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not regulated by on-channel lakes, apparently in response to temperature criteria (Stanford, unpublished). These observations emphasize that the riverine ecosystems are truly four dimensional, with longitudinal (upstream-downstream), lateral (floodplain-uplands), and vertical (hyporheic-phreatic) dimensions (Figure 1); since these spatial dimensions are transient or dynamic over time as a consequence of relativity, temporality is the forth dimension (Ward 1989). Within a given stream reach, distribution and abundance of organisms is a multivariate function of the structural and functional attributes of channel (fluvial), riparian (floodplain,shoreline) and hyporheic (groundwater) habitats as they interact within time and space with the geomorphology and hydrology of the catchment. Clearly, catchments may be characterized as patch-dynamic systems (Pringle et al. 1988, Townsend 1989) and ecological connectivity of patches is a fundamental feature. Many riverine organisms may traverse all three spatial dimensions in the process of completing life cycles (high connectivity), whereas others may be relatively stationary (low connectivity). For example, in the Flathead River, Montana, a gravel bottom system with expansive intermontane floodplains characterized by substantial interstitial flow (Figure 2), certain specialized stoneflies (Insecta: Plecoptera) reside within floodplain groundwaters during the entire larval stage. Indeed, hundreds of these crepuscular stoneflies have been collected in single samples taken from groundwater monitoring wells 2-3 km from the river channel, demonstrating the enormous volume of the hyporheic zone in this river. They are the top consumers in a speciose (80+ species) groundwater food web. Yet, these stoneflies emerge as winged adults from the river channel and fly into the riparian vegetation to mate and produce eggs. The eggs are deposited in the river channel, followed by larval immigration into the hyporheic zone (Stanford and Ward 1988). Many other riverine insects, which commonly characterize the rhithron (cold, swift-flowing, gravel-cobble substratum) habitat of western USA rivers also depend upon riparian vegetation during the flight period, but the larval stage is completed within the channel. Most non-insect zoobenthos and periphyton (attached algae) are essentially obligate channel inhabitants, although they, like most fish species and insect larvae, are often distinctly segregated by temperature, flow, substratum or behavioral criteria within the altitudinal gradient of the stream continuum (e.g., bull charr distribution in Figure 3, see also Resh and Rosenberg 1984, Matthews and Heins 1987). Biodiveristy and bioproduction in rivers are related to a plethora of factors that interact bioenergetically (Figure 4) to determine reproductive success of individulas 7