Bird Activity and Seed Dispersal of a Montane Forest Tree (Dunalia arborescens) in Jamaica

The dispersal system of the neotropical tree Dunalia arborescens (Solanaceae) was examined in a montane mist forest in Jamaica. A total of 16 species of birds representing 14 genera and eight families were recorded feeding on D. arborescens fruits. The most common species feeding were the stripe-headed tanager (Spindalis zena), greater antillean bullfinch (Loxigilla violacea), and the rufous-throated solitaire (Myadestes genibarbis), accounting for 66 percent of the total visits. Intraspecific encounters dominated actions, and interspecific interactions were minimal, the latter was probably due to a superabundance of food and, to a lesser degree, to differences in foraging and feeding behavior. In general, birds arrived and left the feeding tree as individuals or as groups of several individuals of one species. No mixed species flocks were observed arriving or leaving the fruiting tree. Observations on color-marked individuals and on all species feeding on D. arborescens showed that the amount of fruit dependency varied from almost 100 percent in the stripe-headed tanager and the greater antillean bullfinch to less than 30 percent in the greater antillean elaenia (Elaenia fallax) and the jamaican oriole (Icterus leucopteryx). The birds involved exploited a variety of fruits throughout the year, but at any one time ate fruit of a few species. What determined the diet at any one time depended on the fruiting phenology, common-ess of tree, large crop size, and individual preferences. The fruiting period of the different feeding trees in the study area ranged from complete overlap to no overlap; as the number of fruits of one species decreased, the number of another species increased. Staggered fruiting may enable these trees to take advantage of the same bird populations at different times and thus relieve competition for seed dispersers. The high reproductive potential of D. arborescens expressed in the abundance of fruits with many seeds, and the presence of a number of different dispersers of widely different sizes, degree of dependency on fruits and foraging behavior suggest that this tree is opportunistic in nature. It is a species found in forest edges, clearings, and other habitats that are spatially unpredictable. Premium is placed in the dispersal of seeds as widely as possible by the greatest variety of dispersers, because the tree's survival depends upon the rapidity with which it can colonize bare ground and gaps in the primary forest. DESPITE THE IMPORTANCE OF BIRDS as dispersal agents of seeds of many tropical forest trees (Diamond and Terborgh 1967, Janzen 1970, Leck 1971a, Smythe 1971, Pijl 1972, Howe 1977, Regal 1977, and others), little is known about the interaction of birds and trees in insular regions, specificallv in the West Indies. To my knowledge the only published studies on avian seed dispersal in the Caribbean are those in Puerto Rico (Leck 1972a and Cruz 1980) and in Jamaica (Cruz 1974). In those studies, feeding assemblages of birds were studied on the tropical trees Cecropia peltata, Ficus laevwgata, and F. trigonata (Moraceae). Insular studies are of particular importance because the relative simplicity of their biotas allows interactions to be deduced which would be obscured in a more complex mainland context. In addition, because of the reduced number of species on islands, ecological and evolutionary strategies (e.g., in the dispersal of seeds by birds) involved may be different from those in mainland regions. In this paper, I examine the dispersal system of the neotropical tree Dunalia arborescenzs, a member of the nightshade family, Solanaceae. This study will emphasize the determination of ecological and be34 REPRODUCTIVE BOTANY 34-44 1981 havior characteristics of birds that favor seed dispersal and the adaptations present in D. arborescens for the dispersal of its seeds. Factors taken into account include visitation, frequency of exploitation, feeding methods, social and aggressive behavior, fruit phenology and morphology. Dunalia arborescens (L.) Sleumer is a locally common shrub (3 m) or tree (up to 12 m) of submontane and montane secondary thickets and clearings in the West Indies and continental neotropical regio,ns, Mexico to Peru (Adams 1972, Little et al. 1974). It has elliptic leaves, up to 30 cm long ood 14 cm broad, mostly acute or acuminate at both ends, glabrescent on the lamina. The fruits are small (8-11 mm), globose, and orange. Each fruit is 2-celled andi contains many light-yellow seeds about 1.5 mm long. The fruits are borne in clusters of 30 or more, on pedicels 1.35 cm long (fig. 1). A ripening fruit takes about one week to change from green to orange, becoming softer, larger, and juicier. On any particular tree ripe, ripening, and green fruits appear randomly within or between clusters. Ripe fruits first appear in March and are present until July (Adams 1972, Cruz, pers. obs.). This content downloaded from 157.55.39.55 on Tue, 23 Aug 2016 05:04:12 UTC All use subject to http://about.jstor.org/terms FIGURE 1. Branch of Dunalia arborescens showing cluster of fruits varying in degree of ripeness.