Abstract
Understanding drivers of biodiversity is a long-standing goal of basic and applied ecological research. In riverine systems, there remains a critical need to identify these drivers as efforts to manage and protect rivers grow increasingly desperate in the face of global change. We explored one commonly cited potential driver of riverine biodiversity, stream size (e.g., stream order, watershed area, width), using a systematic literature review paired with an analysis of broad-scale macroinvertebrate and fish communities. Of the 165 papers reviewed, we found mostly positive, but no universal, relationship between biodiversity and stream size despite inconsistent use of over 30 measures of stream size. One-third of studies failed to report explanatory mechanisms driving biodiversity–stream size relationships. Across over 4000 macroinvertebrate and fish samples from 1st–8th order streams in the contiguous USA, our analysis showed biodiversity (Shannon diversity, functional diversity, beta diversity) generally increased with measures of stream size. However, because of inconsistent and generally weak relationships between biodiversity and stream size across organismal groups, we emphasize the need to look beyond simple physical stream size measures to understand and predict riverine biodiversity, and strongly suggest that studies search for more mechanistic explanations of biodiversity patterns in lotic systems.
Highlights
Understanding patterns of biodiversity across landscapes is a fundamental goal of both basic and applied ecological research [1,2]
The need to understand drivers of diversity is amplified by human reliance on these systems for drinking water, food and recreation, and by increasing anthropogenic stressors that lead to their degradation
We found that 50% of the papers studying algae found positive biodiversity–stream size relationship relationship with 16% finding no relationship
Summary
Understanding patterns of biodiversity across landscapes is a fundamental goal of both basic and applied ecological research [1,2]. The need to understand drivers of diversity is amplified by human reliance on these systems for drinking water, food and recreation, and by increasing anthropogenic stressors that lead to their degradation. The current and future estimated declines of aquatic organisms due to climate change and anthropogenic alterations are substantial [7,8,9]. These losses come at a time when lotic ecologists are still scrambling to identify the physical and biological processes that determine and predict patterns in biodiversity. The evaluation of water quality and subsequent management decisions are often based on assumed relationships between biodiversity and local environmental drivers [10,11,12]
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