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Strategies shrubby junipers adopt to tolerate drought differ by site

Drought-induced dieback episodes are globally reported among forest ecosystems but they have been understudied in scrublands. Chronically-stressed individuals are supposed to be more vulnerable prior to drought which triggers death. Drought-triggered dieback and mortality events affecting Mediterranean Juniperus phoenicea scrublands were analyzed in two sites with contrasting climate and soil conditions located in Spain. The radial growth patterns of coexisting living and dead junipers, including the calculation of growth statistics used as early-warning signals, quantified growth response to climate, were characterized and the wood C and O isotope discrimination was analyzed. In the inland, continental site with rocky substrates (Yaso, Huesca, N Spain), dead junipers grew less than living junipers about three decades prior to the dieback started in 2016. However, in the coastal, mild site with sandy soils (Doñana, Huelva, SW Spain), dead junipers were smaller but grew more than living junipers about two decades before the dieback onset in 2005. The only common patterns between sites were the higher growth coherence in both living and dead junipers prior to the dieback, and the decrease in growth persistence of dead junipers. Cool and wet conditions in the prior winter and current spring, and cool summer conditions enhanced juniper growth. In Doñana, growth of living individuals was more reduced by warm July conditions than in the case of dead individuals. Higher ?13C values in Yaso indicate also more pronounced drought stress. In Yaso, dead junipers presented lower ?18O values, but the opposite occurred in Doñana suggesting different changes in stomatal conductance prior to death. Warm summer conditions enhance evapotranspiration rates and trigger dieback in this shallow-rooted species, particularly in sites with a poor water-holding capacity. Chronic, slow growth is not always a reliable predictor of drought-triggered mortality. informacion[at] Camarero et al (2020) Dieback and mortality of junipers caused by drought: Dissimilar growth and wood isotope patterns preceding shrub death. Agr Forest Meteorol 291, 108078. DOI 10.1016/j.agrformet.2020.108078
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Predictors of pollinator service

Predictors of pollinator service

Pollinator service is essential for successful sexual reproduction and long-term population persistence of animal-pollinated plants, and innumerable studies have shown that insufficient service by pollinators results in impaired sexual reproduction ("pollen limitation"). Studies directly addressing the predictors of variation in pollinator service across species or habitats remain comparatively scarce, which limits our understanding of the primary causes of natural variation in pollen limitation. This paper evaluates the importance of pollination-related features, evolutionary history and environment as predictors of pollinator service in a large sample of plant species from undisturbed montane habitats in southeastern Spain. Quantitative data on pollinator visitation were obtained for 191 insect-pollinated species belonging to 142 genera in 43 families, and the predictive values of simple floral traits (perianth type, class of pollinator visitation unit, and visitation unit dry mass), phylogeny, and habitat type were assessed. A total of 24,866 pollinator censuses accounting for 5,414,856 flower-min of observation were conducted on 510 different dates. Flowering patch and single flower visitation probabilities by all pollinators combined were significantly predicted by the combined effects of perianth type (open vs. restricted), class of visitation unit (single flower vs. flower packet), mass of visitation unit, phylogenetic relationships, and habitat type. Pollinator composition at insect order level varied extensively among plant species, largely reflecting the contrasting visitation responses of Coleoptera (beetles), Diptera (flies), Hymenoptera (bees) and Lepidoptera (butterflies) to variation in floral traits. For example, Lepidoptera responded positively to increasing mass of visitation unit in species with flowers packets, but negatively in species with single flowers and restrictive perianths. Pollinator composition had a strong phylogenetic component, and the distribution of phylogenetic autocorrelation hotspots of visitation rates across the plant phylogeny differed widely among insect orders. Habitat type was a key predictor of pollinator composition, as major insect orders exhibited decoupled variation across habitat types in visitation rates. Comprehensive pollinator sampling of a regional plant community has shown that pollinator visitation and composition can be parsimoniously predicted by a combination of simple floral features, habitat type and evolutionary history. Ambitious community-level studies can help to formulate novel hypotheses and questions, shed fresh light on long-standing controversies in pollination research (e.g., "pollination syndromes"), and identify methodological cautions that should be considered in pollination community studies dealing with small, phylogenetically-biased plant species samples. informacion[at] Herrera (2019) Flower traits, habitat, and phylogeny as predictors of pollinator service: a plant community perspective. Ecol Monographs DOI 10.1002/ecm.1402