Impact scores of invasive plants are biased by disregard of environmental co-variation and non-linearity

Prioritisation of high-impact species is becoming increasingly important for management of introduced species (‘neobiota’) because of their growing number of which, however, only a small fraction has substantial impacts. Impact scores for prioritising species may be affected by the type of effect model used. Recent studies have shown that environmental co-variation and non-linearity may be significant for effect models of biological invasions. Here, we test for differences in impact scores between simple and complex effect models of three invasive plant species (Heracleum mantegazzianum, Lupinus polyphyllus, Rosa rugosa). We investigated the effects of cover percentages of the invasive plants on species richness of invaded communities using both simple linear effect models (‘basic models’) and more complex linear or nonlinear models including environmental co-factors (‘full models’). Then, we calculated impact scores for each invasive species as the average reduction of species richness predicted by basic and full effect models. All three non-native species had negative effects on species richness, but the full effect models also indicated significant influence of habitat types. Heracleum mantegazzianum had uniform linear effects in all habitats, while effects of L. polyphyllus interacted strongly with habitat type, and R. rugosa showed a marked non-linear relationship. Impact scores were overestimated by basic effect models for H. mantegazzianum and R. rugosa due to disregard of habitat effects and non-linearity, respectively. In contrast, impact of L. polyphyllus was underestimated by the basic model that did not account for the strong interaction of invader cover and habitat type. We conclude that simple linear models will often yield inaccurate impact scores of non-native species. Hence, effect models should consider environmental co-variation and, if necessary, non-linearity of the effects of biological invasions on native ecosystems

Identification of Thresholds in Benthic Macroinvertebrate Communities Associated with Agricultural Land Cover

Agricultural land use affects benthic macroinvertebrate (BMI) community structure but riparian forest may mitigate its impact to within a specific threshold. BMI communities were sampled in small streams within the Grand River, Thames River, and Long Point watersheds in southwestern Ontario. The study assessed the location and amount of agricultural land use associated with variation in BMI assemblage structure. Three land use distribution scenarios were evaluated to isolate specific ranges of agricultural land use at either the riparian or catchment scale, with the adjoining scale covering as wide a gradient of agricultural land use as possible. We did identify thresholds but the amount of variation associated with our thresholds would not enable us to suggest specific target ranges for land use managers looking to incorporate them into their stream biomonitoring programs. Further studies that assess various geologies and share wider gradients will improve upon our findings

Evaluating the ecological realism of plant species distribution models with ecological indicator values

Species distribution models (SDMs) are routinely applied to assess current as well as future species distributions, for example to assess impacts of future environmental change on biodiversity or to underpin conservation planning. It has been repeatedly emphasized that SDMs should be evaluated based not only on their goodness of fit to the data, but also on the realism of the modelled ecological responses. However, possibilities for the latter are hampered by limited knowledge on the true responses as well as a lack of quantitative evaluation methods. Here we compared modelled niche optima obtained from European-scale SDMs of 1,476 terrestrial vascular plant species with empirical ecological indicator values indicating the preferences of plant species for key environmental conditions. For each plant species we first fitted an ensemble SDM including three modeling techniques (GLM, GAM and BRT) and extracted niche optima for climate, soil, land use and nitrogen deposition variables with a large explanatory power for the occurrence of that species. We then compared these SDM-derived niche optima with the ecological indicator values by means of bivariate correlation analysis. We found weak to moderate correlations in the expected direction between the SDM-derived niche optima and ecological indicator values. The strongest correlation occurred between the modelled optima for growing degree days and the ecological indicator values for temperature. Correlations were weaker for SDM-derived niche optima with a more distal relationship to ecological indicator values (notably precipitation and soil moisture). Further, correlations were consistently highest for BRT, followed by GLM and GAM. Our method gives insight into the ecological realism of modelled niche optima and projected core habitats and can be used to improve SDMs by making a more informed selection of environmental variables and modeling techniques

There is a trade‑off between forest productivity and animal biodiversity in Europe

While forest productivity and biodiversity are expected to be correlated, prioritizing either forest productivity or biodiversity can result in different management. Spatial quantification of the congruence between areas suitable for either one can inform planning. Here we quantify the relationship between net primary productivity of European forests and biodiversity of mammals, birds, reptiles, amphibians, and butterflies both separately and in combination, and map their spatial congruence. We used richness maps obtained by stacking species distribution models for these animal species, and average net primary production from 2000 to 2012 using moderate resolution imaging spectroradiometer (MODIS) data. We tested how biodiversity and primary productivity are correlated and quantified the spatial congruence of these two sources. We show the areas where high or low productivity co-occur with high or low biodiversity using a quantile-based overlay analysis. Productivity was positively correlated to overall biodiversity and mammal, herptile and butterfly biodiversity, but biodiversity of birds showed a weak negative correlation. There were no significant differences in the strength of relationship across species groups, while herptiles had stronger relationships with productivity compared to other groups. Overlap analysis revealed significant spatial overlap between productivity and biodiversity in all species groups, except for birds. High value areas for both productivity and biodiversity in all species groups, except birds, co-occurred in the Mediterranean and temperate regions. The areas with high biodiversity of birds are mainly found in the boreal areas of Europe, while for all other species groups these areas are mostly located on the Iberian Peninsula and the Balkan ranges. Based on the presented maps, areas where regulating wood production activities to conserve species can be identified. But the maps also help to identify areas where either biodiversity or productivity is high and focusing on just one aspect is more straightforward

Alien plant invasions and native plant extinctions: a six-threshold framework

CITATION: Downey, P. O. & Richardson, D. M. 2016. Alien plant invasions and native plant extinctions : a six-threshold framework. AoB PLANTS, 8:1-21, doi:10.1093/aobpla/plw047.The original publication is available at https://academic.oup.com/aobplaBiological invasions are widely acknowledged as a major threat to global biodiversity. Species from all major taxonomic groups have become invasive. The range of impacts of invasive taxa and the overall magnitude of the threat is increasing. Plants comprise the biggest and best-studied group of invasive species. There is a growing debate; however, regarding the nature of the alien plant threat—in particular whether the outcome is likely to be the widespread extinction of native plant species. The debate has raised questions on whether the threat posed by invasive plants to native plants has been overstated. We provide a conceptual framework to guide discussion on this topic, in which the threat posed by invasive plants is considered in the context of a progression from no impact through to extinction. We define six thresholds along the ‘extinction trajectory’, global extinction being the final threshold. Although there are no documented examples of either ‘in the wild’ (Threshold 5) or global extinctions (Threshold 6) of native plants that are attributable solely to plant invasions, there is evidence that native plants have crossed or breached other thresholds along the extinction trajectory due to the impacts associated with plant invasions. Several factors may be masking where native species are on the trajectory; these include a lack of appropriate data to accurately map the position of species on the trajectory, the timeframe required to definitively state that extinctions have occurred and management interventions. Such interventions, focussing mainly on Thresholds 1–3 (a declining population through to the local extinction of a population), are likely to alter the extinction trajectory of some species. The critical issue for conservation managers is the trend, because interventions must be implemented before extinctions occur. Thus the lack of evidence for extinctions attributable to plant invasions does not mean we should disregard the broader threat.https://academic.oup.com/aobpla/article/2609604/Alien-plant-invasions-and-native-plant-extinctions?searchresult=1Publisher's versio

Long-term soil and vegetation recovery in five semiarid Montana ghost towns

Five semiarid Montana ghost towns abandoned for more than 45 years were studied to understand better the nature of soil and vegetation recovery following severe human impacts. Discriminant analysis was used to interpret and classify variation among land-use intensity groups. Recovery at the five towns was strongly linked to the degree of the initial soil disturbance, vegetation type, and precipitation. Recovery of the vegetation to ambient conditions was far from complete in all but one town

Do Homebuyers Care about the 'Quality' of Natural Habitats?

We study if homebuyers in Tucson, Arizona care about the condition of natural habitats and if they have preferences between natural and manmade habitats. Using field work data we examine whether homebuyers willingness to pay is influenced by the biological condition of the neighboring riparian habitat and how homebuyers value alternative manmade green areas, specifically golf courses. We also explore the relationship between the field data and remote sensing vegetation indices. The results of a hedonic analysis of houses that sold within 0.2 miles of 51 stratified-random selected riparian survey sites in Tucson, Arizona reveals that homebuyers significantly value habitat quality and negatively value manmade park-like features. Homebuyers are willing to pay twenty percent more to live near a riparian corridor that is densely vegetated and contains more shrub and tree species, particularly species that are dependent on perennial water flow. These environmental premiums are significant, outweighing structural factors such as an additional garage or swimming pool. Likewise, proximity to a riparian habitat with low biological quality or to a golf course lowers property values.Land Economics/Use,

On the development of flow-ecology relationships for streams in coastal watersheds of southern California

2014 Fall.Includes bibliographical references.Linking hydrologic alteration to the biotic responses of streams is essential for understanding and managing the effects of land use changes and other human influences on aquatic ecosystems. This study develops flow-ecology relationships for wadeable streams in coastal watersheds of southern California to understand the ecological effects of urbanization and other sources of hydromodification. Streams in this region are predominately flashy, seasonally intermittent, and fine grained; hence, the inherently harsh disturbance regime is a major determinant of biotic composition. I match biological and geomorphic data with proximate U. S. Geological Survey streamflow gages to examine flow-ecology relationships between benthic macroinvertebrates and the hydrologic and hydraulic regimes of 32 biomonitoring sites spanning a gradient of watershed urbanization. Associations between landscape, streamflow, and biotic metrics indicate that flow permanence and urbanization are overarching and interacting influences on benthic macroinvertebrate assemblages in this region. In particular, flow intermittency and flashiness are significant predictors of both taxonomic and traits-based measures of biotic composition. Urban land cover and road density are significantly correlated with higher flow flashiness and decreasing measures of biotic integrity. Hydraulic metrics describing streambed mobility are strongly positively associated with measures of biotic integrity as a result of high intercorrelation with flow permanence. Thus, it appears that benthic macroinvertebrate assemblages are fundamentally influenced by flow intermittency and urban-induced flashiness in this region. Use of daily discharge data analyzed 3 yrs prior to biological sampling events appears to result in little to no loss of resolution in flow-ecology relationships compared to sub-daily (15-min) and long-term (decadal) flow records. Results also underscore the utility of traits-based analyses and stratification of sites by flow permanence and dominant substrate in revealing mechanistic relationships between flow and biotic metrics. By using gaged sites to identify the flow metrics best describe biological variation, this study provides insight into which elements of the flow regime are most important to model accurately in future efforts to develop a regional hydrologic foundation that will allow the inclusion of ungaged biomonitoring sites in refining flow-ecology relationships