Effects Of Latitudinal Variation Research Articles

Effects of latitudinal variation on field and common garden comparisons between native and introduced groundsel (Senecio vulgaris) populations

Abstract Aims Field and common garden comparisons are commonly performed to test the rapid evolution of increased vigor in introduced plant populations. Latitudinal clines in phenotypic traits can obscure such evolutionary inferences, particularly when native or introduced populations are distributed across large geographic ranges. We tested whether the latitudinal clines influence comparisons between introduced and native populations of Senecio vulgaris. Methods Senecio vulgaris is native to Europe but has been introduced in northeastern and southwestern China. To evaluate the performance in terms of growth and reproduction between native European populations and introduced Chinese populations, we compared plant height, number of branches and number of capitula in field populations in native and introduced ranges and in a common garden in Switzerland. Important Findings The introduced Chinese populations performed better than the native European populations in the field in terms of plant height and number of capitula, which was consistent with the prediction of the evolution of the increased competitive ability (EICA) hypothesis. The Chinese populations produced more capitula than the European populations when the latitudinal cline was considered in the common garden comparison. When we compared the traits of the northeastern Chinese, southwestern Chinese and European populations in both the field and common garden, the northeastern Chinese populations, at latitudes similar to those of the European populations, exhibited greater plant size and more capitula than the European populations in both the field and common garden. However, the southwestern Chinese populations, at latitudes much lower than those of the European populations, did not perform better than the native populations in terms of reproduction. In conclusion, our results suggest that latitudinal clines in phenotypic traits should be considered in field and common garden comparisons when introduced populations are geographically structured.

Effect of Latitudinal Variations in Low-Level Baroclinicity on Eddy Life Cycles and Upper-Tropospheric Wave-Breaking Processes

Abstract An analysis of the potential vorticity gradient and the refractive index in quasigeostrophic (QG) flows on the sphere reveals that the absolute vorticity and the stretching parts have two contradictory effects on the horizontal shape of the baroclinic waves when the full variations of the Coriolis parameter are taken into account in each term. The absolute vorticity effect favors the anticyclonic (southwest–northeast) tilt and anticyclonic wave breaking (AWB) and is stronger in the upper troposphere. In contrast, the stretching effect promotes the cyclonic (northwest–southeast) tilt and cyclonic wave breaking (CWB) and is more efficient at lower levels. A positive eddy feedback acting on the latitudinal variations of the zonal winds is deduced. Because the absolute vorticity and the stretching effects are respectively more and less efficient with increasing latitude, a more northward (southward) jet renders AWB more (less) probable and CWB less (more) probable; the jet is pushed or maintained more northward (southward) by the eddy feedback. Idealized numerical experiments using two aquaplanet models on the sphere, a three-level QG model, and a 10-level primitive equation (PE) model, confirm our analysis. Two strategies are employed: first, a normal-mode approach for jets centered at different latitudes; second, an analysis of long-term integrations of the models where the temperature is relaxed toward zonally as well as nonzonally uniform restoration-temperature profiles located at different latitudes. The positive eddy feedback is much less visible in the QG model and CWB is very rare because it does not contain the stretching effect (because of the constant Coriolis parameter in the stretching term).

The effects of dimethylsulfide upon marine aerosol concentrations

A simplified dimethylsulfide (DMS) oxidation mechanism is used in a box model to predict the vapor source rates of the major sulfur-containing products, methanesulfonic acid and sulfuric acid, in the marine boundary layer. These vapor source rates drive an integral aerosol model that predicts gas-to-particle conversion of the acid species in the presence of water vapor. The effects of latitudinal variations in background hydroxyl radical concentrations, temperatures, and relative humidities upon the predicted aerosol number concentrations are presented, and the sensitivity of the predictions to uncertainties in aerosol model input parameters is discussed. The predictions support a dependence of marine aerosol concentrations on latitude, as noted in some observations. Realistic choices of aerosol model parameters yield number concentrations that are consistent with observed concentrations in remote marine areas.