Fruit Characteristics and Muntiacus muntijak vaginalis (Muntjac) Visits to Individual Plants of Choerospondias axillaris1

THE INFLUENCE OF FRUIT MORPHOLOGY AND NUTRIENT CONTENT on frugivore food selection has been discussed by several authors (McKey 1975, Snow 1981, Howe & Smallwood 1982, Janson 1983, Debussche & Isenmann 1989, Willson et al. 1989). In many studies, frugivore selection was significantly correlated with fruit characteristics such as size (Wheelwright 1985, Alcantara et al. 2000), dry pulp mass (Johnson et al. 1985), pulp to fruit ratio (Howe & Vande Kerckhove 1980, Piper 1986), fruit color (Willson & Melampy 1983, Wheelwright & Janson 1985, Willson et al. 1989), and insect infestation (Herrera 1984). Other studies have contradicted these observations (Chabot & Hicks 1982; Manasse & Howe 1983; Herrera 1985, 1987, 1995; Levey 1988). Many investigations were based on indirect statistical inference and have focused on interspecific comparisons. Comparatively few studies are available on the relationship of dispersers’ selection to morphological and nutritional fruit features of individuals from a single species. Choerospondias axillaris (Roxb.) Burtt et Hill (Anacardiaceae) is a typical pioneer tree species with a relatively large seed (17.5 3 14.3 mm). The plant depends on frugivores for seed dispersal and there are very few seedlings under the canopy of adult trees. We observed that the muntjac (Muntiacus muntijak vaginalis [Boddaert]) is the most important disperser of C. axillaris. The whole fruit is eaten; then the stone is regurgitated at a different location after several hours of rumination. The possibility of selective visits to different individuals by a frugivorous mammal may influence plant gene frequency and its evolution. The species may have evolved certain traits to enhance the attraction of frugivores to secure the dispersal of their seeds away from mother trees. This paper addresses the following questions regarding the interactions between muntjacs and morphological and nutritional aspects of fruits from a single species. First, since the muntjac is the major disperser of C. axillaris seeds, what kind of rewards do muntjacs receive from the fruits? Second, do muntjacs selectively visit individual trees and what are the factors influencing their selection? Our study was conducted within Mengla National Natural Reserve of Xishuangbanna, Yunnan province, China (218249–218539N, 1018229–1018509E), in an area of seasonal humid tropical climate. Average rainfall is ca 1500 mm/yr with the rainy season starting in early May and ending in early October. The greatest rainfall is in August. Annual average temperature is ca 21.08C. The total area is 929 km2 and the elevation ranges from 630 to 1500 m. We randomly located and labeled 30 mature trees (DBH [diameter at breast height] .20cm) before fruiting time at the edge of the Mengla National Natural Reserve at an elevation of 1050 to 1150 m. The minimum distance between trees was ca 40 m, while maximum distance was ca 2000 m. Observation started on 1 June 1999 and ended on 14 September 1999. This covered the entire fruit ripening period of the 19 individuals that fruited. Every four days, two of the authors who were experienced in the identification of animals tracks checked the 19 trees and recorded the presence or absence of fresh muntjac tracks under each tree. Freshly fallen fruit were collected on 19 July 1999 from the ground under these 19 individuals for analysis of nutrient content (18 individuals for mineral elements and 17 for main nutrient analyses) and morphological description (18 individuals). Ten fruits were measured for fruit weight, fruit size, and other morphological data. Methods used to analyze moisture content, total sugar, titratable acid, vitamin C, soluble tannin, crude fiber, starch, and crude fat were the same as in Chen et al. (1999). Fresh pulp samples were collected from fruits of individual trees and dried at less than 408C and then brought to Kunming Biological Geochemistry Laboratory of the Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences, for analysis. The methodologies used for mineral element content analysis are