Herbivores are generally faced with a plethora of resources which differ in quality. Therefore, they should be able to select foods which most closely match their metabolic needs. Here, we tested the ...hypothesis that copepods of the species Acartia tonsa select prey cells based on quality differences within prey species. We assessed age‐specific variation in feeding behaviour and evaluated the potential consequences of such variation for nutrient cycles. Nauplii (young) stages characterized by a low nitrogen to phosphorus (N:P) ratio in their body tissue selected for phosphorus‐rich food, while older copepodite stages with higher body N:P selected for nitrogen‐rich food. Further, the analysis of a 35‐year data set in the southern North Sea revealed a positive correlation between the abundance of nauplii and the ratio of dissolved inorganic N:P, thus suggesting that P‐availability for primary producers declines with the population densities of nauplii. Our findings demonstrate that a combination of stage‐specific selective feeding and body stoichiometry has the potential to affect cycling of limiting nutrients when consumer populations change in composition.
Stoichiometric homeostasis is the ability of an organism to keep its body chemical composition constant, despite varying inputs. Stoichiometric homeostasis therefore constrains the metabolic needs of ...consumers which in turn often feed on resources not matching these requirements. In a broader context, homeostasis also relates to the capacity of an organism to maintain other biological parameters (e.g. body temperature) at a constant level over ambient environmental variations. Unfortunately, there are discrepancies in the literature and ecological and physiological definitions of homeostasis are disparate and partly contradictory. Here, we address this matter by reviewing the existing knowledge considering two distinct groups, regulators and conformers and, based on examples of thermo- and osmoregulation, we propose a new approach to stoichiometric homeostasis, unifying ecological and physiological concepts. We suggest a simple and precise graphical way to identify regulators and conformers: for any given biological parameter (e.g. nutrient stoichiometry, temperature), a sigmoidal relation between internal and external conditions can be observed for conformers while an inverse sigmoidal response is characteristic of regulators. This new definition and method, based on well-studied physiological mechanisms, unifies ecological and physiological approaches and is a useful tool for understanding how organisms are affected by and affect their environment.
Increased reactive nitrogen (Nᵣ) deposition has raised the amount of N available to organisms and has greatly altered the transfer of energy through food webs, with major consequences for trophic ...dynamics. The aim of this review was to: (i) clarify the direct and indirect effects of Nᵣ deposition on forest and lake food webs in N‐limited biomes, (ii) compare and contrast how aquatic and terrestrial systems respond to increased Nᵣ deposition, and (iii) identify how the nutrient pathways within and between ecosystems change in response to Nᵣ deposition. We present that Nᵣ deposition releases primary producers from N limitation in both forest and lake ecosystems and raises plants' N content which in turn benefits herbivores with high N requirements. Such trophic effects are coupled with a general decrease in biodiversity caused by different N‐use efficiencies; slow‐growing species with low rates of N turnover are replaced by fast‐growing species with high rates of N turnover. In contrast, Nᵣ deposition diminishes below‐ground production in forests, due to a range of mechanisms that reduce microbial biomass, and decreases lake benthic productivity by switching herbivore growth from N to phosphorus (P) limitation, and by intensifying P limitation of benthic fish. The flow of nutrients between ecosystems is expected to change with increasing Nᵣ deposition. Due to higher litter production and more intense precipitation, more terrestrial matter will enter lakes. This will benefit bacteria and will in turn boost the microbial food web. Additionally, Nᵣ deposition promotes emergent insects, which subsidize the terrestrial food web as prey for insectivores or by dying and decomposing on land. So far, most studies have examined Nᵣ‐deposition effects on the food web base, whereas our review highlights that changes at the base of food webs substantially impact higher trophic levels and therefore food web structure and functioning.
Les coups de soleil pendant l’enfance et l’adolescence sont des facteurs de risque du mélanome. La prévention primaire repose sur la photoprotection de l’enfant et de l’adolescent. Les principales ...mesures comportent l’éviction solaire, la pratique des activités d’extérieur en dehors des heures d’exposition maximale, l’utilisation de vêtements photoprotecteurs et de produits de protection solaire (PPS) offrant une protection efficace contre les UVB et les UVA.
Sunburns during childhood and intense intermittent sun exposure have been shown to increase the risk of melanoma. Primary prevention of skin cancers stresses the need to practice routine sun-protection behaviors by teenagers and children. Recommended sun safety practices include sun avoidance or limiting outdoor activities in the middle of the day, use of shade for sun protection, wearing of sun-protective clothing and use of sunscreens that efficiently protect from UVB and UVA radiations.
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