Double trouble at high density::Cross-level test of ressource-related adaptive plasticity and crowding-related fitness.

Population size is often regulated by negative feedback between population density and individual fitness. At high population densities, animals run into double trouble: they might concurrently suffer from overexploitation of resources and also from negative interference among individuals regardless of resource availability, referred to as crowding. Animals are able to adapt to resource shortages by exhibiting a repertoire of life history and physiological plasticities. In addition to resource-related plasticity, crowding might lead to reduced fitness, with consequences for individual life history. We explored how different mechanisms behind resource-related plasticity and crowding-related fitness act independently or together, using the water flea Daphnia magna as a case study. For testing hypotheses related to mechanisms of plasticity and crowding stress across different biological levels, we used an individual-based population model that is based on dynamic energy budget theory. Each of the hypotheses, represented by a sub-model, is based on specific assumptions on how the uptake and allocation of energy are altered under conditions of resource shortage or crowding. For cross-level testing of different hypotheses, we explored how well the sub-models fit individual level data and also how well they predict population dynamics under different conditions of resource availability. Only operating resource-related and crowding-related hypotheses together enabled accurate model predictions of D. magna population dynamics and size structure. Whereas this study showed that various mechanisms might play a role in the negative feedback between population density and individual life history, it also indicated that different density levels might instigate the onset of the different mechanisms. This study provides an example of how the integration of dynamic energy budget theory and individual-based modelling can facilitate the exploration of mechanisms behind the regulation of population size. Such understanding is important for assessment, management and the conservation of populations and thereby biodiversity in ecosystems

Blood Protein Concentrations in the First Two Postnatal Weeks That Predict Bronchopulmonary Dysplasia Among Infants Born Before the 28th Week of Gestation

Lung inflammation contributes to the pathogenesis of bronchopulmonary dysplasia (BPD) and may be accompanied by a systematic inflammatory response. The objective of this study was to investigate the role of systemic inflammation in the development of BPD in a cohort of extremely low gestational age newborns (ELGANs) by examining the relationships between inflammation-associated proteins in neonatal blood samples and pulmonary outcomes. Proteins were measured in blood specimens collected on postnatal days 1–3, 5–8 and 12–15 from 932 ELGANs. Increased risk of BPD was associated with elevated blood concentrations of a variety of pro-inflammatory cytokines, adhesion molecules and proteases. Reduced risk was prominently associated with increased concentrations of one chemokine, RANTES. Elevations of inflammatory proteins associated with BPD risk occurred during the first days following birth, and inflammation intensified thereafter. Therefore, exposures that promote inflammation after the first postnatal days may be more critical in the pathogenesis of BPD. Fetal growth restriction, a known BPD risk factor, was not accompanied by proteins elevations and therefore does not appear to be mediated by systemic inflammation. By contrast, mechanical ventilation altered protein levels and may be associated with systemic inflammation