controls (Beg et al., 1994; Jimenez et al., 1994; Tobin et al., 1994). Availability of the food deliberates the population density of species (Ylonen et al., 2003) and reproductive capabilities of any individual (Htwe and Singleton, 2014). As far as the pest species are concerned, precise information of the diet is very important to develop effective targeted approaches. (Lathiya et al., 2008).

In Pakistan, rodents exert a serious limitation on agricultural production by causing extensive losses to cash crops as wheat, rice and sugarcane (Greaves et al., 1975; Greaves and Khan, 1975; Beg and Khan, 1977; Beg et al., 1978, 1979, 1988; Fulk et al., 1980; Fulk and Akhtar, 1981; Shafi and Khan, 1983; Ubaidullah et al., 1989). Indoors, house rat and house mouse depredate on stored grains and other food stuffs in rural and urban homes, grocery shops, wholesale markets and godowns (Ali, 1990; Khan, 1990; Mushtaq-ul-Hassan, 1993). Beg (1986) reported that murid rodents are profoundly important because of their impact on crops from sowing to harvest.

In Pothwar area rodents cause significant damage to the wheat and groundnut crops. Many species of small rodents like Bandicota bengalensis (lesser bandicoot rat), Nesokia indica (short tailed bandicoot rat), Tatera indica (Indian gerbil), Millardia meltada (soft furred field rat) and Mus musculus (house mouse) damage the crops in the Pothwar (Brooks et al., 1988; Hussain et al., 2003).

Diets of the rodents are generally characterized by different methods. One of the common adopted methods is stomach contents analysis or less common fecal analysis. Both the methods have some advantages and disadvantages. Some food items are completely digested in the stomach so fecal contents cannot reveal that material (Jeuniaux, 1961; Hansson, 1970; Neal et al., 1973; Dickman and Huang, 1988; Bergman and Krebs, 1993). Another method is stomach pumping of the rodents without sacrificing them (Kronfeld and Dayan, 1998). This study provides information through stomach contents about the diet of the Indian gerbil in Pothwar, Pakistan.

The study was carried out from February, 2014 to January, 2016. After being snap trapped, samples were brought to the laboratory and were autopsied. Stomachs were cut from the esophagus and were preserved in the freezer. The stomach contents were removed and compared with the reference slides by adopting the procedure described below. In total, 42 stomachs were processed for the diet analysis. Empty or decomposed stomachs were discarded.

The stomach contents were poured in the petri dish and washed with the distilled water. Slides were made following the same procedure as discussed above except the process of grinding. The reason is that the stomach already digested the contents of the food. For each sample, three slides were made. Each slide was tagged with a unique id. Slides were compared with the reference slides for identification. Quantitative results were determined as a measure of the frequency of occurrence. Percentage of relative abundance was also calculated by using the formulae:

Pearson chi-square was used to find out the differences in different food items among different seasons and between two sexes. All differences with p> 0.05 were considered non-significant.

The major diet of Indian gerbil comprised of plant matter (Table I). The plant matters constituted about 74.5% of the total diet and the arthropods constitute 25.5%. Significant difference was observed in the consumption of plant and animal matter (χ 2= 25, df= 1, p<0.05).

Among plant matters, wheat was the major consumed item (33.7%). Field mustard and peanut were consumed almost in equal proportion (16.9 % and 15.6 %, respectively). The consumption of millet was 7.8 %. Mong bean was also consumed in small proportion (0.5%).

Frequency of occurrence (F.O) of wheat was 53.6 % and was highest among all other food categories. F.O of field mustard was 27.2%. F.O of millet was 9.1%. F.O of peanut was 45.5 %. F.O of mong bean was 10.4%. F.O of arthropods was 60.2 %.

Significant difference was observed in the consumption of wheat compared to field mustard (χ 2= 5.6, df= 1, p<0.05), millet (χ2= 16.1, df= 1, p<0.05), peanut (χ2= 6.5, df= 1, p<0.05), and mong bean (χ2= 31.1, df= 1, p<0.05). Mong bean was significantly less consumed than field mustard (χ2= 14.2, df= 1, p<0.05), millet (χ2= 5.4, df= 1, p<0.05) and peanut (χ2= 13.2, df= 1, p<0.05). The order of food consumed by Indian gerbil was wheat > field mustard > peanut > millet > mong bean.

Table I shows the seasonal fluctuations in the diet of Indian gerbil. Significant seasonal difference was observed in the consumption of all the food categories (p<0.05). In all the seasons, plant matter was consumed in different proportions. Among plant matters, wheat was consumed in all seasons.

F.O, frequency of occurrence; R.A, relative abundance of food.; n, No. of stomachs processed. * significantly different in arthropods/insects and plant matter, Values labeled with same alphabets are non-significantly (p>0.05) different in a column.

In spring season, the diet of Indian gerbil comprised of 92.1% of plant matter and 7.9% of arthropods. Significant difference was observed in the consumption of plant and animal matter (χ2= 70.5, df= 1, p<0.05). Among plant matter, field mustard was the major food item consumed by the gerbils (53.1 %).

Proportion of wheat was 31.9%. Millet and mong bean was not observed in any of the stomach sample of spring season. However, peanut was consumed in lower proportion (7.1%). F.O of field mustard was highest (57.1%). F.O of peanut was 14.3%. F.O of arthropods was 28.6%. Significant difference was observed in the consumption of wheat compared to field mustard (χ2= 5.18, df= 1, p<0.05) peanut (χ2= 16.0, df= 1, p<0.05) and field mustard compared to peanut (χ2= 35.2, df= 1, p<0.05). The order of food consumption by Indian gerbil in spring season was field mustard > wheat > peanut.

In summers, the diet of Indian gerbil comprised of 53.3% of plant matter and 46.7% of animal matter or arthropods. Non-significant difference was observed in the consumption of plant and animal matter (χ2= 0.36, df= 1, p>0.05). Among plant matter, wheat was consumed in almost equal proportion of peanut (26.7 and 25.2% respectively). Relative abundance (R.A) of arthropods (46.7%) was the highest in the summer season; mong bean was also consumed in small proportions (1.4 %).

Field mustard and millet were not observed in any of the stomach contents. F.O of arthropods was the highest (69.2%) among all the food categories. F.O of wheat was 30.8%. F.O of peanut was 46.2%. F.O of mong bean was 6.2%. Significant difference was observed in the consumption of wheat and mong bean (χ2= 24.1, df= 1, p<0.05), peanut and mong bean (χ2= 22.1, df= 1, p<0.05). Thus, the order of food consumption by Indian gerbil in summer season was wheat > peanut > mong bean.

In autumn season, millet was the chief staple food of Indian gerbil (85.3%). Wheat and peanut was also observed in small proportions (5.8% and 8.9%, respectively). In autumn, all other food categories were not observed in any of the stomachs. F.O of millet was 43.2%. F.O of wheat and peanut was 15.7 and 32.3, respectively. Significant difference was observed in the consumption of wheat and millet (χ2= 65.5, df= 1, p<0.05) and millet and peanut (χ2= 61.4, df= 1, p<0.05). The order of food consumption by Indian gerbil in autumn season was millet > peanut > wheat.

In winters, the diet of Indian gerbil comprised of 77.2% of plant matter and 22.8% of arthropods. Significant difference was observed in the consumption of plant and animal matter (χ2= 29.1, df= 1, p<0.05). Among plant matter, wheat (42.7 %) was the mostly consumed item by Indian gerbil. Field mustard was the second major item (18.0%) found in the stomach of Indian gerbil in winter. Millet and peanut were also consumed in smaller proportions (8.0% and 7.6%, respectively). Mong bean was consumed in a very small amount (0.9 %). F.O of wheat was 31.8%. F.O of peanut was 27.3%. F.O of arthropods was 24.5%. F.O of field mustard, millet and mong bean was 13.6 %, 4.5% and 4.5% respectively.

Significant difference was observed in the consumption of wheat compared to field mustard (χ2= 17.2, df= 1, p<0.05), millet (χ 2= 33.1, df= 1, p<0.05), peanut (χ2= 33.1, df= 1, p<0.05) and mong bean (χ2= 50.1, df= 1, p<0.05). Field mustard was significantly more consumed than millet (χ2= 3.8, df= 1, p<0.05), peanut (χ2= 3.8, df= 1, p<0.05) and mong bean (χ2= 15.2, df= 1, p<0.05). Mong bean was less consumed than millet (χ2= 5.4, df= 1, p<0.05) and peanut (χ2= 5.4, df= 1, p<0.05). Non-significant difference was observed in the consumption of millet and peanut (p>0.05). The order of food consumption by Indian gerbil in winter season was wheat > field mustard > millet> peanut > mong bean.

Table II. Frequency of occurrence and relative abundance of different food items present in the stomach contents of male and female Indian gerbil.

F.O, frequency of occurrence; R.A, relative abundance of food.; n, No. of stomachs processed.

Table II shows the comparison in the food consumption of male and female Indian gerbil In male samples, plant matter accounted for 73.1% and arthropods accounted for 26.9%. Significant difference was observed in the consumption of plant and animal matter (χ2= 21.16, df= 1, p<0.05). Wheat was the major food item consumed by male Indian gerbil. Other food items consumed were field mustard (20.1%), millet (14.1 %), peanut (7.9%), and mong bean (0.5%). Significant difference was observed in the consumption of wheat compared to millet (χ2= 6.42, df= 1, p<0.05), peanut (χ2= 13.56, df= 1, p<0.05) and mong bean (χ2= 28.12, df= 1, p<0.05). Field mustard consumption was significantly different than peanut (χ2= 5.14, df= 1, p<0.05) and mong bean (χ2= 17.1, df= 1, p<0.05).

The consumption of mong bean was significantly less than the consumption of millet (χ2= 11.26, df= 1, p<0.05) and peanut (χ2= 5.44, df= 1, p<0.05). The order of abundance of food consumed by male Indian gerbil was wheat> field mustard millet > peanut > mong bean

Female Indian gerbil consumed 75.9% of plant matter and 24.1% of arthropods. Significant difference was observed in the consumption of plant and animal matter (χ2= 27.04, df= 1, p<0.05) by female Indian gerbil. Among plant matter, wheat (26.0%) was the chief diet found. Arthropods (24.1%) were the second most consumed. Field mustard and millet were almost equally consumed (18.0% and 20.0%, respectively). Peanut was consumed in small amount (11.9%). Mong bean was not observed in any of the female samples. Significant difference was observed in the consumption of wheat and peanut. The order of food items consumed by female Indian gerbil was wheat > millet > field mustard > peanut. Non-significant difference was observed in the consumption of different food categories between male and female samples (p>0.05).

The study on the diet of an animal is significantly important because food gives important information for ecological research such as conservation, evolution, relationship between animal and its environment. Food is vital for the maintenance of body functions and reproduction. Information obtained from stomach analysis on rodents is the main ecological parameter to study the food preference, habitat association, seasonal fluctuation and the pest status (Campos et al., 2001).

In present study, the stomach analysis showed that the major diet constitutes of plant matter in all the seasons. However, the frequency of each food item varied seasonally. Among plant matter, wheat was the major food item. Animal matter or arthropods were also consumed.

In spring season, field mustard was the major plant matter found in the stomach. This was due to the availability of particular food tem in the spring season. In summer season, the major diet of Indian gerbil consisted of animal matter i.e., insects were consumed in this season. Peanut was also found due to the availability. In autumn season, millet was found in the large proportion in the stomach contents, which indicates that it was most abundant in the season. In winter season, wheat grains were consumed in large amount. The present study thus strongly suggests that Indian gerbil is an opportunistic forager. There is considerable fluctuation in the consumption of different food items, which is in conformity with the variations in the vegetation in the eco-system reflecting the availability of different food items. This could be an indication of their success in wide distribution.

No significant difference was found in the consumption of different food categories among male and female individuals. The difference in the diet of male and female would occur when there would be shortage of particular food item in the environment that rarely happens in the stable environment (Clark, 1980).

In conclusion, Indian gerbil is an opportunistic forager. It eats whatever is available. However, seasonal fluctuations were observed in the diet pattern of this pest species. Moreover, this study could be helpful in the formation of bait for this species, which is prerequisite for the management of the pest species.

This research was conducted under the financial assistance of Pakistan Science Foundation through Grant No. PSF/Res/P-PMAS.AAUR/Bio.446.

This research study was approved by the Ethical committee of PMAS Arid Agriculture University.

The authors have declared no conflict of interest.