The importance of scale in understanding the effect of stream intermittence on aquatic macroinvertebrate diversity

Abstract

AbstractBiotic richness in intermittent reaches (α‐diversity) is generally lower than in perennial reaches. However, variability among intermittent reaches (β‐diversity) is predicted to be higher. Yet how patterns in α‐ and β‐diversity scale up to influence stream network diversity is unclear and has received little attention. In addition, the timing of sampling relative to the resumption of flow in intermittent reaches should influence patterns in diversity. We predicted that early in the wet season, assemblages in intermittent reaches would be recovering from drying and have lower α‐diversity and higher β‐diversity relative to perennial reaches but that these patterns might not be reflected at the stream network scale. In contrast, we predicted that late in the wet season, assemblages in intermittent reaches would recover and α, β, and network diversity would be similar between intermittent and perennial reaches. These predictions were tested with macroinvertebrate assemblages in an eastern Oregon stream network. Early in the wet season, α‐diversity and network diversity were lower in intermittent than perennial reaches; however, β‐diversity was similar between the two types of reaches. Late in the wet season, both α‐diversity and β‐diversity were similar between intermittent and perennial reaches, suggesting recovery of intermittent reaches from drying. However, at the network scale, intermittent reaches continued to have lower diversity indicating a lack of recovery. Rare taxa were particularly vulnerable to flow intermittency. Our results indicate that a consideration of spatial scale, taxa abundance/rarity, and timing of sampling will improve our understanding of the effect of flow intermittence on diversity.