Herbaceous production in South India-limiting factors and implications for large herbivores

This study's goal was to better understand the growth pattern and limitations of the herbaceous production that supports South India's rich large herbivore grazer assemblage. We conducted a fully factorial nitrogen and water (three levels each) treatment field experiment in the herbivore rich South Indian Western Ghats region to determine the seasonal pattern and the extent to which nitrogen and water availability limit herbaceous production. Graminoid production was found to be nitrogen limited. Despite low rainfall, additional water did not significantly increase overall biomass production nor extend growth in the dry season. Accumulated standing biomass was highest in the late wet season (November) and lowest in the dry season (May). Leaf nitrogen was highest in the early wet season (June) and lowest in the late dry season (March). Grazing had a positive effect on grass production by extending the growing season. Biomass production and graminoid leaf nitrogen concentration levels in the study area were similar to other tropical areas in the world. Also similar to other tropical large herbivore areas, the dry season poses an annual challenge for large herbivores in the study area -particularly the smaller bodied species-to satisfy their nutrient requirements

Asian Eden : large herbivore ecology in India

The study of large mammalian herbivore ecology has a strong allometric tradition. The majority of studies that have helped better understand how body mass affects large herbivore ecology in the tropics, from a biological, functional, and ecological perspective, are from Africa. India’s large herbivore assemblage—the richest outside of Africa and with a body mass range similar to Africa’s—is a poorly understood assemblage that has never been studied from the perspective of body mass theory. The goal of this study was to bridge this gap. I tested hypotheses of large herbivore biology and ecology in India based on body mass theory across different spatial, temporal and organizational scales. Data collection and analyses included: a 20 month field study the provided data of forage availability, the seasonal variation in diet, habitat preference and overlap, the timing of parturition, and the life history traits of different body mass large herbivore species in South India; a year long treatment based exclosure field experiment that provided a better understanding of the seasonal variation in graminoid biomass and quality in South India; a country level analysis of the distribution of the large herbivore assemblage with respect to environmental covariates; and a modelling approach to determine the impact of body mass on reproductive biology. Results showed that body mass based principles offered explanations for some, but not all, of what I observed and predicted. This study for the first time proposes that the impact of body mass might explain why some smaller herbivore species show seasonality in annual parturition while some large herbivores species do not. Also, as predicted and similar to Africa, large herbivore species richness in India is highest in areas with high soil nutrients and intermediate moisture levels. Beyond this study, important questions that still remain are “Which environmental and ecological conditions shaped species richness in Africa to be four times higher than what is found in India?” As India remains the last stronghold—Asia’s Eden—for most of Asia’s large herbivores, there is a need for further studies of the biology and ecology of large herbivore species in India. <br/

Contrasting timing of parturition of chital Axis axis and gaur Bos gaurus in tropical South India - the role of body mass and seasonal forage quality

Seasonal variation in forage availability and quality is understood to affect the annual timing of parturition in large herbivores. In India-where seasonal monsoonal rains define variation in forage availability and quality-chital Axis axis exhibit stronger seasonality in parturition than the larger gaur Bos gaurus. We hypothesized that this difference can be explained by forage requirements determined by body mass. We developed a model to simulate changes in leaf biomass and nitrogen content based on plant available moisture and nutrients, and calibrated our model with field data. Our results show that the minimum forage nitrogen content required by lactating gaur was available throughout the year, but that required by lactating chital was available for less than 40% of the year, i.e. during the early wet season, which coincides with the annual peak period of chital births. The three to four month spread of chital births, which begins in the dry season, implies that the period of highest quality is also important for females to replenish maternal reserves for future reproduction and help maximize the growth rate of neonates. This spread also indicates low synchrony of chital births and suggests that predator swamping was less important in influencing their timing of parturition. As monsoonal rain exhibits annual temporal variation, we analyzed our model under different rainfall patterns while keeping the total annual rainfall constant. We found that the difference between the durations of how long forage quality is available to satisfy the minimum requirements of lactating gaur and lactating chital is similar for all simulated patterns. This insensitivity to variable rainfall patterns lends support to our hypothesis that forage requirements determined by body mass is one plausible explanation for the variation in parturition strategies among large herbivores species

Age and sex determination of gaur Bos gaurus (Bovidae)

One reason why the gaur Bos gaurus is a poorly understood species is because there are no reliable data to age and sex individuals. We studied captive gaur for two years in Mysore Zoo, India and Omaha Zoo, USA, and determined age-specific differences in morphological features and physical growth, by measuring shoulder height, of male and female gaur. We fitted von Bertalanffy growth functions to the shoulder height data and found maximum shoulder heights of 175 cm and 147 cm for males and females, respectively. This study ascertained for the first time that the greater the amount of white on the horns of a gaur, the older it is, and that the sexes can be distinguished based on horn shape and size differences. We found that gaur aged 15 months and below can be classified into three age classes, but are difficult to sex. The sex of gaur aged 15–36 months is best determined by a study of their horns. Adult gaur, greater than three years, are easy to sex, but are difficult to classify into single-year age classes and are reliably classified only into two age classes for females and three for males

Diet and habitat-niche relationships within an assemblage of large herbivores in a seasonal tropical forest

There is little understanding of how large mammalian herbivores in Asia partition habitat and forage resources, and vary their diet and habitat selection seasonally in order to coexist. We studied an assemblage of four large herbivores, chital (Axis axis), sambar (Cervus unicolor), gaur (Bos gaurus) and Asian elephant (Elephas maximus), in the seasonal tropical forests of Bandipur and Mudumalai, South India, and tested predictions regarding the species’ seasonal diet browse : graze ratios, habitat selection and habitat-niche preference and overlap. Field data collected for the study included the seasonal variation in grass quality, the seasonal variation in d13C in the species’ faeces and the seasonal variation in the species’ habitat selection and overlap using a grid-based survey. Results of the d13C analyses showed that the chital was more of a grazer in the wet season (-17.9‰to -21.6‰), but that it increased the proportion of browse in its diet in the dry season (-25.6‰ to -27.7‰); the gaur was a grazer for most of the year (-15.3‰to -18.6‰); the sambar preferred to browse throughout the year (-21.1‰to -30.4‰); and that the elephant was a mixed feeder (-14.2‰to -21.4‰). Elephant habitat-niche breadth was high (0.53 in wet and 0.54 in dry) and overlapped equally with that of the other species in both seasons (0.39–0.94). The gaur had the most restricted habitat-niche breadth in both seasons (0.25 in wet and 0.28 in dry), and it switched from the moist deciduous habitat in the dry season to the dry deciduous habitat in the wet season. These results offer the first insights into the seasonal variation in browse : graze diet ratios and the habitat-niche overlap amongst the common largest-bodied mammalian herbivore species found in South India