Abstract
AbstractAimConserving 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.LocationNew River drainage, Appalachian Mountains, USA.MethodsWe 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?ResultsWe 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 conclusionsWe 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.
Highlights
Understanding the factors maintaining suitable stream habitats is crucial for conserving sensitive biota, especially in intensively used landscapes (Weijters, Janse, Alkemade, & Verhoeven, 2009)
Seg‐ ment features only independently explained 3.3% of variation. These findings indicate E. osburni’s recently localized distribution was primarily shaped by the two prop‐ agating pathways: (a) extirpations following the transmission of im‐ pacts from land use disturbance via resistance‐diminishing features (Figure 1a) and (b) persistence in refugia defined by features convey‐ ing resistance to populations at multiple scales (Figure 1b)
For exam‐ ple, E. osburni was extirpated from catchments with more intensive agriculture and, to a lesser extent, urban development, which were enabled by amenable physical features, such as lower elevations and subdued topography associated with carbonate geology (Hack, 1957)
Summary
Understanding the factors maintaining suitable stream habitats is crucial for conserving sensitive biota, especially in intensively used landscapes (Weijters, Janse, Alkemade, & Verhoeven, 2009). Existing frameworks recognize stream habitats are hierarchically organized from catchment to microhabitat spatial scales (Frissell, Liss, Warren, & Hurley, 1986). Within this hierarchy, physical heterogeneity is created by interactions among broad‐ and fine‐scale phenomena, giving rise to sets of filtering mechanisms collectively determining local biotic composition (Poff, 1997). The hierarchal organization of stream habitat often causes the effects of regional land use disturbance to propagate through spatial scales before impacting local habitat and biota (Burdon, McIntosh, & Harding, 2013; Isaak & Hubert, 2001; Maloney & Weller, 2011). Knowing which intermediate‐scale habi‐ tat features propagate or offset land use signals could help managers assess the potential for intensively used landscapes to support sen‐ sitive populations
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