Seed dispersal by Rhesus Macaques (Macaca mulatta)

Common species, defined as those which are widely distributed and/or abundant, tend to be ignored in terms of their conservation and ecological significance. The general understanding is that they are too widespread to be in any danger of extinction and that, in comparison to rare taxa, they do not fulfill critical or specialized ecosystem functions. Very few studies though have actually examined the ecological functions of common species. A text book example of a common species, the rhesus macaque Macaca mulatta, has been intensively studied for many biological aspects, yet nothing is known about its role in maintaining ecosystem structure and functions. In this study, I investigated the role of rhesus macaques in fulfilling an important ecosystem function, namely seed dispersal. Seed dispersal is a critical ecological process that drives tropical forest recruitment and the recolonization and restoration of degraded habitats. Although many primate species are considered important seed dispersers, common macaque species, including the rhesus macaque, have been traditionally undervalued in this regard. However, land use changes resulting in loss of forest cover have led to the loss of large numbers of primate populations globally. In such a scenario, the importance of ecologically resilient primate species, characterized by dietary flexibility and ability to thrive in a variety of habitats, increases manifold. It has, in fact, been suggested that in many parts of tropical and subtropical Asia, where forests are fragmented or native mammal fauna has gone extinct, disturbance‐tolerant macaques like the rhesus macaque Macaca mulatta, the bonnet macaque M. radiata and the long‐tailed macaque M. fascicularis may be the only seed dispersers, especially for the large fruit/seed bearing species. Based on their large group and home range sizes, occasional high levels of frugivory, and dietary flexibility, I predicted that rhesus macaques may be potentially effective seed dispersers. To test my prediction I examined seed dispersal effectiveness in rhesus macaques in terms of (i) number of fruit species dispersed, (ii) rates of seed predation, (iii) seed handling methods and (iv) germination and establishment rates of dispersed seeds. I also investigated how certain ecological and behavioural parameters such as resource availability, fruit trait preference and access to human food subsidies may impact seed dispersal effectiveness in rhesus macaques. Resource availability fluctuates in all ecosystems and the existence of distinct dry and wet seasons regulates the availability of fruits in forests. Studies on rhesus macaque diets have reported extremely variable levels of frugivory. Fruit consumption is often a function of fruit availability in the habitat. Although seasonality in dietary patterns has been noted in rhesus macaques in some studies, levels of frugivory in forest-dwelling rhesus macaques have rarely been studied in relation to fruit availability. Therefore, I examined how seasonal resource availability influences frugivory in rhesus macaques and in turn affects their role as seed dispersers. Primate fruit consumption may be driven by particular fruit characteristics and the latter are generally construed to be adaptations for effective seed dispersal. Hence I also investigated if rhesus macaques show preference for certain fruit species or fruit traits and the implications of this for seed dispersal by rhesus macaques. Throughout history, humans and primates have co-existed in diverse cultures and contexts and provisioning wild primates is a socio-religious tradition in many Asian countries, including India. Provisioned primate troops have been observed to decrease their consumption of natural plant parts, their mean daily and home ranges and spend more time resting and less time feeding and foraging. Since changes in ranging and feeding behavior may bring about changes in the ecological functions of species, the third aspect of my study was to assess how human interference in the form of providing food subsidies to rhesus macaques impacts their role as seed dispersers. I conducted my study July, 2012 to September, 2014 at the Buxa Tiger Reserve in West Bengal, India on two troops of rhesus macaques – Troop C that was wholly dependent on natural resources and Troop D that was provisioned by humans for some months in a year. The methods I used to address my research questions comprised (i) behavioural observations on macaque individuals, (ii) phenological monitoring of tree species, (iii) documentation of fruit and seed traits, (iv) GPS tagging of dispersed seeds and (iv) in situ and ex situ germination experiments. My findings showed that rhesus macaques dispersed 84 % of the 49 species they fed on by spitting or defecation. More than 60% of macaque-handled seeds were deposited outside the tree canopy, 96 % of handled seeds were undamaged and 61 % of the species for which germination tests were performed had enhanced germination. Fifty percent of monitored seeds germinated in situ and 22 % established seedlings. These results attest that rhesus macaques are important seed dispersers in tropical forests. Fruit consumption was positively correlated with fruit availability; the macaques acted as seed dispersers all the year round for a broad range of species. Dietary fruit evenness was negatively correlated with fruit availability. This implies that the macaques showed preference for certain species. In terms of fruit traits, rhesus macaques primarily fed on fruits with juicy-soft pulp and acted as seed predators for those with no discernible pulp. The other preferred fruit traits were soft skins, medium to large seeds and true stone-like seeds. Irrespective of fruit availability, macaque frugivory (and therefore seed dispersal) declined with increasing degree of provisioning. Macaque daily ranges also decreased during provisioning, resulting in shorter dispersal distances. Additionally, macaquehandled seeds were usually deposited on tarmac roads during provisioning periods, thereby precluding seed germination. Wildlife conservation practices are often driven by the risk of species extinction, hence common species are typically overlooked in conservation initiatives. However, although common primate species are highly adaptable, they are not neutral to various anthropogenic pressures such as habitat degradation, forest fragmentation and poaching. The population trend of rhesus macaques is presently unknown but their habitat size is declining rapidly. Due to their commensality, they are also often in conflict with humans and are regarded as pests. The findings of my thesis clearly demonstrate that the rhesus macaque fulfils important ecological functions within its natural habitat and that reduction in rhesus population numbers or even local extinction may result in serious consequences for the ecosystem. Based on the results of my study, I suggest that the regeneration and recruitment of preferred plant species alongside afforestation programmes involving these species may prevent rhesus macaques from gravitating towards human habitations and getting into conflict over shared resources. My study also demonstrates the negative impacts of provisioning on rhesus macaque ecological functions. Preventing or curbing provisioning is however not an easy task as provisioning wild animals is a socio-cultural tradition across much of South and South-East Asia, including India. Hence I recommend the initiation of a nation-wide literacy programme that educates lay citizens about the ill-effects of provisioning and strongly cautions them against the practice. I also advocate the need for rhesus population monitoring programs across the geographic range of the species, so that timely interventions can be made, if required, to ensure that they remain ‘common’ and of ‘least concern’