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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]ebd.csic.es: 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


https://www.sciencedirect.com/science/article/pii/S0168192320301805?dgcid=author#ack0001
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Lifelong effects of trapping experience

Lifelong effects of trapping experience

Long-term monitoring of individually marked animals is usually required for reliable estimation of numerous life history parameters. However, capture, marking and manipulation can dramatically alter the animals' behaviour after capture, and thus affect subsequent recapture success. Here, a pied flycatcher population was used as an example to illustrate the sampling bias resulting from the repeated capture of free-ranging individuals. By using repeated measures of the same individuals obtained during our long-term survey, the interannual response of breeding adults to capture-related stress was specifically evaluated, measured as latency to enter nestboxes equipped with a swing-trap. Moreover, the changes in the mean and variance of bird age with varying trapping effort were examined using subsamples of the data set. Birds without any previous trapping experience entered nests more quickly than experienced ones, after controlling for other factors affecting latency, such as the sex, offspring quality and the order of capture relative to the other pair member. Birds' reluctance to enter the nest furthermore increased as the number of captures in previous years accumulated, implying that individual pied flycatchers became progressively more difficult to capture over the course of the study. These results indicate that repeated exposure to capture stress over an animal's lifetime may induce long-lasting behavioural modifications that may influence trappability of the older segments of the population. This may ultimately lead to sampling bias towards younger ages, especially when effort is limited. The study concludes that systematic age bias due to trapping experience can have important implications for the estimation of variation in a range of traits and should therefore be carefully checked in longitudinal studies. informacion[at]ebd.csic.es: Camacho et al (2017) Lifelong effects of trapping experience lead to age-biased sampling: lessons from a wild bird population.


http://www.sciencedirect.com/science/article/pii/S0003347217301938