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’