Nutritional Ecology of Asian Elephants (Elephas maximus) in Chilla Range of Rajaji National Park, Uttarakhand

Abstract

Responses of animals to the habitat has been the central focus for management of species and of these aspects, nutritional ecology has been the key issue in foraging behaviour studies and habitat studies. Therefore, the study focused on the nutritional aspect of forage selection by Asian elephants (Elephas maximus) in Chilla Range of Rajaji National Park. The main objectives were to determine whether habitat structural heterogeneity or nutritional quality of the selected food plant species was a determinant in the temporal and spatial habitat use by elephants and to determine the reasons behind seasonality in foraging. The study area of 148km2 in Chilla Range of Rajaji National Park was divided into twelve 2x2km grids, and these were further divided into 4 sub-grids each. In each sub-grid, a 1 km long line transect was laid and along this 10m radial plots were placed at 100m intervals. Vegetation data were collected to characterize the habitat structural heterogeneity in terms of number of trees of each species, height of canopy base, canopy volume, percent canopy cover, species diversity, species density and geo-spatial variables such as NDVI, standard deviation of slope, mean elevation and the proximity to water. Parts of 12 most-preferred plant species were collected in the study areas for estimating nitrogen, ash, acid detergent fibre, and macro and micro minerals such as sodium, potassium, calcium, copper, magnesium and zinc. During the study period from December 2008 to May 2009, Elephant response was determined in terms of dung density along the 1km transect in winter and in summer. The total number of trees in each grid varied from 124 to 268. Tree diversity ravged betweel) 0.456-1.454. Height of canopy base was mostly 1.5-3.0 m, although two grids showed extremely high canopy bases. Canopy volume ranged from 165.63m3 to 948.36m3 , although the majority of the grids showed a high variation in canopy volume in terms of standard deviation (SE). The percent canopy cover ranged from 54.13% to 93.72%. Most of the NDVI values were _high in the study area (>0.180), while one grid showed a low value of 0.143. For the standard deviation of slope, the values ranged from a low of 2.46 to a high of 8.46. The mean elevation of the study area ranged froin 391-840m a.s.l. Nutritional values estimated for most of the parameters in winter and summer from selected plant samples collected in the study area showed slight variations 4 between seasons. Percent nitrogen content indicated no seasonal difference (f=0.98, p=0.05, df=ll). The percent acid detergent fibre indicated a difference (P<0.05,df=I I) between the two seasons. Percent ash content was found not significantly different (p=O.l6, p=0.05, df=l1) between seasons. Amongst the macro and micro minerals, sodium content was significantly different across the two seasons. Potassium content was found to be significantly different across the seasons (p<0.05). Calcium content was also found to be significantly different between winter and summer (P<0.05). The copper content could not be compared across the seasons as in summer the levels present in plant samples were too low to be detected by the instrument. The difference in magnesium and zinc content across the two seasons were not significant (p=0.16 and P=0.31). Dung density in the grids across both seasons was non-uniform and highly skewed (p<0.05, df=47). The dung densities in both seasons were related more with the habitat heterogeneity variables than nutritional values obtained in each grid. The relationship between dung density and the number of plants was positive in the winter seasons (R2= 0.2848) and summer (R2= 0.4383), indicating that elephants are highly selective towards areas with higher numbers of woody plants. Plant species diversity indicated no influence on dung density in winter (R2= 0.00005), but showed a negative trend in summer (R2= 0.0154). The height of canopy base was negatively related to dung density, with elephants selecting areas with a mean canopy base height between 1.5-3.0m during both winter (R2=0.2288) and summer (R2=0.174). Dung density showed a negative trend when related to canopy volume in both seasons. The R2 value for winter is 0.2087 and in summer it is 0.1471. Percent canopy cover had a negative influence on the dung densities in winter (R~= 0.083) and in summer (R2= 0.1524). NDVI showed a negative relationship with dung densities in winter (R2=0.01l1) and a positive relationship in summer (R2= 0.1894). The relationship between the standard deviation of slope and dung density showed a negative trend in both winter, (R2=0.0033) as well as in summer (R2=0.0389). The higher elevation grids show a lower d/mg density during both winter (R2=0.216) and summer (R2=O.l443). The relationship between dung density and proximity to water in winter is negative (R2=0.1575) and the relationship remains negative (R2=0.1016) in summer. In relation to nitrogen content and dung density in winter there was a weak positive trend (R2=0.0256), while in summer there was a weak negative trend (R2=0.032). The relationship between dung densities and percent acid detergent fibre (ADF) in winter indicated a weak positive trend (R2=0.0012) and during summer, indicated a weak negative trend (R2=0.0657). In relation to percentage ash content (Fig. 4.29.), dung densities in winter indicated a weak positive trend" (R2=0.0114), while in summer there was a weak negative trend (R2=0.0641). When compared with sodium, dung densities showed a very weak positive trend (R2=0.0092) in winter and a negative trend in summer (R2=0.0834). In winter, when compared with dung densities potassium showed no trend (R2=0.001), but in summer, there was a weak negative trend (R2=0.0076). In winter, calcium does not show any relationship with dung densities (R2=0.0002), while in summer, there is a weak negative trend (R2= 0.0511). Magnesium content does not show any relationship with dung densities (Fig 4.33) in the winter season, (R2=0.0007), while in summer, there is a weak negative trend (R2=0.004). Zinc shows a weak positive trend (R2=0.0298) in winter and a weak negative trend (R2=0.026) in summer. Principal component analysis of nutritional parameters indicated nine components that were influencing dung density distribution in the study area in both the seasons, and hence no single parameter influenced elephant habitat use. The study clearly indicates that the distribution of elephants in Chilla Range of Rajaji National Park is more related to abundance of woody species and proximity of water, than the nutritional content in plant species. Principal component analysis showed that there was no single parameter that influenced dung distribution in the study area. This could be due to the fact that plant species selected for foraging by elephants contained an adequate amount of nutrients in most species for meeting foraging requirements .an d they probably meet their daily requirements by foraging on varied proportions of plant species.