Remaining populations of an upland stream fish persist in refugia defined by habitat features at multiple scales

Abstract

Aim Conserving stream biota could require strategies that preserve habitats conveying resistance to ecological impacts of changing land use and climate. Retrospective analyses of species’ responses to anthropogenic disturbances can inform such strategies. We developed a hierarchical framework to contrast environmental conditions underlying persistence versus extirpation of an imperilled stream fish, Candy Darter (Etheostoma osburni), over decades of changing land use. The decline of E. osburni may broadly represent the challenge of conserving sensitive freshwater species in intensively used upland environments. Location New River drainage, Appalachian Mountains, USA. Methods We surveyed fish and habitat in historically occupied sites to identify population refugia, and used multivariate and spatial analyses to address three questions: (a) what are the environmental correlates of refugia? (b) are the pathways by which land use impacts instream habitat constrained by catchment‐ and/or segment‐scale features? and (c) are E. osburni distributional dynamics spatially structured and explained by fine sediment and warm stream temperatures? Results We confirmed a recently localized distribution similar to other upland species, marked by at least seven extirpations from streams throughout E. osburni's southern range. Catchment‐scale features primarily constrained land use and finer‐scale habitat, leading to either extirpations or population‐supporting refugia defined by features at multiple scales. Refugium habitats contained cooler temperatures and less fine sediment. Rare mismatches between persistence and habitat suitability were explained by network location, suggesting unmeasured environmental gradients and/or dispersal contributed to distributional dynamics. Main conclusions We provided insight at multiple spatial scales into how aquatic species’ distributions become fragmented and localized. Our results demonstrate that natural landscape heterogeneity imparts spatially variable resistance of sensitive species to intensive land uses. By recognizing the scale‐specific features that buffer populations from extirpation, conservation strategies could be tailored to protect naturally occurring refugium habitats and focus restoration in systems where such habitats are broadly lacking.

A new composite abundance metric detects stream fish declines and community homogenization during six decades of invasions

“…Past studies within the UMNR have emphasized declines of a few resident species (Buckwalter et al, 2018;Dunn & Angermeier, 2019), but none has indicated the mass community-and species-level losses in fish diversity suggested by our analysis. This new insight stems from our innovative analytical approach focused on species abundance rather than species occurrence as the measure of spread and decline.…”

Using resiliency, redundancy, and representation in a Bayesian belief network to assess imperilment of riverine fishes

“…In the Other Threats node, we included the combined deleterious effects of Hybridization (i.e., documented presence of hybrids involving the species) and Nonnative Species (i.e., nonnative fish richness) detected within a management unit (Table 1). These threats were factors imperiling multiple southeastern U.S. species listed recently as Endangered under the ESA (e.g., Barrens Topminnow, Fundulus julisia , Ennen et al, 2021; Candy Darter, Etheostoma osburni , Dunn & Angermeier, 2019). The Other Threats node could be adapted to reflect alternative species‐specific threats or habitat conditions (e.g., stream warming, land‐use change, and water quality; Noss et al, 2021) or to explicitly accommodate threats outlined by policy (e.g., Five Factors under ESA; Shirey et al, 2022).…”

Riverscape nesting dynamics of Neosho Smallmouth Bass: To cluster or not to cluster?

“…Our objectives were to quantify the multi‐scale habitat related to the presence and abundance of Neosho Smallmouth Bass nests, to describe factors related to nest aggregations (hereafter “clusters”), and to quantify nest microhabitat conditions. Multi‐scale approaches are increasingly used in warmwater stream‐fisheries research (e.g., Dunn & Angermeier, 2019; Wellemeyer et al., 2019). For example, Dunn and Angermeier (2019) show that imperilled Candy Darter ( Etheostoma osburni ) persistence requires refugia conferred by habitat conditions at local (i.e., temperature, sedimentation) and catchment (i.e., land use) spatial scales.…”

“…Multi‐scale approaches are increasingly used in warmwater stream‐fisheries research (e.g., Dunn & Angermeier, 2019; Wellemeyer et al., 2019). For example, Dunn and Angermeier (2019) show that imperilled Candy Darter ( Etheostoma osburni ) persistence requires refugia conferred by habitat conditions at local (i.e., temperature, sedimentation) and catchment (i.e., land use) spatial scales. However, most efforts to understand hierarchical controls on warmwater stream fish abundance focus on adult fish outside of the reproductive period (but see Peoples et al., 2014).…”