In western North America, hummingbirds can be observed systematically visiting flowers that lack the typical reddish color, tubular morphology, and dilute nectar of "hummingbird flowers". Curious about this behavior, we asked whether these atypical flowers are energetically profitable for hummingbir

Although species interactions are often proposed to be stronger at lower latitudes and elevations, few studies have evaluated the mechanisms driving such patterns. In this study, we assessed whether, and by which mechanisms, abiotic changes associated with elevation altered the outcome of an ant-aph

Hummingbirds foraging for nectar in mountains of the western USA encounter spatially-variable rewards under energetically-demanding environmental conditions. Previous workers have found that hummingbirds respond quickly to the average quantity and quality of reward; in addition, one might expect a r

Despite much recent research on pollination, we have amassed relatively little hard information about how animal pollinators contribute to angiosperm speciation and species distinctiveness. We usually assume that pollinators make important contributions by specializing on plant species and providing

Yellow-bellied marmots Marmota ¯aviventris in the East River Valley of Colorado were live-trapped and individually marked annually from 1962 through 1993. These pooled data were used to produce a demography and life table for these years. Females had signi®cantly better survivorship than males beyon

This study demonstrates the importance of considering multiple predators when measuring direct sublethal effects of predators on prey fitness and indirect effects on lower trophic levels, and attributes the non-additivity of effects of fish and stoneflies on mayfly growth to an interaction modificat

Interactive effects of one species on another may simultaneously influence mortality, growth, and fecundity. To quantify the strength of an interaction between two species, we must therefore use techniques that integrate these various responses into estimates of overall effect. Demographic models of

The potential for a trade-offs between these two components of pollinator service exists when visit duration depends on reward quantity; whether the trade-off is realized will depend on variation in nectar production and on whether pollinators forage systematically.

The evidence did not support the acoustic adaptation hypothesis for these marmot species, and factors other than maximizing long-distance transmission through the environment may be important in the evolution of species-specific marmot alarm calls.