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1. Multispecies conservation of freshwater fish assemblages in response to climate change in the southeastern United States

   https://doi.org/10.1111/ddi.12948  

   VanCompernolle, Michelle ; Knouft, Jason H. ; Ficklin, Darren L. ; Heikkinen, ed., Risto ( June 2019 , Diversity and Distributions)

   Streamflow and water temperature are primary variables influencing the distribution of freshwater taxa. Climate‐induced changes in these variables are already causing shifts in species distributions, with continued changes projected in the coming decades. The Mobile River Basin (MRB), located in the southeastern United States, contains some of the highest levels of temperate freshwater biodiversity in North America. We integrated species distribution data with contemporary and future streamflow and water temperature data as well as other physical habitat data to characterize occurrence probabilities of fish species in the MRB with the goal of identifying current and future areas of high conservation value.

   Mobile River Basin, southeastern United States.

   We used a maximum entropy approach to estimate baseline and future occurrence probability distributions for 88 fish species in the MRB based on model‐generated streamflow and water temperature as well as geologic, topographic and land cover data. Areas of conservation prioritization were identified based on regions that contain suitable habitat for high levels of biodiversity according to baseline and future conditions while accounting for uncertainty associated with multiple future climate projections.

   On average, flow (28%), water temperature (28%) and geology (30%) contribute evenly to determining suitable habitat for fish species in the MRB. Based on baseline and future species distribution model estimates, high priority streams (best 10%) are largely concentrated in the eastern portion of the MRB, with a majority (51%) located within the Coosa and Tallapoosa River systems.

   We provide a framework that uses relevant hydrologic and environmental data in the context of future climatic uncertainty to estimate areas of freshwater conservation opportunity in the coming decades. While streamflow and water temperature represent important habitat for freshwater fishes in the MRB, distributions are also constrained by other aspects of the physical environment.

    

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2. An analysis of threats to endangered animal taxa in California's freshwater systems

   https://doi.org/10.1002/aqc.4057  

   Qin, Gary ; Anderson, Kurt E. ; Cassady, Anna ; Rodriguez, Leonardo ; Syed, Eeman ; Regan, Helen M. ( December 2023 , Aquatic Conservation: Marine and Freshwater Ecosystems)

   This study analysed threats to federally and State‐listed endangered and threatened animal taxa in California, United States, and how threats varied by taxa, habitat use, spatial extent, severity, geographical region and endemic status using threat categories from the International Union for Conservation of Nature (IUCN) Red List Threats Classification Scheme and information from scientific literature and reports.

   A majority of the taxa evaluated were associated with freshwater habitats and were endemic to California. The most threatened taxonomic groups were fish, followed by mammals and birds. The number of threats was mostly evenly distributed across the State's three geographical regions (i.e., North, Central and South), and no single region had a disproportionately high number of endangered animal taxa.

   Freshwater taxa were the most affected in nearly every threat category, suggesting that freshwater taxa are more threatened than their terrestrial and marine counterparts. In descending order, the most prominent threats across all taxa were habitat loss, invasive species, climate change and altered hydrology. Threats identified as high severity also tended to have a high spatial extent and vice versa.

   This study shows that the numerous freshwater faunas in California are disproportionately affected by threats also found in other freshwater systems and Mediterranean‐climate regions, highlighting the scope of the freshwater biodiversity crisis in California. Managing priorities to target the most pervasive threats to endangered freshwater taxa documented in this study will help safeguard freshwater biodiversity against human threats in California and beyond.

    

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3. Broader niches revealed by fossil data do not reduce estimates of range loss and fragmentation of African montane trees

   https://doi.org/10.1111/geb.12909  

   Ivory, Sarah J. ; Russell, James ; Early, Regan ; Sax, Dov F. ; Pandolfi, ed., John ( April 2019 , Global Ecology and Biogeography)

   The climate tolerances of many species are broader than those estimated from current native ranges. Indeed, the niches of some Afromontane trees are up to 50% larger after incorporation of fossil data. This expansion could reduce estimates of species' future range loss owing to climate change but also implies strong non‐climatic limitations on species' current ranges. One such limitation is land use, which fossil data suggest influences Afromontane tree distribution, preventing these trees from occupying warmer conditions than they do currently. We aimed to assess the degree to which the broader climatic tolerances revealed by fossil data buffer projected range loss from climate and land use for Afromontane trees.

   Africa.

   Last 21,000 years.

   Afromontane trees.

   We used species distribution models informed by both current and fossil distributions to project future ranges under climate and land‐use projections.

   We found that projected range reductions are only slightly ameliorated by incorporation of fossil distributions, and these improvements diminish further under severe land‐use or climate change scenarios. Taxa that are less impacted by climate are more impacted by intense land use. Depending on the severity of climate and land use, the geographical extent of Afromontane tree species' ranges will contract by 40–85%, and the trees will be completely lost from large portions of Africa. We projected that the surviving species' ranges will become increasingly fragmented.

   Maintaining Afromontane ecosystems will require mitigation of both climate and land‐use change and protection of areas to optimize connectivity. Our findings caution that species with climate tolerances broader than their current range might not necessarily fare better under strong changes in climate or land use.

    

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4. Trout and invertebrate assemblages in stream pools through wildfire and drought

   https://doi.org/10.1111/fwb.14212  

   Cooper, Scott D. ; Wiseman, Sheila W. ; DiFiore, Bartholomew P. ; Klose, Kristie ( January 2024 , Freshwater Biology)

   Climate change is increasing the frequency, severity, and extent of wildfires and drought in many parts of the world, with numerous repercussions for the physical, chemical, and biological characteristics of streams. However, information on how these perturbations affect top predators and their impacts on lower trophic levels in streams is limited.

   The top aquatic predator in southern California streams is nativeOncorhynchus mykiss, the endangered southern California steelhead trout (trout). To examine relationships among the distribution of trout, environmental factors, and stream invertebrate resources and assemblages, we sampled pools in 25 stream reaches that differed in the presence (nine reaches) or absence (16 reaches) of trout over 12 years, including eight reaches where trout were extirpated during the study period by drought or post‐fire flood disturbances.

   Trout were present in deep pools with high water and habitat quality. Invertebrate communities in trout pools were dominated by a variety of medium‐sized collector–gatherer and shredder invertebrate taxa with non‐seasonal life cycles, whereas tadpoles and large, predatory invertebrates (Odonata, Coleoptera, Hemiptera [OCH]), often with atmospheric breather traits, were more abundant in troutless than trout pools.

   Structural equation modelling of the algal‐based food web indicated a trophic cascade from trout to predatory invertebrates to collector–gatherer taxa and weaker direct negative trout effects on grazers; however, both grazers and collector–gatherers also were positively related to macroalgal biomass. Structural equation modelling also suggested that bottom‐up interactions and abiotic factors drove the detritus‐based food web, with shredder abundance being positively related to leaf litter (coarse particulate organic matter) levels, which, in turn, were positively related to canopy cover and negatively related to flow. These results emphasise the context dependency of trout effects on prey communities and of the relative importance of top‐down versus bottom‐up interactions on food webs, contingent on environmental conditions (flow, light, nutrients, disturbances) and the abundances and traits of component taxa.

   Invertebrate assemblage structure changed from a trout to a troutless configuration within a year or two after trout were lost owing to post‐fire scouring flows or drought. Increases in OCH abundance after trout were lost were much more variable after drought than after fire. The reappearance of trout in one stream resulted in quick, severe reductions in OCH abundance.

   These results indicate that climate‐change induced disturbances can result in the extirpation of a top predator, with cascading repercussions for stream communities and food webs. This study also emphasises the importance of preserving or restoring refuge habitats, such as deep, shaded, perennial, cool stream pools with high habitat and water quality, to prevent the extirpation of sensitive species and preserve native biodiversity during a time of climate change.

    

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5. Thermal acclimation and habitat-dependent differences in temperature robustness of a crustacean motor circuit

   https://doi.org/10.3389/fncel.2023.1263591  

   Stein, Wolfgang ; Torres, Gabriela ; Giménez, Luis ; Espinosa-Novo, Noé ; Geißel, Jan Phillipp ; Vidal-Gadea, Andrés ; Harzsch, Steffen ( October 2023 , Frontiers in Cellular Neuroscience)

   At the cellular level, acute temperature changes alter ionic conductances, ion channel kinetics, and the activity of entire neuronal circuits. This can result in severe consequences for neural function, animal behavior and survival. In poikilothermic animals, and particularly in aquatic species whose core temperature equals the surrounding water temperature, neurons experience rather rapid and wide-ranging temperature fluctuations. Recent work on pattern generating neural circuits in the crustacean stomatogastric nervous system have demonstrated that neuronal circuits can exhibit an intrinsic robustness to temperature fluctuations. However, considering the increased warming of the oceans and recurring heatwaves due to climate change, the question arises whether this intrinsic robustness can acclimate to changing environmental conditions, and whether it differs between species and ocean habitats.

   We address these questions using the pyloric pattern generating circuits in the stomatogastric nervous system of two crab species,Hemigrapsus sanguineusandCarcinus maenasthat have seen a worldwide expansion in recent decades.

   Consistent with their history as invasive species, we find that pyloric activity showed a broad temperature robustness (>30°C). Moreover, the temperature-robust range was dependent on habitat temperature in both species. Warm-acclimating animals shifted the critical temperature at which circuit activity breaks down to higher temperatures. This came at the cost of robustness against cold stimuli inH. sanguineus, but not inC. maenas. Comparing the temperature responses ofC. maenasfrom a cold latitude (the North Sea) to those from a warm latitude (Spain) demonstrated that similar shifts in robustness occurred in natural environments. Our results thus demonstrate that neuronal temperature robustness correlates with, and responds to, environmental temperature conditions, potentially preparing animals for changing ecological conditions and shifting habitats.

    

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