Predation on palm nuts ( Syagrus romanzoffiana) by squirrels ( Sciurus ingrami) in south-east Brazil

Abstract

Although Terborgh (1986) suggested that palm nuts are a 'keystone plant resource' for frugivore communities in tropical forests, few studies exist on seed ecology of palm fruit crop (Bradford & Smith 1977, Pifiero etal. 1984, Vandermeer et ali. 1979). Janzen (1983) suggested that seed predators have a major impact on the structure of plant communities in tropical forests. Squirrels are regarded as important seed dispersers and seed predators (Glanz et ail. 1982, Janzen 1972) depending on the habitat and the fruit availability. These rodents frequently consume hard nuts and their distribution may be related to the distribution of food sources such as palms (Glanz 1982). This paper investigates the utilization of the fruits of the 'geriva', ySyagrus romnanZoffiana (Cham.) Glassmnan by squirrels in a tropical upland semideciduous forest in south-east Brazil. Field observations were made from August 1988 to May 1990 in the 250 ha Santa Genebra Reserve in Campinas (22? 49' S, 470 07' W), Sao Paulo State, Brazil. The climate of the region is characterized by one dry (April to September) and one rainy (October to March) season; annual rainfall during the study period was 1366 mm. The feeding assemblage that utilizes Sjyagruis fruits in Santa Genebra is composed of squirrels Seiinrus ingrami Thomas, a small species about 34 cm in length (H. Bergallo, unpub.), capuchin monkeys Cebus apella Linne and brown howler monkeys Aloucattafiusca Ihering. &yagrus rotinanzofJiana is a common palmi in semideciduous forests in south-east Brazil (H. F. Leitao-Filho, pers. comm.). The fruit is an ovoid drupe 2.5 cm in diameter, with a soft exocarp and woody endocarp. Individuals of this species produce fruit all the year round, each plant producing two bunches at a timie.