B. Divya Cauvery Mudappa
Department of Zoology, Bharathiar University, Coimbatore, Tamil Nadu, INDIA.
The small carnivores of the mammalian Families of Viverridae, Herpestidae, and Mustelidae play very important roles in tropical rainforest ecosystems, as predators, prey, and seed dispersers. These roles have been poorly studied, even as small carnivore communities are undergoing changes due to severe loss and fragmentation of rainforests. This thesis explores the ecology of a small carnivore, the brown palm civet (Paradoxurus jerdoni Blanford 1885), endemic to the rainforests of the Western Ghats hill ranges of India, and also examines changes in the structure of the terrestrial and arboreal small carnivore community as a whole, due to rainforest fragmentation.
The ecology of the brown palm civet, an endemic and nocturnal viverrid, was examined with reference to its role as a seed disperser, and the factors governing its diet composition, and ranging and activity behaviour, in the relatively undisturbed, large tract of rainforest in the Kalakad-Mundanthurai Tiger Reserve (KMTR), between May 1996 and December 1999. The small carnivore community here was compared with that in the rainforest fragments of the Anamalai Hills that were surveyed between January and May 2000. Habitat correlates of the occurrence of small carnivores were also examined.
The brown palm civet was highly frugivorous. Of 1013 scats examined, 91.12% contained seed, fruit or flower remains of native species. Only 14.2% of the scats had invertebrate or vertebrate remains. Fruits of 53 native and 4 introduced species, and flowers of 2 species were eaten. No species contributed >10% to the overall diet, although 10 species accounted for 25-75% of the diet in certain months. There was considerable intra- and inter-annual variation in the diet. Most fruits eaten were of trees and lianas. Compared with non-consumed species, a greater proportion of consumed fruits were drupes or berries, and had moderately thick and watery pulp. Fourteen species of fruits were identified as important for the year-round sustenance of the brown palm civet.
Seeds from scats were viable in 14 of the 17 species assessed, but a greater proportion of defecated seeds germinated in only 2 out of 6 species tested. In 3 species, germination rate was significantly different (2 lower and 1 higher) between defecated and control seeds. The brown palm civet plays a major functional role, as a seed disperser in the rainforests of Western Ghats. They do not damage seeds of the fruits they consume, and assist in dispersing them away from the parent plants, where the seeds have a higher chance of predation. The brown palm civet is also a reliable disperser as it consumes a variety of species, even in times of low overall availability of fruits in the habitat.
Flowering and fruiting phenology of 450 trees of 22 food species was monitored between January 1998 and December 1999 in Sengaltheri, KMTR. Densities of food tree species were estimated from 184 point-centred quarter plots, and their distribution from 327 circular plots of 5 m radius. Pronounced inter- and intra-annual variations were observed in the number of species and individuals with flowers and ripe fruits, as well as in flower and fruit abundance. Excluding Ficus spp., the others were biannual, annual, biennial, or supra-annual in their fruiting periodicity. However, in any given month, a minimum of 3 of these 22 species was in fruit. The phenological pattern of abundance of ripe fruits was strongly influenced by the “mass fruiting” behaviour of the supra-annual species. The food species of the brown palm civet were abundant (53% of the total tree density) in the study area, and most of them tended to be clumped in distribution. A greater number of species were consumed in almost equal proportions, during times of low ripe fruit availability. But, at times of greater food availability, the civets’ choice of some fruits was evident, as one species tended to dominate in the diet.
Factors influencing home range size, activity, and habitat choice of the brown palm civet were examined with data from a radio-telemetry study between March 1998 and December 1999 in Sengaltheri. Five males and two females fitted with activity transmitters, were tracked for 12 to 238 days. Their home ranges varied between 6 and 57 ha, substantially smaller than the home ranges of similar species elsewhere. Body size was positively related to home range size, and individuals in areas with higher tree density, tree species, and basal area, had smaller home ranges than expected.
The civets showed a distinct nocturnal activity regime, being active 79% of the time between dusk and dawn (1800 h - 0600 h), with the exception of two injured animals. The animals spent significantly less time moving and greater time foraging (including feeding) during months of greater fruit availability. The brown palm civets predominantly used Malabar giant squirrel (Ratufa indica) nests for day-bedding. The day-beds were on trees that were larger in girth and height, and also had greater canopy contiguity and number of trees > 30cm girth around it, as compared to random trees in the habitat. These variables correctly classified about 75% of the random and day-bed trees analysed.
A combination of methods, such as track plots, camera-traps, spot-lighting (night walks and drives), and direct sightings were used assess the relative abundance of small carnivores in KMTR and Anamalai Hills. Two endemic species—brown palm civet and Nilgiri marten (Martes gwatkinsi)—were the most frequently sighted nocturnal and diurnal carnivores, respectively, in KMTR. There was a significant decrease in the occurrence of small carnivores in the track plots and camera-traps in the rainforest fragments. The success rate was greater in KMTR in the case of brown palm civet, but not for the small Indian civet and the mongooses. The number of photo-captures and direct sightings of the mongooses (brown and stripe-necked mongoose) were higher in the fragments and the matrix around them than in the undisturbed rainforests. The brown palm civet success rate was positively correlated to altitude. The success rates were not significantly correlated to any of the habitat or site parameters. The brown palm civets occurred even in rainforest fragments that were highly disturbed. Their persistence may be due to the occurrence of food tree species in the fragments, and the presence and protection of relatively large (200 ha) rainforest fragments in an otherwise highly disturbed landscape. The more widespread and omnivorous species exhibited no significant change in relative abundances between KMTR and Anamalais, although they were more common in the latter (fragmented landscape).
Tropical forests and their species diversity are being threatened by extensive deforestation and forest fragmentation. The endemics—brown palm civet and Nilgiri marten are among the small carnivores that are likely to be severely affected among the small carnivores of the Western Ghats, if the present rate of disturbance continues. The brown palm civet is an effective disperser of many rainforest plant species, and is a key player in the dynamics of seed dispersal, germination, and regeneration in rainforests of the Western Ghats. They can also play an important role in maintaining degraded rainforest fragments and to restore them. Although its area requirements in a relatively undisturbed rainforest is one of the smallest known for a viverrid, it will require larger areas in rainforest fragments, which are disturbed and usually have low food tree densities and other resources. The rainforest fragments are also likely to have greater variations in fruit availability due to openness of the habitat, and local climatic changes, necessitating availability of diverse species in the habitat. It is also likely to face competition from other sympatric, but widespread and common species of small carnivores. Therefore, even in a fragmented landscape, conservation efforts should include protection and maintenance of relatively undisturbed and large tracts of forests with high diversity of native trees and lianas. At the same time, efforts should be made to protect even small forest fragments that hold wild populations of many endemics, including the brown palm civet. Restoration efforts can also be made to improve the quality of highly degraded fragments.