Carnivore Fruit-Use and Seed Dispersal of Two Selected Plant Species of the Edwards Plateau, Texas

Abstract

Ashe juniper (Juniperus ashei) and Texas persimmon (Diospyros texana) fruit use and seed dispersal potential by four carnivores were studied on the Edwards Plateau region of Texas. Feces were examined to determine presence of seeds and frequency of occurrence by month from August 1989 to February 1990. Use of fruit species by month followed the pattern of fruit ripening of the two plant species. Texas persimmon fruit was consumed primarily between September and January while Ashe juniper fruit was consumed from October through February. Because large numbers of seeds are present in feces and few are destroyed in mastication and digestion all carnivores studied are considered legitimate dispersal agents of Ashe juniper and Texas persimmon. Dispersal efficiency of carnivores, however, is low due to the location of dispersed seeds (feces) and the clumped seed dispersal patterns. The role of temperate carnivorous mammals as seed dispersal agents of fruit-producing plants has been neglected in the literature (Herrera, 1989). Among tropical mammals, monkeys (Howe, 1980; Estrada and Coates-Estrada, 1984) and bats (Morrison, 1978; Fleming, 1981, 1986; Heithaus, 1982; Gribel, 1988) have been studied intensively in recent years although they have long been recognized as important seed dispersal agents (Ridley, 1930; Krefting and Roe, 1949; van der Pijl, 1982). Recently, the importance of herbivorous mammals in seed dispersal has been documented (Janzen, 1981, 1982, 1984) and to a lesser extent the importance of carnivorous mammals has been noted (Stiles, 1980; Estrada et al., 1984). We know of only one study dealing thoroughly with the extent and significance of carnivores (Herrera, 1989) in seed dispersal of temperate fruit-producing plants. Furthermore, little information is available regarding fruit use by North American carnivorous mammals and the associated potential for seed dispersal. This neglect is curious, because it is well known that many carnivores commonly consume fruits (Davis, 1978; Chapman and Feldhamer, 1982). The fact that early work on seed dispersal placed emphasis on coevolution (Smith, 1970; Snow, 1971; McKey, 1975; Howe and Estabrook, 1977) of fruit and dispersers could explain this neglect. Most temperate carnivores have large home ranges and are nocturnal in habits, making any study of them difficult. Because of this difficulty, most information gathered on carnivores and their possible importance as seed dispersers has been obtained through indirect means: analysis of stomach contents and collection of fecal material and the subsequent analysis of their seed contents (Herrera, 1989). However, little information has been reported regarding seed dispersal potential. Herein we report information gathered on selected carnivorous mammals of the Edwards Plateau of Texas, with respect to fruit use and potential seed dispersal of Ashe juniper (Juniperus ashei) and Texas persimmon (Diospyros texana). Data were collected on the diet of four carnivorous mammals known to include fruits in their diets. Particular importance was given to the season and degree of utilization of these fruits by the carnivores and their potential role in the dispersal of seeds is discussed. MATERIALS AND METHODS-The study was conducted between August 1989 and February 1990 at the Texas A&M University Agricultural Experiment Station at Sonora, Texas. The 1430-ha Station is located 45 km SE of Sonora at approximately 1000W and 300N. Vegetation is generally grassland with scattered individuals or mottes (clumps) of live oak (QuerHWESTERN RALIST 38(2):141-145 E The Southwestern Naturalist TABLE 1--Percent frequency of occurrence (%) and numbers (X ? SD, range) of Ashe juniper and Texas persimmon seeds in carnivore feces collected on the Edwards Plateau, Texas, during the fall and winter months of 1989 and 1990. Texas persimmon Ashe juniper