Although genetic diversity is very important for alien species, which have to cope with new environments, little is known about the role that genetic diversity plays in their invasive success. In this study, we set up a manipulation experiment including three levels of genotypic diversity to test whether genotypic diversity can enhance the invasive ability of alien species, in our case the invasive Spartina alterniflora in China, and to infer the underlying mechanisms. There was no significant relationship between genotypic diversity and parameters of performance in the first year; however, from the summer of the second year onwards, genotypic diversity enhanced four of the six parameters of performance. After two growing seasons, there were significant positive relationships between genotypic diversity and maximum spread distance, patch size, shoot number per patch, and aboveground biomass. Moreover, abundance of the native dominant species Scirpus mariqueter was marginally significantly decreased with genotypic diversity of S. alterniflora, suggesting that enhanced invasive ability of S. alterniflora may have depressed the growth of the native species. There was no significant difference in most measures of performance among six genotypes, but we observed a transgressive over performance in four measures in multiple-genotype patches. At the end of the experiment, there were significant nonadditive effects of genotypic diversity according to Monte Carlo permutations, in six-genotype, but not three-genotype plots. Our results indicated that both additive and nonadditive effects played roles in the positive relationship between genetic diversity and invasion success, and nonadditive effects were stronger as duration increased.

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MacArthur and Wilson's equilibrium theory is one of the most influential theories in ecology. Although evolution on islands is to be important to island biodiversity, speciation has not been well integrated into island biogeography models. By incorporating speciation and factors influencing it into the MacArthur-Wilson model, we propose a generalized model unifying ecological and evolutionary processes and island features. Intra-island speciation may play an important role in both island species richness and endemism, and the contribution of speciation to local species diversity may eventually be greater than that of immigration under certain conditions. Those conditions are related to the per species speciation rate, per species extinction rate, and island features, and they are independent of immigration rate. The model predicts that large islands will have a high, though not the highest, proportional endemism when other parameters are fixed. Based on the generalized model, changes in species richness and endemism on an oceanic island over time were predicted to be similar to empirical observations. Our model provides an ideal starting point for re-evaluating the role of speciation and re-analyzing available data on island species diversity, especially those biased by the MacArthur-Wilson model. MacArthur and Wilson's equilibrium theory [1,2] is one of the most influential theories in biogeography, ecology and conservation biology [3,4]. As the paradigm of island biogeography, this dynamic equilibrium theory explains emergent patterns of species richness and endemism on an island based on two biogeographical processes (immigration and extinction) and on two physical features of the island (area and isolation) [1,2]. This theory has strongly influenced other fields of ecology and conservation biology for forty years and has stimulated many hundreds of studies on patterns of species richness in a great variety of ecosystems and biotas [5]. Evolution on islands is thought to be important on the evolutionary time scale [1,2], but it has not been well considered in the dynamic equilibrium model, even though evolution is commonly used to explain extraordinarily high numbers of endemic species [6,7]. The role of speciation in the species diversity of oceanic islands has long been noted and frequently emphasized [6,[8][9][10][11][12][13]. There have numerous attempts to link evolutionary and ecological dynamics building on the MacArthur-Wilson model [14,15]. However, the challenge of combining evolution, immigration, extinction and island features has not been well fulfilled, and there have been repeated calls for theoreticians to develop new models/theories [3,5,12,16].Using a simple model of island biogeography theory, we previously predicted the relative contributions of speciation and immigration to island species diversity over time [17]. We also provided a theoretical explanation for the positive relationship between percentage endemism and species diversity on islands. In this paper, we extend the simple model ...

In recent years, researchers have devoted considerable attention to identifying the causes of urban environmental pollution. To determine whether migrant populations significantly affect urban environments, we examined the relationship between urban environmental pollutant emissions and migrant populations at the prefectural level using data obtained for 90 Chinese cities evidencing net in-migration. By dividing the permanent populations of these cities into natives and migrants in relation to the population structure, we constructed an improved Stochastic Impacts by Regression on Population, Affluence and Technology model (STIRPAT) that included not only environmental pollutant emission variables but also variables on the cities' attributes. We subsequently conducted detailed analyses of the results of the models to assess the impacts of natives and migrants on environmental pollutant emissions. The main findings of our study were as follows: 1) Migrant populations have significant impacts on environmental emissions both in terms of their size and concentration. Specifically, migrant populations have negative impacts on Air Quality Index (AQI) as well as PM 2.5 emissions and positive impacts on emissions of NO 2 and CO 2 . 2) The impacts of migrant populations on urban environmental pollutant emissions were 8 to 30 times weaker than that of local populations. 3) Urban environmental pollutant emissions in different cities differ significantly according to variations in the industrial structures, public transportation facilities, and population densities.