Spatial asynchrony and cross‐scale climate interactions in populations of a coldwater stream fish

Abstract

Climate change affects populations over broad geographic ranges due to spatially autocorrelated abiotic conditions known as the Moran effect. However, populations do not always respond to broad‐scale environmental changes synchronously across a landscape. We combined multiple datasets for a retrospective analysis of time‐series count data (5–28 annual samples per segment) at 144 stream segments dispersed over nearly 1,000 linear kilometers of range to characterize the population structure and scale of spatial synchrony across the southern native range of a coldwater stream fish (brook trout, Salvelinus fontinalis), which is sensitive to stream temperature and flow variations. Spatial synchrony differed by life stage and geographic region: it was stronger in the juvenile life stage than in the adult life stage and in the northern sub‐region than in the southern sub‐region. Spatial synchrony of trout populations extended to 100–200 km but was much weaker than that of climate variables such as temperature, precipitation, and stream flow. Early life stage abundance changed over time due to annual variation in summer temperature and winter and spring stream flow conditions. Climate effects on abundance differed between sub‐regions and among local populations within sub‐regions, indicating multiple cross‐scale interactions where climate interacted with local habitat to generate only a modest pattern of population synchrony over space. Overall, our analysis showed higher degrees of response heterogeneity of local populations to climate variation and consequently population asynchrony than previously shown based on analysis of individual, geographically restricted datasets. This response heterogeneity indicates that certain local segments characterized by population asynchrony and resistance to climate variation could represent unique populations of this iconic native coldwater fish that warrant targeted conservation. Advancing the conservation of this species can include actions that identify such priority populations and incorporate them into landscape‐level conservation planning. Our approach is applicable to other widespread aquatic species sensitive to climate change.

Effects of episodic stream dewatering on brook trout spatial population structure

“…Valentine et al. (2023) also observed more spatial synchrony for juvenile brook trout than adults across the southern Appalachian region, and they attributed this to regional climate trends that affect fish abundance. Likewise, Kanno et al.…”

Using multi‐scale spatial models of dendritic ecosystems to infer abundance of a stream salmonid

“…Prolonged high summer temperatures can cause physiological stress and adversely affect spawning (Warren et al., 2012; Xu et al., 2010), and high flows during winter and spring can result in bed scouring events that cause high mortality in young‐of‐the‐year (YOY) (Kanno et al., 2015; Roghair et al., 2002). However, there is limited knowledge on how differently trout populations respond to seasonal weather patterns along the environmental gradient across their native range (Valentine et al., 2024).…”

Microgeographic variation in demography and thermal regimes stabilize regional abundance of a widespread freshwater fish

“…Indeed, the naturally fragmented habitats occupied by brook trout could be instrumental in generating microgeographic variation (Wood et al, 2014) and stabilizing dynamics over larger scales, thereby buffering the species against disturbance . While brook trout population dynamics are likely to be more synchronized in southern range margins with warmer climates, recent studies in these regions nonetheless have shown evidence of demographic variation and subtle differences within and among streams (Andrew et al, 2022;Kanno et al, 2016;Valentine et al, 2024), which can covary with watershed geology (Hartman et al, 2007) and elevation (Kanno et al, 2015). Thus, fine-scale portfolio effects could potentially alleviate regional climate-induced extinction risk throughout much of the species range.…”

“…Similarly, only 11 Cape Race populations had sufficient data for this study, which limited the scope of inference when assessing drivers of population variation. Future studies of brook trout could gain more robust insight into the prevalence, causes, and consequences of asynchrony by analyzing more populations with longer time series across a larger portion of their native range, as done in recent studies of salmonids (e.g., Donadi et al, 2023;Valentine et al 2024). Second, the results of this study were based on observations of brook trout age-1 and older, but ignored age-0 (young-of-the-year) individuals that were often too small to be comprehensively sampled by electrofishing (Dolan & Miranda, 2003).…”