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1. Both life‐history plasticity and local adaptation will shape range‐wide responses to climate warming in the tundra plant Silene acaulis

   https://doi.org/10.1111/gcb.13990  

   DeMarche, Megan L.; Doak, Daniel F.; Morris, William F. (December 2017, Global Change Biology)

   Abstract Many predictions of how climate change will impact biodiversity have focused on range shifts using species‐wide climate tolerances, an approach that ignores the demographic mechanisms that enable species to attain broad geographic distributions. But these mechanisms matter, as responses to climate change could fundamentally differ depending on the contributions of life‐history plasticity vs. local adaptation to species‐wide climate tolerances. In particular, if local adaptation to climate is strong, populations across a species’ range—not only those at the trailing range edge—could decline sharply with global climate change. Indeed, faster rates of climate change in many high latitude regions could combine with local adaptation to generate sharper declines well away from trailing edges. Combining 15 years of demographic data from field populations across North America with growth chamber warming experiments, we show that growth and survival in a widespread tundra plant show compensatory responses to warming throughout the species’ latitudinal range, buffering overall performance across a range of temperatures. However, populations also differ in their temperature responses, consistent with adaptation to local climate, especially growing season temperature. In particular, warming begins to negatively impact plant growth at cooler temperatures for plants from colder, northern populations than for those from warmer, southern populations, both in the field and in growth chambers. Furthermore, the individuals and maternal families with the fastest growth also have the lowest water use efficiency at all temperatures, suggesting that a trade‐off between growth and water use efficiency could further constrain responses to forecasted warming and drying. Taken together, these results suggest that populations throughout species’ ranges could be at risk of decline with continued climate change, and that the focus on trailing edge populations risks overlooking the largest potential impacts of climate change on species’ abundance and distribution. 

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2. Plant community response to warming and herbivory on sub-arctic coastal terraces in Western Alaska, 2015 - 2016

   https://doi.org/10.18739/a2hm52m2s  

   Beard, Karen; Choi, Ryan (January 2017, NSF Arctic Data Center)

   To predict future changes in high latitude biomes, it is important to understand how plant communities will respond to increased temperature. Across sub-arctic systems, warming generally increases aboveground biomass in plant communities. Specifically, in arctic graminoid systems, experimental warming has been shown to increase productivity, aboveground biomass and leaf litter production, and stimulate early-season growth. Warming can also decrease species richness, and reduce foliar nitrogen (N) in aboveground biomass over the growing season. Migrating geese are important grazers in arctic and subarctic ecosystems during summer breeding months. Avian herbivores depend on high quality forage (high N) and are often found at high enough densities to impact vegetation communities. Exclosure experiments show that goose herbivory reduces biomass of herbaceous species but increases net above-ground primary production and N concentrations of grazing-tolerant sedges, and sometimes even increases species richness. Goose herbivory also alters plant physiological processes as evidenced by increased N uptake by plants, as well as the biophysical processes that affect N cycling through trampling and fecal deposition. Thus, high-density populations of avian herbivores can have top-down control on their vegetation communities. While increasing global temperatures may increase aboveground biomass and decrease species richness in plant communities, herbivory could potentially mediate, or even reverse, these responses. For example, Post and Pedersen (2008) suggest that herbivory may exacerbate plant response to warming because both effects increase rates of productivity, while simultaneously reducing the effects of warming on aboveground biomass. If the interaction between warming and herbivory causes a shift in plant abundance and community functional groups, this could cascade through the system resulting in changes in nutrient cycling and plant-animal feedbacks. The Yukon-Kuskokwim (Y-K) Delta is one of the largest river deltas in the world and is a globally important breeding area for millions of long-distance migratory waterfowl and shorebird species. The majority of these species nest in high densities close to the ocean among lowland coastal habitat. Geese populations utilize overlapping habitats and shift from more coastal to more interior habitats over the growing season. The expectations for how vegetation responds to increasing temperature and changes in herbivory with climate change will vary for different plant communities. We propose to conduct an experiment that investigates the impact of warming and herbivory on three coastal sub-arctic vegetation communities in the Y-K Delta addressing the following questions: 1) How does warming impact vegetation biomass and community composition; 2) How does herbivory impact species composition and plant functional groups; and 3) How do the different responses to warming and herbivory interact? 

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3. Hotter Temperatures Reduce the Diversity and Alter the Composition of Woody Plants in an Amazonian Forest

   https://doi.org/10.1111/gcb.17555  

   Fortier, Riley P; Kullberg, Alyssa T; Soria Ahuanari, Roy D; Coombs, Lauren; Ruzo, Andrés; Feeley, Kenneth J (November 2024, Global Change Biology)

   Rapid warming and high temperatures are an immediate threat to global ecosystems, but the threat may be especially pronounced in the tropics. Although low‐latitude tree species are widely predicted to be vulnerable to warming, information about how tropical tree diversity and community composition respond to elevated temperatures remains sparse. Here, we study long‐term responses of tree diversity and composition to increased soil and air temperatures at the Boiling River—an exceptional and unique “natural warming experiment” in the central Peruvian Amazon. Along the Boiling River's course, geothermally heated water joins the river, gradually increasing water temperature and subsequently warming the surrounding forest. In the riparian forests along the Boiling River, mean annual and maximum air temperatures span gradients of 4°C and 11°C, respectively, over extremely short distances (< 1 km), with the hottest temperatures matching those predicted for much of the Amazon under future global warming scenarios. Using a new network of 70 woody plant inventory plots situated along the Boiling River's thermal gradient, we observed aca.11% decline in tree α‐diversity per 1°C increase in mean annual temperature. We also found that the tree communities growing under elevated temperatures were generally more thermophilic (i.e., included greater relative abundances of species from hotter parts of the Amazon) than the communities in cooler parts of the gradient. Based on patterns at the Boiling River, we hypothesize that global warming will lead to dramatic shifts in tree diversity and composition in the lowland Amazon, including local extinctions and biotic attrition. 

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4. Growing Degree-Day Measurement of Cyst Germination Rates in the Toxic Dinoflagellate Alexandrium catenella

   https://doi.org/10.1128/aem.02518-21  

   Fischer, Alexis D.; Brosnahan, Michael L. (June 2022, Applied and Environmental Microbiology)

   Rudi, Knut (Ed.)

   ABSTRACT Blooms of many dinoflagellates, including several harmful algal bloom (HAB) species, are seeded and revived through the germination of benthic resting cysts. Temperature is a key determinant of cysts’ germination rate, and temperature–germination rate relationships are therefore fundamental to understanding species’ germling cell production, cyst bed persistence, and resilience to climate warming. This study measured germination by cysts of the HAB dinoflagellate Alexandrium catenella using a growing degree-day ( DD ) approach that accounts for the time and intensity of warming above a critical temperature. Time courses of germination at different temperatures were fit to lognormal cumulative distribution functions for the estimation of the median days to germination. As temperature increased, germination times decreased hyperbolically. DD scaling collapsed variability in germination times between temperatures after cysts were oxygenated. A parallel experiment demonstrated stable temperature–rate relationships in cysts collected during different phases of seasonal temperature cycles in situ over three years. DD scaling of the results from prior A. catenella germination studies showed consistent differences between populations across a wide range of temperatures and suggests selective pressure for different germination rates. The DD model provides an elegant approach to quantify and compare the temperature dependency of germination among populations, between species, and in response to changing environmental conditions. IMPORTANCE Germination by benthic life history stages is the first step of bloom initiation in many, diverse phytoplankton species. This study outlines a growing degree-day ( DD ) approach for comparing the temperature dependence of germination rates measured in different populations. Germination by cysts of Alexandrium catenella , a harmful algal bloom dinoflagellate that causes paralytic shellfish poisoning, is shown to require a defined amount of warming, measured in DD after cysts are aerated. Scaling by DD , the time integral of temperature difference from a critical threshold, enabled direct comparison of rates measured at different temperatures and in different studies. 

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5. In Hot Water: Current Thermal Threshold Methods Unlikely to Predict Invasive Species Shifts in NW Atlantic

   Lancaster, E; Brady, D; Frederich, M (July 2024, Integrative & Comparative Biology)

   As global temperatures continue to rise, accurate predicted species distribution models will be important for forecasting the movement of range-shifting species. These predictions rely on measurements of organismal thermal tolerance, which can be measured using classical threshold concepts such as Arrhenius break temperatures and critical thermal temperatures, or through ecologically relevant measurements such as the temperature at which reproduction and growth occur. Many species, including invasive species, exhibit thermal plasticity, so these thresholds may change based on ambient temperature, life stage, and measurement techniques. Here, we review thermal thresholds for 15 invertebrate species invasive to the Gulf of Maine. The high degree of variability within a species and between applied conceptual frameworks suggests that modeling the future distribution of these species in all ecosystems, but especially in the rapidly warming northwest Atlantic and Gulf of Maine, will be challenging. While each of these measurement techniques is valid, we suggest contextualization and integration of threshold measurements for accurate modeling. 

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