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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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Individual habitat specialization of a successful species

Individual habitat specialization of a successful species

Population expansions of successful species have gained importance as a major conservation and management concern. The success of these ‘winners' is widely attributed to their high adaptability and behavioural plasticity, which allow them to efficiently use opportunities provided by human-modified habitats. However, most of these studies consider conspecifics as ecological equivalents, without considering the individual components within populations. This is critical for a better understanding of the main ecological mechanisms related to the success of winning species. Here, the spatial ecology of the opportunistic yellow-legged gull Larus michahellis, a clear example of a winning species in southern Europe, is investigated to examine its degree of individual specialization in habitat use. To test for such individual strategies, specialization metrics is applied to spatial data obtained from 18 yellow-legged gulls that were GPS-tracked simultaneously during the breeding season. The results revealed that population-level generalism in habitat use in the yellow-legged gull arises through varying levels of individual specialization, and individual spatial segregation within each habitat. Importantly, the combination of individual specialization and individual spatial segregation may reduce intra-specific competition, with these 2 important mechanisms driving the success of this winning species. informacion[at] Navarro et al (2017) Shifting individual habitat specialization of a successful predator living in anthropogenic landscapes. Mar Ecol Prog Ser variability in seabird foraging and migration/av5