Biota Connect Aquatic Habitats throughout Freshwater Ecosystem Mosaics

Abstract

Freshwater ecosystems are linked at various spatial and temporal scales by movements of biota adapted to life in water. We review the literature on movements of aquatic organisms that connect different types of freshwater habitats, focusing on linkages from streams and wetlands to downstream waters. Here, streams, wetlands, rivers, lakes, ponds, and other freshwater habitats are viewed as dynamic freshwater ecosystem mosaics (FEMs) that collectively provide the resources needed to sustain aquatic life. Based on existing evidence, it is clear that biotic linkages throughout FEMs have important consequences for biological integrity and biodiversity. All aquatic organisms move within and among FEM components, but differ in the mode, frequency, distance, and timing of their movements. These movements allow biota to recolonize habitats, avoid inbreeding, escape stressors, locate mates, and acquire resources. Cumulatively, these individual movements connect populations within and among FEMs and contribute to local and regional diversity, resilience to disturbance, and persistence of aquatic species in the face of environmental change. Thus, the biological connections established by movement of biota among streams, wetlands, and downstream waters are critical to the ecological integrity of these systems. Future research will help advance our understanding of the movements that link FEMs and their cumulative effects on downstream waters.

Featured Collection Introduction: Connectivity of Streams and Wetlands to Downstream Waters

“…Schofield et al. () review the literature on how movements of aquatic and semiaquatic biota connect freshwater habitats over various temporal and spatial scales (Figure ). Finally, Goodrich et al.…”

“…Streams and wetlands serve numerous functions for downstream waters and their populations, by acting as sources of colonists, food, and genetic diversity; as refuges from adverse abiotic and biotic conditions; and as complementary or obligate habitats for the maturation and reproduction of fish, amphibians, and invertebrates (Schofield et al. ). Because many aquatic species are capable of moving overland (e.g., by active flight, walking, wind dispersal), biological connections can be more widespread, complex, and variable than hydrologic connections, and habitats that seem to be hydrologically isolated are often highly connected by movements of aquatic biota (Figure ).…”

“…In reality, biological connectivity is best assessed as the cumulative effects of multiple species moving, via multiple pathways and across multiple habitat types, to make use of the full range of resources found in spatially and temporally variable wetlands, streams, rivers, lakes, ponds, and other freshwater habitats found throughout watersheds (Schofield et al. ).…”

“…; Schofield et al. ). For example, while the probability of a large‐magnitude transfer of sediment or organisms from any given headwater stream in a given year might be low (i.e., a low‐frequency connection when each stream is considered individually), headwater streams are the most abundant type of stream in most watersheds.…”

“…Similarly, cumulative export of invertebrates from headwater to downstream waters can be substantial, especially in intermittent and ephemeral streams, as terrestrial invertebrates accumulate in these channels during dry periods and are then transported downstream in wet periods (Schofield et al. ).…”