Extreme heat events and the vulnerability of endemic montane fishes to climate change

Abstract

Identifying how close species live to their physiological thermal maxima is essential to understand historical warm-edge elevational limits of montane faunas and forecast upslope shifts caused by future climate change. We used laboratory experiments to quantify the thermal tolerance and acclimation potential of four fishes (Notropis leuciodus, N. rubricroceus, Etheostoma rufilineatum, E. chlorobranchium) that are endemic to the southern Appalachian Mountains (USA), exhibit different historical elevational limits, and represent the two most species-rich families in the region. All-subsets selection of linear regression models using AIC c indicated that species, acclimation temperature, collection location and month, and the interaction between species and acclimation temperature were important predictors of thermal maxima (T max ), which ranged from 28.5 to 37.2°C. Next, we implemented water temperature models and stochastic weather generation to characterize the magnitude and frequency of extreme heat events (T extreme ) under historical and future climate scenarios across 25 379 stream reaches in the upper Tennessee River system. Lastly, we used environmental niche models to compare warming tolerances (acclimation-corrected T max minus T extreme ) between historically occupied versus unoccupied reaches. Historical warming tolerances, ranging from +2.2 to +10.9°C, increased from low to high elevation and were positive for all species, suggesting that T max does not drive warm-edge (low elevation) range limits. Future warming tolerances were lower (−1.2 to +9.3°C) but remained positive for all species under the direst warming scenario except for a small proportion of reaches historically occupied by E. rufilineatum, indicating that T max and acclimation potentials of southern Appalachian minnows and darters are adequate to survive future heat waves. We caution concluding that these species are invulnerable to 21st century warming because sublethal thermal physiology remains poorly understood. Integrating physiological sensitivity and warming exposure demonstrates a general and fine-grained approach to assess climate change vulnerability for freshwater organisms across physiographically diverse riverscapes.

The combined effects of climate change and river fragmentation on the distribution of Andean Amazon fishes

“…These interacting sources of uncertainties in species' responses to environmental changes may produce incongruences and delays affecting the likelihood of future range shifts projected by our SDMs. Recent studies from temperate regions where long‐term monitoring programs, species‐habitat associations, physiological tolerances, or fine physical environmental data are available, were able to integrate some of these sources of uncertainty in their predictive framework (e.g., Alexander et al., 2018; Kearney & Porter, 2009; Troia & Giam, 2019). Despite the lack of information from tropical environments and their biota, contrasting responses to global change results can be expected from tropical fishes.…”

Magnitude–duration relationships of physiological sensitivity and environmental exposure improve climate change vulnerability assessments

“…Subsequent implementations of the warming tolerance approach have refined more precise drivers of warming tolerance, including the role of short‐term acclimation (Comte et al 2017a, Troia and Giam 2019) and intraspecific variation in thermal sensitivity (Villeneuve et al 2021). Exposure estimates have also been refined by downscaling macroclimate to microclimate (Pincebourde and Casas 2015) and simulating extreme heat events (Troia and Giam 2019). The current study contributes to these refinements by explicitly assessing the interaction between magnitude and duration for organismal sensitivity and environmental exposure (sensu Rezende et al 2014).…”

“…The current study demonstrates that the duration–magnitude framework is effective, but can be improved by incorporating intraspecific variation in sensitivity and extending the prolonged duration beyond 24 h. Third, there is a need for spatially explicit projections of warming tolerance at the spatial extents at which management action is implemented (Tingley et al 2014, Gilby et al 2021). The current study relied on discrete temperature monitoring stations, but high‐resolution, spatially contiguous projections (Troia and Giam 2019) should be sought as high spatiotemporal resolution become increasingly accessible (e.g. Hydroclim; <https://www.hydroclim.org>).…”

“…Alternatively, studies conducted at finer spatial resolutions have sought to characterize T hab more precisely. For example, Pincebourde and Casas (2015) used a biophysical model to downscale macroclimate to microclimate and Troia and Giam (2019) used stochastic weather generation to estimate the magnitude and frequency of extreme heat events. These studies provide conservationists with warming tolerances that can be interpreted absolutely – that is, positive values indicate a margin of safety for a particular taxon in a precise location whereas negative values indicate risk of thermal death.…”

Multi‐scale relationships in thermal limits within and between two cold‐water frog species uncover different trends in physiological vulnerability

“…Many species from montane environments, where natural temperature gradients often track elevation gradients, have already begun shifting their distributions upslope in response to warming temperatures (Chen et al, 2011;Comte & Grenouillet, 2013;Freeman et al, 2018;Tingley et al, 2012). The magnitude of these shifts is partly dependent on organismal thermal physiology (Troia & Giam, 2019), which may be shaped by the environment.…”