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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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.

Anthropogenic nutrient enrichment stimulates primary production and threatens natural communities worldwide. Herbivores may counteract deleterious effects of enrichment by increasing their consumption of primary producers. However, field tests of herbivore control are often done by adding nutrients at small (e.g., sub-meter) scales, while enrichment in real systems often occurs at much larger scales (e.g., kilometers). Therefore, experimental results may be driven by processes that are not relevant at larger scales. Using a mathematical model, we show that herbivores can control primary producer biomass in experiments by concentrating their foraging in small enriched plots; however, at larger, realistic scales, the same mechanism may not lead to herbivore control of primary producers. Instead, other demographic mechanisms are required, but these are not examined in most field studies (and may not operate in many systems). This mismatch between experiments and natural processes suggests that many ecosystems may be less resilient to degradation via enrichment than previously believed.

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 ...

Abstract. The protection of predators inside marine reserves is expected to generate trophic cascades with predator density increasing but prey density decreasing; however, predators and prey often both increase inside reserves. This mismatch between the expected and observed change in prey density has been explained because prey also are harvested; that is, the protection of prey compensates for the additional predation inside the reserve. Here, we show that this mechanism alone cannot increase densities of predator and prey; other mechanisms are required, and we hypothesized that movement of predator and/or prey might provide such a mechanism. We therefore built two spatially implicit two-patch predator-prey models with movement of predator and prey between reserve and fishing grounds. We show that post-settlement movement of predators (but not prey) altered the strength of trophic cascades and could increase densities of both predator and focal prey. We further built a more general model that shows that predator post-settlement movement can reinforce and even supplement the effect of two previously investigated mechanisms producing trophic cascades: a prey size refuge and predator density-dependent mortality. Our study increases understanding of mechanisms that can alter the strength (and direction) of prey responses inside marine reserves and highlights the importance of movement in human-induced heterogeneous systems.

Determining the degree to which predation affects prey abundance in natural communities constitutes a key goal of ecological research. Predators can affect prey through both consumptive effects (CEs) and nonconsumptive effects (NCEs), although the contributions of each mechanism to the density of prey populations remain largely hypothetical in most systems. Common statistical methods applied to time‐series data cannot elucidate the mechanisms responsible for hypothesized predator effects on prey density (e.g., differentiate CEs from NCEs), nor can they provide parameters for predictive models. State‐space models (SSMs) applied to time‐series data offer a way to meet these goals. Here, we employ SSMs to assess effects of an invasive predatory zooplankter, Bythotrephes longimanus, on an important prey species, Daphnia mendotae, in Lake Michigan. We fit mechanistic models in an SSM framework to seasonal time series (1994–2012) using a recently developed, maximum‐likelihood–based optimization method, iterated filtering, which can overcome challenges in ecological data (e.g., nonlinearities, measurement error, and irregular sampling intervals). Our results indicate that B. longimanus strongly influences D. mendotae dynamics, with mean annual peak densities of B. longimanus observed in Lake Michigan estimated to cause a 61% reduction in D. mendotae population growth rate and a 59% reduction in peak biomass density. Further, the observed B. longimanus effect is most consistent with an NCE via reduced birth rates. The SSM approach also provided estimates for key biological parameters (e.g., demographic rates) and the contribution of dynamic stochasticity and measurement error. Our study therefore provides evidence derived directly from survey data that the invasive zooplankter B. longimanus is affecting zooplankton demographics and offer parameter estimates needed to inform predictive models that explore the effect of B. longimanus under different scenarios, such as climate change.

Theoretical studies of marine protected areas (MPAs) suggest that more mobile species should exhibit reduced local effects (defined as the ratio of the density inside vs. outside of the MPA). However, empirical studies have not supported the expected negative relationship between the local effect and mobility. We propose that differential, habitat-dependent movement (i.e., a higher movement rate in the fishing grounds than in the MPA) might explain the disparity between theoretical expectations and empirical results. We evaluate this hypothesis by building two-patch box and stepping-stone models and show that increasing disparity in the habitat-specific movement rates shifts the relationship between the local effect and mobility from negative (the previous theoretical results) to neutral or positive (the empirical pattern). This shift from negative to positive occurs when differential movement offsets recruitment and mortality differences between the two habitats. Thus, local effects of MPAs might be caused by behavioral responses via differential movement rather than by, or in addition to, reductions in mortality. In addition, the benefits of MPAs, in terms of regional abundance and fishing yields, can be altered by the magnitude of differential movement. Thus, our study points to a need for empirical investigations that disentangle the interactions among mobility, differential movement, and protection.