Johannes J Le Roux

• PhD
• Professor at Macquarie University

Native species can evolve rapidly in response to utilising invasive species as novel resources. We investigated the genetic and trait differentiation of the Australian soapberry bug Leptocoris tagalicus across three biotypes: those feeding on invasive Cardiospermum grandiflorum in New South Wales (NSW) and Queensland (Qld), invasive C. halicacabum...

Ecosystem functioning is influenced by biological diversity, ecological interactions, and abiotic conditions. Human interactions with ecosystems can cause major changes in how they function when involving changes in the vegetation cover and structure (i.e., land use change). This study examines how land use change affects the diversity of arbuscula...

Inferring general biogeographic patterns in the sub-Antarctic region has been challenging due to the disparate geological origins of its islands and archipelagos-ranging from Gondwanan fragments to uplifted seafloor and more recently formed volcanic islands-and the remoteness of these island systems, spread around the austral continental landmasses...

The ability to reproduce via multiple strategies is crucial for the invasion success of alien plant species. Here, we use Carpobrotus taxa (species and hybrids) to explore how trade-offs between and within these strategies may influence plant invasion dynamics. Native to South Africa, Carpobrotus plants are globally prominent in coastal ecosystems,...

The successful management of invasive alien species is hampered when they share habitats with native congeners. However, in some instances, the status of resident congeners (as alien or native) in the invaded range is unknown, further complicating management efforts. Here, we investigate the genetic relationships between Cardiospermum balloon vine...

Invasive alien species pose significant threats to coastal ecosystems worldwide. Carpobrotus sp. pl. is one of the most threatening invasive species to biodiversity in coastal regions globally. Carpobrotus species are known to modify soil conditions and impact the diversity and composition of soil microbial communities in the invaded areas. In this...

To understand the success of invasive alien species, it is necessary to evaluate the site-specific eco-evolutionary challenges they face in their new environments. We explored whether the rearrangement of genetic diversity is linked to the invasiveness of Prosopis juliflora by (i) comparing different stages of invasion (founding vs invasive populat...

To separate the effects of the abiotic and biotic soil components on plant growth, researchers can compare plants grown in sterilised and unsterilised soil (unsterilised soil approach). However, using this approach can be problematic if the abiotic component of the soil is affected by the sterilisation treatment, which is often the case. We aimed t...

A large number of non‐native trees (NNTs) have been introduced globally and widely planted, contributing significantly to the world's economy. Although some of these species present a limited risk of spreading beyond their planting sites, a growing number of NNTs are spreading and becoming invasive leading to diverse negative impacts on biodiversit...

Acacia longifolia (Andrews) Willd. is a legume native to southeast mainland Australia and Tasmania and has two described subspecies: A. l. subsp. longifolia and A. l. subsp. sophorae. The species has been introduced around the world and is considered invasive in several Mediterranean-type climate regions, including in South America, South Africa, a...

Acacia longifolia is an aggressive invader in Mediterranean-type ecosystems severely impacting biodiversity and ecosystem functions. The species’ invasiveness has been linked to its ability to thrive in nutrient poor soils, high seed production, and quick establishment after fire. In this study, we identify and compare the bacterial endophytes of A...

Invasive plants often impact the abiotic and biotic conditions of the ecosystems they invade. These impacts can persist after the removal of the invader as legacy effects that may hamper restoration. We assessed whether the invasion of Cumberland Plain Woodland in Australia by African Olive impacts the performance of native species through legacy e...

Rodents are important hosts for ectoparasites, such as fleas, ticks, and mites, which means they are also important intermediate hosts for many zoonotic diseases. As anthropogenic environments bring humans and rodents into closer contact, an understanding of host–ectoparasite ecology is essential to predict and manage disease spillover risks. We ai...

The genus Carpobrotus N.E.Br. comprises between 12 and 25 species, most of which are native to South Africa. Some Carpobrotus species are considered among the most damaging invasive species in coastal dune systems worldwide. In their introduced areas, these species represent a serious threat to native species and significantly impact soil condition...

Background and aims Invasive plants often alter soil abiotic and biotic conditions which can benefit their own growth while harming native species. The impacts on native species may persist as legacy effects after the invasive species has been controlled and removed. This study focused on the Critically Endangered Cumberland Plain Woodland (CPW) ve...

The legume Acacia longifolia (Andrews) Willd. is native to southeast mainland Australia and Tasmania and has two described subspecies: A. l. ssp. longifolia and A. l. ssp. sophorae . The species has been introduced around the world and is considered invasive in several Mediterranean-type climate regions, including in South America, South Africa, an...

Temperature and scarcity of water are the main constraints to the activity of small organisms living in desert regions, as they are exposed to high day temperatures and need to evolve adaptations to these harsh conditions. Several insects living in arid regions have evolved physiological adaptations that enable them to survive dry conditions. Ants...

Acacia longifolia (Sydney golden wattle) is considered one of the most problematic plant invaders in Mediterranean-type ecosystems. In this study, we investigate the species’ invasion history by comparing the genetic diversity and structure of native (Australia) and several invasive range (Brazil, Portugal, South Africa, Spain, and Uruguay) populat...

Nine new genera, 17 new species, nine new combinations, seven epitypes, three lectotypes, one neotype, and 14 interesting new host and / or geographical records are introduced in this study. New genera: Neobarrmaelia (based on Neobarrmaelia hyphaenes ), Neobryochiton (based on Neobryochiton narthecii ), Neocamarographium (based on Neocamarographium...

Invasive Australian acacias cause substantial biodiversity impacts in South Africa's Core Cape Subregion (CCR) via positive plant-soil feedbacks, driven by high growth rates and leaf litter input by these legumes and their associations with nitrogen-fixing rhizobia. However, it is unclear whether acacia-induced soil abiotic conditions, or the assoc...

Biological invasions in remote areas that experience low human activity provide unique opportunities to elucidate processes responsible for invasion success. Here we study the most widespread invasive plant species across the isolated islands of the Southern Ocean, the annual bluegrass, Poa annua. To analyze geographic variation in genome size, gen...

Allelopathy is frequently invoked as important for successful invasion by non-native plants. Yet, the effects of specific phytochemicals of invasive plants on soil microbes remain unexplored. Here we used manipulative experiments and next generation sequencing analyses to investigate how sesquiterpene lactones (STLs) of invasive Mikania micrantha i...

One of the most compelling explanations for floral trait diversification and speciation in angiosperms is the process of pollinator shifts. The African genus, Ferraria, is a relatively small and understudied group of irises which interacts with many distinct pollinator groups and exhibits large variation in floral scent and colour. We built a phylo...

Extensive morphological diversity in the invasive L. camara species complex has resisted clear taxonomic characterisation, yet molecular studies to date have revealed minimal genetic structure. Analysis of thousands of genome-wide markers successfully detects differentiation among sub-lineages within the complex, revealing that two of the morpholog...

A longstanding question in evolutionary biology is how natural selection and environmental pressures shape the mitochondrial genomic architectures of organisms. Mitochondria play a pivotal role in cellular respiration and aerobic metabolism, making their genomes functionally highly constrained. Evaluating selective pressures on mitochondrial genes...

Knowledge of the introduction history and spread dynamics of invasive species can provide important insights for management (Ens et al. in Environ Rev (in press), 2022), however such information is often unavailable for accidental introductions. Here we infer how the European shore crab, Carcinus maenas , and its congener, the Mediterranean shore c...

Novel species of fungi described in this study include those from various countries as follows: Australia, Agaricus albofoetidus, Agaricus aureoelephanti and Agaricus parviumbrus on soil, Fusarium ramsdenii from stem cankers of Araucaria cunninghamii, Keissleriella sporoboli from stem of Sporobolus natalensis, Leptosphaerulina queenslandica and Pes...

Mutualisms can be disrupted when non-native plants are introduced into novel environments, potentially impacting their establishment success. Introduced species can reassemble mutualisms by forming novel associations with resident biota or by maintaining familiar associations when they are co-introduced with their mutualists. Invasive Australian Ac...

This chapter summarises the ecological conditions and demographic processes that underlie most biological invasions and how these create unique opportunities for rapid evolution to occur. The chapter discusses the roles of founder events, inbreeding, genetic drift, migration, mutation, natural selection, and non-assortative mating in causing rapid...

This chapter evaluates the historical contexts within which individual biotic interactions have evolved and how these influence the establishment success of exotic species. The effects of past evolution on different biotic interactions, or so-called eco-evolutionary experience, emphasise the role of preadaptations to various interaction types in pr...

A paradigm shift occurred in the field of evolutionary biology during the 1990s. Biologists, who traditionally viewed evolution as a slow process, came to the realisation that evolution can often be rapid, sometimes occurring over timescales as short as a few generations. Much of the empirical evidence underlying this paradigm shift came from studi...

This chapter reviews the mechanisms underlying, and dynamics of, rapid evolution in invasive species. By synthesising recent research, the relative roles of adaptive (abiotic and biotic) and non-adaptive (founder events, bottlenecks, drift, spatial sorting) processes in causing rapid evolution in invasive species are discussed. Traits that often un...

This chapter discusses the use of evolutionary biology in invasive species management. Understanding the historical evolutionary context of host–enemy relationships, i.e. co-evolution, can assist the selection of more efficient biological control agents. Moreover, rapid evolution in biocontrol agents for enhanced exploitation of target hosts can be...

This chapter describes the evolutionary consequences of biological invasions for native species. As abundant resources (e.g. hosts or prey) or threats (e.g. predators), invasive species impose strong selection pressures on native species that may lead to rapid evolutionary responses. This chapter considers the direct impacts of invasive species on...

Epigenetic variation provides an important, but complex, layer of information involving gene regulation. Epigenetic variation represents various biochemical modifications of the genetic code (DNA) that influence gene expression, best known for its role in governing plastic responses to changing environmental conditions. This chapter summarises the...

This chapter provides an overview of the field of invasion genetics: the use of population genetics and genomics, phylogeography, and phylogenetics to better understand the ecology and evolutionary biology of invasive species. Continuous advances in molecular biology have made genetic tools central in addressing applied (e.g. invasive species manag...

The patchy distribution of trees typical of savannas often results in a discontinuous distribution of water, nutrient resources, and microbial communities in soil, commonly referred to as “islands of fertility”. We assessed how this phenomenon may affect the establishment and impact of invasive plants, using the invasion of Opuntia stricta in South...

Invasive plants often impact soil conditions, notably through changes in soil chemistry and microbial community composition, potentially leading to altered soil functionality. We determine the impacts of invasive nitrogen-fixing Australian Acacia trees on soil chemistry and function (carbon, nitrogen, and phosphorus cycling) in South Africa’s Core...

AimsUnderstanding the contributions of abiotic and biotic conditions to soil microbial diversity, structure, and function, remains a central focus in soil biology and biogeochemistry. Here we aim to determine how geography and host plant identity influence these different components of rhizosphere bacterial communities and endosymbionts associated...

Soil microbial community coalescence, where entire microbial communities mix and interact under new conditions, is a widespread phenomenon whose applicability for targeted root microbiome assembly has not been studied. Whether soil mixing can lead to predictable outcomes for community assembly and functioning of specific functional groups, for exam...

The link between the successful establishment of alien species and propagule pressure is well‐documented. Less known is how humans influence the post‐introduction dynamics of invasive alien populations. The latter requires studying parallel invasions by the same species in habitats that are differently impacted by humans. We analysed microsatellite...

The context‐depency of biological invasions makes it difficult to understand why some species become succesfull invaders and others not. Such understanding requires studying closely‐related invasive and non‐invasive alien taxa sharing the same introduction history in the same environment. We identified this unusual situation in Kenya where the indi...

Background and aims: Invasive species may undergo rapid evolution despite very limited standing genetic diversity. This so-called genetic paradox of biological invasions assumes that an invasive species has experienced (and survived) a genetic bottleneck and then underwent local adaptation in the new range. In this study, we test how often Austral...

American foulbrood (AFB) is a serious and near-global disease of honey bees and was recently discovered in South Africa. The causative pathogen, Paenibacillus larvae, comprises various strains. It is currently unknown which of these are present in South Africa and what their distribution is. We address this issue by genotyping P. larvae isolates us...

Background and aims Allelopathy is frequently invoked as being important for successful invasion by non-native plants. Yet, the effects of specific phytochemicals of invasive plants on soil microbes remain unexplored. Methods Here we used manipulative experiments and next generation sequencing (NGS) approaches to investigate how the sesquiterpene l...

Accurate taxonomic identification of alien species is crucial to detect new incursions, prevent or reduce the arrival of new invaders and implement management options such as biological control. Globally, the taxonomy of non-native Prosopis species is problematic due to misidentification and extensive hybridization. We performed a genetic analysis...

Invasive plants often change a/biotic soil conditions to increase their competitiveness. We compared the microbially mediated soil nitrogen (N) cycle of invasive Mikania micrantha and two co‐occurring native competitors, Persicaria chinensis and Paederia scandens. We assessed how differences in plant tissue N content, soil nutrients, N cycling rate...

The growing interest in commercial cultivation of bamboos (Poaceae subfamily Bambusoideae) has led to the introduction of new alien species into South Africa. The rate at which bamboos are being planted in South Africa is a cause for concern because of the impacts of bamboo invasions in other parts of the world. To understand the risks associated w...

This book contains 23 chapters divided into seven parts. Part I reviews the key hypotheses in invasion ecology that invoke biotic interactions to explain aspects of plant invasion dynamics; and reviews models, theories and hypotheses on how invasion performance and impact of introduced species in recipient ecosystems can be conjectured according to...

Selecting native species for restoration is often done without proper ecological background, particularly with regard to how native and invasive species interact. Here, we provide insights suggesting that such information may greatly enhance restoration success. The performance of the native vine, Pueraria lobata, and that of the invasive bitter vi...

Aim: To compare genetic diversity and structure between Acacia dealbata populations sampled across the species’ native range in Australia and from its non-native ranges in Chile, Madagascar, New Zealand, Portugal, La Réunion island, South Africa and the United States, and to investigate the most likely introduction scenarios to non-native ranges. L...

The flora of sub-Antarctic Marion Island forms part of the unique South Indian Ocean Biogeographic Province, and is under threat from climate change and invasive species. Current information on the flora is necessary to rapidly identify and manage future changes. We conducted a literature search on the taxonomy of indigenous vascular plant species...

Sustainably managed non-native trees deliver economic and societal benefits with limited risk of spread to adjoining areas. However, some plantations have launched invasions that cause substantial damage to biodiversity and ecosystem services, while others pose substantial threats of causing such impacts. The challenge is to maximise the benefits o...

Sustainably managed non-native trees deliver economic and societal benefits with limited risk of spread to adjoining areas. However, some plantations have launched invasions that cause substantial damage to biodiversity and ecosystem services, while others pose substantial threats of causing such impacts. The challenge is to maximise the benefits o...

There is interest in understanding how cultivation, plant genotype, climate, and soil conditions influence the biogeography of root nodule bacterial communities of legumes. For crops from regions with relict wild populations, this is of even greater interest because the effects of cultivation on symbiont communities can be revealed, which is of par...

Coastal dunes are ecosystems of high conservation value that are strongly impacted by human disturbances and biological invasions in many parts of the world. Here we assessed how urbanization and Carpobrotus edulis invasion affect soil bacterial communities on the north-western coast of Spain, by comparing the diversity, structure and composition o...

Understanding how plant-associated microbial communities assemble and the role they play in plant performance are major goals in microbial ecology. For nitrogen-fixing rhizobia, community assembly is generally driven by host plant selection and soil conditions. Here, we aimed to determine the relative importance of neutral and deterministic process...

Our ability to predict invasions has been hindered by the seemingly idiosyncratic context-dependency of individual invasions. However, we argue that robust and useful generalisations in invasion science can be made by considering “invasion syndromes” which we define as “a combination of pathways, alien species traits, and characteristics of the rec...

Biological invasions severely impact on marine ecosystems around the world, but to date management is rare and has not previously been attempted in Africa. This study documents a trial management programme aimed at informing a national management strategy for the invasive European shore crab, Carcinus maenas, in South Africa. The approach involved...

Le Roux et al. suggest that documented increases in local plant richness in response to climate change should consider the nature of ‘new’ species. They find that species responsible for increases in richness in areas that have experienced significant disturbance and climate change are often invasive and/or weedy species.

Ecological interactions, especially those that are beneficial (i.e. mutualism) or detrimental (i.e. parasitism), play important roles during the establishment and spread of alien species. This chapter explores the role of these interactions during biological invasions in South Africa, covering a wide range of taxonomic groups and interaction types....

The Novel Weapons Hypothesis postulates that the release of allelochemicals by alien plants can inhibit the growth of evolutionary naı¨venaı¨ve native plants. On the other hand, when species share a recent evolutionary history, recognition of phytochemicals from neighboring plants can have adaptive value by providing cues to signal suitable conditi...

Hybridisation between invasive and native species represents a significant threat to biodiversity. The Mallard Duck (Anas platyrhynchos) is known to hybridise with numerous closely related Anas species in regions where they have been introduced, threatening the genetic integrity of native ducks and in some instances contributing to their extinction...

Soil microbial community coalescence, whereby entire microbial communities mix and compete in a new environmental setting, is a widespread phenomenon whose applicability for targeted root microbiome assembly has not been studied. Using a legume shrub adapted to nutrient poor soil, we tested for the first time how the assembly of communities of rhiz...

There is interest in understanding the factors behind the biogeography of root-associated bacteria due to the joint effects that plant host, climate, and soil conditions can have on bacterial diversity. For legume crops with remaining wild populations, this is of even more importance, because the effects of cropping on undisturbed root-associated b...

Understanding how plant-associated microbial communities assemble and the roles they play in plant performance are major goals in microbial ecology. For nitrogen-fixing rhizobia, assemblages are mostly determined by filtering by the host as well as abiotic soil conditions. However, for legumes adapted to highly variable environments and nutrient-po...

This book contains 23 chapters divided into seven parts. Part I reviews the key hypotheses in invasion ecology that invoke biotic interactions to explain aspects of plant invasion dynamics; and reviews models, theories and hypotheses on how invasion performance and impact of introduced species in recipient ecosystems can be conjectured according to...

What makes some species successful invaders while others fail, and why some invaders have major impacts in invaded ecosystems are pivotal questions that are attracting major research effort. The increasing availability of high resolution, georeferenced stable isotope landscapes (‘isoscapes’), coupled with the commercialization of stable isotope‐enr...

Mutualistic plant-microbial functioning relies on co-adapted symbiotic partners as well as conducive environmental conditions. Choosing particular plant genotypes for domestication and subsequent cultivar selection can narrow the gene pools of crop plants to a degree that they are no longer able to benefit from microbial mutualists. Elevated minera...

Mutualistic plant-microbial functioning relies on co-adapted symbiotic partners as well as conducive environmental conditions. Choosing particular plant genotypes for domestication and subsequent cultivar selection can narrow the gene pools of crop plants to a degree that they are no longer able to benefit from microbial mutualists. Elevated minera...

During the Anthropocene, humans are changing the Earth system in ways that will be detectable for millennia to come [1]. Biologically, these changes include habitat destruction, biotic homogenization, increased species invasions, and accelerated extinctions [2]. Contemporary extinction rates far surpass background rates [3], but they seem remarkabl...

Data sheets on pests recommended for regulation

Data sheets on pests recommended for regulation

Data sheets on pests recommended for regulation

Data sheets on pests recommended for regulation

Following their establishment in new communities, invasive species may cause evolutionary changes in resident native species. This is clearly true for phytophagous insects, which may adapt rapidly when utilising abundant and widespread introduced hosts. The balloon vines Cardiospermumhalicacabum and C.grandiflorum were introduced to South Africa ap...

Alpha taxonomy has played an important role in understanding and describing biodiversity in many animal taxa, but the issue of cryptic species has posed taxonomic challenges in many taxa including ants. These taxonomic challenges underline the need for more integrative approaches when delimitating species. An integrative taxonomic approach combines...