Nutritional and Physical Attributes of Seeds of Some Common Sagebrush-Steppe Plants: Some Implications for Ecological Theory and Management

Abstract

A study was conducted to identify seed attributes which might influence granivore preferences. Physical and chemical characteristics were estimated for seeds of 7 common sagebrush-steppe species (Artemisia tridentata, Bromus tectorum, Oryzopsis hymenoides, Pascopyrum smithii, Purshia tridentata, Stipa comata and Stipa viriduia) and 1 sacrifice food species (Panicum miliaceum). Seed-weights and caloric contents were determined, as well as % composition contributed by 5 organic, 3 inorganic and 5 synthetically defined fractions (including crude protein, solvent extract, structural and soluble carbohydrates and lignin). Results indicate that 70 soluble carbohydrate may be a good predictor of granivore seed preference. The generality of this or any other predictor is unknown, since sufIiciently detailed seed attribute data are unavailable for most species. For management scenarios involving seeds subject to predation, such data would help effectively translate ecological understanding of granivory into more efficient management practices. In any land management effort involving direct seeding or depending upon the natural input of seeds, the manager must consider those biotic and abiotic factors which may ultimately affect the successful establishment of the desired vegetation. While abiotic influences such as seedbed characteristics, germination requirements, and soil nutrient levels have been routinelyacknowledged and manipulated, biotic interactions affecting the seeds have often been ignored. One biotic factor which may limit plant establishment is granivory, the consumption of seeds by animals. Since the publication of Janzen's (1971) pivotal review of seed predation by animals, awareness of the potential importance of granivory in the structure and functioning of many ecosystems has expanded and matured. Yet despite the considerable research already conducted, relatively little attention has been devoted to the integration of ecological studies of granivory with vegetation management. Rangelands may be particularly appropriate systems for attempting such an integration, since they occur in relatively xeric habitats, where seeds may be an important food resource ".. .coupling primary production to the infrequent, unpredictable precipitation that limits the productivity of most arid ecosystems" (Brown et al. 1979). Insects (especially ants), birds, and small mammals consume large quantities of seeds on native rangelands (Nelson et al. 1970, Pulliam and Brand 1975, Goebel and Berry 1976, Everett et al. 1978, Whitford 1978) and manipulative field studies have demonstrated that granivores, via their seed selection, can affect the species composition of their plant community (Inouye et al. 1980). It follows, then, that understanding patterns of granivory might con-Authors are graduate student and Professor of

A mast‐seeding desert shrub regulates population dynamics and behavior of its heteromyid dispersers

“…A simple explanation for the strong preference for Indian ricegrass exhibited by kangaroo rats in this and numerous other studies (Kelrick and MacMahon ; Longland et al. ; Veech ) is that its seeds contain >50% of soluble carbohydrates.…”

Seed harvesting is influenced by associational effects in mixed seed neighbourhoods, not just by seed density

“…). Soluble carbohydrates are thought to predict the relative preference of seeds in sagebrush communities (see Kelrick & MacMahon ; Kelrick et al . ) because they are a water‐efficient energy source and their relative percentage is a good measure of available digestible energy.…”

Granivory rates by rodents, insects, and birds at different microsites in the Patagonian steppe

“…Other studies have shown that granivore preferences were correlated with assimilation efficiency (Soholt 1973, Whitford 1978, Withers 1982, Price 1983). In fact, at the Intermountain Great Basin (Kelrick and MacMahon 1985, Kelrick et al 1986) 7 different native seeds were offered to rodents, ants, and birds, and granivore preferences was correlated to the concentration of soluble carbohydrates and water in the seeds. Our results on cellulose, lignin, and ashes showed that Mulinum values were similar to the least preferred seed at Kelrick et al's study ( Artemisia tridentata ) and Phalaris to the most preferred seed ( Purshia tridentata ).…”

“…Rates of seed removal and the relative importance of each granivore group vary among arid regions (Mares and Rosenzweig 1978, Morton 1985, Kerley 1991, Kelt et al 1996, Lopez de Casenave et al 1998) and several reasons may account for these differences. In arid environments, seeds vary in size, shape, presence of projections, thickness of the coat, chemical composition, amount and timing of dissemination (Kelrick and MacMahon 1985, Brown and Ojeda 1987), and granivores vary in their ability to handle different seeds (Pulliam and Brand 1975, Price and Brown 1983). Environmental, historical, and biogeographical factors may also determine the differences in granivory found across arid and semi‐arid regions of the world (Mares and Rosenzweig 1978, Mares 1993, Kelt et al 1996, Folgarait et al 1998).…”