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1. 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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2. 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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3. Bryophytes in fir waves: Forest canopy indicator species and functional diversity decline in canopy gaps

   https://doi.org/10.1111/jvs.12718  

   Berdugo, Monica B. ; Dovciak, Martin ; Nakashizuka, ed., Tohru ( March 2019 , Journal of Vegetation Science)

   Bryophytes can cover three quarters of the ground surface, play key ecological functions, and increase biodiversity in mesic high‐elevation conifer forests of the temperate zone. Forest gaps affect species coexistence (and ecosystem functions) as suggested by the gap and gap‐size partitioning hypotheses (GPH,G_SPH). Here we test these hypotheses in the context of high‐elevation forest bryophyte communities and their functional attributes.

   Spruce–fir forests on Whiteface Mountain, NY,USA.

   We characterized canopy openness, microclimate, forest floor substrates, vascular vegetation cover, and moss layer (cover, common species, and functional attributes) in three canopy openness environments (gap, gap edge, forest canopy) across 20 gaps (fir waves) (n = 60); the functional attributes were based on 16 morphologic, reproductive, and ecological bryophyte plant functional traits (PFTs). We testedGPHandG_SPHrelative to bryophyte community metrics (cover, composition), traits, and trait functional sensitivity (functional dispersion;FDis) using indicator species analysis, ordination, and regression.

   Canopy openness drove gradients in ground‐level temperature, substrate abundance and heterogeneity (beta diversity), and understory vascular vegetation cover. TheGPHwas consistent with (a) the abundance patterns of forest canopy indicator species (Dicranum fuscescens,Hypnum imponens, andTetraphis pellucida), and (b)FDisbased on threePFTs (growth form, fertility, and acidity), both increasing with canopy cover. We did not find support forGPHin the remaining species or traits, or forG_SPHin general; gap width (12–44 m) was not related to environmental or bryophyte community gradients.

   The observed lack of variation in most bryophyte metrics across canopy environments suggests high resistance of the bryophyte layer to natural canopy gaps in high‐elevation forests. However, responses of forest canopy indicator species suggest that canopy mortality, potentially increased by changing climate or insect pests, may cause declines in some forest canopy species and consequently in the functional diversity of bryophyte communities.

    

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4. Vascular epiphytes show low physiological resistance and high recovery capacity to episodic, short‐term drought in Monteverde, Costa Rica

   https://doi.org/10.1111/1365-2435.13613  

   Williams, Cameron B. ; Murray, Jessica G. ; Glunk, Andrew ; Dawson, Todd E. ; Nadkarni, Nalini M. ; Gotsch, Sybil G. ; Oliveira, ed., Rafael ( July 2020 , Functional Ecology)

   Tropical montane cloud forests support abundant epiphytic vascular plant communities that serve important ecosystem functions, but their reliance on atmospheric inputs of water may make them susceptible to the drying effects of rising cloud bases and more frequent droughts.

   We conducted a common garden experiment to explore the combined effects of decreasing cloud influence—lower humidity, warmer temperature, brighter light—and meteorological drought (i.e. absence of rain) on the physiology and morphology of vascular epiphytes native to primary forests of Monteverde, Costa Rica. The epiphytes, which exhibited C₃photosynthesis, were sourced from a lower montane cloud forest (CF) or a rainforest (RF) below the current cloud base and transplanted into nearby shadehouses (CF or RF shadehouse respectively). Vapour pressure deficit (VPD) and light availability, measured as photosynthetically active radiation, were 2.5 and 3.1 times higher in the RF than the CF shadehouse. Half of the plants were subjected to a severe 4‐week drought followed by a recovery period, and the other half were watered controls.

   Plants subjected to low VPD/light conditions of the CF shadehouse were physiologically and morphologically resistant to the drought treatment. However, compared to control plants, both sources of plants subjected to high VPD/light conditions of the RF shadehouse experienced declines in maximum net photosynthesis (A_max), stomatal conductance (g_s) and the proportion of healthy leaves (those not exhibiting chlorosis, desiccation or necrosis). At peak drought, leaves from the RF were 19% thinner than controls. Within 7–14 days after rewatering,A_max,g_sand leaf health recovered to nearly the levels of controls. Growth rate, mortality and phenology were unaffected by the treatments.

   The divergent responses to drought in the CF versus RF shadehouses, combined with the recovery in the RF shadehouse, indicate that these epiphytes possess adaptive properties that confer low resistance, but high recovery capacity, to episodes of short‐term drought over a range of cloud influence. In addition, the reduction inA_maxsuggests stomatal regulation that favours water conservation over carbon acquisition, a strategy that may inform epiphyte responses to rising clouds and increasing drought frequency expected in the long term.

   A freePlain Language Summarycan be found within the Supporting Information of this article.

    

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5. High Heterogeneity in Canopy Temperature Among Co‐occurring Tree Species in a Temperate Forest

   https://doi.org/10.1029/2020JG005892  

   Yi, Koong ; Smith, Jake W. ; Jablonski, Andrew D. ; Tatham, Elizabeth A. ; Scanlon, Todd M. ; Lerdau, Manuel T. ; Novick, Kimberly A. ; Yang, Xi ( December 2020 , Journal of Geophysical Research: Biogeosciences)

   Trees regulate canopy temperature (T_c) via transpiration to maintain an optimal temperature range. In diverse forests such as those of the eastern United States, the sensitivity ofT_cto changing environmental conditions may differ across species, reflecting wide variability in hydraulic traits. However, these links are not well understood in mature forests, whereT_cdata have historically been difficult to obtain. Recent advancement of thermal imaging cameras (TICs) enablesT_cmeasurement of previously inaccessible tall trees. By leveraging TIC and sap flux measurements, we investigated how co‐occurring trees (Quercus alba,Q. falcata, andPinus virginiana) change theirT_cand vapor pressure deficit near the canopy surface (VPD_c) in response to changing air temperature (T_a) and atmospheric VPD (VPD_a). We found a weaker cooling effect for the species that most strongly regulates stomatal function during dry conditions (isohydric;P. virginiana). Specifically, the pine had higherT_c(up to 1.3°C) and VPD_c(up to 0.3 kPa) in the afternoon and smaller sensitivity of both∆T(=T_c − T_a) and∆VPD (=VPD_c − VPD_a) to changing conditions. Furthermore, significant differences inT_cand VPD_cbetween sunlit and shaded portions of a canopy implied a non‐evaporative effect onT_cregulation. Specifically,T_cwas more homogeneous within the pine canopy, reflecting differences in leaf morphology that allow higher canopy transmittance of solar radiation. The variability ofT_camong species (up to 1.3°C) was comparable to the previously reported differences in surface temperature across land cover types (1°C to 2°C), implying the potential for significant impact of species composition change on local/regional surface temperature.

    

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