By: Kristin Abt
The Lion-tailed Macaque (Macaca silenus) is an endangered cercopithecine primate native to the Western Ghats region of India, described as one of the primary hotspots of biodiversity in the world (Kumara & Singh, 2004). IUCN (2010) estimates a mere 2,500 mature individuals with a total population size of 4,000 individuals. Furthermore, these monkeys (LTMs) exist in an estimated 47 subpopulations in 7 locations. Their serious status merits continuing intense and collaborative research on their demographics, current pressures, and the effects of habitat fragmentation, which appears to be the primary concern for their long-term survival in the wild.
Ecology and Distribution
These Old World monkeys have cheek pouches with simple stomachs, long, non-prehensile tails, an opposable hallux and pollex, hardened ischial callosities, and close, downward facing nostrils. They are diurnal with complex, matrilineal social systems normally with one adult male and one subadult male to multiple females and their offspring. Males disperse and females display estrus swellings to advertise their reproductive status. They have an average group size of 18 with a range of 7 to 40 individuals (Umapathy & Kumar, 2000b). Compared to other macaque species, Umapathy and Kumar point out that they have a slower life history with females reproducing first at 6.6 years and having a birth rate of 0.31 infants/female/year thereafter. This overall low prolificacy with delayed sexual maturity, long interbirth interval, and low population turnover presents an additional challenge when groups must respond to external survival pressures.
The LTM differs from other macaque species additionally through its primarily arboreal nature. Menon and Poirier (1996) emphasize this characteristic through the documentation of 3 falls and one subsequent death from tree gaps. In places with incontiguous canopy cover, individuals exhibited a strong preference to exert considerable effort to cross large holes in the canopy without descending to the ground. Ramachandran and Joseph (2000) discuss the conservation and sustainability implications of this in that LTMs failed to range into adjacent areas disrupted by fire or eucalypt and teak plantations in order to exhaust nearby resources in neighboring forest fragments.
Individuals are found only in the Western Ghats region in the three states of Kerala, Karnataka, and Tamil Nadu and have been studied extensively in such national and private evergreen forests as Silent Valley in the Palghat district (Ramachandran & Joseph, 2000), the Indira Gandhi Wildlife Sanctuary in Anamalai Hills (Umapathy & Kumar, 2000a & b), Brahmagiri-Makut and Sirsi-Honnovara (Kumara and Singh 2004), the Puthuthotam Cardamom Forest (Menon & Poirier, 1996), and the Kudremukh Forest Complex (Kumara & Singh, 2008). Within these locations, it has been found that the LTMs prefer habitat primarily between 300m asl – 900m asl (Kumara & Singh, 2008). It is estimated that almost 40% of the remaining population exist as small groups found in isolated, highly fragmented forests in these areas (Umapathy & Kumar, 2000a). As one goes from South to North within their range, group size has been shown to increase (Kumara & Singh, 2004).
Within their habitat, LTMs serve as “one of the most important habitat specialist primates in India” (Ramachandran & Joseph, 2000). Sushma and Singh (2006) found that compared to other arboreal mammals, such as bonnet macaques (Macaca radiata), Nilgiri langurs (Semnopithecus johnii), and the Indian giant squirrel (Ratufa indica), LTMs have the narrowest niche breadth with some overlap with bonnet macaques, which indicates a degree of competition where these animals must coexist. Ramachandran and Joseph (2000) point out that they seldom range outside of their evergreen forest even into the deciduous areas. They also reported that LTMs feed primarily (91%) on plant matter with the remainder consisting of invertebrates, which is a higher amount than other macaque species (Sushma & Singh, 2006). Ramachandran & Joseph (2000) found that they formed significant associations with 6 major tree species, especially Cullenia. These are needed in the proper abundance in order to sustain the primates; however, some flexibility is present. Menon and Poirier (1996) note that, in times of food scarcity, individuals supplement their diet with Artocarpus and Coffea trees in nearby forested plantations. Because they are highly frugivorous and consume large amounts of figs (Sushma & Singh, 2006), they must range significant distances in order to find sufficient food for the group. Fruit, as a seasonal and patchy resource, offers a lot of carbohydrates, but not a good amount of protein. As a result, invertebrates comprise a relatively large amount of their diet in order to provide the necessary nutrition for successful reproduction (Umapathy & Kumar, 2000a). Juveniles spend a significantly larger amount of time feeding on these, suggesting their importance for proper growth and development, as well.
Conservation Threats due to Habitat Fragmentation
When primate groups are found in highly fragmented habitat, this presents serious survival pressures for themselves and for those individuals in neighboring forests without the opportunity for gene flow. McGarigal and Cushman (2002) define habitat fragmentation as a “landscape level process in which a specific habitat is progressively subdivided into smaller and more isolated fragments.” They further discuss how it encompasses a change in landscape composition, structure, and function. Because habitat fragmentation, along with habitat loss, is considered to be one of the main influences causing the incredible mass extinction of species that is currently occurring, studying the effects of this in order to produce urgent and important management strategies is paramount.
Thus far, a number of studies of the LTM have discovered relevant consequences to the habitat fragmentation continually occurring within their range. In reference to the demographics of social groups, the effects of habitat fragmentation have been to significantly change the composition naturally found in contiguous and undisturbed sections of forest. Specifically, Umapathy and Kumar (2000b) found near significance with smaller fragments containing larger group sizes compared to larger fragments. Also, it appears that there is more likely to be two adult males in a social group of a small fragment than the typical one male: multiple females found in larger fragment sizes. Significantly, there is a positive correlation between fragment size and the number of immatures and birth rate. The authors cite possible factors for this as increased predation pressures and resource shortages. Kumara and Singh (2004) classified health of a population by a high overall presence of groups with the modal group size, favorable sex ratio, and a large percentage of immature individuals; therefore, the findings from the previous study provide further support to their criteria as valid to use when investigating the demographics of LTMs in fragmented areas.
Studies have also investigated how vegetation status in relation to level of fragmentation affects these primates. Umapathy and Kumar (2000a) found that individuals spent significantly less time feeding on invertebrates, a key component to their diet, in smaller fragments. Additionally, the least disturbed fragments contained the highest plant abundance. In areas with colonized species, such as mangos and guava, the macaques added these to their diet, which might slightly compensate for the loss in space and flora diversity; however, it could also contribute to human-wildlife conflict. Furthermore, these researchers (2000b) also demonstrated a positive correlation between the quality of vegetation and the amount of fragmentation.
Along with demographic and dietary changes, significant changes occur in disturbed populations with respect to the groups’ overall behaviors and activity patterns. Menon and Poirier (1996) studied individuals in a private forest that experienced selective logging and clearing for planting on the floor and found that the primates used the ground often for ranging and foraging out of necessity, but still much preferred the trees – even when travelling in such a manner presented serious and mortal danger due to the lack of sufficient canopy continuity. They were also forced to cross roads and raid fruit in neighboring plantations, which resulted in human-wildlife conflict and deterrence measures implemented. Furthermore, the individuals needed to increase their time ranging, which seriously impacted their ability to feed and engage in necessary social behaviors. Especially relevant to small, isolated populations is the inability to disperse naturally, which Debinski and Holt (2000) discuss and, consequently, suggest corridors for landscape connectivity, especially for highly mobile animals. Without proper gene flow and the opportunities for appropriate social groups to form, the long-term survival of this species is severely threatened, which is already evidenced by the results of lower numbers of juveniles in these fragmented groups.
In addition to the restriction of available habitat and isolation of existing groups, human-wildlife conflict has placed significant pressure on their survival. Along with plantations cultivated for teak and eucalypt and areas that are clear felled for tea and coffee, humans also use the forest areas for wood gathering, logging, and hunting of the LTMs and other fauna (Kumara & Singh, 2000b; Menon & Poirier, 1996). Fragments also increase the likelihood of the macaques coming into human contact and the likelihood that humans will disturb the forest.
As with so many conservation stories, this one can greatly benefit from increased attention, education, and priority at numerous levels. Over recent years, the LTM has featured less prominently in North American zoo collections despite its endangered status, declining populations, charismatic appearance, and active nature (Association of Zoos and Aquariums, 1998). Additionally, few conservation and education efforts are currently in place to support its population (AZA, 1998). While research into its populations and its behavioral ecology are important to further understand the species, additional efforts to increase gene flow between populations, protect its forest habitat, and address conflicts with agriculture are needed for this macaque species to persist.
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