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1. Thermal tolerance varies with dim‐light foraging and elevation in large carpenter bees (Hymenoptera: Apidae: Xylocopini)

   https://doi.org/10.1111/een.12842  

   Gonzalez, Victor H. ; Hranitz, John M. ; Percival, Catherine R. ; Pulley, Kristen L. ; Tapsak, Stephen T. ; Tscheulin, Thomas ; Petanidou, Theodora ; Barthell, John F. ( January 2020 , Ecological Entomology)

   1. Thermal tolerance has a strong predictive power for understanding the ecology and distribution of organisms, as well as their responses to changes in land use and global warming. However, relatively few studies have assessed thermal tolerances for bees.

   2. The present study aimed to determine whether the critical thermal maximum (CT_max) of carpenter bees (Apidae: genusXylocopaLatreille) varies with different patterns of foraging activity and elevation. In addition, the influence of body size, body water content and relative age was examined with respect to their CT_maxand differences in thoracic temperature (T_th) among species were evaluated.

   3. The CT_maxof one crepuscular (Xylocopaolivieri) and two diurnal species (XylocopaviolaceaandXylocopairis) of carpenter bees was assessed at sea level on the Greek island of Lesvos. To detect variation as a result of elevation, the CT_maxof a population ofX. violaceaat 625 m.a.s l. was assessed and compared with that from sea level.

   4.Xylocopa olivieridisplayed a similar CT_maxto that ofX. violaceabut lower than that ofX. iris. Body size, body water content, and relative age did not affect CT_max. InX. violacea, CT_maxdecreased with elevation and all three species have highT_thindependent of ambient temperatures.

   5. The results of the present study are consistent with variations in CT_maxpredicted by broad spatial and temporal patterns reported for other insects, including honey and bumble bees. The implications of the results are discussed aiming to understand the differences in the foraging pattern of these bees.

    

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2. Photosystem II heat tolerances characterize thermal generalists and the upper limit of carbon assimilation

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

   Perez, Timothy M. ; Socha, Annika ; Tserej, Olga ; Feeley, Kenneth J. ( January 2021 , Plant, Cell & Environment)

   The heat tolerance of photosystem II (PSII) may promote carbon assimilation at higher temperatures and help explain plant responses to climate change. Higher PSII heat tolerance could lead to (a) increases in the high‐temperature compensation point (T_max); (b) increases in the thermal breadth of photosynthesis (i.e. the photosynthetic parameter Ω) to promote a thermal generalist strategy of carbon assimilation; (c) increases in the optimum rate of carbon assimilation P_optand faster carbon assimilation and/or (d) increases in the optimum temperature for photosynthesis (T_opt). To address these hypotheses, we tested if the T_crit, T₅₀and T₉₅PSII heat tolerances were correlated with carbon assimilation parameters for 21 plant species. Our results did not support Hypothesis 1, but we observed that T₅₀may be used to estimate the upper thermal limit for T_maxat the species level, and that community mean T_critmay be useful for approximating T_max. The T₅₀and T₉₅heat tolerance metrics were positively correlated with Ω in support of Hypothesis 2. We found no support for Hypotheses 3 or 4. Our study shows that high PSII heat tolerance is unlikely to improve carbon assimilation at higher temperatures but may characterize thermal generalists with slow resource acquisition strategies.

    

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3. Trade‐offs between morphology and thermal niches mediate adaptation in response to competing selective pressures

   https://doi.org/10.1002/ece3.5990  

   Uiterwaal, Stella F. ; Lagerstrom, Ian T. ; Luhring, Thomas M. ; Salsbery, Miranda E. ; DeLong, John P. ( January 2020 , Ecology and Evolution)

   The effects of climate change—such as increased temperature variability and novel predators—rarely happen in isolation, but it is unclear how organisms cope with multiple stressors simultaneously. To explore this, we grew replicateParamecium caudatumpopulations in either constant or variable temperatures and exposed half to predation. We then fit thermal performance curves (TPCs) of intrinsic growth rate (r_max) for each replicate population (N = 12) across seven temperatures (10°C–38°C). TPCs ofP. caudatumexposed to both temperature variability and predation responded only to one or the other (but not both), resulting in unpredictable outcomes. These changes in TPCs were accompanied by changes in cell morphology. Although cell volume was conserved across treatments, cells became narrower in response to temperature variability and rounder in response to predation. Our findings suggest that predation and temperature variability produce conflicting pressures on both thermal performance and cell morphology. Lastly, we found a strong correlation between changes in cell morphology and TPC parameters in response to predation, suggesting that responses to opposing selective pressures could be constrained by trade‐offs. Our results shed new light on how environmental and ecological pressures interact to elicit changes in characteristics at both the individual and population levels. We further suggest that morphological responses to interactive environmental forces may modulate population‐level responses, making prediction of long‐term responses to environmental change challenging.

    

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4. Thermal niche variation among individuals of the poison frog, Oophaga pumilio , in forest and converted habitats

   https://doi.org/10.1111/btp.12691  

   Rivera‐Ordonez, Juana M. ; Justin Nowakowski, A. ; Manansala, Adrian ; Thompson, Michelle E. ; Todd, Brian D. ( August 2019 , Biotropica)

   The conversion of natural habitats to human land uses often increases local temperatures, creating novel thermal environments for species. The variable responses of ectotherms to habitat conversion, where some species decline while others persist, can partly be explained by variation among species in their thermal niches. However, few studies have examined thermal niche variation within species and across forest‐land use ecotones, information that could provide clues about the capacity of species to adapt to changing temperatures. Here, we quantify individual‐level variation in thermal traits of the tropical poison frog,Oophaga pumilio, in thermally contrasting habitats. Specifically, we examined local environmental temperatures, field body temperatures (T_b), preferred body temperatures (T_pref), critical thermal maxima (CT_max), and thermal safety margins (TSM) of individuals from warm, converted habitats and cool forests. We found that frogs from converted habitats exhibited greater meanT_bandT_prefthan those from forests. In contrast,CT_maxandTSMdid not differ significantly between habitats. However,CT_maxdid increase moderately with increasingT_b, suggesting that changes inCT_maxmay be driven by microscale temperature exposure within habitats rather than by mean habitat conditions. AlthoughO. pumilioexhibited moderate divergence inT_pref,CT_maxappears to be less labile between habitats, possibly due to the ability of frogs in converted habitats to maintain theirT_bbelow air temperatures that reach or exceedCT_max. Selective pressures on thermal tolerances may increase, however, with the loss of buffering microhabitats and increased frequency of extreme temperatures expected under future habitat degradation and climate warming.

   Abstract in Spanish is available with online material.

    

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5. Thermal traits predict the winners and losers under climate change: an example from North American ant communities

   https://doi.org/10.1002/ecs2.3645  

   Roeder, Karl A. ; Bujan, Jelena ; de Beurs, Kirsten M. ; Weiser, Michael D. ; Kaspari, Michael ( July 2021 , Ecosphere)

   Across the globe, temperatures are predicted to increase with consequences for many taxonomic groups. Arthropods are particularly at risk as temperature imposes physiological constraints on growth, survival, and reproduction. Given that arthropods may be disproportionately affected in a warmer climate—the question becomes which taxa are vulnerable and can we predict the supposed winners and losers of climate change? To address this question, we resurveyed 33 ant communities, quantifying 20‐yr differences in the incidence of 28 genera. Each North American ant community was surveyed with 30 1‐m²plots, and the incidence of each genus across the 30 plots was used to estimate change. From the original surveys in 1994–1997 to the resurveys in 2016–2017, temperature increased on average 1°C (range, −0.4°C to 2.5°C) and ~64% of ant genera increased in more than half of the sampled communities. To test Thermal Performance Theory's prediction that genera with higher average thermal limits will tend to accumulate at the expense of those with lower limits, we quantified critical thermal maxima (CT_max: the high temperatures at which they lose muscle control) and minima (CT_min: the low temperatures at which ants first become inactive) for common genera at each site. Consistent with prediction, we found a positive decelerating relationship between CT_maxand the proportion of sites in which a genus had increased. CT_min, by contrast, was not a useful predictor of change. There was a strong positive correlation (r = 0.85) between the proportion of sites where a genus was found with higher incidence after 20 yr and the average difference in number of plots occupied per site, suggesting genera with high CT_maxvalues tended to occupy more plots at more sites after 20 yr. Thermal functional traits like CT_maxhave thus proved useful in predicting patterns of long‐term community change in a dominant, diverse insect taxon.

    

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