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1. Thermal Plasticity Changes Competitive Ability Across a Woodland Salamander Hybrid System

   https://doi.org/10.1111/eth.13552  

   James, Emmy; Muñoz, Martha M (February 2025, Ethology)

   ABSTRACT Temperature mediates performance in ectotherms, affecting their ability to grow, survive, and reproduce. Aggression and evasion are key examples of thermally dependent behaviors that can impact fitness. However, we know relatively little about how the thermal plasticity of such behaviors varies among close relatives and impacts competitive outcomes. Woodland salamanders (Genus:Plethodon) from the Appalachian Mountains are distributed across wide thermal gradients in accordance with latitude or elevation. These plethodontid (lungless) salamanders compete for space and develop hybrid zones where territories overlap among species. Plethodontids tend to exhibit increased aggression at warmer temperatures, suggesting that as temperatures rise, behavioral interactions may be altered in ways that impact hybrid zone dynamics. It is thus far unclear, however, how salamander hybrids, which may encroach on their parent populations and drive competitive exclusion, respond behaviorally to warming. Here, we used staged bouts to examine the effects of temperature on aggression and evasion in thePlethodon shermaniandPlethodon teyahaleehybrid system from the southern Appalachians. The behavior of salamanders from parent populations, particularlyP. shermani,appears to be more sensitive to thermal changes than that of hybrid individuals. Additionally, evasive behavior was significantly more plastic than aggressive behavior in response to warming. Our results suggest that rising temperatures may increase competition for preferable microhabitats, but the effects on behavior among parental and hybrid salamanders will be asymmetric. Temperature may therefore alter the outcomes of competition, determining which populations can persist under rapid warming. 

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2. Live fuel moisture and water potential exhibit differing relationships with leaf‐level flammability thresholds

   https://doi.org/10.1111/1365-2435.14423  

   Boving, Indra; Celebrezze, Joe; Salladay, Ryan; Ramirez, Aaron; Anderegg, Leander_D L; Moritz, Max (November 2023, Functional Ecology)

   Abstract In semi‐arid regions where drought and wildfire events often co‐occur, such as in Southern California chaparral, relationships between plant hydration, drought‐ and fire‐adapted traits may explain landscape‐scale wildfire dynamics. To examine these patterns, fire scientists and plant physiologists quantify hydration in plants via mass‐based metrics of water content, including live fuel moisture, or pressure‐based metrics of physiological status, such as xylem water potential; however, relationships across these metrics, plant traits and flammability remain unresolved.To determine the impact of hydration on tissue‐level flammability (leaves and stems), we conducted laboratory dehydration tests across wet and dry seasons in which we simultaneously measured xylem water potential, live fuel moisture and flammability. We tested two widespread chaparral shrubs,Adenostoma fasciculatumandCeanothus megacarpus.Live fuel moisture showed a threshold‐type relationship with tissue flammability (increased ignitability and combustibility at specific hydration levels) that aligned with drought‐response traits (turgor loss point) and fire behaviour (increased fire likelihood and spread) identified at the landscape scale. Water potential was the better predictor of flammability in linear statistical models.A. fasciculatumwas more flammable thanC. megacarpus, and both species were more flammable during the wet growing season, suggesting seasonal growth or drought‐related tissue characteristics other than moisture content, such as lignin or chemical content, are critical for determining flammability.Our results suggest a mechanism for landscape‐scale increases in flammability at specific levels of drought stress. Integration of drought‐related traits, such as the turgor loss point, might improve models of wildfire risk in drought‐ and fire‐prone systems. Read the freePlain Language Summaryfor this article on the Journal blog. 

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3. Stem and leaf xylem of angiosperm trees experiences minimal embolism in temperate forests during two consecutive summers with moderate drought

   https://doi.org/10.1111/plb.13384  

   Guan, X.; Werner, J.; Cao, K.‐F.; Pereira, L.; Kaack, L.; McAdam, S. A.; Jansen, S. (December 2022, Plant Biology)

   Abstract Drought events may increase the likelihood that the plant water transport system becomes interrupted by embolism. Yet our knowledge about the temporal frequency of xylem embolism in the field is frequently lacking, as it requires detailed, long‐term measurements.We measured xylem embolism resistance and midday xylem water potentials during the consecutive summers of 2019 and 2020 to estimate maximum levels of embolism in leaf and stem xylem of ten temperate angiosperm tree species. We also studied vessel and pit membrane characteristics based on light and electron microscopy to corroborate potential differences in embolism resistance between leaves and stems.Apart fromA.pseudoplatanusandQ.petraea, eight species experienced minimum xylem water potentials that were close to or below those required to initiate embolism. Water potentials corresponding to ca. 12% loss of hydraulic conductivity (PLC) could occur in six species, while considerable levels of embolism around 50% PLC were limited toB.pendulaandC.avellana. There was a general agreement in embolism resistance between stems and leaves, with leaves being equally or more resistant than stems. Also, xylem embolism resistance was significantly correlated to intervessel pit membrane thickness (T_PM) for stems, but not to vessel diameter and total intervessel pit membrane surface area of a vessel.Our data indicate that low amounts of embolism occur in most species during moderate summer drought, and that considerable levels of embolism are uncommon. Moreover, our experimental andT_PMdata show that leaf xylem is generally no more vulnerable than stem xylem. 

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4. Heat alters diverse thermal tolerance mechanisms: An organismal framework for studying climate change effects in a wild bird

   https://doi.org/10.1111/1365-2435.14704  

   Woodruff, Mary J; Tsueda, Susanna N; Cutrell, Tiernan S; Guardado, Ethan A; Rusch, Douglas B; Buechlein, Aaron; Rosvall, Kimberly A (January 2025, Functional Ecology)

   Abstract The ability to cope with heat is likely to influence species success amidst climate change. However, heat coping mechanisms are poorly understood in wild endotherms, which are increasingly pushed to their thermoregulatory limits.We take an organismal approach to this problem, unveiling how behavioural and physiological responses may allow success in the face of sublethal heat. We experimentally elevated nest temperatures for 4 h to mimic a future climate scenario (+4.5°C) during a critical period of post‐natal development in tree swallows (Tachycineta bicolor).Heat‐exposed nestlings exhibited marked changes in behaviour, including movement to cooler microclimates in the nest. They panted more and weighed less than controls at the end of the four‐hour heat challenge, suggesting panting‐induced water loss. Physiologically, heat induced high levels of heat shock protein (HSP) gene expression in the blood, alongside widespread transcriptional differences related to antioxidant defences, inflammation and apoptosis.Critically, all nestlings survived the heat challenge, and those exposed to milder heat weremorelikely to recruit into the breeding population. Early life but sub‐lethal heat may therefore act as a selective event, with the potential to shape population trajectories.Within the population, individuals varied in their physiological response to heat, namely in HSP gene expression, which exhibited higher mean and higher variance in heat‐exposed nestlings than in controls. Heat‐induced HSP levels were unrelated to individual body mass, or among‐nest differences in brood size, temperature, and behavioural thermoregulation. Nest identity explained a significant amount of HSP variation, yet siblings in the same nest differed by an average of ~4‐fold and individuals in the population differed by as much as ~100‐fold in their HSP response. This massive variation extends previous laboratory work in model organisms showing that heat shock proteins may harbour cryptic phenotypic variation.These results shed light on oft‐ignored elements of thermotolerance in wild birds at a critical stage of post‐natal development. By highlighting the scope of heat‐induced HSP gene expression and coupling it with a suite of organismal traits, we provide a framework for future testing of the mechanisms that shape species success in the face of change. Read the freePlain Language Summaryfor this article on the Journal blog. 

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5. Drought‐tolerant grassland species are generally more resistant to competition

   https://doi.org/10.1111/1365-2745.14243  

   Mount, Hailey E.; Smith, Melinda D.; Knapp, Alan K.; Griffin‐Nolan, Robert J.; Collins, Scott L.; Atkins, David H.; Stears, Alice E.; Laughlin, Daniel C. (February 2024, Journal of Ecology)

   Abstract Plant populations are limited by resource availability and exhibit physiological trade‐offs in resource acquisition strategies. These trade‐offs may constrain the ability of populations to exhibit fast growth rates under water limitation and high cover of neighbours. However, traits that confer drought tolerance may also confer resistance to competition. It remains unclear how fitness responses to these abiotic conditions and biotic interactions combine to structure grassland communities and how this relationship may change along a gradient of water availability.To address these knowledge gaps, we estimated the low‐density growth rates of populations in drought conditions with low neighbour cover and in ambient conditions with average neighbour cover for 82 species in six grassland communities across the Central Plains and Southwestern United States. We assessed the relationship between population tolerance to drought and resistance to competition and determined if this relationship was consistent across a precipitation gradient. We also tested whether population growth rates could be predicted using plant functional traits.Across six sites, we observed a positive correlation between low‐density population growth rates in drought and in the presence of interspecific neighbours. This positive relationship was particularly strong in the grasslands of the northern Great Plains but weak in the most xeric grasslands. High leaf dry matter content and a low (more negative) leaf turgor loss point were associated with high population growth rates in drought and with neighbours in most grassland communities.Synthesis: A better understanding of how both biotic and abiotic factors impact population fitness provides valuable insights into how grasslands will respond to extreme drought. Our results advance plant strategy theory by suggesting that drought tolerance increases population resistance to interspecific competition in grassland communities. However, this relationship is not evident in the driest grasslands, where above‐ground competition is likely less important. Leaf dry matter content and turgor loss point may help predict which populations will establish and persist based on local water availability and neighbour cover, and these predictions can be used to guide the conservation and restoration of biodiversity in grasslands. 

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