Biodiversity: towards a unifying theme for river ecology

1. A broadened concept of biodiversity, encompassing spatio-temporal hetero geneity, functional processes and species diversity, could provide a unifyi ng theme for river ecology. 2. The theoretical foundations of stream ecology often do not reflect fully the crucial roles of spatial complexity and fluvial dynamics in natural ri ver ecosystems, which has hindered conceptual advances and the effectivenes s of efforts at conservation and restoration. 3. Inclusion of surface waters (lotic and lentic), subsurface waters (hypor heic and phreatic), riparian systems (in both constrained and floodplain re aches), and the ecotones between them (e.g. springs) as interacting compone nts contributing to total biodiversity, is crucial for developing a holisti c framework of rivers as ecosystems. 4. Measures of species diversity, including alpha, beta and gamma diversity , are a result of disturbance history, resource partitioning, habitat fragm entation and successional phenomena across the riverine landscape. A hierar chical approach to diversity in natural and altered river-floodplain ecosys tems will enhance understanding of ecological phenomena operating at differ ent scales along multidimensional environmental gradients. 5. Re-establishing functional diversity (e.g. hydrologic and successional p rocesses) across the active corridor could serve as the focus of river cons ervation initiatives. Once functional processes have been reconstituted, ha bitat heterogeneity will increase, followed by corresponding increases in s pecies diversity of aquatic and riparian biota.