RESUMEN
Using diffusion processes, I model stochastic individual growth, given exogenous hazards and starvation risk. By maximizing survival to final size, optimal life histories (e.g. switching size for habitat/dietary shift) are determined by two ratios: mean growth rate over growth variance (diffusion coefficient) and mortality rate over mean growth rate; all are size dependent. For example, switching size decreases with either ratio, if both are positive. I provide examples and compare with previous work on risk-sensitive foraging and the energy-predation trade-off. I then decompose individual size into reversibly and irreversibly growing components, e.g. reserves and structure. I provide a general expression for optimal structural growth, when reserves grow stochastically. I conclude that increased growth variance of reserves delays structural growth (raises threshold size for its commencement) but may eventually lead to larger structures. The effect depends on whether the structural trait is related to foraging or defence. Implications for population dynamics are discussed.
Asunto(s)
Metabolismo Energético , Crecimiento y Desarrollo , Modelos Biológicos , Ecosistema , Dinámica Poblacional , Modelos de Riesgos Proporcionales , Inanición , Procesos EstocásticosRESUMEN
We performed a transplant experiment to compare the life histories and morphologies of five geographically representative antlion Myrmeleon hyalinus populations along a sharp climatic gradient, from a Mediterranean climate in Israel's north to a desert climate in the south. Larvae were raised in two environmental chambers simulating Mediterranean and desert climates to investigate the extent to which the different populations exhibit phenotypic plasticity. Along the north-to-south climatic gradient, we observed a gradient in body mass prior to pupation and in pupation rate. Mediterranean populations suffered higher mortality rate when exposed to desert conditions, whereas the mortality rate of desert populations was consistent between Mediterranean and desert conditions. Our results regarding body mass, pupation rate and mortality rate suggest that Mediterranean populations had a more flexible response compared with desert populations. An analysis of digital photographs was used to measure population morphological differences, which were usually indicative of a decrease in trait size along the north-to-south gradient. We show how climatic gradients translate into phenotypic differences in an antlion population and provide a morphometric tool to distinguish between instar stages.
Asunto(s)
Clima Desértico , Insectos/crecimiento & desarrollo , Metamorfosis Biológica/fisiología , Animales , Biometría , Tamaño Corporal/fisiología , Insectos/anatomía & histología , Insectos/fisiología , Larva/anatomía & histología , Larva/crecimiento & desarrollo , Larva/fisiología , Estaciones del Año , TemperaturaRESUMEN
Polycythemia vera (PV) is a myeloproliferative disorder characterized by thrombotic and, less often, bleeding complications. Many mechanisms have been advanced to explain the occurrence of these complications, none of them satisfactory. We examined a cohort of 27 patients with PV, secondary erythrocytosis, and essential thrombocythemia for coagulation and fibrinolytic parameters, including euglobulin lysis test, D-dimer, and alpha2 antiplasmin. Ten of the 27 patients developed one or more thrombotic complications during the study. We found no clinical correlation between the studied parameters and the complications. Three patients, one of each group, with elevated serum alpha2 antiplasmin levels, developed severe arterial or venous thromboses.