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The sensitivity of ensemble simulations of deep convective events in the southeastern United States to initial‐condition (IC) errors is examined by imposing idealized moisture perturbations at small and large scales. Four severe weather events are considered, ranging from a springtime frontal system to convection driven almost exclusively by daytime heating. Events with strong synoptic‐scale forcing were insensitive to the scale of IC errors, but weakly forced events exhibited greater sensitivity to small‐scale than large‐scale IC errors. Additional ensemble simulations of idealized convective systems suggest that the greater sensitivity to small‐scale IC errors of the weakly forced cases arises from their higher sensitivity to the strength and location of the first convective elements. Ensemble spread and predictability are characterized by two measures: the ratio of the perturbation kinetic energy (KE) about the ensemble mean to the background KE and the neighborhood‐based fractions skill score (FSS) of hourly precipitation with respect to that in an unperturbed reference simulation. For simulations of both observed events and idealized convective systems, the FSS appears to be a more discriminating indicator of differences in predictability between different convective events. [ABSTRACT FROM AUTHOR]

The current view of network emergence is predominantly influenced by path-dependent mechanisms where immediately preceding network structures inform current network positions. However, less explored is the ongoing sensitivity of future network positions to the composition and structure of newcomers' first partnerships. Building on the social categorization literature, we develop a model of the ongoing direct and moderating effects of newcomers' first network partnership on their status. We test our model using a panel of 272 U.S. venture capital firms from the 1980 to 2004 period and show that the reputation of newcomers' first partners exerts a positive influence on their future status (over and above intermediate network conditions). We find that this positive influence is stronger for those newcomers whose first partners formed a cohesive network. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract The impact that an exotic species can have on the composition of the community it enters is a function of its abundance, its particular species traits and characteristics of the recipient community. In this study we examined species composition in 14 sites burned in fires fuelled by non-indigenous C4 grasses in Hawaii Volcanoes National Park, Hawaii. We considered fire intensity, time since fire, climatic zone of site, unburned grass cover, unburned native cover and identity of the most abundant exotic grass in the adjacent unburned site as potential predictor variables of the impact of fire upon native species. We found that climatic zone was the single best variable for explaining variation in native cover among burned sites and between burned and unburned pairs. Fire in the eastern coastal lowlands had a very small effect on native plant cover and often stimulated native species regeneration, whereas fire in the seasonal submontane zone consistently caused a decline in native species cover and almost no species were fire tolerant. The dominant shrub, Styphelia tameiameia, in particular was fire intolerant. The number of years since fire, fire intensity and native cover in reference sites were not significantly correlated with native species cover in burned sites. The particular species of grass that carried the fire did however, have a significant effect on native species recovery. Where the African grass Melinis minutiflora was a dominant or codominant species, fire impacts were more severe than where it was absent regardless of climate zone. Overall, the impacts of exotic grass-fuelled fires on native species composition and cover in seasonally dry Hawaiian ecosystems was context specific. This specificity is best explained by differences between the climatic zones in which fire occurred. Elevation was the main physical variable that differed among the climatic zones and it alone could explain a large percentage of the variation in native cover... [ABSTRACT FROM AUTHOR]