Stand structure of a primate rich rainforest region in the central Western Ghats of southern India

Although ranging up to the snowy region of Japan and Himalayan mountains, most primates live in warm tropical and subtropical climates. Further, though some of the primate species have adapted to live on ground, most of the primates live in trees. Therefore, the tropical regions with a wide diversity of vegetation harbor variety of primate species. In India, the Western Ghats of southern India and the northeastern Himalayan region are characterized by rainforests as well as deciduous forests. This floral diversity in these hills has provided several habitat types and many primate species inhabit these forests including some of the species even being sympatric (Molur et al. 2003). The Western Ghats of southern India range along the west coast covering a north-south length of about 1600km. Because of the monsoons, the ridge and the western slopes of the Ghats receive high rain fall resulting in tropical evergreen rainforests. The eastern slopes of these hills are rain shadow and dominated by deciduous and scrub forests. Due to the diversity of habitat types, faunal diversity and a high degree of endemism, the Western Ghats have been considered as one of the ‘hottest hotspots’ of global biodiversity (Myers et al. 2000). The Western Ghats harbor several primate taxa including the Mysore Slender Loris (Loris lydekkerianus lydekkerianus) and Malabar Slender Loris (L. l. malabaricus), endemic and Endangered Lion-tailed Macaque (Macaca silenus), endemic and Vulnerable Nilgiri Langur (Trachypithecus johnii), Darkbellied Bonnet Macaque (Macaca radiata radiata) and Pale-bellied Bonnet Macaque (M. r. diluta), and several taxa of Hanuman Langurs (Semnopithecus achates, S. priam, S. hypoleucos, S. thersites). In order to understand the feeding ecology of a species, it is important


INTRODUCTION
Although ranging up to the snowy region of Japan and Himalayan mountains, most primates live in warm tropical and subtropical climates.Further, though some of the primate species have adapted to live on ground, most of the primates live in trees.Therefore, the tropical regions with a wide diversity of vegetation harbor variety of primate species.In India, the Western Ghats of southern India and the northeastern Himalayan region are characterized by rainforests as well as deciduous forests.This floral diversity in these hills has provided several habitat types and many primate species inhabit these forests including some of the species even being sympatric (Molur et al. 2003).
The Western Ghats of southern India range along the west coast covering a north-south length of about 1600km.Because of the monsoons, the ridge and the western slopes of the Ghats receive high rain fall resulting in tropical evergreen rainforests.The eastern slopes of these hills are rain shadow and dominated by deciduous and scrub forests.Due to the diversity of habitat types, faunal diversity and a high degree of endemism, the Western Ghats have been considered as one of the 'hottest hotspots' of global biodiversity (Myers et al. 2000).The Western Ghats harbor several primate taxa including the Mysore Slender Loris (Loris lydekkerianus lydekkerianus) and Malabar Slender Loris (L.l. malabaricus), endemic and Endangered Lion-tailed Macaque (Macaca silenus), endemic and Vulnerable Nilgiri Langur (Trachypithecus johnii), Darkbellied Bonnet Macaque (Macaca radiata radiata) and Pale-bellied Bonnet Macaque (M.r. diluta), and several taxa of Hanuman Langurs (Semnopithecus achates, S. priam, S. hypoleucos, S. thersites).
In order to understand the feeding ecology of a species, it is important that the habitat is described in terms of its stand structure, species' distribution, richness and abundance, and importance value of each plant species.This may also help identify keystone species (Paine 1969;Stiling 2004).
A few studies in the past have provided description of primate habitats in the Western Ghats.Ramachandran & Joseph (2000) described the stand structure in Silent Valley, an important habitat of the rainforest primates in the Western Ghats.Primates were mostly found in areas with tree associations of Cullenia-Palaquium, Mesua-Palaquium and Mesua-Calophyllum.Lion-tailed Macaques were absent in areas with associations of Poeciloneuron-Palaquium, Poeciloneuron-Ochlandra and Calophyllum-Ochlandra.In the Anaimalai Hills of the Western Ghats, primates inhabited the rainforest regions dominated by Cullenia exarillata, Ficus microcarpa, Ficus exasperata and Melisoma pinnata (Sushma & Singh 2006).Krishnamani & Kumar (2000) studied several rainforest primate habitats in Karnataka and found that five tree species including Poeciloneuron indicum, Myristica dactyloides, Dimocarpus longan, Olea dioica and Aglaia elaegnoidea had the highest number of individuals.However, large areas inhabited by primates in the Western Ghats have not yet been quantitatively described for the vegetation characteristics.
In most of the places in the Western Ghats, Lion-tailed Macaques, Nilgiri Langurs and Malabar Slender Loris are sympatric in the rainforests of the ridge and the Western slopes, and Bonnet Macaques, Hanuman Langurs and Mysore Slender Loris are sympatric in relatively drier forests of the eastern slopes (Singh et al. 1997;Kumara & Singh 2004).However, north of Brahmagiri Hills in the Coorg District of the state of Karnataka, Lion-tailed Macaques, Bonnet Macaques, Hanuman Langurs and Malabar Slender Loris are found as sympatric species in several ranges of rainforests.The rainforest region to the north of Sharavathy River and south of Aghnashini River is one such region which, due to the high abundance of primates, has been regarded as one of the most potential regions for long-term primate conservation (Kumara & Singh 2004).In this article, we describe the vegetation structure of this prime primate habitat.

Study site:
We carried out the present study in the rainforests of the Western Ghats lying between 14 0 15'-14 0 25'N & 74 0 35'-74 0 47'E in the Gerusoppa Forest Range of Honnavara Forest Division in the State of Karnataka, India (Fig. 1).This forest region constitutes the northern limit of the evergreen forests of the plains and low elevations of southern India (Pascal 1988).Champion & Seth (1968) broadly classify this forest as 'west coast tropical evergreen forest'.The forest is primarily distinguished as Persea macrantha-Diospyros spp.-Holigarna spp.type with abundance of heleiophilic or light tolerant species.The official status of the forest is a Reserve Forest with interspersed revenue lands (Kumara & Singh 2004).Four primate species including the Endangered Lion-tailed Macaque (Macaca silenus) (Kumar et al. 2008), Bonnet Macaque (Macaca radiata), taxonomically controversial Hanuman Langur (Semnopithecus entellus achates) (Molur et al. 2003) and Malabar Slender Loris (Loris lydekkerianus malabaricus) inhabit the study area.This place is one of the few places in the Western Ghats of India where four primate species are sympatric.
Data collection: Between April 2006 and March 2007, we laid 10 belt transects traversing through the study site covering almost all vegetation types of the study area.The length of transects varied from 150 to 300 m covering a total length of 2050m.On each side of a belt transect, we included 10m width as vegetation sampling plots amounting to a total sampling area of 4.1ha.Inside each sampling plot, all plants (excluding climbers, lianas and herbs) with a girth more than 12cm were numbered with aluminum tags.However, we sorted the trees with a girth of >30cm for vegetation analysis.We identified the plant species with the help of field guide books (Gamble 1935;Pascal & Ramesh 1997).In most of the cases, we preserved sample plant parts including leaf, flower and fruit for confirmation of identification by plant taxonomists.We identified most of the plants up to the species level.
The vegetation analysis including density, dominance and frequency (Curtis & McIntosh 1950) and importance value index (Curtis 1959) of different tree species were estimated using the following methods: Basal area = πr 2 (where r is radius of the plant girth at breast height) (Basal area represents dominance of a plant species) Density = total number of plants of any species/ number of plots Frequency = (number of plots with the presence of a species/number of plots) x 100 Relative dominance = (dominance of a plant species/ total dominance of all plant species) x 100 Relative frequency = (frequency of a plant species/ total frequency of all plant species) x 100 Relative density = (density of a plant species/ total density of all plant species) x 100 Importance Value Index (IVI) = Relative dominance+Relative frequency+Relative density We recorded the data on feeding by primates through instantaneous scan sampling (Altmann 1974).On the basis of feeding records, we identified the use of high IVI plant species by the three diurnal primates including Liontailed Macaque, Bonnet Macaque and Hanuman Langur.

RESULTS
In this section, we present the data on tree species, their abundance and IVI, and their use by the primate species.
Table 1 presents the data on tree species, their density, dominance and percent frequency in the study area.We recorded a total of 81 tree species belonging to 33 families in the sampled area.All species were almost randomly distributed in all sample plots.
Table 2 presents the data on relative density, relative abundance, relative frequency and IVI (arranged in a descending order) of the tree species in the study area.Knema attenuata had the highest IVI followed by Aglaia roxburghii, Syzygium gardneri, Hopea ponga, Olea dioica, Dimocarpus longan and Holigarna grahamii.All other tree species had an IVI value smaller than 8.00.
Table 3 presents the data on the proportion of consumption (of total diet) of items from the top ten tree species by the primates.Knema attenuata and Holigarna grahamii were used by all primate species.Rest of the tree species were foraged by some primate species or the other.Only Olea dioica and Ficus nervosa were used by a single primate species.
Table 4 lists the common tree species used by different primate species' pairs.Almost all of the high IVI tree species were used by more than one primate species.There were also several tree species that were used exclusively by one primate species or the other (Table 5).

DISCUSSION
The study of stand structure helps in not only describing the vegetation type and the abundance of various tree species etc., but also in identification of keystone species in a forest.The Western Ghats are characterized by several ecozones.The present study     area marks the northern end of the distribution of low and medium elevation dipterocarp forests (Pascal 1998).This region is also the northern end of the distribution of the threatened Lion-tailed Macaques (Kumara & Singh 2004).
The results of the present study reveal that the rainforests to the north and south of Sharavathy and Aghnashini rivers respectively in the Western Ghats are characterized by a high diversity of vegetation including lianas, shrubs and trees.Many tree species were distributed throughout the study area, but these might not be considered as important trees species.Only a few tree species were important by dominance, density and frequency.High IVI value is considered only for those species which have a major impact on community and are defined as major vegetation type.Some tree species such as Garcinia gummigutta, Litsea sp., Diospyros sp., Caryota urens, Cassine glauca, Garcinia morella, Mimusops elengi etc were also distributed almost throughout the study site, but these were poor in density or dominance.Even important tree species such as Syzygium gardneri and Olea dioica were poor in their overall density compared to the other important tree species.However, they had a large ground cover with high basal area.
Of the 81 plant species recorded in the study area, 62 (76.54%) were used for feeding by one primate species or the other.The primarily folivorous langurs used the largest number of plant species followed by the primarily frugivorous macaques.All of the high IVI tree species were used by the primates indicating that the characteristic vegetation of the region is also a major food resource for the primates.
In the present study, the important tree species might be considered as the keystone species.Keystone species may not necessarily be the dominant species, though a dominant species has an effect on community because it is common (Paine 1966(Paine , 1969;;Stiling 2004).Generally, keystone species are those whose absence has an effect on overall foodchain of the community.However, producers are also considered as keystone prey in some cases as those are mostly used by maximum number of consumers; palm-nuts, figs and nectar could be keystone prey because they are critical to tropical forest fruit-eating guilds including primates, rodents and many birds (Terborgh 1983).In the present study area, the important tree species were also important fodder plants for different primate species.Out of the major resource trees of primates, more than 50 percent were the important tree species in the present study area, and some important trees were also used as minor diet by the primates.In the rainforests of the Western Ghats south of the Palghat Gap, Cullenia exarillata is the keystone species for primates as it constitutes a major food resource in the Anaimalai Hills (Sushma & Singh 2004) and in the forests of the Silent Valley (Joseph & Ramachandran 2001).Knema attenuata and Syzygium gardneri could be considered as the keystone tree species in the present study area according to their presence as well as their use as major resource items.All three primate species used different plant part of these two trees as major food items and some resource items were also shared by different species-pairs.Retention of such tree species, therefore, is a key element in the forest management of this primate rich region which, at present, does not form a part of the 'protected area' network for wildlife conservation.

Figure 1 .
Figure 1.Map of the study area.Aghnashini and Sharavathy are the major rivers and other place names indicate forest ranges

Table 4 . Common fodder plants used by different species-pairs
* -High IVI species; ^ -Vegetation other than trees