Qinfeng Guo

The ecological niche and reciprocal prediction of the disjunct distribution of an invasive species: the example of Ailanthus altissima

Knowledge of the ecological niches of invasive species in native and introduced ranges can inform management as well as ecological and evolutionary theory. Here, we identified and compared factors associated with the distribution of an invasive tree, Ailanthus altissima, in both its native Chinese and introduced US ranges and predicted potential US distribution. For both ranges separately, we selected suites of the most parsimonious logistic regression models of occurrence based on environmental variables and evaluated these against independent data. We then incorporated information from both ranges in a simple Bayesian model to predict the potential US distribution. Occurrence of A. altissima in both ranges exhibited a unimodal response to temperature variables. In China, occurrence had negative relationships with topographic wetness and forest cover and positive relationships with precipitation and agricultural and urban land use. In the US, A. altissima was associated with intermediate levels of forest cover and precipitation. The Bayesian model identified 58–80% of 10-arc minute grid cells in the conterminous US as containing suitable areas for A. altissima. The best model developed from Chinese data applied to the US matched most areas of observed occurrence but under-predicted occurrence in lower probability areas. This discrepancy is suggestive of a broadening of the ecological niche of A. altissima and may be due to such factors as less intense competition, increased potency of allelopathy, and novel genotypes formed from multiple introductions. The Bayesian model suggests that A. altissima has the potential to substantially expand its distribution in the US.

Macrosystems ecology: novel methods and new understanding of multi-scale patterns and processes

As the global biomes are increasingly threatened by human activities, understanding of macroscale patterns and processes is pressingly needed for effective management and policy making. Macrosystems ecology, which studies multiscale ecological patterns and processes, has gained growing interest in the research community. However, as a relatively new field in ecology, research in macrosystems ecology is facing various challenges. In this special issue, we highlight the following two latest exciting developments in this thriving field: (1) novel tools and methods and (2) new understandings on macroscale patterns and processes. While we believe that the contributions featured in this issue provide promising advancements in macrosystems ecology, we also see multiple challenges for future research including (1) multidisciplinary approaches for long-term and multiscale studies and (2) scaling local patterns and processes to broader scales.

Natural and human dimensions of a quasi-wild species:the case of kudzu

The human dimensions of biotic invasion are generally poorly understood, even among the most familiar invasive species. Kudzu (Pueraria montana (Lour.) Merr.) is a prominent invasive plant and an example of quasi-wild species, which has experienced repeated introduction, cultivation, and escape back to the wild. Here, we review a large body of primary scientific and historic records spanning thousands of years to characterize the complex relationships among kudzu, its natural enemies, and humans, and provide a synthesis and conceptual model relevant to the ecology and management of quasi-wild invasive species. We documented over 350, mostly insect, natural enemy species and their impacts on kudzu in its native East Asian range. These natural enemies play a minor role in limiting kudzu in its native range, rarely generating severe impacts on populations of wild kudzu. We identified a number of significant influences of humans including dispersal, diverse cultural selection, and facilitation through disturbances, which catalyzed the expansion and exuberance of kudzu. On the other hand, harvest by humans appears to be the major control mechanism in its native areas. Humans thus have a complex relationship with kudzu. They have acted as both friend and foe, affecting the distribution and abundance of kudzu in ways that vary across its range and over time. Our conceptual model of kudzu emphasizes the importance of multiple human dimensions in shaping the biogeography of a species and illustrates how kudzu and other quasi-wild species are more likely to be successful invaders.

Evidence of biotic resistance to invasions in forests of the Eastern USA

AbstractContext Detecting biotic resistance to biological invasions across large geographic areas may require acknowledging multiple metrics of niche usage and potential spatial heterogeneity in associations between invasive and native species diversity and dominance.ObjectivesDetermine (1) if native communities are resistant to biological invasions at macroscales; (2) the metrics that best quantify biotic resistance at these scales; and (3) the degree to which the direction and magnitude of invader-native associations vary with scale and/or location.Methods Using a mixed-effects modeling framework to account for potential sub-regional and cross-scale variability in invader-native associations, we modeled the species richness and cover of invasive plants in 42,626 plots located throughout Eastern USA forests in relationship to plot-level estimates of native tree biomass, species richness, and evolutionary diversity.ResultsWe found (1) native tree biomass and evolutionary diversity, but not species richness, to be negatively associated with invader establishment and dominance, and thus indicative of biotic resistance; (2) evidence that evolutionary diversity limits invader dominance more than it does invader establishment; (3) evidence of greater invasion resistance in parts of the agriculturally-dominated Midwest and in and around the more-contiguous forests of the Appalachian Mountains; and (4) the magnitude to which native tree biomass and evolutionary diversity limit invasion varies across the ranges of these metrics.Conclusions These findings illustrate the improved understanding of biotic resistance to invasions that is gained by accounting for sub-regional variability in ecological processes, and underscores the need to determine the factors leading to spatial heterogeneity in biotic resistance.

Biotic resistance to exotic invasions: its role in forest ecosystems, confounding artifacts, and future directions

Biotic resistance, the ability of communities to resist exotic invasions, has long attracted interest in the research and management communities. However, inconsistencies exist in various biotic resistance studies and less is known about the current status and knowledge gaps of biotic resistance in forest ecosystems. In this paper, we provide a brief review of the history and mechanisms of the biotic resistance hypothesis, and summarize the central topics and knowledge gaps related to biotic resistance with a special emphasis on forest ecosystems. Overall, although the amount of research efforts on biotic resistance in forest ecosystems has increased since the mid-2000s, aspects such as resistance to exotic pests and pathogens remain understudied. In addition, we synthesize ecological and statistical explanations of observed inconsistencies and provide suggestions for future research directions. Some of the observed inconsistencies on biotic resistance can be attributed to (1) the interactive or additive effects of other ecological processes and (2) the statistical artifacts of modifiable areal unit problem. With the advancement of new statistical knowledge and tools, along with availability of big data, biotic resistance research can be greatly improved with the simultaneous consideration of key ecological processes, the attention to various scales involved, and the addition of understudied systems.