Abstract. Ecosystem management is management driven by explicit goals, executed by policies, protocols, and practices, and made adaptable by monitoring and research based on our best understanding of the ecological interactions and processes necessary to sustain ecosystem composition, structure, and function.In recent years, sustainability has become an explicitly stated, even legislatively mandated, goal of natural resource management agencies. In practice, however, management approaches have often focused on maximizing short-term yield and economic gain rather than long-term sustainability. Several obstacles contribute to this disparity, including: ( 1) inadequate information on the biological diversity of environments; (2) widespread ignorance of the function and dynamics of ecosystems; (3) the openness and interconnectedness of ecosystems on scales that transcend management boundaries; (4) a prevailing public perception that the immediate economic and social value of supposedly renewable resources outweighs the risk of future ecosystem damage or the benefits of alternative management approaches. The goal of ecosystem management is to overcome these obstacles.Ecosystem management includes the following elements: (1) Sustainability. Ecosystem management does not focus primarily on "deliverables" but rather regards intergenerational sustainability as a precondition. (2) Vol. 6, No.3 goals that specify future processes and outcomes necessary for sustainability. (3) Sound ecological models and understanding. Ecosystem management relies on research performed at all levels of ecological organization. (4) Complexity and connectedness. Ecosystem management recognizes that biological diversity and structural complexity strengthen ecosystems against disturbance and supply the genetic resources necessary to adapt to long-term change.(5) The dynamic character of ecosystems. Recognizing that change and evolution are inherent in ecosystem sustainability, ecosystem management avoids attempts to "freeze" ecosystems in a particular state or configuration. (6) Context and scale. Ecosystem processes operate over a wide range of spatial and temporal scales, and their behavior at any given location is greatly affected by surrounding systems. Thus, there is no single appropriate scale or time frame for management. (7) Humans as ecosystem components. Ecosystem management values the active role of humans in achieving sustainable management goals. (8) Adaptability and accountability. Ecosystem management acknowledges that current knowledge and paradigms of ecosystem function are provisional, incomplete, and subject to change. Management approaches must be viewed as hypotheses to be tested by research and monitoring programs.The following are fundamental scientific precepts for ecosystem management.(1) Spatial and temporal scale are critical. Ecosystem function includes inputs, outputs, cycling of materials and energy, and the interactions of organisms. Boundaries defined for the study or management of one process are often inapp...

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▪ Abstract  We summarize the influences of harvester ants of the genus Pogonomyrmex on communities and ecosystems. Because of nest densities, the longevity of nests, and the amount of seed harvested and soil handled, harvester ants have significant direct and indirect effects on community structure and ecosystem functioning. Harvester ants change plant species composition and diversity near their nests. These changes result from differential seed predation by the ants, their actions as seed dispersers and competitors with other granivores, and the favorable soil conditions they create through their digging. Their nest building creates islands of increased nutrient density. In some areas, the effects of their activities may be so pervasive that plant community structure is strongly influenced. Ant removal studies, which would reveal their total impact, have generally not been done. Granivore removals have been conducted in North America where ants are of lesser importance than small mammals, in contrast to other areas (except Israel) where ants are dominant granivores. We review the influence of harvester ants on their competitors, predators, and nest associates, and catalog the factors that influence their foraging patterns and consequently their local distribution. The harvesting habit in ants since it was first scientifically confirmed by Moggridge has excited an exceptional degree of interest and surprise. But in truth, when one considers all the conditions, the wonder is that it is not more widely distributed.      Henry Christopher McCook ( 138 , p. 116)

Granivore-seed interactions involve a feedback between granivore seed selectivity and seed availability. We examined this feedback to determine how seed preferences by the western harvester ant, Pogonomyrmex occidentalis, related to seed availability and, in turn, affected the soil seed pool. Preferences were estimated from natural diets as well as from experiments that controlled seed size, relative availability, and distance from ant nests.Seed availability to ants varied with season and over 2 yr. Colony activity and seed intake rates were correlated with seed availability. Seed preference by ants was correlated with the seasonal availability of preferred species, but not with unpreferred seeds. From the soil seed pool, ants preferentially harvested small, sound seeds. They removed 9-26% of the potentially viable seed pool each year, and as much as 100% of available preferred species. Seed densities were lower 2-7 m from nests, where foraging activity was concentrated, than 7-12 m from nests. In controlled preference experiments, P. occidentalis was unselective near nests, but preferred large seeds with higher assimilable energy content in trials 1 O m from nests. A relatively low foraging activity > 7 m, however, suggests that this distance-dependent preference is rarely manifested in natural conditions and does not measurably affect soil seed dynamics.Our results point to the importance of studying diet choice in a natural context; preferences measured under experimental conditions may not correspond to natural diets. Such discrepancies in food preference measurements will affect predictions about how consumers influence the population dynamics of resource organisms.

Vertebrate carrion decomposition and nutrient cycling have both direct and indirect effects on the soil properties, fauna, and flora associated with an animal's carcass. While few comprehensive quantitative studies have been undertaken, those that have show considerable variability in decomposition processes and rates, their regulating variables, and the resultant ecosystem effects. In this two-part study, decomposition rates of vertebrate species were measured in a semiarid, shrub-steppe environment (Wyoming, USA). First, decomposition loss rates of mass, energy, and nutrients were measured for rat carcasses (Rattus norvegicus) in four seasons and two microsites (surface and underground burrows). Decomposition rates varied significantly between microsites (burrow . surface in spring and summer) and among seasons (spring . summer . autumn ' winter), with mass loss amounts linearly correlated with ambient air temperatures. Energy and nutrient losses were related to phased carcass organ/tissue losses, with energy, K, Na, N, and S being lost more quickly than skeletal components (P, Mg, Ca). Overall, the nutrient loss sequence was K ¼ Na .Carcass quality (N concentration) declined through time as a function of decay stage. Second, decomposition rates of 10 vertebrate species (mule deer [Odocoileus hemionus], dog [Canis familiaris], white-tailed jackrabbit [Lepus townsendii], Uinta ground squirrel [Spermophilus armatus], least chipmunk [Tamias minimus], deer mouse [Peromyscus maniculatus], Magpie [Pica hudsonia], Sage Sparrow [Amphispiza belli], terrestrial garter snake [Thamnophis elegans], and northern leopard frog [Lithobates pipiens])were measured with vertebrate scavengers present or absent. Mass loss rates varied among species and were generally faster in the presence of scavengers. Carcass body mass, N content, or labile/recalcitrant fractions did not correlate with decomposition rate, though surface area to volume ratios of mammal carcasses were positively correlated with wet-mass decomposition rate. Nutrient measures of sub-carcass soils showed soil N, P, and Na increased during decomposition. Increased soil nutrient amounts represented up to 15.6% of the available carcass N, 28.8% of carcass P, and 28.7% of carcass Na. At a landscape scale in the shrubsteppe ecosystem, carrion decomposition constituted ,1% of the nutrient-cycling budget but contributed significantly to localized soil nutrient dynamics.

This study established the preferences of shrubsteppe granivores among seeds of 6 common sagebrushsteppe plants and related the preferences observed to physical and nutritional attributes of the seeds. Seeds of big sagebrush (Artemisia tridentata), cheatgrass (Bromus tectorum), Indian ricegrass (Oryzopsis hymenoides), western wheatgrass (Pascopyrum smithii), bitterbrush (Purshia tridentata) and green needlegrass (Stipa viridula) were placed in groups of petri dishes designed such that seed removal could be ascribed to either diurnal vertebrates, nocturnal vertebrates or ants. Though absolute quantities of seeds removed varied among the 3 granivore classes, calculations of preference based on weights of each seed species removed by each granivore class indicated that all 3 ranked the seeds similarly. Preference hierarchies of the 3 granivore classes were highly positively correlated with both calories per seed and % soluble carbohydrate of the seeds. The first correlation supports a basic prediction of optimal foraging theory -that foragers should maximize energy intake per unit time spent foraging. Both correlations emphasize the role of seed nutritional qualities in granivore seed selectivity in that soluble carbohydrate is a water-efficient energy source and its percentage is a good indicator of the digestible energy available in a food item. A corollary experiment comparing granivore use of an exotic seed (millet [Panicum miliaceum]) and a preferred native seed (Oryzopsis) demonstrated a distinct preference for the exotic. Since millet seeds are particularly high in % soluble carbohydrate, this result reinforced the apparent value of this nutritional attribute as a predictor of granivore seed preference. Among many seed resource characteristics upon which granivore seed selectivity might operate, our results indicate that individual species' nutritional composition may be particularly important. Thus, inferences about seed selectivity and resource partitioning among arid-land granivores should be interpreted with caution, especially those based on experiments using seed introductions, since the influence of seed nutritional attributes has not been widely acknowledged heretofore.

The spatial distribution of diaspores in seed banks can be significantly affected by physical processes that act on diaspores after they reach the soil surface. We examined how diaspore morphology and soil particle size affect diaspore incorporation into soil in a disturbed alpine ecosystem on the Beartooth Plateau, Montana, USA. Diaspores of alpine species with varying morphology were sown over soils of five different particle sizes and later collected from three depths. Regardless of diaspore morphology, the total number of diaspores trapped increased with increasing particle size until a threshold soil particle size was reached above which no more diaspores were trapped. At small particle sizes (0.5—1.0 and 1.0—2.0 mm) small diaspores and diaspores with adhesive seed coats were trapped, but most large diaspores moved horizontally across the surface and were not trapped. The majority of those diaspores trapped were at the 0—1 cm depth at small particle sizes. At large particles sizes (2.0—4.0, 4.0—8.0, and 8.0—16.0 mm) high numbers of large diaspores were trapped, and more diaspores moved vertically through the soil column. In small particle size soils small diaspores reached greater depths than large diaspores. Diaspores with adhesive seed coats responded more like large diaspores in terms of vertical movement. Diaspore length and eccentricity (length/width) were highly correlated with entrapment at small particle sizes and appeared to have the greatest effect on horizontal movement. Mass and width were significantly correlated with numbers of diaspores trapped in large particle sizes and were influencing vertical movement. Models based on the Weibull probability distribution were used to describe diaspore "survival" on the soil surface and to describe vertical movement in the soil column. This study indicates that on exposed soils in windy environments diaspore morphology and soil particle size greatly affect the spatial distribution of diaspores in seed banks. For diaspores of a given species, the optimal soil type traps a high number of diaspores but precludes significant downward movement.