Climate change and biological invasions are primary threats to global biodiversity that may interact in the future. To date, the hypothesis that climate change will favour non‐native species has been ...examined exclusively through local comparisons of single or few species. Here, we take a meta‐analytical approach to broadly evaluate whether non‐native species are poised to respond more positively than native species to future climatic conditions. We compiled a database of studies in aquatic and terrestrial ecosystems that reported performance measures of non‐native (157 species) and co‐occurring native species (204 species) under different temperature, CO2 and precipitation conditions. Our analyses revealed that in terrestrial (primarily plant) systems, native and non‐native species responded similarly to environmental changes. By contrast, in aquatic (primarily animal) systems, increases in temperature and CO2 largely inhibited native species. There was a general trend towards stronger responses among non‐native species, including enhanced positive responses to more favourable conditions and stronger negative responses to less favourable conditions. As climate change proceeds, aquatic systems may be particularly vulnerable to invasion. Across systems, there could be a higher risk of invasion at sites becoming more climatically hospitable, whereas sites shifting towards harsher conditions may become more resistant to invasions.
Invasion by exotic plant species can profoundly affect native plant species performance and the inferred proximate cause is typically competition. We used invaded grasslands in the semi-arid Western ...USA to separate resource competition from structural interference of an exotic grass on native forb performance, specifically evaluating the role of competition from living vegetation versus litter accumulation (hereafter, thatch). We simultaneously tested whether a positive thatch-feedback exists for the dominant exotic grass species,
Bromus diandrus
. Thatch and
B. diandrus
density were manipulated and coupled with native seed addition to separate the effect of
B. diandrus
competition relative to thatch accumulation. To determine the response of native forb species and
B. diandrus
to varying thatch abundance, we created a gradient of thatch densities and measured species response, soil moisture and light availability. The thatch of
B. diandrus
greatly reduced native forb performance (number of individuals and biomass) and resulted in near complete exclusion of many species. The effect of living
B. diandrus
density on native forb performance was minimal and inconsistent. Forb performance and light availability both exhibited exponential declines with thatch build-up suggesting that light reduction is a primary mechanism through which thatch affects forbs. Simultaneous with forb suppression,
B. diandrus
performance was positively affected by thatch, consistent with a positive feedback initiated by invasion of this species. Our results demonstrate that thatch accumulation, rather than competition for resources, is the primary cause of native species decline in grasslands invaded by this exotic annual grass. In addition, the dominance of
B. diandrus
in many invaded grasslands may be reinforced through a positive thatch-feedback and require active management, such as grazing or fire, to be broken.
Non‐native species with growth forms that are different from the native flora may alter the physical structure of the area they invade, thereby changing the resources available to resident species. ...This in turn can select for species with traits suited for the new growing environment. We used adjacent uninvaded and invaded grassland patches to evaluate whether the shift in dominance from a native perennial bunchgrass, Nassella pulchra, to the early season, non‐native annual grass, Bromus diandrus, affects the physical structure, available light, plant community composition and community‐weighted trait means. Our field surveys revealed that the exotic grass B. diandrus alters both the vertical and horizontal structure creating more dense continuous vegetative growth and dead plant biomass than patches dominated by N. pulchra. These differences in physical structure are responsible for a threefold reduction in available light and likely contribute to the lower diversity, especially of native forbs in B. diandrus‐dominated patches. Further, flowering time began earlier and seed size and plant height were higher in B. diandrus patches relative to N. pulchra patches. Our results suggest that species that are better suited (earlier phenology, larger seed size and taller) for low light availability are those that coexist with B. diandrus, and this is consistent with our hypothesis that change in physical structure with B. diandrus invasion is an important driver of community and trait composition. The traits of species able to coexist with invaders are rarely considered when assessing community change following invasion; however, this may be a powerful approach for predicting community change in environments with high anthropogenic pressures, such as disturbance and nutrient enrichment. It also provides a means for selecting species to introduce when trying to enhance native diversity in an otherwise invaded community.
Land use intensification can greatly reduce species richness and ecosystem functioning. However, species richness determines ecosystem functioning through the diversity and values of traits of ...species present. Here, we analyze changes in species richness and functional diversity (FD) at varying agricultural land use intensity levels. We test hypotheses of FD responses to land use intensification in plant, bird, and mammal communities using trait data compiled for 1600+ species. To isolate changes in FD from changes in species richness we compare the FD of communities to the null expectations of FD values. In over one-quarter of the bird and mammal communities impacted by agriculture, declines in FD were steeper than predicted by species number. In plant communities, changes in FD were indistinguishable from changes in species richness. Land use intensification can reduce the functional diversity of animal communities beyond changes in species richness alone, potentially imperiling provisioning of ecosystem services.
• Background and Aims Global environmental change will affect non-native plant invasions, with profound potential impacts on native plant populations, communities and ecosystems. In this context, we ...review plant functional traits, particularly those that drive invader abundance (invasiveness) and impacts, as well as the integration of these traits across multiple ecological scales, and as a basis for restoration and management. • Scope We review the concepts and terminology surrounding functional traits and how functional traits influence processes at the individual level. We explore how phenotypic plasticity may lead to rapid evolution of novel traits facilitating invasiveness in changing environments and then 'scale up' to evaluate the relative importance of demographic traits and their links to invasion rates. We then suggest a functional trait framework for assessing per capita effects and, ultimately, impacts of invasive plants on plant communities and ecosystems. Lastly, we focus on the role of functional trait-based approaches in invasive species management and restoration in the context of rapid, global environmental change. • Conclusions To understand how the abundance and impacts of invasive plants will respond to rapid environmental changes it is essential to link trait-based responses of invaders to changes in community and ecosystem properties. To do so requires a comprehensive effort that considers dynamic environmental controls and a targeted approach to understand key functional traits driving both invader abundance and impacts. If we are to predict ftiture invasions, manage those at hand and use restoration technology to mitigate invasive species impacts, future research must focus on functional traits that promote invasiveness and invader impacts under changing conditions, and integrate major factors driving invasions from individual to ecosystem levels.
The increased occurrences of drought and fire may be contributing to the loss of biodiverse ecosystems in Mediterranean regions. Specifically, the conversion of diverse native shrublands, such as ...chaparral, to non‐native annual grassland by fire is of great conservation concern in California. To avoid or slow the loss of chaparral, it is important to understand the underlying causes of landscape conversion. Studies investigating the interaction of multiple potential drivers are particularly crucial to identification of vulnerable areas of the landscape. Here we used aerial imagery to evaluate vegetation transitions between chaparral, sage scrub, grassland, and tree domination and their potential drivers within Ventura County, CA, a strongly Mediterranean climate region. We used random forest algorithms and conditional inference trees to determine the climatic, topographic, and fire‐related variables contributing most to vegetation change. Our results support that chaparral conversion to grass (27% of chaparral plots) is a result of landscape position, fire, and drought acting in tandem. In particular, lower elevation, southwest‐facing slopes that experience a postfire drought are at very high likelihood of conversion to non‐native annual grass. Additionally, our results show that these grasslands, once formed, rarely convert to other community types. Therefore, protecting shrub‐dominated areas that are most likely to convert (low elevation, more southwest‐facing slopes, and less annual precipitation) is crucial to preserving native vegetation diversity.
Background and Aims If large genomes are truly saturated with unnecessary 'junk' DNA, it would seem natural that there would be costs associated with accumulation and replication of this excess DNA. ...Here we examine the available evidence to support this hypothesis, which we term the 'large genome constraint'. We examine the large genome constraint at three scales: evolution, ecology, and the plant phenotype. Scope In evolution, we tested the hypothesis that plant lineages with large genomes are diversifying more slowly. We found that genera with large genomes are less likely to be highly specious - suggesting a large genome constraint on speciation. In ecology, we found that species with large genomes are under-represented in extreme environments - again suggesting a large genome constraint for the distribution and abundance of species. Ultimately, if these ecological and evolutionary constraints are real, the genome size effect must be expressed in the phenotype and confer selective disadvantages. Therefore, in phenotype, we review data on the physiological correlates of genome size, and present new analyses involving maximum photosynthetic rate and specific leaf area. Most notably, we found that species with large genomes have reduced maximum photosynthetic rates - again suggesting a large genome constraint on plant performance. Finally, we discuss whether these phenotypic correlations may help explain why species with large genomes are trimmed from the evolutionary tree and have restricted ecological distributions. Conclusion Our review tentatively supports the large genome constraint hypothesis.
Despite obvious impacts of nonnative species in many ecosystems, the long-term outcome of competition between native and exotic species often remains unclear. Demographic models can resolve the ...outcome of competition between native and exotic species and provide insight into conditions favoring exclusion vs. coexistence. California grasslands are one of the most heavily invaded ecosystems in North America. Although California native perennial bunchgrasses are thought to be restricted to a fraction of their original abundance, the eventual outcome of competition with invasive European annual grasses at a local scale (competitive exclusion, stable persistence, or priority effects) remains unresolved. Here, we used a two-species discrete time population growth model to predict the outcome of competition between exotic annual and native perennial grasses in California, and to determine the demographic traits responsible for the outcome. The model is parameterized with empirical data from several field experiments. We found that, once introduced, annual grasses persist stably with little uncertainty. Although perennial grasses are competitively excluded on average, the most likely range of model predictions also includes stable coexistence with annual grasses. As for many other perennial plants, native bunchgrass population growth is highly sensitive to the survival of adults. Management interventions that improve perennial adult survival are likely to be more effective than those that reduce exotic annual seed production or establishment, reduce competition, or increase perennial seedling establishment. Further empirical data on summer survival of bunchgrass adults and competitive effects of annuals on perennials would most improve model predictions because they contribute most to the uncertainty in the predicted outcome for the perennial grass. This work demonstrates how demographic approaches can clarify the outcome of competition between native and exotic species, identify key targets for future empirical work, and predict the effectiveness of management interventions. Such studies are critical both for understanding the impacts of invasion and for targeting management responses that maximize the benefit to native species.
We situate the contemporary crisis of COVID‐19 deaths in seniors’ care facilities within the restructuring and privatisation of this sector. Through an ethnographic comparison in a for‐profit and ...nonprofit facility, we explore what we identify as brutal and soft modes of privatisation within publicly subsidised long‐term seniors’ care in Vancouver, British Columbia, and their influence on the material and relational conditions of work and care. Workers in both places are explicit that they deliver only bare‐bones care to seniors with increasingly complex care needs, and we document the distinct forms and extent to which these precarious workers give gifts of their time, labour and other resources to compensate for the gaps in care that result from state withdrawal and the extraction of profits within the sector. We nonetheless locate more humane and hopeful processes in the nonprofit facility, where a history of cooperative relations between workers, management and families suggest the possibility of re‐valuing the essential work of care.
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