RESUMEN
Future changes in climate, together with rising atmospheric CO 2 ${\text{CO}}_{2}$ , may reorganise the functional composition of ecosystems. Without long-term historical data, predicting how traits will respond to environmental conditions-in particular, water availability-remains a challenge. While eco-evolutionary optimality theory (EEO) can provide insight into how plants adapt to their environment, EEO approaches to date have been formulated on the assumption that plants maximise carbon gain, which omits the important role of tissue construction and size in determining growth rates and fitness. Here, we show how an expanded optimisation framework, focussed on individual growth rate, enables us to explain shifts in four key traits: leaf mass per area, sapwood area to leaf area ratio (Huber value), wood density and sapwood-specific conductivity in response to soil moisture, atmospheric aridity, CO 2 ${\text{CO}}_{2}$ and light availability. In particular, we predict that as conditions become increasingly dry, height-growth optimising traits shift from resource-acquisitive strategies to resource-conservative strategies, consistent with empirical responses across current environmental gradients of rainfall. These findings can explain both the shift in traits and turnover of species along existing environmental gradients and changing future conditions and highlight the importance of both carbon assimilation and tissue construction in shaping the functional composition of vegetation across climates.
RESUMEN
Pesticides are increasingly recognised as a threat to freshwater biodiversity, but their specific ecological effects remain difficult to distinguish from those of co-occurring stressors and environmental gradients. Using mesocosms we examined the effects of an organophosphate insecticide (malathion) on stream macroinvertebrate communities concurrently exposed to a suite of stressors typical of streams in agricultural catchments. We assessed the specificity of the SPEcies At Risk index designed to determine pesticide effects in mesocosm trials (SPEARmesocosm). This index determines the log abundance proportion of taxa that are considered physiologically sensitive to pesticides. Geographic variation in pesticide sensitivity within taxa, coupled with variation between pesticides and the effects of co-occurring stressors may decrease the accuracy of SPEARmesocosm. To examine this, we used local pesticide sensitivity assessments based on rapid toxicity tests to develop two new SPEAR versions to compare to the original SPEARmesocosms index using mesocosm results. We further compared these results to multivariate analyses and community indices (e.g. richness, abundance, Simpson's diversity) commonly used to assess stressor effects on biota. To assess the implications of misclassifying species sensitivity on SPEAR indices we used a series of simulations using artificial data. The impacts of malathion were detectable using SPEARmesocosm, and one of two new SPEAR indices. All three of the SPEAR indices also increased when exposed to other agricultural non-pesticide stressors, and this change increased with greater pesticide concentrations. Our results support that interactions between other non-pesticide stressors with pesticides can affect SPEAR performance. Multivariate analysis and the other indices used here identified a significant effect of malathion especially at high concentrations, with little or no evidence of effects from the other agricultural stressors.
Asunto(s)
Plaguicidas , Contaminantes Químicos del Agua , Animales , Ecosistema , Monitoreo del Ambiente , Invertebrados , Plaguicidas/análisis , Plaguicidas/toxicidad , Ríos , Contaminantes Químicos del Agua/análisis , Contaminantes Químicos del Agua/toxicidadRESUMEN
BACKGROUND AND OBJECTIVE: Oxygen is used in many clinical scenarios, however the variable performance of nasal cannulae makes determining the precise fraction of inspired oxygen (FiO2 ) difficult. We developed a novel method for measurement of the tracheal FiO2 using a catheter placed via bronchoscopy. We investigate the effects of oxygen delivery, respiratory rate, mouth position and estimated minute ventilation (VE ) on the FiO2 delivered by nasal cannulae. METHODS: The catheter was placed in 20 subjects. Tracheal gas concentrations were analysed during six 5-min treatments controlling for oxygen delivery rate, respiratory rate and mouth position. Ventilation was monitored with respiratory inductive plethysmography (RIP). The FiO2 delivered by nasal cannulae was compared between treatments, and we investigated the relationships among the FiO2 , alveolar partial pressure of oxygen (PA O2 ) and VE . RESULTS: The FiO2 increased by 0.038/L/min of oxygen. Respiratory rate had a significant effect on the FiO2 . A normal respiratory rate of 15 breaths/min and oxygen supplementation via nasal cannula at 2 L/min resulted in an FiO2 of 0.296; however, FiO2 decreased by 0.012 at 20 breaths/min and 0.004 at 10 breaths/min. The mean FiO2 decreased by 0.024 with the mouth open. The FiO2 and PA O2 were observed to decrease with increasing VE . CONCLUSIONS: Continuous measurement of the FiO2 using a transtracheal catheter provides detailed insight into inspiratory changes of the FiO2 delivered by nasal cannulae. Our study confirms that respiratory rate, VE and mouth position significantly influence the inspired oxygen concentration. These parameters should be accounted for when prescribing oxygen.