Moussab/ORKG-training-evaluation-set huggingface dataset:
Research field: Ecology and Evolutionary Biology
Title: Loss of native herbaceous species due to woody plant encroachment facilitates the establishment of an invasive grass
Abstract: Although negative relationships between diversity (frequently measured as species richness) and invasibility at neighborhood or community scales have often been reported, realistic natural diversity gradients have rarely been studied at this scale. We recreated a naturally occurring gradient in species richness to test the effects of species richness on community invasibility. In central Texas savannas, as the proportion of woody plants increases (a process known as woody plant encroachment), herbaceous habitat is both lost and fragmented, and native herbaceous species richness declines. We examined the effects of these species losses on invasibility in situ by removing species that occur less frequently in herbaceous patches as woody plant encroachment advances. This realistic species removal was accompanied by a parallel and equivalent removal of biomass with no changes in species richness. Over two springs, the nonnative bunchgrass Bothriochloa ischaemum germinated significantly more often in the biomass-removal treatment than in unmanipulated control plots, suggesting an effect of native plant density independent of diversity. Additionally, significantly more germination occurred in the species-removal treatment than in the biomass-removal treatment. Changes in species richness had a stronger effect on B. ischaemum germination than changes in plant density, demonstrating that niche-related processes contributed more to biotic resistance in this system than did species-neutral competitive interactions. Similar treatment effects were found on transplant growth. Thus we show that woody plant encroachment indirectly facilitates the establishment of an invasive grass by reducing native diversity. Although we found a negative relationship between species richness and invasibility at the scale of plots with similar composition and environmental conditions, we found a positive relationship between species richness and invasibility at larger scales. This apparent paradox is consistent with reports from other systems and may be the result of variation in environmental factors at larger scales similarly influencing both invasibility and richness. The habitat loss and fragmentation associated with woody plant encroachment are two of many processes that commonly threaten biodiversity, including climate change. Many of these processes are similarly likely to increase invasibility via their negative effects on native diversity.
Extracted statement — Investigated species: Plants
Research field: Ecology and Evolutionary Biology
Title: Diversity-invasibility across an experimental disturbance gradient in Appalachian forests
Abstract: Research examining the relationship between community diversity and invasions by nonnative species has raised new questions about the theory and management of biological invasions. Ecological theory predicts, and small-scale experiments confirm, lower levels of nonnative species invasion into species-rich compared to species-poor communities, but observational studies across a wider range of scales often report positive relationships between native and nonnative species richness. This paradox has been attributed to the scale dependency of diversity-invasibility relationships and to differences between experimental and observational studies. Disturbance is widely recognized as an important factor determining invasibility of communities, but few studies have investigated the relative and interactive roles of diversity and disturbance on nonnative species invasion. Here, we report how the relationship between native and nonnative plant species richness responded to an experimentally applied disturbance gradient (from no disturbance up to clearcut) in oak-dominated forests. We consider whether results are consistent with various explanations of diversity-invasibility relationships including biotic resistance, resource availability, and the potential effects of scale (1 m2 to 2 ha). We found no correlation between native and nonnative species richness before disturbance except at the largest spatial scale, but a positive relationship after disturbance across scales and levels of disturbance. Post-disturbance richness of both native and nonnative species was positively correlated with disturbance intensity and with variability of residual basal area of trees. These results suggest that more nonnative plants may invade species-rich communities compared to species-poor communities following disturbance.
Extracted statement — Investigated species: Plants
Research field: Ecology and Evolutionary Biology
Title: Control of plant species diversity and community invasibility by species immigration: seed richness versus seed density
Abstract: Brown, R. L. and Fridley, J. D. 2003. Control of plant species diversity andcommunity invasibility by species immigration: seed richness versus seed density. –Oikos 102: 15–24.Immigration rates of species into communities are widely understood to inﬂuencecommunity diversity, which in turn is widely expected to inﬂuence the susceptibilityof ecosystems to species invasion. For a given community, however, immigrationprocesses may impact diversity by means of two separable components: the numberof species represented in seed inputs and the density of seed per species. Theindependent effects of these components on plant species diversity and consequentrates of invasion are poorly understood. We constructed experimental plant commu-nities through repeated seed additions to independently measure the effects of seedrichness and seed density on the trajectory of species diversity during the develop-ment of annual plant communities. Because we sowed species not found in theimmediate study area, we were able to assess the invasibility of the resultingcommunities by recording the rate of establishment of species from adjacent vegeta-tion. Early in community development when species only weakly interacted, seedrichness had a strong effect on community diversity whereas seed density had littleeffect. After the plants became established, the effect of seed richness on measureddiversity strongly depended on seed density, and disappeared at the highest level ofseed density. The ability of surrounding vegetation to invade the experimentalcommunities was decreased by seed density but not by seed richness, primarilybecause the individual effects of a few sown species could explain the observedinvasion rates. These results suggest that seed density is just as important as seedrichness in the control of species diversity, and perhaps a more important determi-nant of community invasibility than seed richness in dynamic plant assemblages.
Extracted statement — Investigated species: Plants
Research field: Ecology and Evolutionary Biology
Title: Aquatic plant community invasibility and scale-dependent patterns in native and invasive species richness
Abstract: Invasive species richness often is negatively correlated with native species richness at the small spatial scale of sampling plots, but positively correlated in larger areas. The pattern at small scales has been interpreted as evidence that native plants can competitively exclude invasive species. Large-scale patterns have been understood to result from environmental heterogeneity, among other causes. We investigated species richness patterns among submerged and floating-leaved aquatic plants (87 native species and eight invasives) in 103 temperate lakes in Connecticut (northeastern USA) and found neither a consistently negative relationship at small (3-m2) scales, nor a positive relationship at large scales. Native species richness at sampling locations was uncorrelated with invasive species richness in 37 of the 60 lakes where invasive plants occurred; richness was negatively correlated in 16 lakes and positively correlated in seven. No correlation between native and invasive species richness was found at larger spatial scales (whole lakes and counties). Increases in richness with area were uncorrelated with abiotic heterogeneity. Logistic regression showed that the probability of occurrence of five invasive species increased in sampling locations (3 m2, n = 2980 samples) where native plants occurred, indicating that native plant species richness provided no resistance against invasion. However, the probability of three invasive species' occurrence declined as native plant density increased, indicating that density, if not species richness, provided some resistance with these species. Density had no effect on occurrence of three other invasive species. Based on these results, native species may resist invasion at small spatial scales only in communities where density is high (i.e., in communities where competition among individuals contributes to community structure). Most hydrophyte communities, however, appear to be maintained in a nonequilibrial condition by stress and/or disturbance. Therefore, most aquatic plant communities in temperate lakes are likely to be vulnerable to invasion.
Extracted statement — Investigated species: Plants
Research field: Ecology and Evolutionary Biology
Title: Species richness and exotic species invasion in middle Tennessee cedar glades in relation to abiotic and biotic factors
Abstract: Abstract Abiotic factors, particularly area, and biotic factors play important roles in determining species richness of continental islands such as cedar glades. We examined the relationship between environmental parameters and species richness on glades and the influence of native species richness on exotic invasion. Field surveys of vascular plants on 40 cedar glades in Rutherford County, Tennessee were conducted during the 2001–2003 growing seasons. Glades were geo-referenced to obtain area, perimeter, distance from autotour road, and degree of isolation. Amount of disturbance also was recorded. Two-hundred thirty two taxa were found with Andropogon virginicus, Croton monanthogynus, Juniperus virginiana, Panicum flexile, and Ulmus alata present on all glades. The exotics Ligustrum sinense, Leucanthemum vulgare, and Taraxacum officinale occurred on the majority of glades. Lobelia appendiculata var. gattingeri, Leavenworthia stylosa, and Pediomelum subacaule were the most frequent endemics. Richness of native, exotic and endemic species increased with increasing area and perimeter and decreased with increasing isolation (P ≤ 0.03); richness was unrelated to distance to road (P ≥ 0.20). Perimeter explained a greater amount of variation than area for native and exotic species, whereas area accounted for greater variation for endemic species. Slope of the relationship between area and total richness (0.17) was within the range reported for continental islands. Disturbed glades contained a higher number of exotic and native species than nondisturbed ones, but they were larger (P ≤ 0.03). Invasion of exotic species was unrelated to native species richness when glade size was statistically controlled (P = 0.88). Absence of a relationship is probably due to a lack of substantial competitive interactions. Most endemics occurred over a broad range of glade sizes emphasizing the point that glades of all sizes are worthy of protection.
Extracted statement — Investigated species: Plants
Research field: Ecology and Evolutionary Biology
Title: Spatial heterogeneity explains the scale dependence of the native-exotic diversity relationship
Abstract: While small-scale studies show that more diverse native communities are less invasible by exotics, studies at large spatial scales often find positive correlations between native and exotic diversity. This large-scale pattern is thought to arise because landscapes with favorable conditions for native species also have favorable conditions for exotic species. From theory, we proposed an alternative hypothesis: the positive relationship at large scales is driven by spatial heterogeneity in species composition, which is driven by spatial heterogeneity in the environment. Landscapes with more spatial heterogeneity in the environment can sustain more native and more exotic species, leading to a positive correlation of native and exotic diversity at large scales. In a nested data set for grassland plants, we detected negative relationships between native and exotic diversity at small spatial scales and positive relationships at large spatial scales. Supporting our hypothesis, the positive relationships between native and exotic diversity at large scales were driven by positive relationships between native and exotic beta diversity. Further, both native and exotic diversity were positively correlated with spatial heterogeneity in abiotic conditions (variance of soil depth, soil nitrogen, and aspect) but were uncorrelated with average abiotic conditions, supporting the spatial-heterogeneity hypothesis but not the favorable-conditions
Extracted statement — Investigated species: Plants
Research field: Ecology and Evolutionary Biology
Title: Darwin's naturalization conundrum: dissecting taxonomic patterns of species invasions
Abstract: Darwin acknowledged contrasting, plausible arguments for how species invasions are influenced by phylogenetic relatedness to the native community. These contrasting arguments persist today without clear resolution. Using data on the naturalization and abundance of exotic plants in the Auckland region, we show how different expectations can be accommodated through attention to scale, assumptions about niche overlap, and stage of invasion. Probability of naturalization was positively related to the number of native species in a genus but negatively related to native congener abundance, suggesting the importance of both niche availability and biotic resistance. Once naturalized, however, exotic abundance was not related to the number of native congeners, but positively related to native congener abundance. Changing the scale of analysis altered this outcome: within habitats exotic abundance was negatively related to native congener abundance, implying that native and exotic species respond similarly to broad scale environmental variation across habitats, with biotic resistance occurring within habitats.
Extracted statement — Investigated species: Plants
Research field: Ecology and Evolutionary Biology
Title: Invasibility of experimental grassland communities: the role of earthworms, plant functional group identity and seed size
Abstract: Invasions of natural communities by non-indigenous species threaten native biodiversity and are currently rated as one of the most important global-scale environmental problems. The mechanisms that make communities resistant to invasions and drive the establishment success of seedlings are essential both for management and for understanding community assembly and structure. Especially in grasslands, anecic earthworms are known to function as ecosystem engineers, however, their direct effects on plant community composition and on the invasibility of plant communities via plant seed burial, ingestion and digestion are poorly understood. In a greenhouse experiment we investigated the impact of Lumbricus terrestris, plant functional group identity and seed size of plant invader species and plant functional group of the established plant community on the number and biomass of plant invaders. We set up 120 microcosms comprising four plant community treatments, two earthworm treatments and three plant invader treatments containing three seed size classes. Earthworm performance was influenced by an interaction between plant functional group identity of the established plant community and that of invader species. The established plant community and invader seed size affected the number of invader plants significantly, while invader biomass was only affected by the established community. Since earthworm effects on the number and biomass of invader plants varied with seed size and plant functional group identity they probably play a key role in seedling establishment and plant community composition. Seeds and germinating seedlings in earthworm burrows may significantly contribute to earthworm nutrition, but this deserves further attention. Lumbricus terrestris likely behaves like a ‘farmer’ by collecting plant seeds which cannot directly be swallowed or digested. Presumably, these seeds are left in middens and become eatable after partial microbial decay. Increased earthworm numbers in more diverse plant communities likely contribute to the positive relationship between plant species diversity and resistance against invaders.
Extracted statement — Investigated species: Plants
Research field: Ecology and Evolutionary Biology
Title: Abiotic constraints eclipse biotic resistance in determining invasibility along experimental vernal pool gradients
Abstract: Effective management of invasive species requires that we understand the mechanisms determining community invasibility. Successful invaders must tolerate abiotic conditions and overcome resistance from native species in invaded habitats. Biotic resistance to invasions may reflect the diversity, abundance, or identity of species in a community. Few studies, however, have examined the relative importance of abiotic and biotic factors determining community invasibility. In a greenhouse experiment, we simulated the abiotic and biotic gradients typically found in vernal pools to better understand their impacts on invasibility. Specifically, we invaded plant communities differing in richness, identity, and abundance of native plants (the "plant neighborhood") and depth of inundation to measure their effects on growth, reproduction, and survival of five exotic plant species. Inundation reduced growth, reproduction, and survival of the five exotic species more than did plant neighborhood. Inundation reduced survival of three species and growth and reproduction of all five species. Neighboring plants reduced growth and reproduction of three species but generally did not affect survival. Brassica rapa, Centaurea solstitialis, and Vicia villosa all suffered high mortality due to inundation but were generally unaffected by neighboring plants. In contrast, Hordeum marinum and Lolium multiflorum, whose survival was unaffected by inundation, were more impacted by neighboring plants. However, the four measures describing plant neighborhood differed in their effects. Neighbor abundance impacted growth and reproduction more than did neighbor richness or identity, with growth and reproduction generally decreasing with increasing density and mass of neighbors. Collectively, these results suggest that abiotic constraints play the dominant role in determining invasibility along vernal pool and similar gradients. By reducing survival, abiotic constraints allow only species with the appropriate morphological and physiological traits to invade. In contrast, biotic resistance reduces invasibility only in more benign environments and is best predicted by the abundance, rather than diversity, of neighbors. These results suggest that stressful environments are not likely to be invaded by most exotic species. However, species, such as H. marinum, that are able to invade these habitats require careful management, especially since these environments often harbor rare species and communities.
Extracted statement — Investigated species: Plants
Research field: Ecology and Evolutionary Biology
Title: Predicting the landscape-scale distribution of alien plants and their threat to plant diversity
Abstract: Abstract: Invasive alien organisms pose a major threat to global biodiversity. The Cape Peninsula, South Africa, provides a case study of the threat of alien plants to native plant diversity. We sought to identify where alien plants would invade the landscape and what their threat to plant diversity could be. This information is needed to develop a strategy for managing these invasions at the landscape scale. We used logistic regression models to predict the potential distribution of six important invasive alien plants in relation to several environmental variables. The logistic regression models showed that alien plants could cover over 89% of the Cape Peninsula. Acacia cyclops and Pinus pinaster were predicted to cover the greatest area. These predictions were overlaid on the current distribution of native plant diversity for the Cape Peninsula in order to quantify the threat of alien plants to native plant diversity. We defined the threat to native plant diversity as the number of native plant species (divided into all species, rare and threatened species, and endemic species) whose entire range is covered by the predicted distribution of alien plant species. We used a null model, which assumed a random distribution of invaded sites, to assess whether area invaded is confounded with threat to native plant diversity. The null model showed that most alien species threaten more plant species than might be suggested by the area they are predicted to invade. For instance, the logistic regression model predicted that P. pinaster threatens 350 more native species, 29 more rare and threatened species, and 21 more endemic species than the null model would predict. Comparisons between the null and logistic regression models suggest that species richness and invasibility are positively correlated and that species richness is a poor indicator of invasive resistance in the study site. Our results emphasize the importance of adopting a spatially explicit approach to quantifying threats to biodiversity, and they provide the information needed to prioritize threats from alien species and the sites that need urgent management intervention.
Extracted statement — Investigated species: Plants
Research field: Ecology and Evolutionary Biology
Title: Filling in the gaps: modelling native species richness and invasions using spatially incomplete data
Abstract: Detailed knowledge of patterns of native species richness, an important component of biodiversity, and non‐native species invasions is often lacking even though this knowledge is essential to conservation efforts. However, we cannot afford to wait for complete information on the distribution and abundance of native and harmful invasive species. Using information from counties well surveyed for plants across the USA, we developed models to fill data gaps in poorly surveyed areas by estimating the density (number of species km−2) of native and non‐native plant species. Here, we show that native plant species density is non‐random, predictable, and is the best predictor of non‐native plant species density. We found that eastern agricultural sites and coastal areas are among the most invaded in terms of non‐native plant species densities, and that the central USA appears to have the greatest ratio of non‐native to native species. These large‐scale models could also be applied to smaller spatial scales or other taxa to set priorities for conservation and invasion mitigation, prevention, and control efforts.
Extracted statement — Investigated species: Plants
Research field: Ecology and Evolutionary Biology
Title: Species diversity and biological invasions: relating local process to community pattern
Abstract: In a California riparian system, the most diverse natural assemblages are the most invaded by exotic plants. A direct in situ manipulation of local diversity and a seed addition experiment showed that these patterns emerge despite the intrinsic negative effects of diversity on invasions. The results suggest that species loss at small scales may reduce invasion resistance. At community-wide scales, the overwhelming effects of ecological factors spatially covarying with diversity, such as propagule supply, make the most diverse communities most likely to be invaded.
Extracted statement — Investigated species: Plants