The duality of drought: Pelagic‐ and benthic‐spawning stream fishes show opposing responses to drought in the southern Great Plains

Abstract

Streamflow is a primary determinant of fish assemblage structure in riverine systems, but alteration of natural flow regimes can result in fish assemblage shifts through the process of environmental filtering. Because natural drought conditions reduce and homogenize streamflow in a manner comparable to projections for climate change in some regions, drought could serve as a proxy for expected future flow conditions. We investigated the effects of drought as a temporally dynamic environmental filter of the occurrence of two guilds of fishes, benthic‐spawners (BS) that deposit adhesive ova along the benthic zone of rivers and pelagic‐spawners (PS) that release semi‐buoyant, non‐adhesive ova into the pelagic zone of rivers. We developed species‐specific random forest models to estimate annual probability of occurrence for three BS and four PS minnow species at three sites in the upper Brazos River, Texas for the period 1950‐2018. We then used a generalized additive mixed effects model to assess the relationship between drought intensity and likelihood of occurrence to test (H1) whether reproductive modes differed in response to drought, and whether response to drought was (H2) spatially or (H3) temporally variable. We found support for (H1) as two of four PS species (Shoal Chub Macrhybopsis hyostoma; Smalleye Shiner Notropis buccula) declined and two of three BS species increased as drought intensified, support for (H2) as responses to drought varied by gage location, and no support for (H3) as drought response was consistent for periods 1950‐1979 and 1980‐2018. These findings offer insight into the future of riverine fish assemblages as climate change is expected to exacerbate regional drought conditions. Management of PS fishes during extreme drought in the southern Great Plains may require strategies such as (1) rescues of fish from drying reaches, (2) captive holding and propagation, and (3) assisted recolonization following subsidence of drought conditions.

Conservation at the nexus of niches: Multidimensional niche modeling to improve management of Prairie Chub

“…Future research may also focus only on abiotic and movement factors; our study suggests that adding in biotic interactions decreases model performance compared to the abiotic‐only model. Until such research is conducted, our findings support the assertation that environmental filtering exudes a stronger effect on species distributions than biological interactions (Giam and Olden 2016; Nguyen et al 2023).…”

“…Biological interactions are contributing, at least in part, to the current distribution of Prairie Chub. Although the effects of environmental filtering generally outweigh the effects of biological interactions within Great Plains prairie streams (Nguyen et al 2023, this special section), strong species interactions can affect stream fish distributions (Giam and Olden 2016). In some prairie streams, the introduction of nonnative species has contributed to rapid replacement of native species through competition (Hoagstrom et al 2010) or hybridization and introgression (Wilde and Echelle 1992).…”

Avoiding a macabre future for Macrhybopsis—A special section on improving management and conservation of chubs

“…Wedgeworth et al (2023, this special section) and Perkin et al (2023a, this special section) study flow–recruitment relationships for the Prairie Chub and the Shoal Chub, respectively, and separately report positive correlations between streamflow variability and hatch success in regulated rivers. Nguyen et al (2023, this special section) show that drought‐mediated changes in flow regime cause reduced occurrence of pelagic‐spawning species such as the Shoal Chub, with implications for managing populations under increasingly dry conditions in southern Great Plains rivers.…”

“…the Shoal Chub, respectively, and separately report positive correlations between streamflow variability and hatch success in regulated rivers. Nguyen et al (2023, this special section) show that drought-mediated changes in flow regime cause reduced occurrence of pelagic-spawning species such as the Shoal Chub, with implications for managing populations under increasingly dry conditions in southern Great Plains rivers. We hope that the papers included in this special section will inspire future work on the ecology and management of chubs.…”