Moussab/ORKG-training-evaluation-set huggingface dataset:
Research field: Ecology and Evolutionary Biology
Title: Assessing the Relative Importance of Disturbance, Herbivory, Diversity, and Propagule Pressure in Exotic Plant Invasion
Abstract: The current rate of invasive species introductions is unprecedented, and the dramatic impacts of exotic invasive plants on community and ecosystem properties have been well documented. Despite the pressing management implications, the mechanisms that control exotic plant invasion remain poorly understood. Several factors, such as disturbance, propagule pressure, species diversity, and herbivory, are widely believed to play a critical role in exotic plant invasions. However, few studies have examined the relative importance of these factors, and little is known about how propagule pressure interacts with various mechanisms of ecological resistance to determine invasion success. We quantified the relative importance of canopy disturbance, propagule pressure, species diversity, and herbivory in determining exotic plant invasion in 10 eastern hemlock forests in Pennsylvania and New Jersey (USA). Use of a maximum-likelihood estimation framework and information theoretics allowed us to quantify the strength of evidence for alternative models of the influence of these factors on changes in exotic plant abundance. In addition, we developed models to determine the importance of interactions between ecosystem properties and propagule pressure. These analyses were conducted for three abundant, aggressive exotic species that represent a range of life histories: Alliaria petiolata, Berberis thunbergii, and Microstegium vimineum. Of the four hypothesized determinants of exotic plant invasion considered in this study, canopy disturbance and propagule pressure appear to be the most important predictors of A. petiolata, B. thunbergii, and M. vimineum invasion. Herbivory was also found to be important in contributing to the invasion of some species. In addition, we found compelling evidence of an important interaction between propagule pressure and canopy disturbance. This is the first study to demonstrate the dominant role of the interaction between canopy disturbance and propagule pressure in determining forest invasibility relative to other potential controlling factors. The importance of the disturbance-propagule supply interaction, and its nonlinear functional form, has profound implications for the management of exotic plant species populations. Improving our ability to predict exotic plant invasions will require enhanced understanding of the interaction between propagule pressure and ecological resistance mechanisms.
Extracted statement — Investigated species: Plants
Research field: Ecology and Evolutionary Biology
Title: The importance of quantifying propagule pressure to understand invasion: an examination of riparian forest invasibility
Abstract: The widely held belief that riparian communities are highly invasible to exotic plants is based primarily on comparisons of the extent of invasion in riparian and upland communities. However, because differences in the extent of invasion may simply result from variation in propagule supply among recipient environments, true comparisons of invasibility require that both invasion success and propagule pressure are quantified. In this study, we quantified propagule pressure in order to compare the invasibility of riparian and upland forests and assess the accuracy of using a community's level of invasion as a surrogate for its invasibility. We found the extent of invasion to be a poor proxy for invasibility. The higher level of invasion in the studied riparian forests resulted from greater propagule availability rather than higher invasibility. Furthermore, failure to account for propagule pressure may confound our understanding of general invasion theories. Ecological theory suggests that species-rich communities should be less invasible. However, we found significant relationships between species diversity and invasion extent, but no diversity-invasibility relationship was detected for any species. Our results demonstrate that using a community's level of invasion as a surrogate for its invasibility can confound our understanding of invasibility and its determinants.
Extracted statement — Investigated species: Plants
Research field: Ecology and Evolutionary Biology
Title: Modeling Invasive Plant Spread: The Role of Plant-Environment Interactions and Model Structure
Abstract: Alien plants invade many ecosystems worldwide and often have substantial negative effects on ecosystem structure and functioning. Our ability to quantitatively predict these impacts is, in part, limited by the absence of suitable plant-spread models and by inadequate parameter estimates for such models. This paper explores the effects of model, plant, and environmental attributes on predicted rates and patterns of spread of alien pine trees (Pinus spp.) in South African fynbos (a mediterranean-type shrubland). A factorial experimental design was used to: (1) compare the predictions of a simple reaction-diffusion model and a spatially explicit, individual-based simulation model; (2) investigate the sensitivity of predicted rates and patterns of spread to parameter values; and (3) quantify the effects of the simulation model's spatial grain on its predictions. The results show that the spatial simulation model places greater emphasis on interactions among ecological processes than does the reaction-diffusion model. This ensures that the predictions of the two models differ substantially for some factor combinations. The most important factor in the model is dispersal ability. Fire frequency, fecundity, and age of reproductive maturity are less important, while adult mortality has little effect on the model's predictions. The simulation model's predictions are sensitive to the model's spatial grain. This suggests that simulation models that use matrices as a spatial framework should ensure that the spatial grain of the model is compatible with the spatial processes being modeled. We conclude that parameter estimation and model development must be integrated pro- cedures. This will ensure that the model's structure is compatible with the biological pro- cesses being modeled. Failure to do so may result in spurious predictions.
Extracted statement — Investigated species: Plants
Research field: Ecology and Evolutionary Biology
Title: ECOLOGICAL RESISTANCE TO BIOLOGICAL INVASION OVERWHELMED BY PROPAGULE PRESSURE
Abstract: Models and observational studies have sought patterns of predictability for invasion of natural areas by nonindigenous species, but with limited success. In a field experiment using forest understory plants, we jointly manipulated three hypothesized determinants of biological invasion outcome: resident diversity, physical disturbance and abiotic conditions, and propagule pressure. The foremost constraints on net habitat invasibility were the number of propagules that arrived at a site and naturally varying resident plant density. The physical environment (flooding regime) and the number of established resident species had negligible impact on habitat invasibility as compared to propagule pressure, despite manipulations that forced a significant reduction in resident richness, and a gradient in flooding from no flooding to annual flooding. This is the first experimental study to demonstrate the primacy of propagule pressure as a determinant of habitat invasibility in comparison with other candidate controlling factors.
Extracted statement — Investigated species: Plants
Research field: Ecology and Evolutionary Biology
Title: Reproductive potential and seedling establishment of the invasive alien tree Schinus molle (Anacardiaceae) in South Africa
Abstract: Schinus molle (Peruvian pepper tree) was introduced to South Africa more than 150 years ago and was widely planted, mainly along roads. Only in the last two decades has the species become naturalized and invasive in some parts of its new range, notably in semi-arid savannas. Research is being undertaken to predict its potential for further invasion in South Africa. We studied production, dispersal and predation of seeds, seed banks, and seedling establishment in relation to land uses at three sites, namely ungrazed savanna once used as a military training ground; a savanna grazed by native game; and an ungrazed mine dump. We found that seed production and seed rain density of S. molle varied greatly between study sites, but was high at all sites (384 864–1 233 690 seeds per tree per year; 3877–9477 seeds per square metre per year). We found seeds dispersed to distances of up to 320 m from female trees, and most seeds were deposited within 50 m of putative source trees. Annual seed rain density below canopies of Acacia tortillis, the dominant native tree at all sites, was significantly lower in grazed savanna. The quality of seed rain was much reduced by endophagous predators. Seed survival in the soil was low, with no survival recorded beyond 1 year. Propagule pressure to drive the rate of recruitment: densities of seedlings and sapling densities were higher in ungrazed savanna and the ungrazed mine dump than in grazed savanna, as reflected by large numbers of young individuals, but adult : seedling ratios did not differ between savanna sites. Frequent and abundant seed production, together with effective dispersal of viable S. molle seed by birds to suitable establishment sites below trees of other species to overcome predation effects, facilitates invasion. Disturbance enhances invasion, probably by reducing competition from native plants.
Extracted statement — Investigated species: Plants
Research field: Ecology and Evolutionary Biology
Title: Dispersal and recruitment limitation in native versus exotic tree species: life-history strategies and Janzen-Connell effects
Abstract: Life-history traits of invasive exotic plants are typically considered to be exceptional vis-a-vis native species. In particular, hyper-fecundity and long range dispersal are regarded as invasive traits, but direct comparisons with native species are needed to identify the life-history stages behind invasiveness. Until recently, this task was particularly problematic in forests as tree fecundity and dispersal were difficult to characterize in closed stands. We used inverse modelling to parameterize fecundity, seed dispersal and seedling dispersion functions for two exotic and eight native tree species in closed-canopy forests in Connecticut, USA. Interannual variation in seed production was dramatic for all species, with complete seed crop failures in at least one year for six native species. However, the average per capita seed production of the exotic Ailanthus altissima was extraordinary:  40 times higher than the next highest species. Seed production of the shade tolerant exotic Acer platanoides was average, but much higher than the native shade tolerant species, and the density of its established seedlings ( 3 years) was higher than any other species. Overall, the data supported a model in which adults of native and exotic species must reach a minimum size before seed production occurred. Once reached, the relationship between tree diameter and seed production was fairly flat for seven species, including both exotics. Seed dispersal was highly localized and usually showed a steep decline with increasing distance from parent trees: only Ailanthus altissima and Fraxinus americana had mean dispersal distances  10 m. Janzen-Connell patterns were clearly evident for both native and exotic species, as the mode and mean dispersion distance of seedlings were further from potential parent trees than seeds. The comparable intensity of Janzen-Connell effects between native and exotic species suggests that the enemy escape hypothesis alone cannot explain the invasiveness of these exotics. Our study confirms the general importance of colonization processes in invasions, yet demon strates how invasiveness can occur via divergent colonization strategies. Dispersal limitation of Acer platanoides and recruitment limitation of Ailanthus altissima will likely constitute some limit on their invasiveness in closed-canopy forests.
Extracted statement — Investigated species: Plants
Research field: Ecology and Evolutionary Biology
Title: Invasive alien plants infiltrate bird-mediated shrub nucleation processes in arid savanna
Abstract: 1 The cultivation and dissemination of alien ornamental plants increases their potential to invade. More specifically, species with bird‐dispersed seeds can potentially infiltrate natural nucleation processes in savannas. 2 To test (i) whether invasion depends on facilitation by host trees, (ii) whether propagule pressure determines invasion probability, and (iii) whether alien host plants are better facilitators of alien fleshy‐fruited species than indigenous species, we mapped the distribution of alien fleshy‐fruited species planted inside a military base, and compared this with the distribution of alien and native fleshy‐fruited species established in the surrounding natural vegetation. 3 Abundance and diversity of fleshy‐fruited plant species was much greater beneath tree canopies than in open grassland and, although some native fleshy‐fruited plants were found both beneath host trees and in the open, alien fleshy‐fruited plants were found only beneath trees. 4 Abundance of fleshy‐fruited alien species in the natural savanna was positively correlated with the number of individuals of those species planted in the grounds of the military base, while the species richness of alien fleshy‐fruited taxa decreased with distance from the military base, supporting the notion that propagule pressure is a fundamental driver of invasions. 5 There were more fleshy‐fruited species beneath native Acacia tortilis than beneath alien Prosopis sp. trees of the equivalent size. Although there were significant differences in native plant assemblages beneath these hosts, the proportion of alien to native fleshy‐fruited species did not differ with host. 6 Synthesis. Birds facilitate invasion of a semi‐arid African savanna by alien fleshy‐fruited plants, and this process does not require disturbance. Instead, propagule pressure and a few simple biological observations define the probability that a plant will invade, with alien species planted in gardens being a major source of propagules. Some invading species have the potential to transform this savanna by overtopping native trees, leading to ecosystem‐level impacts. Likewise, the invasion of the open savanna by alien host trees (such as Prosopis sp.) may change the diversity, abundance and species composition of the fleshy‐fruited understorey. These results illustrate the complex interplay between propagule pressure, facilitation, and a range of other factors in biological invasions.
Extracted statement — Investigated species: Plants
Research field: Ecology and Evolutionary Biology
Title: Propagule pressure hypothesis not supported by an 80-year experiment on woody species invasion
Abstract: Ecological filters and availability of propagules play key roles structuring natural communities. Propagule pressure has recently been suggested to be a fundamental factor explaining the success or failure of biological introductions. We tested this hypothesis with a remarkable data set on trees introduced to Isla Victoria, Nahuel Huapi National Park, Argentina. More than 130 species of woody plants, many known to be highly invasive elsewhere, were introduced to this island early in the 20th century, as part of an experiment to test their suitability as commercial forestry trees for this region. We obtained detailed data on three estimates of propagule pressure (number of introduced individuals, number of areas where introduced, and number of years during which the species was planted) for 18 exotic woody species. We matched these data with a survey of the species and number of individuals currently invading the island. None of the three estimates of propagule pressure predicted the current pattern of invasion. We suggest that other factors, such as biotic resistance, may be operating to determine the observed pattern of invasion, and that propagule pressure may play a relatively minor role in explaining at least some observed patterns of invasion success and failure.
Extracted statement — Investigated species: Plants
Research field: Ecology and Evolutionary Biology
Title: Planting intensity, residence time, and species traits determine invasion success of alien woody species
Abstract: We studied the relative importance of residence time, propagule pressure, and species traits in three stages of invasion of alien woody plants cultivated for about 150 years in the Czech Republic, Central Europe. The probability of escape from cultivation, naturalization, and invasion was assessed using classification trees. We compared 109 escaped-not-escaped congeneric pairs, 44 naturalized-not-naturalized, and 17 invasive-not-invasive congeneric pairs. We used the following predictors of the above probabilities: date of introduction to the target region as a measure of residence time; intensity of planting in the target area as a proxy for propagule pressure; the area of origin; and 21 species-specific biological and ecological traits. The misclassification rates of the naturalization and invasion model were low, at 19.3% and 11.8%, respectively, indicating that the variables used included the major determinants of these processes. The probability of escape increased with residence time in the Czech Republic, whereas the probability of naturalization increased with the residence time in Europe. This indicates that some species were already adapted to local conditions when introduced to the Czech Republic. Apart from residence time, the probability of escape depends on planting intensity (propagule pressure), and that of naturalization on the area of origin and fruit size; it is lower for species from Asia and those with small fruits. The probability of invasion is determined by a long residence time and the ability to tolerate low temperatures. These results indicate that a simple suite of factors determines, with a high probability, the invasion success of alien woody plants, and that the relative role of biological traits and other factors is stage dependent. High levels of propagule pressure as a result of planting lead to woody species eventually escaping from cultivation, regardless of biological traits. However, the biological traits play a role in later stages of invasion.
Extracted statement — Investigated species: Plants
Research field: Ecology and Evolutionary Biology
Title: Propagule pressure and resource availability determine plant community invasibility in a temperate forest understorey
Abstract: Few field experiments have examined the effects of both resource availability and propagule pressure on plant community invasibility. Two non-native forest species, a herb and a shrub (Hesperis matronalis and Rhamnus cathartica, respectively), were sown into 60 1-m 2 sub-plots distributed across three plots. These contained reconstructed native plant communities in a replaced surface soil layer in a North American forest interior. Resource availability and propagule pressure were manipulated as follows: understorey light level (shaded/unshaded), nutrient availability (control/fertilized), and seed pressures of the two non-native species (control/low/high). Hesperis and Rhamnus cover and the above-ground biomass of Hesperis were significantly higher in shaded sub-plots and at greater propagule pressures. Similarly, the above-ground biomass of Rhamnus was significantly increased with propagule pressure, although this was a function of density. In contrast, of species that seeded into plots from the surrounding forest during the growing season, the non-native species had significantly greater cover in unshaded sub-plots. Plants in these unshaded sub-plots were significantly taller than plants in shaded sub-plots, suggesting a greater fitness. Total and non-native species richness varied significantly among plots indicating the importance of fine-scale dispersal patterns. None of the experimental treatments influenced native species. Since the forest seed bank in our study was colonized primarily by non-native ruderal species that dominated understorey vegetation, the management of invasions by non-native species in forest understoreys will have to address factors that influence light levels and dispersal pathways.
Extracted statement — Investigated species: Plants
Research field: Ecology and Evolutionary Biology
Title: Habitat, dispersal and propagule pressure control exotic plant infilling within an invaded range
Abstract: Deep in the heart of a longstanding invasion, an exotic grass is still invading. Range infilling potentially has the greatest impact on native communities and ecosystem processes, but receives much less attention than range expansion. ‘Snapshot' studies of invasive plant dispersal, habitat and propagule limitations cannot determine whether a landscape is saturated or whether a species is actively infilling empty patches. We investigate the mechanisms underlying invasive plant infilling by tracking the localized movement and expansion of Microstegium vimineum populations from 2009 to 2011 at sites along a 100-km regional gradient in eastern U.S. deciduous forests. We find that infilling proceeds most rapidly where the invasive plants occur in warm, moist habitats adjacent to roads: under these conditions they produce copious seed, the dispersal distances of which increase exponentially with proximity to roadway. Invasion then appears limited where conditions are generally dry and cool as propagule pressure tapers off. Invasion also is limited in habitats >1 m from road corridors, where dispersal distances decline precipitously. In contrast to propagule and dispersal limitations, we find little evidence that infilling is habitat limited, meaning that as long as M. vimineum seeds are available and transported, the plant generally invades quite vigorously. Our results suggest an invasive species continues to spread, in a stratified manner, within the invaded landscape long after first arriving. These dynamics conflict with traditional invasion models that emphasize an invasive edge with distinct boundaries. We find that propagule pressure and dispersal regulate infilling, providing the basis for projecting spread and landscape coverage, ecological effects and the efficacy of containment strategies.
Extracted statement — Investigated species: Plants