Biotic Invasion Research Articles

Climate change and plant pathogens: Understanding dynamics, risks and mitigation strategies

AbstractClimate change is reshaping the interactions between plants and pathogens, exerting profound effects on global agricultural systems. Elevated tropospheric ozone levels due to climate change hinder plant photosynthesis and increase vulnerability to biotic invasion. The prevailing atmospheric conditions, including temperature and humidity, profoundly influence fungal pathogenesis, as each stage of a pathogen's life cycle is intricately linked to temperature variations. Likewise, climate change alters bacterial behaviour, fostering increased production of extracellular polysaccharides by plant‐pathogenic bacteria in warmer temperatures. Heat‐adapted bacteria, such as Burkholderia glumea and Ralstonia solanacearum, are emerging as significant global threats as temperature rise. Viruses, too, respond dynamically to climate shifts, with certain species favouring warmer climates for replication, resulting in expanded geographical ranges and modified transmission patterns. Nematodes, formidable constraints in crop production, exhibit temperature‐dependent life cycles and would have potentially accelerated proliferation and distribution as global warming progresses. Molecular‐level changes in pathogenesis, induced by temperature fluctuations, influence various pathogens, thereby impacting their virulence and interactions with host plants. Modelling studies predict changes in disease risks and distributions under future climate scenarios, highlighting the necessity of integrating climate data into crop disease models for accurate forecasts. Mechanistic and observational models illustrate pathogen behaviours amidst changing environmental conditions, providing crucial insights into future disease dynamics. In addition, controlled experiments study disease responses under simulated climate scenarios, underscoring the urgency for comprehensive research to devise effective resistance strategies against severe plant diseases.

A review of the Late Ordovician (Katian) Richmondian Invasion of eastern Laurentia

Biotic Immigration Events in which a group of organisms that originated in one geographic region invade and become established in a new geographic region are common during Earth history. Many such events have been documented from the fossil record and have significantly impacted diversification patterns and processes during the history of life. One of the best studied of these events is the Richmondian Invasion, which constituted several waves of biotic invasion from multiple source regions into the Cincinnati Basin of eastern Laurentia during the Katian Stage. The major features of this invasion were first appreciated during the early 1900s and have received significant study since that time. General patterns of the Richmondian Invasion, including the influx of >60 taxa that span ecological roles and taxonomic groups, differential survival of generalist taxa relative to specialist taxa, and significant restructuring of paleocommunities have been well documented and establish this invasion as a “coordinated invasion” within the Invasion Hierarchy of Stigall et al. (2019). Substantial research to further delineate and clarify the details of the Richmondian Invasion has progressed on multiple fronts over the past two decades. These novel analyses into sedimentology, stratigraphy, and geochemistry coupled with detailed paleoecology, evolutionary, and biogeographic studies provide a framework for increased synthesis and understanding of invasion dynamics during this interval. In this contribution, the current state of knowledge of the Richmondian Invasion is reviewed and some of the key implications for understanding both Ordovician diversification and other intervals of Earth history are examined.

Insights for modern invasion ecology from biotic changes of the Clarksville Phase of the Richmondian Invasion (Ordovician, Katian)

AbstractThe frequency of biotic invasions in modern ecosystems is increasing due to global trade moving taxa outside their native ranges and climate change facilitating establishment of taxa in previously inhospitable regions. Thus, developing a holistic understanding of biotic invasions and how they impact ecosystems over different timescales—from annual to geologic timescales—is vital. Herein we examine a geologically brief invasion event, the Clarksville Phase of the Richmondian Invasion. Prior analyses have established general ecological and evolutionary patterns across the entire Richmondian Invasion, but recent sequence stratigraphic refinement makes analysis of individual invasion pulses possible for the first time. We examine biotic change across the Clarksville Phase and identify invasion impacts on diversity, paleocommunity composition, and niche stability. Invader arrival and success was strongly linked to increased propagule pressure facilitated by sea-level changes. Invaders initially colonized deep subtidal environments and then moved offshore facilitated by rapid niche evolution during the invasion interval. Invasive taxa that attained the largest population sizes belonged to previously underutilized ecological guilds. Overall, the introduction of the invasive taxa resulted in increased diversity that was maintained into the postinvasion interval accompanied by a change in community composition in which the invaders became dominant paleocommunity members. Combined, these analyses document a biotic invasion facilitated by climate change that increased local diversity through invaders occupying underutilized ecospace and competition-related niche contraction on millennial timescales. Developing a long-term perspective to accompany shorter-term studies facilitates predicting the long-term impacts of modern invasions and creating better-informed policies and practices.

Urbanization driving changes in plant species and communities – A global view

The urban landscape is becoming the environment most familiar to most of humanity, which has consequences for society, the environment, and biodiversity. Here, we present a systematic review of current research integrating several areas of urban ecology to evaluate how plants are responding to urbanization. We found that most studies were conducted in Europe and North America. The most represented biome was that of Temperate Broadleaf and Mixed Forests. The majority of studies reported negative consequences of urbanization. The Urban Drivers most commonly cited as responsible for changes in plant species and communities were Land Cover Change and Biotic Invasion. In general, urbanization reduces the richness of plant species and pollinators' availability. It also homogenizes the environment, promotes the invasion of non-native species, causes changes in phenological events, and presents difficulties for plant growth. However, some species show evidence of adaptation to these adversities through their phenotypic plasticity and the evolution of traits that make individuals resilient to the urban environment. Although it has been established that urbanization imposes novel selective pressures resulting in unique adaptations to city life, patterns of changes in biodiversity in response to urbanization can vary by region, biomes, city history, and the taxa studied. The Urban Drivers responsible for floristic responses work simultaneously by modifying the environment. Therefore, it is challenging to predict response patterns of plants under urban growth. It is necessary to outline strategies for continuous monitoring to document the progress of species in perpetuating themselves in the face of urbanization. • The Urban Drivers responsible for floristic responses work simultaneously by modifying the environment. • Land Cover Change and Biotic Invasion are the most common Urban Drivers responsible for plant species and communities changes. • Most research on plants and urbanization is conducted in Temperate regions. • Plant species show resilience to urbanization through phenotypic plasticity and evolution of traits. • Patterns of changes in biodiversity in response to urbanization can vary by region, biomes, city history, and the taxa studied.

Invasion of Alien Senna Spectabilis Causes Loss of Natural Vegetation in the Wayanad Wildlife Sanctuary of India and Edaphic Factors of the Invaded Areas Assist its Profuse Sprouting

The Indian region because of its diverse climatic and environmental conditions is highly vulnerable to biotic invasion. In the Wayanad Wildlife Sanctuary of India we studied the effect of the invasion of one of the alien species, Senna spectabilis , on natural vegetation and analyzed whether the edaphic factors of invaded regions induce its profuse sprouting. We observed that the invasion of S. spectabilis leads to a drastic loss in the natural vegetation there. No ground cover was found in the invaded region whereas heavy sprouting of S. spectabilis seeds was detected. The reappearance of lost flora with high diversity and species richness were noticed in the regions where S. spectabilis were manually eradicated. A study on the seed germination under laboratory conditions showed that the seeds of S. spectabilis are highly dormant and scarification using concentrated H 2 SO 4 or water incubation induces its germination. Further analysis of soil samples of the invaded area revealed that soils are acidic and have high water holding capacity. The results imply that the invasion of S. spectabilis is a major threat to the indigenous plant diversity and edaphic factors of the invaded areas assist the profuse sprouting.

How mycorrhizas can help forests to cope with ongoing climate change?

The ongoing climate change have multi-faceted effects not only on metabolism of plants, but also on the soil properties and mycorrhizal fungal community. Under climate change the stability of the entire forest ecosystems and the carbon balance depend to a large degree on the interactions between trees and mycorrhizal fungi. The main drivers of climate change are CO<sub>2</sub> enrichment, temperature rise, altered precipitation patterns, increased N deposition, soil acidification and pollutants, ecosystem fragmentation and habitat loss, and biotic invasion. These drivers can impact mycorrhizal community directly and indirectly. We discussed the influence of each driver on mycorrhizal community and outlined how mycorrhizas play an important role in the resilience and recovery of forest ecosystems under climate change, by mitigating detrimental effects of CO<sub>2</sub> enrichment, temperature rise, drought, lack of nutrients, soil acidification, pollutants, pests, and diseases. Conservation of the overall biodiversity in forest ecosystems as well as providing the most favourable conditions for the development of mycorrhizae can contribute to increasing the resilience of forest ecosystems to climate change.

Disruption of the competitive balance between foundational tree species by interacting stressors in a temperate deciduous forest

Abstract The complex effects of global environmental changes on ecosystems result from the interaction of multiple stressors, their direct impacts on species and their indirect impacts on species interactions. Air pollution (and resulting depletion of soil base cations) and biotic invasion (e.g. beech bark disease [BBD] complex) are two stressors that are affecting the foundational tree species of northern hardwood forests, sugar maple and American beech, in northeastern North America. At the Hubbard Brook Experimental Forest in New Hampshire, a watershed‐scale calcium (Ca) addition in 1999 restored soil Ca that had been lost as a result of acid deposition in a maple‐beech forest that was severely affected by BBD beginning in the 1970s. We present historic data from the reference watershed for BBD progression, 20 years of comparative forest data from the treated and reference watersheds, and tree demographic rates for the most recent decade. We hypothesized that mitigation of soil acidification on the treated watershed in the presence of BBD would favour improved performance of sugar maple, a species that is particularly sensitive to base cation depletion. We observed significant responses of seed production, seedling bank composition, sapling survival and recruitment, and tree mortality and growth to the restoration of soil Ca, indicating that acid rain depletion of soil base cations has influenced demographic rates of maple and beech. Overall, the reduced performance of sugar maple on acidified soils may indirectly favour the persistence of diseased beech trees and a greater abundance of beech vegetative sprouts, effectively promoting the chronic presence of severe BBD in the population. Synthesis. The shifting conditions created by global change have altered long‐term demographic rates and may thereby impact competitive interactions in the current centre of these species ranges and have more profound implications for species persistence and migration potential than previously anticipated.

Human settlements in headwater catchments are associated with generalist stream food webs

While a variety of anthropogenic impacts on lotic biodiversity have been documented, food-web responses to catchment development are poorly understood. We selected 27 stream food webs of comparable quality and conducted an analysis to assess the effect of catchment development on food-web structure. We quantified population densities, built-up area, and proximity to urban centres, and calculated a Settlement Index for each catchment using Principal Components Analysis. We also calculated the percentage of agricultural land cover in each catchment. Next, we assessed the correlations between the structural properties of food-webs (species richness, connectance, mean food-chain length, linkage density, trophic generality, and trophic vulnerability) and the Settlement Index as well as agricultural land cover. We found that linkage density, trophic vulnerability (number of consumers per species), and trophic generality (number of resources per species) were higher in streams with greater Settlement Index, indicating a reduction in specialisation. However, no clear trends were observed for species richness, connectance, and mean food-chain length. Agricultural land cover was also not related to food-web structure. We propose that the reduction in specialisation may be driven by species turnover and feeding plasticity, as biotic invasion or species impoverishment was not evident.

Invasive alien plant species: Their impact on environment, ecosystem services and human health.

Ecological perturbations caused by biotic invasion have been identified as a growing threat to global sustainability. Invasive alien plants species (IAPS) are considered to be one of the major drivers of biodiversity loss and thereby altering the ecosystem services and socio-economic conditions through different mechanisms. Although the ecological impacts of IAPS are well documented, there is a dearth of studies regarding their economic quantification, livelihood considerations, biotechnological prospects (phytoremediation, bioenergy, phyto-synthesis of nanoparticles, biomedical, industrial applications etc.) and human health risk assessments of IAPS. In this context, the current panoramic review aimed to investigate the environmental, socio-ecological and health risks posed by IAPS as well as the compounded impact of IAPS with habitat fragmentation, climate and land use changes. To this end, the need of an integrated trans-disciplinary research is emphasized for the sustainable management of IAPS. The management prospects can be further strengthened through their linkage with geo-spatial technologies (remote sensing and GIS) by mapping and monitoring the IAPS spread. Further, the horizon of IAPS management is expanded to ecological indicator perspectives of IAPS, biosecurity, and risk assessment protocols with critical discussion. Moreover, positive as well as negative implications of the IAPS on environment, health, ecosystem services and socio-economy (livelihood) are listed so that a judicious policy framework could be developed for the IAPS management in order to mitigate the human health implications.

The unknown followers: Discovery of a new species of Sycobia Walker (Hymenoptera: Epichrysomallinae) associated with Ficus benjamina L. (Moraceae) in the Neotropical region

Biotic invasion in mutualistic communities is of particular interest due to the possible establishment of new relationships with native species. Ficus species are widely cultivated as ornamental plants, and they host specific communities of chalcid wasps that are strictly associated with the fig inflorescences. Some introduced fig species are capable of establishing new relationships with the local fig wasps, and fig wasp species may also be concomitantly introduced with their host plants. Ficusbenjamina L. is widely cultivated across the world, but the associated fig wasps are not reported outside of the species native range. We describe for the first time a non-pollinating fig wasp associated with F.benjamina inflorescences outside its native distribution. Sycobiahodites Farache & Rasplus, sp. n. is the third known species of the genus and was recorded in populations of F.benjamina introduced in the Neotropical region throughout several localities in Argentina, Brazil and Colombia. Sycobia is a gall-inducing non-pollinating fig wasp genus associated with fig trees in the Oriental and Australasian regions. This species competes with pollinators for oviposition sites and may hinder the future establishment of the native pollinator of F.benjamina, Eupristinakoningsbergeri Grandi, 1916 in the New World. However, the occurrence of a gall inducing species in this host plant may open ecological opportunities for the establishment of species belonging to other trophic levels such as cleptoparasite and parasitoid wasps.

Factors shaping avian alien species richness in Australia vs Europe

AbstractAimWe aim to examine the relative importance of human activity‐related and natural variables in shaping spatial patterns of alien bird species richness at the continental scale for Australia. We examine the drivers shaping establishment of alien birds in Australia in the framework of the human activity hypothesis and the biotic acceptance hypothesis (the “rich get richer” model of biotic invasion), and directly compare our results to Europe.LocationContinental Australia, Tasmania, Continental Europe, United Kingdom.MethodsWe use compiled atlas data on alien bird richness in continental Australia and Tasmania together and separately, records of known alien bird introduction events compiled from various sources and a suite of biogeographic variables to evaluate drivers of alien bird richness at a 50‐km resolution in Australia. We use hierarchical portioning and spatial generalized linear models to quantify the relative contribution of each environmental variable to alien bird richness. We then compare our results directly to those from a previous continental‐scale study in Europe and in the UK.ResultsWe identify 24 established alien bird species across Australia (including nearshore islands and Tasmania) and present a detailed map of alien bird richness in Australia. We discover that in Australia, native bird species richness and land cover heterogeneity are the strongest predictors of alien bird richness at a 50‐km resolution, supporting the “rich get richer” model of species invasion.Main conclusionsOur results are contrary to Europe, where the human activity hypothesis was best supported. By performing a cross‐continental comparison of drivers of alien bird richness, we show that processes shaping alien establishment and spread can vary across continents with variable human impact history and should be examined on a case‐by‐case basis before endorsing general hypotheses.

Fungal community homogenization, shift in dominant trophic guild, and appearance of novel taxa with biotic invasion

AbstractInvasion by non‐native plants may fundamentally restructure the soil fungal community. The invasive plant, Alliaria petiolata, produces secondary compounds suppressive to mycorrhizal fungi and may therefore be expected to have generally negative effects on other components of the fungal community. Here, we compared fungal biomass, diversity, community composition, and the relative abundance of fungal trophic guilds, along with edaphic properties of soils collected from uninvaded and invaded plots across six temperate forests. Invaded plots were differentiated from uninvaded plots by lower variation in fungal community composition (beta diversity) and soil properties, higher fungal richness and community evenness (alpha diversity), and a suite of novel saprotrophic and pathotrophic fungi that were consistently present across the invaded landscape and absent from uninvaded forest patches. Invaded plots also had lower ectomycorrhizal but higher saprotrophic and pathotrophic relative abundance, despite there being no difference in fungal biomass between invasion statuses. We hypothesize that shifts in the fungal community with invasion may directly impact plant disease response, soil nutrient cycling processes, and plant performance of the invasive and native plant communities.

Biotic invasion, niche stability, and the assembly of regional biotas in deep time: comparison between faunal provinces

AbstractBiotic invasions in the fossil record provide natural experiments for testing hypotheses of niche stability, speciation, and the assembly and diversity of regional biotas. We compare ecological parameters (preferred environment, occupancy, median abundance, rank abundance) of genera shared between faunal provinces during the Richmondian Invasion in the Late Ordovician on the Laurentian continent. Genera that spread from one faunal province to the other during the invasion (invading shared genera) have high Spearman rank correlations (>0.5) in three of four ecological parameters, suggesting a high level of niche stability among invaders. Genera that existed in both regions prior to and following the invasion (noninvading shared genera) have low correlations (<0.3) and suggest niche shift between lineages that diverged at least 8 Myr earlier. Niche shift did not accumulate gradually over this time interval but appears to have occurred in a pulse associated with the onset of the Taconic orogeny and the switch from warm-water to cool-water carbonates in southern Laurentia.

Does tallgrass prairie restoration enhance the invasion resistance of post-agricultural lands?

There is building interest in the use of ecological restoration to enhance the biotic invasion resistance of disturbed lands. However, few studies have rigorously examined the effect of community restoration on biotic invasion resistance under conditions of controlled invader propagule pressure. Results are presented from a field experiment conducted in a post-agricultural grassland in eastern Kansas to explore the interplay of tallgrass prairie restoration and invader propagule pressure in modulating plant invasion. Seed additions of multiple native and non-native species were used to provide a general test of biotic invasion resistance under varied propagule availability. Restoration increased plant diversity, increased above ground productivity, reduced the availability of light, soil moisture and bare soil microsites and strongly suppressed the invasion of all species sown into the experiment, including the highly invasive exotic legume, Lespedeza cuneata. In the absence of restoration, L. cuneata rapidly dominated plots where it had been sown, particularly at the highest propagule pressure. Results of multiple regression modelling suggested that restoration most likely increased community resistance to L. cuneata invasion through changes in functional guild composition rather than through changes in species diversity. Overall our study indicates that restoration of abandoned agricultural land to native tallgrass prairie can enhance invasion resistance in the face of substantial invader propagule pressures by altering community composition to dominance by native species that are efficient in utilizing resources.

A continent invaded

book reviews ISSN 1948-6596 A continent invaded Invasion Biology and Ecological Theory: Insights from a Continent in Transformation. Herbert H. T. Prins & Iain J. Gordon (editors), 2014, Cambridge University Press. 540 pp. £65.00 (hardback) ISBN 9781107035812; http://www.cambridge.org/ There is little doubt that Invasion Biology has come of age. Look inside any volume of your fa- vourite ecological journal and you will find studies of the dynamics and impacts of alien and invasive species. Entire research laboratories focus their research specifically on mitigating the problems caused by invasive pests, weeds and pathogens. As well as preventing new invasions, there has always been considerable ecological insight gained from studying the behaviour of alien spe- cies in novel recipient communities and environ- ments. Australia has an illustrious (perhaps nefari- ous) history of biological invasions and (as any international visitor knows) now boasts one of the most enviable quarantine and biosecurity enforce- ment programs in the world. In this book, the editors return to the foun- dations of ecological theory and examine our cur- rent understanding of invasion biology through a series of 11 hypotheses (or insights). Together, these 11 hypotheses provide a reference to the fundamental ideas behind invasion biology as a discipline. In each of the empirical chapters the au- thors have been asked to evaluate the support for these hypotheses, from their own examples and perspectives. The book draws its examples una- shamedly, and exclusively, from Australia, and is divided into two discrete sections. The first section ‘Ancient invaders’ considers (mostly) the pre- human biotic invasion of Gondwanan Australia, while the second ‘Modern invaders’ deals with hu- man-mediated introductions. There is no obvious link developed between the two sections, other than that invasions (whatever their flavour) may be expected to share certain ecological commonalities. The editors claim that ‘The book is quite simply organised’. Yet, they have made little at- tempt to explain why we are reading about any of the particular species (or clades) included in the book, or to explain the order in which the chapters are grouped. The majority of the chapters are ter- restrial, with a great predominance of mammal and bird studies; from the diverse Meliphagid hon- eyeaters and endemic Australian parrots to Charadriiforme waders. Bird invasions have attract- ed considerable scientific research effort (Blackburn et al. 2009). Nevertheless, I was surprised by the large number and variety of avian examples includ- ed in the book, at the expense of many other taxa. Two particularly interesting chapters consider mi- gratory tendency in birds; an important trait linked to the success of natural colonisation, and the fail- ure of human-assisted translocations. Australia is popularly known for its marsupi- als, which arrived in the Australian part of the southern supercontinent Gondwana around 65 Mya and then underwent a spectacular evolution- ary radiation that led to seven orders and at least 31 families. Less well-known, I suspect, are the in- vasion histories of the murine rodents and ptero- podid bats, also included in this book. The single aquatic (marine mammal) example is the phyloge- ography of sirenians, and the invasion of the du- gong (Dugong dugon) into Northern (tropical) Aus- tralia at the transition of the Oligocene to the Mio- cene (about 25 Mya) following the arrival (invasion) of its tropical food source, seagrass. Plants are fur- ther considered through comparisons of the an- cient (and modern) invasion of species in the flow- ering Clade Mimosoideae, and a single chapter on the modern global invasions of Australian Eucalyp- tus, Acacia and Casuarina species, and Melaleuca quinquenervia, outside of Australia. Two chapters on Australia’s geological and climatic history provide a good reference to the tectonic movement and changing climates of Aus- tralia. I found it disappointing, however, that the definitions for these stages of invasion were framed (in one case) around Australia’s mammal fauna and not more generally across a broader set of flora and fauna. I was also unsure why these defining chapters were not placed before the frontiers of biogeography 7.2, 2015 — © 2015 the authors; journal compilation © 2015 The International Biogeography Society

When and how do species achieve niche stability over long time scales?

Niche conservation is not ubiquitous among all species or all environmental changes. Identifying the underlying basis for variable species responses is important for conservation efforts and macroevolutionary theory and requires comparing multiple clades and types of environmental change. To examine this issue, niche stability was analyzed for a phylogenetically diverse suite of invertebrates that inhabited the epicontinental seas of eastern North America during the Late Ordovician Period (∼450 Ma). These taxa experienced fluctuating sea level and a regional biotic invasion event, the Richmondian invasion, during nine time slices spanning approximately three million years. Niche models were generated with Maxent and niche stability was assessed via geographic overlap, niche similarity, and environmental parameters.These taxa exhibited high fidelity habitat tracking and stable ecological niches during the pre‐invasion interval characterized by gradual sea‐level changes, whereas taxa exhibited statistically lower niche stability and more niche evolution during and after the Richmondian invasion. Conversely, environmental parameter similarity between niche models of adjacent time slices was lowest during the pre‐invasion interval and increased following the Richmondian invasion. Declining niche similarity and geographic stability coincident with increasing environmental parameter similarity indicates ecological niche change resulted from contracting species' realized niches to a subset of the original fundamental niche dimensions rather than shifting to new ecospace. Niche contraction is interpreted as a response to increased competition from invasive species, which may have arisen from adaptation, sorting (differential birth and death processes) and/or ecological fitting. These results indicate that consideration of multiple hierarchical levels, temporal scales and ecological contexts will yield new insights into the processes that generate both macroevolutionary and ecological patterns. They also suggest the widely employed assumption of niche conservatism through time and space may be more frequently valid for intervals of gradual abiotic change than for biotic changes caused by invasive species.

Assessing resilience and state‐transition models with historical records of cheatgrass Bromus tectorum invasion in North American sagebrush‐steppe

Summary Resilience‐based approaches are increasingly being called upon to inform ecosystem management, particularly in arid and semi‐arid regions. This requires management frameworks that can assess ecosystem dynamics, both within and between alternative states, at relevant time scales. We analysed long‐term vegetation records from two representative sites in the North American sagebrush‐steppe ecosystem, spanning nine decades, to determine if empirical patterns were consistent with resilience theory, and to determine if cheatgrass Bromus tectorum invasion led to thresholds as currently envisioned by expert‐based state‐and‐transition models (STM). These data span the entire history of cheatgrass invasion at these sites and provide a unique opportunity to assess the impacts of biotic invasion on ecosystem resilience. We used univariate and multivariate statistical tools to identify unique plant communities and document the magnitude, frequency and directionality of community transitions through time. Community transitions were characterized by 37–47% dissimilarity in species composition, they were not evenly distributed through time, their frequency was not correlated with precipitation, and they could not be readily attributed to fire or grazing. Instead, at both sites, the majority of community transitions occurred within an 8–10 year period of increasing cheatgrass density, became infrequent after cheatgrass density peaked, and thereafter transition frequency declined. Greater cheatgrass density, replacement of native species and indication of asymmetry in community transitions suggest that thresholds may have been exceeded in response to cheatgrass invasion at one site (more arid), but not at the other site (less arid). Asymmetry in the direction of community transitions also identified communities that were ‘at‐risk’ of cheatgrass invasion, as well as potential restoration pathways for recovery of pre‐invasion states. Synthesis and applications. These results illustrate the complexities associated with threshold identification, and indicate that criteria describing the frequency, magnitude, directionality and temporal scale of community transitions may provide greater insight into resilience theory and its application for ecosystem management. These criteria are likely to vary across biogeographic regions that are susceptible to cheatgrass invasion, and necessitate more in‐depth assessments of thresholds and alternative states, than currently available.

Eradication of invasive herbivores: usefulness and limits for biological conservation in a changing world

Over the past 25 years, the international scientific community has recognized that biotic invasion is a major anthropogenic threat to ecosystems worldwide (Mack et al., 2000). More recently, it has been shown that in addition to major ecological impacts on many Earth biotas (Walther et al., 2002), climate change is expected to benefit invaders (Frenot et al., 2005; Walther et al., 2009). Facing such probable synergistic threats, we need a strong scientific background both to better understand these processes and to advise conservation managers and the public (Towns, 2011). The longterm monitoring of ecosystems undergoing restoration programmes, following eradication of one or several invasive species, is not only a major way to assess the impact of invaders but it can also reveal some of the unpredicted negative effects associated with management actions (Zavaleta, Hobbs & Mooney, 2001; Courchamp, Chapuis & Pascal, 2003; Bergstrom et al., 2009). When eradication projects take place in archipelagoes, the variety of islands often offer contrasting situations in terms of the presence/ absence of introduced species, and monitoring provides invaluable information, including comparisons with control sites (Chapuis, Frenot & Lebouvier, 2002; Croll et al., 2005; Fukami et al., 2006; Towns et al., 2009). The Iles Kerguelen, where our study was carried out (Brodier et al., 2011), offered such a situation. When restoration programmes were initiated on the Iles Kerguelen in 1991 (Chapuis et al., 1995), the expected trajectory of vegetation cover after the rabbit eradication was the recovery of native plant communities. Specifically, we predicted the re-establishment of the keystone native species, the Kerguelen cabbage, Pringlea antiscorbutica, extirpated by rabbits (Chapuis, Barnaud & Bousses, 1994). Then, following the re-colonization event, we predicted that the most favourable habitats would be rehabilitated with a subsequent improvement in both native vertebrate (burrowing seabirds) and macroinvertebrate communities. Twenty years later, our initial predictions are neither fully supported nor rejected. The removal of rabbits from Ile Verte was beneficial to blue petrels, Halobaena caerulea, as expected, and to its native predator, the brown skua, Catharacta skua (Brodier et al., 2011). However, converse to expectations, the increase in blue petrels did not result directly from the restoration of the plant cover but through an apparently more complex mechanism involving interspecific competition with rabbits. Suppressing rabbits’ interference in burrow occupancy by breeding blue petrels highlighted an unreported competition process with a closely related sympatric petrel species, the Antarctic prion, Pachyptila desolata (Bonnaud & Courchamp, 2011). Therefore, the rabbit eradication restored competitive processes between native species, a result inaccessible without longterm monitoring of the ecosystem as a whole. Concerning changes in the vegetation cover, our monitoring programme demonstrated that our initial assumption was partly wrong, mainly in relation to the unexpected consequences of climate change: after rabbit eradication on three islands (Chapuis et al., 2001), native communities did not restore. In fact, native monospecific Acaena magellanica communities started to regress, allowing an important increase of invasive plant species (Chapuis, Frenot & Lebouvier 2004). Invasion has been facilitated by the regression of A. magellanica due to the increased frequency of summer droughts, a trend observed over the last 15 years in Iles Kerguelen (Lebouvier et al., 2011). As a consequence, an increase in soil erosion has also been detected, particularly on the main island where rabbits affect plant cover (Robin, Chapuis & Lebouvier, 2011). Unexpected cascade effects that could only be detected, thanks to the long-term monitoring in the context of climate change, raise new issues with regard to the biological conservation in the context of restoration. In our view, environmental managers are now facing three options on Kerguelen: (1) ‘Laissez faire’, to investigate the consequences of climate change on the dynamics of communities (including biotic and abiotic interactions); (2) pursue the rabbit removal to improve plant cover in areas threatened by erosion processes, even if promoting the development of invasive plant species (at least in the medium term); and (3) limit the development of invasive plants while maintaining enough cover to fix soils and prevent erosion, using rabbit as an auxiliary species (see Walther et al., 2009). This latter option has gained some indirect support, as documented by one of us (JLC) in February 2011. On Ile du Cimetiere, rabbits have been maintained at low density over recent Animal Conservation. Print ISSN 1367-9430

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.

Response of Mycorrhizal Diversity to Current Climatic Changes

Form and function of mycorrhizas as well as tracing the presence of the mycorrhizal fungi through the geological time scale are herein first addressed. Then mycorrhizas and plant fitness, succession, mycorrhizas and ecosystem function, and mycorrhizal resiliency are introduced. From this, four hypotheses are drawn: (1) mycorrhizal diversity evolved in response to changes in Global Climate Change (GCC) environmental drivers, (2) mycorrhizal diversity will be modified by present changes in GCC environmental drivers, (3) mycorrhizal changes in response to ecological drivers of GCC will in turn modify plant, community, and ecosystem responses to the same, and (4) Mycorrhizas will continue to evolve in response to present and future changes in GCC factors. The drivers of climate change examined here are: CO2 enrichment, temperature rise, altered precipitation, increased N-deposition, habitat fragmentation, and biotic invasion increase. These impact the soil-rhizosphere, plant and fungal physiology and/or ecosystem(s) directly and indirectly. Direct effects include changes in resource availability and change in distribution of mycorrhizas. Indirect effects include changes in below ground allocation of C to roots and changes in plant species distribution. GCC ecological drivers have been partitioned into four putative time frames: (1) Immediate (1–2 years) impacts, associated with ecosystem fragmentation and habitat loss realized through loss of plant-hosts and disturbance of the soil; (2) Short-term (3–10 year) impacts, resultant of biotic invasions of exotic mycorrhizal fungi, plants and pests, diseases and other abiotic perturbations; (3) Intermediate-term (11–20 year) impacts, of cumulative and additive effects of increased N (and S) deposition, soil acidification and other pollutants; and (4) Long-term (21–50+ year) impacts, where increased temperatures and CO2 will destabilize global rainfall patterns, soil properties and plant ecosystem resilience. Due to dependence on their host for C-supply, orchid mycorrhizas and all heterotrophic mycorrhizal groups will be immediately impacted through loss of habitat and plant-hosts. Ectomycorrhizal (ECM) associations will be the principal group subject to short-term impacts, along with Ericoid mycorrhizas occurring in high altitude or high latitude ecosystems. This is due to susceptibility (low buffer capacity of soils) of many of the ECM systems and that GCC is accentuated at high latitudes and altitudes. Vulnerable mycorrhizal types subject to intermediate-term GCC changes include highly specialized ECM species associated with forest ecosystems and finally arbuscular mycorrhizas (AM) associated with grassland ecosystems. Although the soils of grasslands are generally well buffered, the soils of arid lands are highly buffered and will resist even fairly long term GCC impacts, and thus these arid, largely AM systems will be the least affect by GCC. Once there are major perturbations to the global hydrological cycle that change rainfall patterns and seasonal distributions, no aspect of the global mycorrhizal diversity will remain unaffected.