Exotic ladybirds for biological control of herbivorous insects – a review

Since the late 19th century, exotic ladybirds (Coleoptera: Coccinellidae) have been used extensively for suppressing herbivorous insects of economic importance. In recent decades, the introduction of non‐native biological control (BC) agents has been greatly limited due to the awareness of the potential non‐target effects of introductions. Nonetheless, recent episodes of biological invasions of economically important pests have raised the need to carefully consider whether the expected benefits of pest control go beyond the possible environmental risks of introduction. To better understand the factors that contributed to successful BC programs, here we review the literature behind classical and augmentative BC using exotic ladybirds. Additionally, by means of case studies, we discuss the BC efficacy of selected exotic species, e.g., Coccinella septempunctata L., Harmonia axyridis (Pallas), and Hippodamia variegata (Goeze), and their position within the communities of predators in the introduced areas of USA, Canada, and Chile. In Europe, much of the research on exotic ladybirds has been conducted on the undesired impact of H. axyridis. Therefore, we summarize the risk assessment data for this species and review the field research investigating the ecological impact on European aphidophagous predators. According to the BIOCAT database of classical BC programs, 212 ladybird species belonging to 68 genera have been released in about 130 years of BC activity, with 14.6% of introductions having resulted in partial, substantial, or complete control of the target pest. However, because post‐release evaluation of establishment and BC success has not always been conducted, this rate could underestimate the successful cases. Among other factors, ladybird establishment and pest suppression mostly depend on (1) intrinsic factors, i.e., high voracity, synchronized predator‐prey life cycle, and high dispersal ability, and (2) extrinsic factors, i.e., adaptability to the new environment and landscape composition. This review contributes to improved understanding of ladybirds as exotic BC agents.     

Spatial Genetic Heterogeneity in Populations of a Newly Invasive Whitefly in China Revealed by a Nation-Wide Field Survey

Background

Even though introductions of exotic species provide ready-made experiments of rapid evolution, few studies have examined the genetic structure of an exotic species shortly after its initial introduction and subsequent spread. To determine the genetic structure of its populations during the initial introduction, we investigated the invasive sweet potato whitefly (Bemisia tabaci Q, commonly known as B. tabaci biotype Q) in China, which was introduced in approximately 2003. A total of 619 B. tabaci Q individuals in 20 provinces throughout China were collected and analyzed using five microsatellite loci.

Results

The introduced populations of B. tabaci Q in China represent eight genetic clusters with different geographic distributions. The populations in Yunnan Province, where B. tabaci Q was first detected, are genetically different from the other populations in China.

Conclusion

The introduced populations of B. tabaci Q in China have high spatial genetic heterogeneity. Additional research is required to determine whether the heterogeneity results from multiple introductions, rapid evolution following one or few introductions, or some combination of multiple introductions and rapid evolution. The heterogeneity, however, is inconsistent with a single introduction at Yunnan Province, where B. tabaci Q was first detected, followed by spread.     

Fronts,jumps and secondary introductions suggested as different invasion patterns in marine species,with an increase in spread rates over time

Not all introduced (invasive) species in a region will spread from a single point of introduction. Long-distance dispersal or further introductions can obscure the pattern of spread, but the regional importance of such processes is difficult to gauge. These difficulties are further compounded when information on the multiple scale process of invasive species range expansion is reduced to one-dimensional estimates of spread (e.g. km yr⁻¹). We therefore compared the results of two different metrics of range expansion: maximum linear rate of spread and accumulation of occupied grid squares (50 × 50 km) over time. An analysis of records for 54 species of introduced marine macrophytes in the Mediterranean and northeast Atlantic revealed cases where the invasion process was probably missed (e.g. Atlantic Bonnemaisonia hamifera) and suggested cases of secondary introductions or erratic jump dispersal (Dasysiphonia sp. and Womersleyella setacea). A majority of species analysed showed evidence for an accumulation of invaded sites without a clear invasion front. Estimates of spread rate are increasing for more recent introductions. The increase is greater than can be accounted for by temporally varying search effort and implies a historical increase in vector efficiency and/or a decreased resistance of native communities to invasion.     

De novo Genome Assembly of the Fungal Plant Pathogen Pyrenophora semeniperda

Pyrenophora semeniperda (anamorph Drechslera campulata) is a necrotrophic fungal seed pathogen that has a wide host range within the Poaceae. One of its hosts is cheatgrass (Bromus tectorum), a species exotic to the United States that has invaded natural ecosystems of the Intermountain West. As a natural pathogen of cheatgrass, P. semeniperda has potential as a biocontrol agent due to its effectiveness at killing seeds within the seed bank; however, few genetic resources exist for the fungus. Here, the genome of P. semeniperda isolate assembled from sequence reads of 454 pyrosequencing is presented. The total assembly is 32.5 Mb and includes 11,453 gene models encoding putative proteins larger than 24 amino acids. The models represent a variety of putative genes that are involved in pathogenic pathways typically found in necrotrophic fungi. In addition, extensive rearrangements, including inter- and intrachromosomal rearrangements, were found when the P. semeniperda genome was compared to P. tritici-repentis, a related fungal species.     

Mortality of exotic and native seeds in invaded and uninvaded habitats

We examined seed survival in exotic- and native-dominated grasslands by placing seeds of a once-pervasive native grass species, Nassella pulchra, and two of the most common, widespread exotic grass species, Avena fatua and Bromus hordeaceus, in mesh bags in the field for 3 months. Compared to germination of unexposed seeds not placed in the field, exotic species experienced an approximately 40% reduction in viability, whereas the mortality experienced by the native species was <20%. Despite these differences, germination rates of exposed seeds were similar between native and exotic species because native N. pulchra seeds had lower initial viability prior to entering the seed bank. Seed mortality did not differ based on whether seeds were placed in habitats dominated by exotic or native grasses. Rather, our results suggest that re-establishment of native N. pulchra must focus on maximizing seed viability and survival, and that A. fatua and B. hordeaceus overcome relatively higher losses of viable seeds in the seed bank, potentially by producing large numbers of highly viable seeds.     

A population model for predicting the successful establishment of introduced bird species

One of the strongest generalities in invasion biology is the positive relationship between probability of establishment and the numbers of individuals introduced. Nevertheless, a number of significant questions remain regarding: (1) the relative importance of different processes during introduction (e.g., demographic, environmental, and genetic stochasticity, and Allee effects); (2) the relative effects of propagule pressure (e.g., number of introductions, size of introductions, and lag between introductions); and (3) different life history characteristics of the species themselves. Here, we adopt an individual-based simulation modeling approach to explore a range of such details in the relationship between establishment success and numbers of individuals introduced. Our models are developed for typical exotic bird introductions, for which the relationship between probability of establishment and the numbers of individuals introduced has been particularly well documented. For both short-lived and long-lived species, probability of establishment decreased across multiple introductions (compared with a single introduction of the same total size), and this decrease was greater when inbreeding depression was included. Sensitivity analyses revealed four predictors that together accounted for >95 % of model performance. Of these, R ₀ (the average number of daughters produced per female over her lifetime) and propagule pressure were of primary importance, while random environmental effects and inbreeding depression exerted lesser influence. Initial founder size is undoubtedly going to be important for ensuring the persistence of introduced populations. However, we found the demographic traits, which influence how introduced individuals behave, to have the greatest effect on establishment success.     

The problem of introduced species in management and mitigation

One hundred years ago the striped bassMorone saxatilis was introduced in the San Francisco Bay estuarine system from the east coast of the United States. It was part of our national policy at the time to transplant all potentially useful species everywhere else. The policy was facilitated by completion of the transcontinental railroad in 1869. As a result, the present ichthyofauna of the San Francisco Bay area is largely alien. Introduction of eastern oystersCrassostrea virginica resulted in the inadvertent introduction of many species of invertebrates. Identification of these introduced species was not realized as a problem until recently, and no one knows how many exotic species there are. In other parts of the world there are examples of similar introductions, e.g.Crepidula fornicata andRhithropanopeus harrisi in Europe. Although it is now the policy to frown upon and prohibit introductions, they cannot be prevented and the process still continues, as witnessed by the examples ofElminus modestus in Europe andPalaemon macrodactylus in California. In the USA the recently developed idea of “mitigation,” the artificial replacement of disturbed or destroyed areas by development of quasi-natural areas in compensation, has been accompanied, at the hands of inexperienced practitioners, by potentially dangerous introductions of exotic species. The assumption, for example, that cordgrass(Spartina) should be equally beneficial everywhere in the world has led to the disrupting introduction of potentially hybridizing species in New Zealand and aggressive immigrants in Oregon marshes. This situation calls for more sophisticated understanding of the role of introduced species in natural aquatic ecosystems, and a higher degree of competence in systematic biology.     

Introduced brown algae in the North East Atlantic, with particular respect toUndaria pinnatifida (Harvey) suringar

The recent introduction of the macroalgaUndaria pinnatifida (Harvey) Suringar into the North Atlantic is the latest of a large number of introductions, which have occurred over many years. Some have been deliberate introductions for mariculture or research, while most have been accidental, via vectors such as shipping and shellfish imports. Not all newly recorded species are introductions; some are thought to be merely extensions of distribution, e.g.Laminaria ochroleuca, while others may have been overlooked previously, e.g.Scytosiphon dotyi. Subsequent to its accidental introduction into the waters around the Mediterranean French coast at Sete, most likely with imported oysters,Undaria was deliberately introduced into the North Atlantic, to Brittany, in 1983 by IFREMER for commercial exploitation.Undaria has since spread from the original sites in Brittany, and is now established at several sites on the south coast of England. This paper discusses the introduced brown algae in the North Atlantic and outlines the establishment ofUndaria in the UK.     

Harvester ant seed removal in an invaded sagebrush ecosystem: Implications for restoration

A better understanding of seed movement in plant community dynamics is needed, especially in light of disturbance‐driven changes and investments into restoring degraded plant communities. A primary agent of change within the sagebrush‐steppe is wildfire and invasion by non‐native forbs and grasses, primarily cheatgrass (Bromus tectorum). Our objectives were to quantify seed removal and evaluate ecological factors influencing seed removal within degraded sagebrush‐steppe by granivorous Owyhee harvester ants (Pogonomyrmex salinus Olsen). In 2014, we sampled 76 harvester ant nests across 11 plots spanning a gradient of cheatgrass invasion (40%–91% cover) in southwestern Idaho, United States. We presented seeds from four plant species commonly used in postfire restoration at 1.5 and 3.0 m from each nest to quantify seed removal. We evaluated seed selection for presented species, monthly removal, and whether biotic and abiotic factors (e.g., distance to nearest nest, temperature) influenced seed removal. Our top model indicated seed removal was positively correlated with nest height, an indicator of colony size. Distance to seeds and cheatgrass canopy cover reduced seed removal, likely due to increased search and handling time. Harvester ants were selective, removing Indian ricegrass (Achnatherum hymenoides) more than any other species presented. We suspect this was due to ease of seed handling and low weight variability. Nest density influenced monthly seed removal, as we estimated monthly removal of 1,890 seeds for 0.25 ha plots with 1 nest and 29,850 seeds for plots with 15 nests. Applying monthly seed removal to historical restoration treatments across the western United States showed harvester ants can greatly reduce seed availability at degraded sagebrush sites; for instance, fourwing saltbush (Atriplex canescens) seeds could be removed in <2 months. Collectively, these results shed light on seed removal by harvester ants and emphasize their potential influence on postfire restoration within invaded sagebrush communities.     

Geographic Population Structure of the Sugarcane Borer,Diatraea saccharalis (F.) (Lepidoptera: Crambidae), in the Southern United States

The sugarcane borer moth, Diatraea saccharalis, is widespread throughout the Western Hemisphere, and is considered an introduced species in the southern United States. Although this moth has a wide distribution and is a pest of many crop plants including sugarcane, corn, sorghum and rice, it is considered one species. The objective was to investigate whether more than one introduction of D. saccharalis had occurred in the southern United States and whether any cryptic species were present. We field collected D. saccharalis in Texas, Louisiana and Florida in the southern United States. Two molecular markers, AFLPs and mitochondrial COI, were used to examine genetic variation among these regional populations and to compare the sequences with those available in GenBank and BOLD. We found geographic population structure in the southern United States which suggests two introductions and the presence of a previously unknown cryptic species. Management of D. saccharalis would likely benefit from further investigation of population genetics throughout the range of this species.     

Deposition of exotic bird-dispersed seeds into three habitats of a fragmented landscape in the northeastern United States

Dispersal by frugivorous birds facilitates invasion by many exotic plants. We measured the seed rain of ornithochorous native and exotic plants at three habitats of a fragmented landscape of the northeastern United States for 1 year. We studied maple-beech forests, old fields, and abandoned conifer plantations. Across all sites we collected 2,196 ornithochorous seeds, including seeds from six exotic species and 10 native species. The majority (90%) of collected seeds were from exotic species. Seed dispersal was broadly similar among habitats, though seed rain of exotic species was higher in old fields than forested habitats. Seed rain was not strongly influenced by artificial perches for most species. However, seeds of exotic species were more commonly found in traps under an artificial perch in old fields. Seed rains for the exotic Elaeagnus umbellata, Rhamnus cathartica, and Rosa multiflora were positively associated with local density of mature plants. Seed rain of R. cathartica was positively associated with abundance of seedlings but not saplings, suggesting that post-dispersal mortality was important. Seed dispersal of the exotic Lonicera spp. was high in all habitats, accounting for 66% of all seeds collected. With the exception of Lonicera spp., seed rain of common exotic invaders was affected by the abundance of seed sources, and these species might be effectively controlled by elimination of local fruiting plants. Fruits of Lonicera morrowii, which has extensively invaded our area, are apparently a common component in the diet of frugivores.     

Multiple introductions and invasion pathways for the invasive ctenophore Mnemiopsis leidyi in Eurasia

The introduction and spread of non-indigenous species (NIS) in marine ecosystems accelerated during the twentieth century owing to human activities, notably international shipping. Genetic analysis has proven useful in understanding the invasion history and dynamics of colonizing NIS and identifying their source population(s). Here we investigated sequence variation in the nuclear ribosomal Internal Transcribed Spacer region of the ctenophore Mnemiopsis leidyi, a species considered one of the most invasive globally. We surveyed four populations from the native distribution range along the Atlantic coasts of the United States and South America, as well as six populations in the introduced range from the Black, Azov, Caspian and Baltic seas. Allelic and nucleotide diversity of introduced populations were comparable to those of native populations from which they were likely drawn. Introduced populations typically exhibited lower genetic differentiation (F _ST = ?0.014?C0.421) than native populations (F _ST = 0.324?C0.688). Population genetic analyses supported the invasion of Eurasia from at least two different pathways, the first from the Gulf of Mexico (e.g., Tampa Bay) to the Black Sea and thence to the Caspian Sea, the second from the northern part of the native distribution range (e.g., Narragansett Bay) to the Baltic Sea. The relatively high genetic diversity observed in introduced populations is consistent with large inocula and/or multiple invasions, both of which are possible given ballast water transport and the extensive native distribution of the ctenophore in the Atlantic Ocean.     

Avian Migrants Facilitate Invasions of Neotropical Ticks and Tick-Borne Pathogens into the United States

Migratory birds have the potential to transport exotic vectors and pathogens of human and animal health importance across vast distances. We systematically examined birds that recently migrated to the United States from the Neotropics for ticks. We screened both ticks and birds for tick-borne pathogens, including Rickettsia species and Borrelia burgdorferi. Over two spring seasons (2013 and 2014), 3.56% of birds (n = 3,844) representing 42.35% of the species examined (n = 85) were infested by ticks. Ground-foraging birds with reduced fuel stores were most commonly infested. Eight tick species were identified, including seven in the genus Amblyomma, of which only Amblyomma maculatum/Amblyomma triste is known to be established in the United States. Most ticks on birds (67%) were neotropical species with ranges in Central and South America. Additionally, a single Ixodes genus tick was detected. A total of 29% of the ticks (n = 137) and no avian blood samples (n = 100) were positive for infection with Rickettsia species, including Rickettsia parkeri, an emerging cause of spotted fever in humans in the southern United States, a species in the group of Rickettsia monacensis, and uncharacterized species and endosymbionts of unknown pathogenicity. No avian tick or blood samples tested positive for B. burgdorferi, the etiologic agent of Lyme disease. An extrapolation of our findings suggests that anywhere from 4 to 39 million exotic neotropical ticks are transported to the United States annually on migratory songbirds, with uncertain consequences for human and animal health if the current barriers to their establishment and spread are overcome.     

Molecular Evidence for an Extreme Genetic Bottleneck During Introduction of an Invading Grass to California

Although exotic species cause tremendous economic and ecological loss, we know relatively little about the post-introduction evolutionary dynamics of the invasive species themselves. Barbed goatgrass, Aegilops triuncialis L., is a cleistogamous annual grass with a native range throughout the Mediterranean Basin and Asia and introduced to California during the last century. It is considered a serious noxious range weed and is one of the few exotic plant species that is invading serpentine soil habitats. We examined whether patterns of molecular variation are consistent with a single or multiple introduction events into California and further, if individual populations show evidence for a genetic bottleneck during introduction. Fingerprinting patterns, using microsatellite loci derived from Triticum aestivum, were investigated for 57 Eurasian accessions, broadly spanning the native range and for 108 individuals from 11 localities in California. There is strong evidence for an extreme bottleneck in this species as it colonizes its new range because we detected only three multilocus genotypes occurring in California and 36 genotypes in Eurasia. In California one of the genotypes differs from one other by only one fragment and only occurs in one individual. This suggests two separate introductions. Each population is composed of highly uniform individuals and the two main genotypes are geographically separated. A. triuncialis is still expanding its range in California despite genomic uniformity after a strong bottleneck and its recently increased rate of spread is not correlated to a high within-population variability created by multiple introductions.     

Species introduced from nearby sources have a more homogenizing effect than species from distant sources: evidence from plants and fishes in the USA

Biotic homogenization is occurring in many biota as widespread introduced species are replacing unique native species. Although efforts to document homogenization have increased, no studies have explicitly compared the homogenizing effects of species introduced from distant areas to the homogenizing effects of species introduced from more proximate areas. The author analysed three data sets, at different scales and in different taxa, that distinguish species introduced from distant sources (e.g. outside the US) from species introduced from less distant sources (e.g. within the United States). These data include: plant introductions among eight major US cities and fish introductions among 12 US states and among 10 watersheds from New York state. The authors found that, for all data sets, species introduced from less distant sources (within the US) have a greater homogenizing effect on community composition than species from more distant sources (outside the US). In agreement with other studies, the author also find that, in terms of absolute numbers, introductions from nearby sources are far more frequent than introduction of species from distant sources. While tentative, these findings point out the importance of considering species introduced from nearby areas (e.g., extralimital native species) when discussing biotic homogenization from human activities.     

Native granivores reduce the establishment of native grasses but not invasive <Emphasis Type="Italic">Bromus tectorum</Emphasis>

Seed predation can structure plant communities by imposing strong population controls on some species but not others. In this context, studies from various ecosystems report that native granivores selectively forage for seeds from native species over seeds from exotic invaders, which could disproportionately favor the establishment of invaders and facilitate their dominance in communities. However, few studies have connected selective foraging for native seeds to differential patterns of establishment among native and invasive species. Thus, the extent to which preferential foraging for native seeds favors the establishment of invasive plants is unclear. Here, we used experimental seed additions and exclosure treatments at five field sites distributed across?≈?80,000 km² of the Great Basin Desert, USA to compare the effects of rodent foraging on the establishment of less-preferred cheatgrass (Bromus tectorum—an annual species native to Eurasia that is exotic and highly invasive across the Great Basin) and four species of more-preferred native grasses that commonly co-occur with cheatgrass. Rodent foraging reduced the establishment of each native species by at least 80% but had no effect on the establishment of cheatgrass, and this finding was consistent across study sites. Our results suggest that selective foraging for native species may favor the establishment of cheatgrass over native grasses, potentially exacerbating one of the most extensive plant invasions in North America.     

Frugivory by introduced black rats (Rattus rattus) promotes dispersal of invasive plant seeds

Oceanic islands have been colonized by numerous non-native and invasive plants and animals. An understanding of the degree to which introduced rats (Rattus spp.) may be spreading or destroying seeds of invasive plants can improve our knowledge of plant-animal interactions, and assist efforts to control invasive species. Feeding trials in which fruits and seeds were offered to wild-caught rats were used to assess the effects of the most common rat, the black rat (R. rattus), on 25 of the most problematic invasive plant species in the Hawaiian Islands. Rats ate pericarps (fruit tissues) and seeds of most species, and the impacts on these plants ranged from potential dispersal of small-seeded (≤1.5 mm length) species via gut passage (e.g., Clidemia hirta, Buddleia asiatica, Ficus microcarpa, Miconia calvescens, Rubus rosifolius) to predation where <15% of the seeds survived (e.g., Bischofia javanica, Casuarina equisetifolia, Prosopis pallida, Setaria palmifolia). Rats consumed proportionally more seed mass of the smaller fruits and seeds than the larger ones, but fruit and seed size did not predict seed survival following rat interactions. Although invasive rat control efforts focus on native species protection, non-native plant species, especially those with small seeds that may pass internally through rats, also deserve rat control in order to help limit the spread of such seeds. Black rats may be facilitating the spread of many of the most problematic invasive plants through frugivory and seed dispersal in Hawaii and in other ecosystems where rats and plants have been introduced.     

Origin of the Dengue Fever Mosquito,Aedes aegypti,in California

Dengue fever is among the most widespread vector-borne infectious diseases. The primary vector of dengue is the Aedes aegypti mosquito. Ae. aegypti is prevalent in the tropics and sub-tropics and is closely associated with human habitats outside its native range of Africa. While long established in the southeastern United States of America where dengue is re-emerging, breeding populations have never been reported from California until the summer of 2013. Using 12 highly variable microsatellite loci and a database of reference populations, we have determined that the likely source of the California introduction is the southeastern United States, ruling out introductions from abroad, from the geographically closer Arizona or northern Mexico populations, or an accidental release from a research laboratory. The power to identify the origin of new introductions of invasive vectors of human disease relies heavily on the availability of a panel of reference populations. Our work demonstrates the importance of generating extensive reference databases of genetically fingerprinted human-disease vector populations to aid public health efforts to prevent the introduction and spread of vector-borne diseases.     

Lack of Host Specialization on Winter Annual Grasses in the Fungal Seed Bank Pathogen Pyrenophora semeniperda

Generalist plant pathogens may have wide host ranges, but many exhibit varying degrees of host specialization, with multiple pathogen races that have narrower host ranges. These races are often genetically distinct, with each race causing highest disease incidence on its host of origin. We examined host specialization in the seed pathogen Pyrenophora semeniperda by reciprocally inoculating pathogen strains from Bromus tectorum and from four other winter annual grass weeds (Bromus diandrus, Bromus rubens, Bromus arvensis and Taeniatherum caput-medusae) onto dormant seeds of B. tectorum and each alternate host. We found that host species varied in resistance and pathogen strains varied in aggressiveness, but there was no evidence for host specialization. Most variation in aggressiveness was among strains within populations and was expressed similarly on both hosts, resulting in a positive correlation between strain-level disease incidence on B. tectorum and on the alternate host. In spite of this lack of host specialization, we detected weak but significant population genetic structure as a function of host species using two neutral marker systems that yielded similar results. This genetic structure is most likely due to founder effects, as the pathogen is known to be dispersed with host seeds. All host species were highly susceptible to their own pathogen races. Tolerance to infection (i.e., the ability to germinate even when infected and thereby avoid seed mortality) increased as a function of seed germination rate, which in turn increased as dormancy was lost. Pyrenophora semeniperda apparently does not require host specialization to fully exploit these winter annual grass species, which share many life history features that make them ideal hosts for this pathogen.     

Red brome (<Emphasis Type="Italic">Bromus rubens</Emphasis> subsp. <Emphasis Type="Italic">madritensis</Emphasis>) in North America: possible modes for early introductions,subsequent spread

Although invasions by exotic plants have increased dramatically as human travel and commerce have increased, few have been comprehensively described. Understanding the patterns of invasive species spread over space and time will help guide management activities and policy. Tracing the earliest appearances of an exotic plant reveals likely sites of introduction, paving the way for genetic studies to quantify founder events and identify potential source populations. Red brome (Bromus madritensis subsp. rubens) is a Mediterranean winter annual grass that has invaded even relatively undisturbed areas of western North America, where it threatens native plant communities. This study used herbarium records and contemporary published accounts to trace the early introductions and subsequent spread of red brome in western North America. The results challenge the most frequently cited sources describing the early history of this grass and suggest three possible modes for early introductions: the California Gold Rush and Central Valley wheat, southern California shipping, and northern California sheep. Subsequent periods of most rapid spread into new areas, from 1930 to 1942, and of greatest spread into new regions, during the past 50 years, coincide with warm Pacific Decadal Oscillation regimes, which are linked to increased winter precipitation in the southwestern USA and northern Mexico. Global environmental change, including increased atmospheric CO₂ levels and N deposition, may be contributing to the success of red brome, relative to native species.