Biological Invasions

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Online ISSN: 1573-1464
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Distribution of Pinus spp. growing areas (native forests and plantations) across the Palearctic region (where the European bark beetles are native) as well as in the Southern Hemisphere (SH) and North and Central (N&C) America.
Sources Critchfield and Little (1966), Farjon and Filer (2013) and Lantschner et al. (2017)
Sum of the potential distribution of the 51 European pine bark beetle species in the pine plantations zones of the Southern Hemisphere and the Americas. Red colors indicate regions with a high number of species predicted to established, while blue colors show regions were a low number of species is predicted to occur
Generalized linear regression curves of invasion probability of pine European bark beetle species in the Southern Hemisphere and the Americas, as a function of each significant predictive variable. HS: highly specialized, S: specialized, I: intermediate, G: generalist. The grey area represents 95% confidence interval. p values and goodness of fit are shown in Table 4. Overlapping gray points become blackish
Largely assisted by global trade, alien insect species are being introduced into new territories at unprecedented rates. Among forest insects, pine bark beetles (Coleoptera: Curculionidae, Scolytinae) are a large and diverse group commonly recognized as successful invaders and important tree mortality agents in pine forests and commercial plantations. In this study, we collected information on the native and invaded distribution of 51 European bark beetles developing in Pinus species. We analyzed their invasion history in the Southern Hemisphere and the Americas and explored several factors that can help explain their invasion success: (1) propagule pressure: interception frequency in the non-native range(2) invasibility: potential establishment area based on climatic matching and host availability and (3) invasiveness: biological traits of the bark beetles (i.e., feeding habit, host range, body size, mating system, colonization behavior). We found that most (87%) of the introductions of the species to new regions occurred in the period 1960–2013, and that variables related with the three main factors were relevant in explaining invasion success. Propagule pressure was the factor that best explained bark beetle invasion probability, followed by invasibility of the novel area. In turn, biological attributes like mating system, body size and host range were also relevant, but showed a lower relative importance. Our study contributes to understand the main factors that explain forest insect invasion success. This information is critical for predicting future invasions to new regions and optimizing early-detection and biosecurity policies.
Resident-invader interactions may vary in strength and direction depending on the environmental context. Competitive interactions (indicated by “-”) are likely to be more important for shaping plant communities and invasion resistance in productive, resource rich environments, while facilitative interactions (indicated by “ + ”) may be more important in less productive, resource poor environments where residents ameliorate environmental stress (Bertness and Callaway 1994; He et al. 2013)
Sample plot locations within the Ochoco National Forest located in central Oregon, U.S.A. Plots were positioned in three vegetation types representing a gradient of increasing productivity and assumed resource availability: scab-flats, low sage-steppe, and ephemeral wet meadows
a Estimated median resident biomass (g/m²) excluding Ventenata dubia (
modified from Tortorelli et al. 2022) and bV. dubia height (cm) with 95% confidence intervals at three distinct vegetation types representing a productivity gradient
a Boxplots of Ventenata dubia biomass by treatment and vegetation type. b-c Estimated ratio of V. dubia biomass and 95% confidence intervals for contrasts by treatment and vegetation type for b the cleared & seeded vs. uncleared and seeded treatments, and c the seeded treatment vs. unseeded controls after controlling for 2019 ventenata biomass. Dashed line represents no difference in V. dubia biomass
The success of introduced plant species is influenced by interactions with the resident community, and these interactions can vary in strength and direction depending on environmental context. Understanding how interacting biotic and abiotic factors influence invasion is critical to managing invasions and assessing invasion susceptibility across multiple ecosystems, especially for recently introduced species in beginning stages of invasion where early detection, eradication, and prevention are critical for effective control. Here we use an in-situ biomass removal and seed addition experiment to investigate how resident species influence invasion success by a rapidly spreading invasive annual grass, ventenata (Ventenata dubia) across a productivity gradient composed of three distinct vegetation types in central Oregon, U.S.A. In contrast to our predictions, the removal of residents did not have a clear effect on ventenata success, and the effect did not vary by vegetation type. Instead, our results suggest that the ventenata invasion is more strongly driven by dispersal limitations and microsite condition than species interactions. These findings have important implications for managing invasions in non-forest ecosystems where common management actions such as prescribed burning, grazing, and planting native species involve the alteration of above-ground biomass, and for expanding invasion frameworks to aid the management of future invasive species.
Map of the west coast of North America showing current patterns during: a Summer and b Winter. Location abbreviations are: VICC = Vancouver Island Coastal Current, BS = Barkley Sound, NS = Nootka Sound, QS = Quatsino Sound. Currents indicated in red are relatively warm, those in blue, cold. Note the warm north-flowing Davidson Current in winter. During a strong El Niño this current can exceed 50 km per day and can last from September to April (Austin and Barth 2002; Huyer et al. 1998)
First sightings of Carcinus maenas (green circles), and Pachygrapsus crassipes (purple triangles) in the Salish Sea and adjacent open coast as of Fall 2020. A single C. maenas from Price Bay (PB) settled during the 1997/98 El Niño and the Sooke Basin population (SB) originated from the introduction of live C. maenas prior to 2010. Five sites were seeded during the 2015/16 El Niño: WB = Westcott Bay (2015), PB = Padilla Bay (2016), DS = Dungeness National Wildlife Refuge (2015 & 2016), SqB = Sequim Bay (2016) and PTB = Port Townsend Bay (2016). For subsequent sighting see Behrens Yamada et al. (2021a) and First sightings of P. crassipes followed strong El Niño events: OZ = Ozette (1991/92 and 2015/16), TI = Tatoosh Island (1982/83), NB = Neah Bay (2015/16), SW = Shipwreck Point (2015/16), BA = Bamfield in Barkley Sound (1994/95, 1997/98, 2015/16), UC-Ucluelet (2015/16), TO = Tofino (2015/16), Nootka Sound (2015/16). Canadian sightings for P. crassipes are from Fig. 1a and Table S1 in Boulding et al. (2020)
Major El Niño events and oceanic heat waves are linked to the range expansion of many marine species. For the shores of the northeast Pacific, we compared range expansion in the European green crab, Carcinus maenas, which was introduced to San Francisco Bay prior to 1990, to that of the native lined-shore crab, Pachygrapsus crassipes. The initial northern range limit of these species was central California and southern Oregon, respectively. Both species increased their northern range along the open coast to northern Oregon, Washington and Vancouver Island after strong El Niño events. C. maenas, however, in just a matter of decades, successfully established populations in estuaries from Oregon to inlets on the west coast of Vancouver Island, and possibly also in the Salish Sea, while P. crassipes, never has in recorded history. We hypothesize that this difference in invasion success is due to the shorter larval duration of C. maenas, < 2 months, compared to that of P. crassipes, 3–4 months and timing of larval release, winter for both species. Because the residency times of water in the inlets of the west coast of Vancouver Island are typically 1–2 months, they can act as incubators for the larvae of C. maenas, while those of P. crassipes are likely flushed out to the open sea before they can complete their development. We propose that the life history of a species coupled with the hydrodynamic setting in which its pelagic larvae develop contribute to the success of range expansion.
Map of the study area, including sample points and overlapping protected areas
Predictions from Model 1 of the probability of co-occurrence between each host and the Shiny Cowbird among the three habitats. Dots represent the posterior mean of the prediction, and the error bars represent the 95% credible intervals
Posterior distributions generated from Model 1 of the number of sites in each habitat where each host co-occurred with a cowbird
Posterior distributions generated from Model 1 of the number of sites in each habitat where each host occurred without a cowbird
Invasive species threaten island biodiversity globally. For example, the Shiny Cowbird (Molothrus bonariensis) parasitizes many of Puerto Rico’s endemic species, particularly in the open forests in the island’s southwest. Less is known, however, about cowbird parasitism in the agro-ecological highlands, which contain a patchwork of forests, shaded-coffee plantations, and coffee farms without shade. In this paper, we estimated co-occurrence rates, a potential indicator of parasitism rates, between the cowbird and four host species across these three land uses, hypothesizing that cowbirds would most likely co-occur with their hosts in shaded-coffee farms. We also hypothesized that the presence of host species would increase the probability of cowbird occurrence. To investigate these hypotheses, we developed three Bayesian hierarchical occupancy models: one where the hosts and parasite occurred independently, one that used the latent host species richness as a predictor of cowbird occurrence, and one that used each latent host occurrence state as predictors. These methods addressed observation errors and appropriately propagated error to our predictions of co-occurrence rates. We selected the best performing model using WAIC, then used it to predict co-occurrence rates. While there was some evidence that host species richness increased the probability of cowbirds, the parsimonious model assumed no interaction. With this model, we found that cowbirds were more likely to overlap with certain hosts in shaded-coffee plantations. This may suggest increased parasitism at these plantations, potentially presenting challenges for managers who advocate for shade restoration to gain ecological services such as biodiversity conservation.
Invasive alien species (IAS) rank among the most significant drivers of species extinction and ecosystem degradation resulting in significant impacts on socio-economic development. The recent exponential spread of IAS in most of Africa is attributed to poor border biosecurity due to porous borders that have failed to prevent initial introductions. In addition, countries lack adequate information about potential invasions and have limited capacity to reduce the risk of invasions. Horizon scanning is an approach that prioritises the risks of potential IAS through rapid assessments. A group of 28 subject matter experts used an adapted methodology to assess 1700 potential IAS on a 5-point scale for the likelihood of entry and establishment, potential socio-economic impact, and impact on biodiversity. The individual scores were combined to rank the species according to their overall potential risk for the country. Confidence in individual and overall scores was recorded on a 3-point scale. This resulted in a priority list of 120 potential IAS (70 arthropods, 9 nematodes, 15 bacteria, 19 fungi/chromist, 1 viroid, and 6 viruses). Options for risk mitigation such as full pest risk analysis and detection surveys were suggested for prioritised species while species for which no immediate action was suggested, were added to the plant health risk register and a recommendation was made to regularly monitor the change in risk. By prioritising risks, horizon scanning guides resource allocation to interventions that are most likely to reduce risk and is very useful to National Plant Protection Organisations and other relevant stakeholders.
the data inferred from populations, infra-and component communities of parasites and the application of a macroecological approach in the analysis of complex and frequently hidden relationships in host-parasite systems. This comparative analysis draws on parasite data across regions and host species at different organizational (population vs. community) and hierarchical (infra vs. component community) levels of parasites. Our framework based on assessing and analysis of parasitological and ecological indexes, including descriptors of parasite species richness (individual and total), infection parameters, parasite aggregation (Taylor´s power law) and macroeco-logical models (abundance-variance and abundance-occupancy relationships), can produce mechanistic explanations of the Enemy Release Hypothesis and unravel host-parasite relationships of an invasive host and its parasites. Moreover, abundance-variance and abundance-occupancy relationships, core-satellite species hypothesis, patterns on the aggregation and the frequency distribution of prevalence, infrapopu-lation size and individual parasite species richness provide useful tools to distinguish co-introduced and acquired parasites in communities of the inva-sive host based on quantitative descriptors. We hope that our framework becomes widely applied as it can potentially contribute to enhance future practice and research in biodiversity conservation and control of invasive species. Abstract Despite considerable research effort, many aspects of the host-parasite relationships and parasite spatial distribution in invasive hosts remain poorly understood due to complex and context-dependent phenomena related to both the bioinva-sions and the parasitism. Using macroecological patterns and theory is a useful approach to analyzing parasitological observations, but in practice parasite ecology and classical macroecology are disconnected. We propose a new framework that can use the conventional parasitology sampling data much more effectively. The innovative concept combines
Round Goby CPUA (number of fish × (m²)⁻¹) in sampling locations along the Ausable River in 2017 and 2018 (n = 45 sites) and Big Otter Creek in 2018 (n = 50 sites). Sites where Round Goby was not detected (CPUA = 0) are outlined in black
Broken-stick regression models and CPUA for Round Goby (solid blue line, blue dots; Adj. R² = 0.51, 0.53 for the Ausable River and Big Otter Creek, respectively) and Percidae species (dashed black line, open dots; Adj. R² = 0.26, 0.57 for the Ausable River and Big Otter Creek, respectively) at sampling locations along the Ausable River and Big Otter Creek in relation to the distance from river mouth (km). Percidae species from the Ausable River used in the model included: Johnny Darter (Etheostoma nigrum), Blackside Darter (Percina maculata), Greenside Darter (Etheostoma blennioides), Rainbow Darter (Etheostoma caeruleum), and Logperch (Percina caprodes), whereas Percidae species from Big Otter Creek used in the model included: Johnny Darter, Blackside Darter, and Logperch. Percidae species collected in < 5% of sites within a tributary were excluded from analyses
Broken-stick regression models and CPUA for Round Goby and individual Percidae species in sampling locations along the Ausable River (top panel) and Big Otter Creek (bottom panel) in relation to the distance from river mouth (km). Percidae species displayed for the Ausable River included: Johnny Darter (Etheostoma nigrum), Blackside Darter (Percina maculata), Greenside Darter (Etheostoma blennioides), Rainbow Darter (Etheostoma caeruleum), and Logperch (Percina caprodes), whereas Percidae species displayed for Big Otter Creek included: Johnny Darter, Blackside Darter, and Logperch. Percidae species collected in < 5% of sites within a tributary were excluded from analyses
Boxplots comparing diversity metrics between site groupings in Big Otter Creek (top, a–e; lower sites: 13.1–14.1 km from river mouth, n = 13; middle sites: 35.8–49.9 km from river mouth, n = 9; upper sites: 71.2–83.6 km from river mouth, n = 5), and the Ausable River (bottom, f–j; lower sites: 11.2–17.7 km from river mouth, n = 16; middle sites: 32.1–75.6 km from river mouth, n = 12 sites; upper sites: 91.6–126.4 km from river mouth, n = 17). Diversity metrics include: Evenness (a, f), Shannon–Wiener Index (b, g), CPUA of all sampled fishes excluding Round Goby (c, h), CPUA of all sampled fishes including Round Goby (d, i), and CPUA of Round Goby. Boxplots represent the median, minimum, maximum, and first and third quartiles of sites in each site grouping
Species accumulation curves for Big Otter Creek (lower sites: 13.1–14.1 km from river mouth, n = 13; middle sites: 35.8–49.9 km from river mouth, n = 9; upper sites: 71.2–83.6 km from river mouth, n = 5) and the Ausable River (lower sites: 11.2–17.7 km from river mouth, n = 16; middle sites: 32.1–75.6 km from river mouth, n = 12 sites; upper sites: 91.6–126.4 km from river mouth, n = 17). Error bars are ± one standard deviation
Numerous fish species in the Laurentian Great Lakes have been negatively impacted by the establishment of the invasive Round Goby ( Neogobius melanostomus ). However, limited understanding exists as to how Round Goby has impacted small-bodied native benthic fishes after its secondary invasion into tributaries of the Laurentian Great Lakes. To investigate Round Goby impacts on darter species (family Percidae) in tributary ecosystems, catch per unit area (CPUA) of native and non-native fishes from two riverine ecosystems in Southwestern Ontario (Ausable River, Big Otter Creek) were analyzed. Spatial analyses indicated Round Goby CPUA was highest proximate to the Great Lakes, with a sharp decline in CPUA at sites upstream from each lake (Round Goby CPUA approached zero after 18 and 14 km in the Ausable River and Big Otter Creek, respectively). There was some evidence of a negative relationship between the CPUA of Round Goby and several darter species along the tributary gradients, with moderately negative co-occurrence between Round Goby and Rainbow Darter in the Ausable River and Johnny Darter and Percidae species overall in Big Otter Creek. However, overwhelming evidence of negative associations between Round Goby and all darter species was not found. The negative relationship between the CPUA of Round Goby and some darter species was observed over similar time periods since establishment but greater spatial scales than in previous studies, and therefore has important implications for understanding the ecological impacts of Round Goby in tributary ecosystems.
Java, Bali and Lombok with cities where bird markets were surveyed from August 2016 to June 2019 and areas where alien invasive mynas have been observed in grey. Cities with a disproportionate large number of potentially alien invasive mynas for sale are highlighted
Invasive alien mynas offered for sale in ten cities on Java, Bali and Lombok, Indonesia, showing the mean number (± SD) of invasive alien mynas per survey (bars) and the proportion (± SD) of invasive alien mynas of the total number of mynas for sale (circles). Cities are listed from west to east. Depicted is a Javan myna Acridotheres javanicus
Asking prices (Mean ± SD) of five species of Acridotheres mynas in the bird markets of Java, Bali and Lombok, Indonesia, showing higher prices for the legally protected black-winged myna A. melanopterus than for the native unprotected Javan myna A. javanicus or the non-native common myna A. tristis and crested myna A. cristatellus. The proportion of the government recommended minimum monthly wage is for the city of Jakarta. The photo shows birds, including black-winged mynas, for sale at Jatinegara bird market in Jakarta
In Southeast Asia, mynas (genus Acridotheres ) are amongst the most invasive bird species. Information is largely lacking as to where they have established themselves. The spread of invasive, non-native mynas is partially or largely driven by the massive trade in these species as songbirds. While preventing unintentional introductions early is the most effective management option, these species continue to be traded in bird markets throughout the region. We focus on the trade of native and non-native species of mynas, and the establishment of non-native mynas on the Indonesian islands of Java, Bali, and Lombok. Between 2016 and 2019, through field surveys and use of citizen science data (e.g., Burungnesia, iNaturalist, birding reports), we assessed where non-native mynas have been recorded in the wild on these three islands; through bird market surveys we established in which cities these birds are traded. We recorded common myna in Yogyakarta, one of our three survey areas. Combining all records, the areas where alien invasive mynas are established are Greater Jakarta (common and jungle myna), Yogyakarta (common myna), Bali (common and bank myna) and Lombok (common and Javan myna). Two-thirds of the records come from farmlands, home gardens and urbanised areas. In the bird markets, we recorded ~ 23,000 mynas of five species for sale, with Greater Jakarta, Bali and Lombok standing out as areas with high numbers of potentially invasive alien species offered for sale. Restrictions on the sale of wild-caught birds are not adhered to. Well-intended policies concerning the breeding and sale of legally protected species, whereby 10% of the stock is bred to be released in the wild, exacerbate the risk of the establishment of non-native species. We surmise that one of the most effective ways to reduce the risk of the accidental or deliberate release of potentially invasive alien mynas (and indeed other birds) into the wild is for governments and conservationists to work more closely with the retailers who hold the key to informing and educating consumers.
Mean days to first flower (± SEM) of A invasive and native range genotypes and B variation among genotypes within each range
Mean total biomass (± SEM) of A invasive and native range M. polymorpha genotypes and B variation among genotypes within each range. Mean above:belowground biomass ratios (± SEM) of C invasive and native range genotypes and D variation among genotypes within each range
Mean seed number (± SEM) of A invasive and native range genotypes of M. polymorpha and B variation among genotypes within each range
Non-linear relationships between M. polymorpha seed number and A total biomass, B above:belowground biomass ratio, and C days to flower, for invasive and native range genotypes ± 95% CI
Novel ecological interactions can drive natural selection in non-native species and trait evolution may increase the likelihood of invasion. We can gain insight into the potential role of evolution in invasion success by comparing traits of successful individuals in the invasive range with the traits of individuals from the native range in order to determine which traits are most likely to allow species to overcome barriers to invasion. Here we used Medicago polymorpha, a non-native legume species from the Mediterranean that has invaded six continents around the world, to quantify differences in life history traits among genotypes collected from the native and invasive range and grown in a common greenhouse environment. We found significant differences in fruit and seed production and biomass allocation between invasive and native range genotypes. Invasive genotypes had greater fecundity, but invested more energy into belowground growth relative to native genotypes. Beyond the variation between ranges, we found additional variation among genotypes within each range in flowering phenology, total biomass, biomass allocation, and fecundity. We found non-linear relationships between some traits and fitness that were much stronger for plants from the invasive range. These trait differences between ranges suggest that stabilizing selection on biomass, resource allocation, and flowering phenology imposed during or after introduction of this species may increase invasion success.
Distribution of native and non-native occurrence records of (a) Cichla kelberi, and (b) Cichla ocellaris across the limits of the countries and Freshwater Ecoregions of the World
Global environmental suitability derived from the ENM consensus model for aCichla kelberi, and bCichla ocellaris calibrated with native + non-native occurrences datasets. Very low (suitability < 0.2), low (0.2–0.4), moderate (0.4–0.6), high (0.6–0.8), and very high (> 0.8)
Location of the top 10 potential hotspots for the occurrence of Cichla kelberi and Cichla ocellaris among Freshwater Ecoregions of the World, ranked by the summed area with moderate, high and very high environmental suitability derived from the ENM consensus models calibrated with native + non-native occurrences datasets. Moderate suitability (0.4–0.6), high (0.6–0.8), and very high (> 0.8)
Distribution of native and non-native occurrence records of aCichla kelberi, and bCichla ocellaris. Native and non-native records are enclosed by ellipses encompassing 95% of the data and by the Extent of Occurrence limit, estimated by the Minimum Convex Polygon method
Environmental space of native and non-native occurrences of aCichla kelberi, and bCichla ocellaris, summarized by the Principal Component Analysis (PCA1 and PCA2) using 24 environmental variables (bioclimatic, topographic, and hydrographic). Squares—native records; dots—non-native records; and crosses—whole environment included in the analysis. Symbols are enclosed by ellipses encompassing 95% of the data
Peacock basses (genus Cichla) are Amazonian piscivorous fish that have been widely introduced into freshwater systems and caused great ecological impacts. Our goal was to assess the worldwide distribution of Cichla ocellaris and C. kelberi to delineate their niche and predict the most suitable areas for their invasion using data available in the scientific literature. We combined ecological niche models to identify hotspots of environmental suitability and invasion risk worldwide, in addition to niche similarity analysis in the geographic space, principal component analysis in the environmental space, and bias metric to assess niche changes between native and non-native ranges. We found 373 records (88 native and 285 non-native populations) for the occurrence of C. kelberi and C. ocellaris in several ecoregions around the world. Native populations were restricted to Amazonian and Tocantins-Araguaia ecoregions. Suitable areas for both species were concentrated within the tropical climatic zone. Amid the top 10 ecoregions more suitable for their occurrence there are four in Africa, one in Asia and also one in Brazil. The Upper Parana ecoregion deserves special highlight due to its prevalence in the number of non-native records and also of suitable areas for new invasions. There was a great increase in the Extent of Occurrence of non-native occurrences compared to native records. We found a moderate niche overlap in the geographical space and a high overlap in the environmental space between native and non-native ranges for both species, suggesting niche conservatism, but with some dissimilarity, higher for C. ocellaris.
Non-indigenous species (NIS) pose a major threat to biodiversity and the functioning and services of ecosystems. Despite their rapid spread in coastal waters worldwide, biotic invasions are widely disregarded in marine conservation planning. To guide conservation actions, a better understanding of the underlying mechanisms determining the success of NIS are therefore needed. Here we develop a combined modelling approach to identify the key drivers and community assembly processes determining the occurrence of invasive benthic invertebrates, using Danish coastal waters as a case study. To reflect factors affecting the introduction, establishment and spread of NIS throughout the area, we compiled long-term monitoring data on NIS, as well as information on commercial shipping, environmental conditions and estimates of larvae settling densities derived from drift model simulations informed by species traits. We then applied a set of species distribution models to identify the key drivers determining the occurrence of NIS. Our results demonstrate a significant positive effect of vessel activity, a negative effect of depth and bottom salinity, as well as a positive effect of the simulated settling densities on the probability of presence. Taken together, our results highlight the role of commercial shipping, habitat characteristics and passive advection of early-life stages on the presence of NIS. Our combined modelling approach provide improved process understanding on the key community assembly processes determining the presence of NIS and may serve to guide monitoring, management and conservation planning in order to limit future invasions and their negative consequences on coastal ecosystems.
The Pacific epizoic brittle star Ophiothela mirabilis Verrill, 1867 has widely spread and colonized hosts at high densities along the Western Atlantic. We assessed the impacts of O. mirabilis on the feeding performance of the preferred host Leptogorgia punicea (Milne Edwards and Haime, 1857) through in situ experiments using incubation chambers and estimated its putative effects on the benthic-pelagic coupling processes of a rocky shore system. The feeding rates and heterotrophic carbon inputs of L. punicea treatments with high colonization by O. mirabilis (5.4 ± 0.6 individuals cm⁻² of host area; mean ± standard deviation) were compared to host controls naturally without brittle stars. No significant differences in host feeding performance were observed between the control and treatments. Overall, L. punicea ingested 3,047,118 ± 1,843,183 particles g DW (dry weight)⁻¹ h⁻¹, corresponding to 116.1 ± 159.0 µg of carbon (C) g DW⁻¹ h⁻¹. Therefore, although octocorals hosting O. mirabilis may have impaired polyp opening and extension, their feeding performance remains similar. In this sense, the impact of O. mirabilis on the carbon flux of the rocky shore system driven by octocoral ingestion is minimal. The grazing rate of 49.9 ± 68.3 mg C m⁻² day⁻¹ highlights the significant role of L. punicea in such benthic-pelagic coupling processes. Notwithstanding, further laboratory and field experimental studies assessing the effects on host taxa with distinct morphological and functional features are needed to better understand the responses of the recipient hard-bottom systems along the Western Atlantic to increasing densities of O. mirabilis.
Mean ± standard error seed retention times (min) of four bird species fed Pyracantha angustifolia fruits in captivity (H-value = 9.37, P < 0.02, df = 3). Different letters above the means indicate significant differences
Box and whisker plot (minimum to maximum) of Pyracantha angustifolia germination time in days for three treatments, namely ingested by birds (n = 805 seeds), manually depulped by hand (n = 199 seeds) and whole fruits (n = 38 fruits). Boxes represent median, bordered by 25th and 75th percentiles. Different letters on top of boxes indicate statistical significance (H-value = 43.21, P < 0.05, df = 2) and whiskers indicate minimum and maximum values
Cumulative Pyracantha angustifolia germination success (percentage of seeds germinated) with the number of days after planting for seeds defecated by Purple-crested Turacos (TU), Red-winged Starlings (ST), Speckled Mousebirds (MO) and Dark-capped Bulbuls (BU). Germination from manually depulped (DP) fruits and seeds planted as whole fruits (WL) are also shown. Germination was recorded for 58 days in total
Invasive alien plants can use animal-plant interactions to increase their invasiveness. This study investigated the role of frugivorous birds in seed dispersal, germination success and germination time of the alien plant Pyracantha angustifolia (Franch.) C.K. Schneid. (Rosaceae) in South African high elevation grasslands. We monitored which bird species fed on the fruit of the invasive P. angustifolia in farms in the Free State Province using timed-focal and opportunistic observations, and camera traps aimed at fruiting branches and fallen fruits on the ground. Nine bird species visited P. angustifolia shrubs to perch or feed on fruits, but only one (Speckled Mousebird) fed on the fruits during timed-focal observations. Camera trap footage and opportunistic observations revealed a further three bird species (African Pied Starlings, Crested Barbets, Red-eyed Barbets), domestic horses and goats, and two rodent species feeding on fruits. To assess the effect of ingestion by avian frugivores on P. angustifolia germination success and time, P. angustifolia fruits were fed to captive Cape White-eyes (Zosterops virens), Dark-capped Bulbuls (Pycnonotus tricolor), Purple-crested Turacos (Gallirex porphyreolophus), Red-winged Starlings (Onychognathus morio) and Speckled Mousebirds (Colius striatus); frugivores present in the invasive range of P. angustifolia in South Africa. Seeds collected from bird excreta, whole fruits, and depulped fruits were grown under greenhouse conditions and germination times recorded. All captive bird species, except for Cape White-eyes, ingested the seeds; Cape White-eyes fed on fruit pulp only. Bird species with relatively larger body mass had longer seed retention times compared with the smaller bird species. Germination success of both depulped and ingested P. angustifolia seeds was significantly higher (> 80%) than for seeds from whole fruits (7%). Ingestion by the four avian frugivore species did not affect germination time and success; instead, the birds facilitate the spread and germination of seeds by removing the fruit pulp and spreading the seed away from the parent shrubs.
The establishment of non-indigenous species in the Antarctic, an ecosystem isolated for millions of years, could dramatically alter its unique and endemic biota. In coastal waters, calcified species (e.g., echinoderms, gastropods, bivalves) of benthic communities will be particularly vulnerable to shell-crushing (i.e., durophagous) predators such as crabs. The magnitude of changes in the community structure of shallow Antarctic waters potentially produced by such non-indigenous predators will depend on the innate vulnerability of these species (e.g., shell characteristics) and their potential to respond to novel threats (e.g., behavior, shell thickening). This study aims to evaluate the potential interaction between shell-crushing predators and the limpet Nacella concinna, an endemic Antarctic species and one of the most abundant and conspicuous gastropods in intertidal and shallow subtidal zones of the Antarctic. First, we showed that the king crab Lithodes santolla, a representative species of a group of crabs likely to invade Antarctic waters, was able to break the shell of N. concinna and consume it in the laboratory. We then assessed the shell-breaking force of N. concinna living in four Antarctic habitats (two intertidal and two subtidal) and found wide variation in this trait. Finally, we examined shell-breaking force of a subantarctic congener, N. deurata, which naturally coexists with shell-crushing predators in its native range, and found its shell-breaking force to be similar to the strongest populations of the Antarctic species. Taking into account the crushing claw force of crabs and their high consumption rate of limpets, N. concinna will be highly vulnerable to this kind of durophagous predators and may have limited reaction norms for increasing any inducible defenses such as the thickening and hardening of the shell or changes in their behavior in the face of the almost inevitable invasion of shell-crushing predators into the Antarctic marine ecosystem.
Invasive species removal is a common focus in restoration ecology, but the ultimate goal of native plant species recovery and habitat recovery is often elusive. Control of invasive Tamarix spp. shrubs in the American Southwest has only sometimes led to increased native species cover; this is of particular concern for the protection of bird habitat, including the endangered Southwestern willow flycatcher (Empidonax extimus trailii, abbr. SWFL) that nests readily in Tamarix when native Salix canopy is absent. If we can identify the conditions that lead to more native trees as well as habitat protection for the SWFL, we can prioritize restoration efforts more effectively and reduce conflict between conservation goals. To determine whether reduction in the invasive Tamarix led to more Salix cover, we compiled data on vegetation, soils, and geographic conditions in 260 sites where Tamarix had been subject to control efforts and 132 positive and negative reference sites. We found that (1) reduction in Tamarix only increased Salix cover in wetter sites and was greater when a particular low-disturbance removal method was used; however, the increase did not typically compensate for the overall losses in canopy cover, and (2) Salix cover was generally highest in locations with low drought stress, as reflected by soil properties, distance to water, and climate. These results suggest that the presence and recovery of Salix is dependent on its relatively narrow environmental niche, in contrast with Tamarix’s broader one. Thus, although abundance of Salix and Tamarix was negatively correlated, this is likely because of Salix’s different niche, as much as or more than direct interspecific competition. Our findings demonstrate that removal of an invasive species does not necessarily lead to reestablishment of the native species they appeared to displace. We suggest that in the case of promoting habitat for SWFL and other birds, outcomes of restoration activity can be improved by focusing Tamarix removal efforts on sites more likely to promote Salix growth based on environmental characteristics.
Richness of root flavonoids in woody invasive (in grey) and non-invasive (in white) species. The quartiles 0.05, 0.25, 0.75, and 0.95 are shown in each box. The line inside each box corresponds to the median, and the square inside each box corresponds to the mean. *P < 0.05
Phylogeny and average root flavonoid richness for 81 woody species from the literature. Bars shaded gray indicate taxa classified as invasive and black bars indicate taxa classified as non-invasive. Flavonoid richness values were relativized and subtracted from the mean
Total amount of root flavonoids in woody invasive (in grey) and non-invasive (in white) species. The quartiles 0.05, 0.25, 0.75, and 0.95 are shown in each box. The line inside each box corresponds to the median, and the square inside each box corresponds to the mean
Invasive plants, particularly woody ones, cause signifcant ecological and economic losses. However, many factors that underlie the plant invasion process are not well known. There is evidence that some plant traits can be indicators of the degree of invasiveness in woody plants. However, root characters, such as the quantity and diversity of secondary metabolites, have been poorly studied. Flavonoids are widely distributed metabolites in plants and are involved in important biological interactions that take place in the soil. They have been related to increases in defense against pathogens, communication with mutualistic organisms, particularly with arbuscular mycorrhizal fungi and nitrogen fxing bacteria, and with allelopathic efects on neighboring plants. If favonoids are costly to produce and/or implicated in novel interactions established by successful woody invaders, we could expect invasive species to produce unique favonoids compared to non-invasive ones. We assessed the literature to evaluate whether the production of favonoids in roots vary among woody invasive and non-invasive species. Specifcally, we tested the efect of invasive status on favonoid richness, composition, and abundance in roots. We also assessed for indicator favonoids whose presence and abundance refect the invasive status. Invasive woody species had higher favonoid richness in roots than non-invasive, particularly within the chemical subgroups favonols and favones. Our results suggest that root favonoids play an important role in determining the invasion success of woody plants.
Roseau cane scale haplotype network. Result of statistical parsimony analysis (TCS 1.21) on the dataset restricted to samples of N. biwakoensis. Haplotype names are formatted as “country/regional abbreviation” “#”. Countries/regions are abbreviated as: Chi = China, HK = Hong Kong, Kor = South Korea, Nip = Japan (Nippon), Tai = Taiwan, USA = United States. Countries/regions are organized by color, specific localities are referenced by patterns. The legend includes abbreviated locality names; full locality details are listed in Table 1
Roseau cane scale collection site map. A plot of collection sites and haplogroup distributions by locality
Full haplotype network. The result of statistical parsimony analysis (TCS 1.21) on the full dataset, including N. biwakoensis and two potential cryptic species: Nipponaclerda sp. 1 (UND1) from Hirose River, Japan, and Nipponaclerda sp. 2 (UND2) from Guigang, China and Viet Nam. Haplotype names are formatted as “species identifier” “country abbreviation” “#”. Countries are abbreviated as: Chi = China, Nip = Japan (Nippon), Vtn = Viet Nam
MaxEnt East Asia. Climate suitability results for points in East Asia based on publicly available samples of P. australis in the GBIF database for the Full dataset (top left), the Palearctic dataset (top right), the Indo-Malaysian dataset (bottom left), and the Japanese dataset (bottom right), as estimated using MaxEnt
MaxEnt North America. Climate suitability results for points in the Gulf Coast region based on publicly available samples of P. australis in the GBIF database for the Full dataset (top left), the Palearctic dataset (top right), the Indo-Malaysian dataset (bottom left), and the Japanese dataset (bottom right), as estimated using MaxEnt
The recent decline of Phragmites australis stands in the Mississippi River Delta is due, in part, to damage from herbivory by the non-native roseau cane scale, Nipponaclerda biwakoensis. In Louisiana, P. australis communities, known locally as roseau cane, protect the marsh ecosystem from erosion and storm-related impacts, stabilize shipping channels, and shield oil and inland infrastructure. Intense infestations by N. biwakoensis have contributed to widespread dieback of reeds in this region since 2016. Identifying suitable biological control agents from the source population is key to managing the invasive population of N. biwakoensis and protecting the delicate marsh ecosystem. Therefore, we used mitochondrial COI sequence data, drawn from collections of N. biwakoensis spanning the native and invasive range, to identify the origin of the established population in Louisiana and Texas. Network analysis using TCS 1.21 revealed a rich diversity of 57 unique COI haplotypes distributed across the native range in East Asia. Relationships among the sampled haplotypes indicate that N. biwakoensis was likely introduced to the United States from northeastern China. Specimens from the USA are nested among a group of haplotypes all originating from China, and the samples belong to a haplotype that was otherwise only collected in Beijing and Hebei. In contrast, modeling of habitat suitability based on host plant records from across East Asia, using MaxEnt 3.4.4, identified southeastern China as the best location to search for potential natural enemies to match the climatic conditions in the Mississippi River Delta. These two pieces of evidence provide critical guidance to focus future biological control efforts, and we discuss the importance of examining both genetic and environmental data when searching for potential biological control agents. Additionally, we identified two cryptic species of Nipponaclerda on Phragmites, one in Japan and another in Viet Nam. This research offers new depths of perspective on population structure for a rarely studied group of scale insects, the flat grass scales (Aclerdidae). Together the evaluation of scale insect genetics and ecological niche modeling will optimize foreign exploration efforts for biological control agents.
Changes in abundance of reptilian and avian predators and reptilian prey after arrival of cane toads. Shown are average number of a snakes, b monitor lizards, c dragons, and d avian nest predators encountered on surveys during pre- and post-toad years. Error bars indicate standard error (SE). Arrows indicate timing of cane toad arrival
Observed shifts in predators depredating nests of purple-crowned fairy-wrens, an endangered indicator species of monsoonal northern Australia. Depicted is the total number of nest predation events by monitor lizards, avian predators, snakes, and centipedes, respectively, pre- and post-toad arrival. N = 22 nests pre-toad and 26 nests post-toad
of changes in strength of trophic links following cane toad invasion at a riparian site. Depicted are relationships between predators and prey a before and b after the arrival of toads. Red arrows indicate the direct negative effect of toads on monitor lizard abundance, and black arrows indicate observed negative effects of predators on purple-crowned fairy-wren nest success; percentages indicate the percentage of nest predation events by each class of predator (monitor lizards, snakes, avian predators, centipedes; N = 22 nests pre-toad and 26 nests post-toad). Dashed arrows indicate predicted predation by monitor lizards on prey. Thickness of arrows indicates strength of effects. Photos: brown goshawk, Horner’s dragon, common tree snake, and purple-crowned fairy-wren—Australian Wildlife Conservancy/N. Teunissen; Merten’s water monitor and Scolopendrid centipede—Australian Wildlife Conservancy /M. Roast
Invasive species often have catastrophic direct effects on native species through increased competition and predation. Less well understood are indirect, cascading effects across trophic levels. To reveal trophic disruptions caused by invasive species, it is necessary to document interactions between species at different trophic levels and across guilds. Here, we take this approach to quantify the impact of the invasion of cane toads at a riparian site in the Kimberley, northwest Australia. These toads are toxic to many native vertebrate predators and following toad arrival we observed the expected severe population decline in monitor lizards. Contrary to expectations however, this did not facilitate species in the next trophic level down: the abundance of their reptilian prey, as well as nest success of a songbird whose nests were predominantly depredated by monitor lizards, remained unchanged. Instead, detailed observations suggest a change in the suite of nest predators, with monitor lizards being replaced by other—mainly avian—predators, possibly reflecting their release from competitors that are more efficient nest predators. Hence, our findings highlight complex indirect effects of an invasive species across trophic levels and indicate that trophic cascades can go undetected when failing to include direct observations on predator–prey interactions.
Sampling map of E. johnstonei included in this study throughout the Lesser Antilles. All Lesser Antillean islands are shown as single sampling localities for simplicity. Non-Lesser Antillean sampling localities are depicted separately in right-insets. The left-inset elevation map depicts the island of Montserrat, showing within island sampling localities. Within-island sampling localities for other Lesser Antillean islands are available in Supplementary Information (Fig S1; Table S3). All site colors correspond to the mitochondrial clades (see Fig. 2). Islands with a native congeneric Eleutherodactylus species are denoted by an asterisk (*) and a native Pristimantis species by double asterisks (**)
Mitochondrial (12S, cytb) BEAST time tree for E. johnstonei and closely related species sampled in this study. Major clades are colored and correspond to sampling localities in Fig. 1. Each haplotype is represented by a single sequence; for ease of viewing, individual haplotypes are not labelled. Node bars depict 95% intervals of divergence time estimate, time scales are divided by geological epoch, and nodes with posterior probabilities greater than 0.9 are marked with black circles and those greater than 0.8 with grey circles
Minimum-spanning networks and nuclear gene trees of six nuclear loci (Casr, Grm2, Kiaa2013, Med13, Tyr, and Vps18), as well as concatenated nuclear tree of six loci. Each hash denotes a single polymorphism for haplotype networks. For trees, nodes with greater than 0.8 posterior probability are denoted by black circles. All colors correspond to major mitochondrial lineages (see Fig. 2). Labeled western and eastern clades on our concatenated nuclear tree correspond with major mitochondrial clades
Boxplots of male and female body size (mm) divided by major mitochondrial clade: eastern and western Lesser Antilles. *** P < 0.001
Cryptogenic species are those whose native and introduced ranges are unknown. The extent and long history of human migration rendered numerous species cryptogenic. Incomplete knowledge regarding the origin and native habitat of a species poses problems for conservation management and may confound ecological and evolutionary studies. The Lesser Antilles pose a particular challenge with regard to cryptogenic species because these islands have been anthropogenically connected since before recorded history. Here, we use population genetic and phylogeographic tools in an attempt to determine the origin of Eleutherodactylus johnstonei , a frog species with a potentially widespread introduced range and whose native range within the Lesser Antilles is unknown. Based on elevated estimates of genetic diversity and within-island geographic structure not present elsewhere in the range, we identify Montserrat as the native island of E. johnstonei . We also document two major clades within E. johnstonei , only one of which is the primary source of introduced populations throughout the Americas. Our results demonstrate the utility of genetic tools for resolving cryptogenic species problems and highlight E. johnstonei as a potential system for understanding differences in invasive potential among sister lineages.
Study area. Alto Ricaurte region (Boyacá, Colombia)
The predicted increase in species richness as distance to rivers and roads decreases. The curves are fitted according to the optimal ZINB model. Distance to cities is excluded as it is not an important model term
List of plant species registered in the Alto Ricaurte region
Invasive and potentially invasive plant species were recorded along roadsides
Invasive and potentially invasive plant species were recorded along riverbanks
Cities and towns can be conceptualized as invasion hotspots. The connections created by roads or highways facilitate the mobility of these species, expanding their range of distribution and contributing to their expansion through the landscape to other urban areas or nearby natural and semi-natural ecosystems. Here we describe the actual distribution of invasive plants in a region of Colombia and determine the role that urban centers, road edges, and rivers have in shaping their distribution. We mapped—at high resolution—the distribution of exotic species in the Alto Ricaurte region (Boyacá, Colombia), specifically in the towns of Villa de Leyva, Sáchica, Sutamarchán, and Arcabuco and connecting roads. Initially, a list of 40 exotic plant species with invasive potential was assembled: 26 of which were mapped in the region. Then, we used Poisson models to test whether invasive species appear more frequently near cities, roads, and riverbanks. We found that roadside and riverbank areas host more exotic species than more distant zones. Our findings suggest that roads and rivers are efficient dispersal corridors connecting different invasive hotspots with other landscape elements. Urban centers act as islands of invasion and roads and rivers as corridors for species dispersal. This invasion scenario is already causing economic and ecological damage: roads are heavily deteriorated byR. communis, K. densiflora, and C. jubata, while P. aquilinum and M. minutiflora may increase the occurrence of fires in the region.
Community assembly theory provides the context for understanding native community structure and interpreting the relationship between native plant traits and native consumer abundance. a Species from the regional species pool pass through abiotic and biotic filters to determine the composition and relative abundance of plant species, as well as the distribution of native plant functional traits. b The abundance distribution of the resulting community of native plants is mapped out along a trait axis of functional effect traits relevant to consumers. c Niches of three consumers, expressed as resource utilization curves relative to their plant-derived resource base, with two specialists (x and z) and one generalist (y). d Consumer community structure expressed as the relative abundance of each species as a function of the relevant plant-derived resource base. e Exotic plant invasion reassembles or restructures the plant community and thereby the abundance-distribution of functional effect traits relevant to consumers. f Consumer niches along the plant-derived resource base, which are a product of the historical ecological/evolutionary context that formed them. With altered resources, some species may express broader niches than previously possible (dotted line, species y). g Consumer niches are mapped onto the altered plant resource base to understand or predict restructuring of the consumer community following plant invasion. In this example, the invader became more abundant than the native plants and strongly shifted the community-level distribution of plant functional effect traits and the associated relative abundance of resources for consumers, especially suppressing plant species (and associated resources) at the upper end of the trait value range and increasing plants and associated resources at the lower end of the range. The result is a shift in the consumer community with an increased abundance of specialist x, modestly decreased abundance of generalist y, and strongly decreased abundance of specialist z, as a function of the shift in plant functional effect traits and corresponding resources relevant to the consumers
The plant trait of greatest relevance to native web-building spiders in Intermountain grasslands of the western United States is plant architecture and overall structural complexity of the plant community. This community-level functional effect trait can be mapped out (a) as a function of structural differences (low to high complexity) among plant functional groups. b The habitat niches of the two primary spider guilds can be mapped onto this niche space to show that the orb weavers are generalists capable of utilizing a range of plant architectures, whereas the irregular web spiders are more specialized, using primarily the most structurally complex perennial forbs. These niche requirements, given the available habitat resource base, translate to (c) comparable abundance of the two spider guilds. d Overall, plant invaders differ from the native plants in having more complex architectures, shifting the resource axis toward greater structural complexity. e Mapping this new resource axis onto the spider niches shows that this shift aligns more with the specialists with the overall result that (f) while both spider groups increase in abundance, the specialists increase much more than the generalists. Note, given that the new resource base extends beyond the former system and yet is incorporated into both niches, this suggests a shift in realized niches (indicated by dotted vs solid curves in (e) to incorporate this new resource base, a shift which is linked to phenotypic plasticity for the irregular web spiders
a The abundance distribution of native plants in an Arizona semi-desert grassland mapped out along a gradient of seed size, one of the functional effect traits relevant to rodent consumers (see also Fig. 4). b Rodents in this community can be categorized by feeding guild (opportunists: Baiomys taylori, Dipodomys merriami, Reithrodontomys fulvescens, Sigmodon arizonae, and S. ochrognathus, and granivores: Chaetodipus hispidus, C. penicillatus, and Perognathus flavus), whose niches can be expressed as resource utilization curves relative to the resource base of seed sizes (small to large). c Rodent community structure can be expressed as the relative fitness/abundance of each feeding guild as a function of seed size. d Invasion by Eragrostis lehmanniana restructures the plant community and the abundance-distribution of seed sizes, now dominated by small seeds. e Rodent niches along the seed size resource base. Based on this information (in d and e), we can map the rodent niches (f) onto the altered resource base (seed size) to understand restructuring of the rodent community as a function of plant invasion. In this example, as the invading grass becomes dominant, it shifts the seed resource axis toward smaller seed sizes by suppressing large-seeded plants and producing small seeds. The result is a decline in abundance of the granivores, particularly those favoring larger seeds, and increased abundance of opportunists
a Vegetation cover provides another functional effect trait relevant to the rodents in the same Arizona semi-desert grassland (Fig. 3), such that we also can plot the abundance distribution of native plants along this resource axis. b Niches of three guilds of rodents can be expressed as resource utilization curves relative to the resource axis of vegetation cover (sparse cover: C. penicillatus, D. merriami, P. flavus, and S. ochrognathus, moderate cover: C. hispidus, and dense cover: B. taylori, R. fulvescens, and S. arizonae). c Rodent community structure expressed as the relative fitness/abundance of each species’ guild as a function of vegetation cover (sparse to dense). d Invasion by Eragrostis lehmanniana restructures the plant community and the abundance-distribution of vegetation cover, now dominated by dense cover. e Rodent niches can be integrated with the altered vegetation cover resource base (d) to understand (f) restructuring of the rodent community as a function of plant invasion. In this example, the invading grass becomes dominant and produces more cover, shifting the relative abundance of resources for rodents, especially suppressing the guild that prefers sparse cover. The result is a decline in abundance of the sparse cover rodents and increased abundance of the dense cover species. Combining the effects of the shifts in this resource axis with the changes in the seed resource axis (Fig. 3) help to explain overall patterns of the impacts of E. lehmanniana invasion on the rodent community
Plant invasions can alter food resources and habitat conditions that structure animal communities. These effects are negative for many native animals, but neutral or even positive for others. Understanding why we see this variation in responses is critical for mitigating invasion outcomes, yet we lack a synthetic framework to explain and potentially predict effects of invasive plants on native animals. We propose a trait-based framework for understanding how invasive plants affect native fauna, which draws on community assembly, niche, and trait theories to define the mechanisms by which invasive plants alter ecological conditions relevant to native animals. This approach moves beyond prior frameworks by explicitly accounting for the context dependency that defines most ecological interactions and invasion outcomes. Namely, by characterizing the plant community in terms of functional effect traits (e.g., seed size) relevant to consumers and quantifying those traits along a consumer resource axis, we can map the functional relationship between plant resources and animals. We can then delineate how plant invaders alter the plant community and associated resource axes to restructure consumer communities. We apply this framework to case studies of rodents, spiders, and birds to demonstrate the process and explore its utility. For example, we show that by focusing on how a nonnative grass altered seed sizes (relative to the native plant community), we can better understand declines in abundance of granivorous rodents and increases in opportunists. This approach can elucidate which native animals will be most likely affected by plant invasion, as well as how and why they might respond. Moreover, these mechanistic explanations provide working hypotheses for how invasive plants impact native animals more generally, with potential for predicting impacts of future invaders.
Estimates of spatial synchrony (Bjørnstad 2020) in L. dispar growth rates from the Northern, Midwestern, and Southern regions, 1999–2015
Region-specific mean L. dispar growth rates by mean minimum January A and mean maximum July B temperature for each pair of years (e.g., 1999–2000, …. 2014–2015). Fitted lines are estimated using locally-weighted polynomial regression
Relationship between primary and secondary host species cohesion, and mean L. dispar growth rates in the Northern A and Southern B regions. Mean growth rates were averaged across all years (1999–2015). The size of the circles is proportional to the growth rate; the largest-sized circles represent growth rates ≥ 2 or ≤  − 2, and the smallest sized circles are 0. Grey circles are positive growth rates and open circles are negative growth rates
Observed A and predicted B spatially-explicit mean L. dispar growth rates, 1999–2015. Predicted growth rates are derived from region-specific GAM models that incorporate temperature, and when applicable to the region, primary and secondary host plant cohesion (Table 4). Observed and predicted growth rates from some states are shown even though they were not included in the analysis (i.e., Iowa, Kentucky, and Tennessee); data from these states were excluded due to limited spatial and temporal extent of L. dispar monitoring. Predictions in Kentucky and Tennessee were based on the Southern region GAM model, and predictions in Iowa were based on the Midwestern region GAM model
Lymantria dispar (L.), formerly known in the U.S.A. as the gypsy moth, has been a major pest species in North American forests for > 100 years. Due to the economic and ecological consequences of L. dispar outbreaks, many aspects of its population biology and ecology have been studied. However, as L. dispar continues to spread into new areas, it remains important to understand its invasion dynamics in newly established populations where prior research is lacking. In this study, we used a 16-year spatially-referenced dataset to quantify the spatial dynamics of L. dispar population growth rates along its expanding population front from Minnesota to North Carolina. We then used this information in a spatially-explicit modeling framework to quantify the role of temperatures, primary and secondary L. dispar host plant density, and the fragmentation of primary and secondary host plants, on L. dispar population growth rates. Across the invasion front, temperatures were significant predictors of growth rates. The basal area of host plants, often used to predict L. dispar risk, was not a significant predictor in any region along the invasion front. Instead, primary and secondary host plant cohesion (i.e., reduced fragmentation), were significant predictors of growth rates, with the exception of areas where host plants are generally scarce. The results highlight geographical differences in how temperature and host plant fragmentation affect L. dispar growth rates, and underscore the role that secondary host plants can play in establishing populations. The results inform the development of improved risk models of L. dispar invasion.
The enemy release hypothesis states that introduced plants have a competitive advantage due to their release from co-evolved natural enemies (i.e., herbivores and pathogens), which allows them to spread rapidly in new environments. This hypothesis has received mixed support to date, but previous studies have rarely examined the herbivore community, plant damage, and performance simultaneously and largely ignored below-ground herbivores. We tested for enemy release by conducting large scale field surveys of insect diversity and abundance in both the native (United Kingdom) and introduced (New Zealand) ranges of three dock (Rumex, Polygonaceae) species: R. conglomeratus Murray (clustered dock), R. crispus L. (curly dock) and R. obtusifolius L. (broad-leaved dock). We captured both above- and below-ground insect herbivores, measured herbivore damage, and plant biomass as an indicator for performance. In the introduced range, Rumex plants had a lower diversity of insect herbivores, all insect specialists present in the native range were absent and plants had lower levels of herbivore damage on both roots and leaves. Despite this, only R. crispus had greater fresh weight in the introduced range compared to the native range. This suggests that enemy release, particularly from below-ground herbivores, could be a driver for the success of R. crispus plants in New Zealand, but not for R. conglomeratus and R. obtusifolius.
Alien plants classified as invasive, perennial and annual alien plants (naturalized + casual) ranked according to the logarithmic sum of environmental (striated bar) and socio-economic (solid bar) impact scores of GISS
Number of alien plant species according their invasive status in different habitats in Iran
The distribution of 52 alien plants in Iran and their invasion status. The numbers above each graph are mean GISS score (min-max) for each ecological zone
Like other developing countries, Iran is threatened by alien plants because of its rich native biodiversity, a wide range of climatic conditions and lack of regulation for importing new plants. In this study, we describe the characteristics, distribution, potential impacts of 52 alien plants based on Generic Impact Scoring System (GISS) assessment and their management. Species were selected from those identified to be invasive or with the risk to be invasive of those introduced to Iran over the past 30 years. From the 52 selected alien plants, the most common were herbaceous and annual plants from the Fabaceae and Asteraceae families. South America and Eastern Asia are the main areas of origin to Iran. The highest portion of naturalized plants are detected in croplands as weed. Eichhornia crassipes and Ailanthus altissima had the highest GISS environmental and socio-economic impact score of the 13 invasive alien plants we identified, and Pueraria montana var. lobata and Hydrilla verticillate had the highest scores of the casual and naturalized species. The Hircanian zone was the most invaded area and it could be considered as a potential biological invasion hotspot in Iran. Non-selective alien plant management and a high reliance on herbicide application, especially those with high potential of herbicide resistance, could be main obstacles of successful alien species removal or control. Iran requires specific management programs to tackle the introduction and spread of alien plants and to reduce their impacts on biodiversity, ecosystem services and human livelihoods. Considering the high diversity of climatic conditions in Iran, from arid to subtropical, studies on the effect of climate change on new invasions or range expansion of current invaders and their impacts should also be a priority.
Schematic diagram of the experimental design
Effects of transgenerational plasticity on morphological properties of offspring ramets (F1 generations). The colors in the columns represent different maternal light treatments. The same lower case letters are not significantly different at P = 0.05. Values are means ± standard errors, n = 8
Effects of transgenerational plasticity on photosynthetic property of offspring ramets (F1 generation). The colors in the columns represent different maternal light treatments. The same lower case letters are not significantly different at P = 0.05. Values are means ± standard errors, n = 8
Effects of transgenerational plasticity on number of ramets and total stolon length of offspring ramets (F1 generation). The colors in the columns represent different maternal light treatments. The same lower case letters are not significantly different at P = 0.05. Values are means ± standard errors, n = 8
Effects of transgenerational plasticity on leaf, stem, root and total biomass of offspring ramets (F1 generation). The colors in the columns represent different maternal light treatments. The same lower case letters are not significantly different at P = 0.05. Values are means ± standard errors, n = 8
  • Xiao XiaoXiao Xiao
  • Linxuan HeLinxuan He
  • Xiaomei ZhangXiaomei Zhang
  • [...]
  • Jinsong ChenJinsong Chen
Phenotype of plant offspring may be affected by particularly maternal environmental conditions, which is named as transgenerational plasticity. Transgenerational plasticity enhances the fitness of offspring under the maternal environmental conditions. Transgenerational plasticity may promote the successful invasion of alien plants, particularly those with clonal growth. However, few studies have compared transgenerational plasticity between alien invasive clonal plants and their congeneric native ones. A pot experiment with the invasive herb Wedelia trilobata and its congeneric native species Wedelia chinensis was conducted to investigate effects of light conditions (low vs. high light treatment) experienced by mother ramets on morphological and photosynthetic properties of offspring ramets subjected to the low light treatment. Compared with those of offspring ramets from mother ramets subjected to the high light treatment, leaf area, potential maximum net photosynthetic rate (Pmax) and biomass accumulation of offspring ramets from mother ramets subjected to the low light treatment were significantly greater in W. trilobata than W. chinensis. Opposite pattern was observed in number of offspring ramets. We conclude that effects of transgenerational plasticity on growth performance could be species-specific between invasive plant and its congeneric native one. Positive effect of transgenerational plasticity on number of offspring ramets was not transformed into growth advantages of native species W. chinensis during its later establishment. However, favorable effects of transgenerational plasticity on capturing light resource could enhance competitive ability and promote successful invasion of W. trilobata.
Locations colonized by the highly invasive golden mussel, Limnoperna fortunei in Beijing, China. Solid circles are surveillance sites confirmed by both environmental DNA (eDNA)-based method and traditional field surveys, while open circles denote positive signals by eDNA only
Zhan et al. (Biological Invasions, 2015, 17:3073–3080) stressed that China’s South-to-North Water Transfer Project (SNWTP) – the world’s largest constructed water diversion - could create an invasion highway by facilitating spread of non-native species, including invasive golden mussel Limnoperna fortunei. However, most available literature indicated that golden mussels could not survive the cold winter in Northern China. We proposed that phenotypic plasticity and rapid environmental adaptation, combined with relatively high water temperature derived from wastewater treatment plant effluents and a large potential inoculum continuously transported from southern source populations, could jointly contribute to golden mussel spread into northern locations. We conducted surveillance for the species both before and after the waterway was opened in late 2014 in the diversion destination - Beijing. While all surveys in the whole area were negative between 2014-2018, we detected rapid geographical expansions in 2019-2021 across multiple waterbodies based on traditional field surveys and environmental DNA (eDNA)-based methods. Surprisingly, we subsequently observed populations that had successfully survived a cold winter in Beijing. The SNWTP may facilitate further spread of cold-adapted populations, placing high-latitude areas at risk. This case study highlights the need for robust scientific assessment and management to predict and mitigate non-native species’ distributional changes that may accompany large-scale hydraulic projects.
Graphical representation of box tree moth (Cydalima perspectalis) population genetic structure estimated using the Bayesian clustering approach implemented in STRUCTURE. Results for the full dataset, native range dataset, and invaded range dataset respectively are represented. The population codes appear below the plots (see Table 1). Each individual is represented by a vertical line, and each color represents a particular genetic cluster. In bold is the best K for each STRUCTURE analysis (full dataset, native range alone and invaded range alone, respectively), as defined by STRUCTURE Harvester
Box tree moth (Cydalima perspectalis) invasion scenarios revealed by the ABC analyses. (A) Introduction pathways from Asia to Europe. (B) Dispersal pathways across the invaded range. Note: These figures depict the most likely invasion scenarios arising from the analyses. In Europe, countries where the box tree moth has been observed are colored in red. In Asia, the most likely source area of the box tree moth revealed by our results is colored in blue. The yellow stars indicate the first places where C. perspectalis was detected—in Germany and in the Netherlands in 2007 (Krüger 2008; Van der Straten and Muus 2010). The arrows indicate the most probable invasion pathways
Identifying the invasion routes of non-native species is crucial to understanding invasions and customizing management strategies. The box tree moth, Cydalima perspectalis , is native to Asia and was recently accidentally introduced into Europe as a result of the ornamental plant trade. Over the last 15 years, it has spread across the continent and has reached the Caucasus and Iran. It is threatening Buxus trees in both urban areas and forests. To investigate the species’ invasion routes, native and invasive box tree moth populations were sampled, and moth’s genetic diversity and structure were compared using microsatellite markers. Our approximate Bayesian computation analyses strongly suggest that invasion pathways were complex. Primary introductions originating from eastern China probably occurred independently twice in Germany and once in the Netherlands. There were also possibly bridgehead effects, where at least three invasive populations may have served as sources for other invasive populations within Europe, with indication of admixture between the two primary invasive populations. The bridgehead populations were likely those in the countries that play a major role in the ornamental plant trade in Europe, notably Germany, the Netherlands, and Italy. All these invasion processes likely facilitated its fast expansion across Europe and illustrate the role played by the ornamental plant trade not only in the moth’s introduction from China but also in the species’ spread across Europe, leading to an invasion with a complex pattern.
Mean allocation ratios (top of colored bars) and error bars (±\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\pm$$\end{document} SE) from size-independent model for each taxon (color) within each nutrient level (rows) at each site (columns). The number of individual stems within each subgroup are indicated above their respective bars. The native is not invasive while both the non-native and hybrid are considered invasive in the Great Lakes region. Coefficients from the mixed effects linear model are in Table S5 and an ANOVA of the model is in Table 1a
Size-dependent model mean sexual reproductive allocation predictions (dark lines) for each taxon (color and shape) within each nutrient level (rows) at each site (columns). The native is not invasive while both the non-native and hybrid are considered invasive in the Great Lakes region. Symbols indicate observed data with color and shape indicating taxon. Shading indicates the range of estimates among mesocosms due to their random effect. Coefficients from the mixed effects nonlinear model are in Table S3a and an ANOVA of the model is in Table 1b. Sample sizes for each taxon × nutrient × site combination are in Fig. 1
Logistic regression predictions for probability of flowering at a given size for each taxon (row and color) at each nutrient level (low = dotted line, medium = dashed line, high = solid line). Symbols represent observed data at low (open), medium (shaded), high (solid fill) nutrient levels, with color indicating taxon, and were spread around 0 and 1 for visibility. The native is not invasive while both the non-native and hybrid are considered invasive in the Great Lakes region. Too few data points were available to fit a model for the native taxon. Coefficients from the logistic regression model are in Table S6 and ANOVA results for the model are in Table S5
Invasive species increasingly threaten ecosystems worldwide making it important to better understand the traits, including sexual reproductive allocation and its plasticity, that make certain species more successful invaders than others. Size differences between native and non-native invasive congeners are common, yet, when comparing allocation within and among species many studies fail to consider the size-dependency (allometry) of allocation patterns. Using a mesocosm experiment conducted at two locations and incorporating a nutrient gradient, we compared sexual reproductive allocation and its plasticity (correcting for size) between three closely related taxa of cattails with varying degrees of invasiveness: Typha latifolia (native, non-invasive), Typha angustifolia (non-native, invasive), Typha × glauca (their hybrid, invasive). We found that the non-native and hybrid taxa (both invasive) allocated more to sexual reproduction than the native, non-invasive taxon even after correcting for aboveground plant size. However, the non-native and hybrid taxa did not differ from each other when accounting for plant size, even though a size-independent analysis indicated they did. This reveals these two taxa differed in plant size, not allocation patterns. Surprisingly, the most invasive taxon (the hybrid) was the least plastic in sexual reproductive allocation in response to nutrients at one site. Our study adds to the growing body of literature suggesting trait values rather than trait plasticity contribute to invasiveness, but ours is unique in its size-dependent analysis of sexual reproductive allocation, its plasticity, and differential taxon invasiveness.
Possible niche shift scenarios between regions. Axes represent two different example environmental gradients across which a niche shift could be observed. Areas occupied in a species’ native range (N) are shown by the green shaded circle; areas occupied in two different introduced ranges (I1, and I2) are shown by the purple and orange circles respectively. A Niche shifts are consistent across independent ranges. B Niche shifts are inconsistent across independent ranges. C Niche shifts occur in some ranges, whilst the niche is conserved in others. D Two niche dynamics that can lead to niche shifts are shown. Niche expansion (blue) refers to areas of analogue, or overlapping, climate space between the native and introduced ranges that are only occupied in the introduced range. Niche unfilling (red) refers to areas of analogue climate space that are only occupied in the native range. Dashed circles denote available climate space for the native range (green) and introduced range (purple)
Distribution of Rumex conglomeratus (top), Rumex crispus (middle) and Rumex obtusifolius (bottom) records included in our study, plotted as black points at 50% opacity. Records span temperate and tropical zones. The areas used to determine background climates are displayed by shaded minimum convex polygons and are the same for each species to allow direct comparison: Native range–Teal; Western North America–Magenta; Eastern Australia–Orange; New Zealand–Green. New Zealand is also displayed in the inset of each distribution map for better visualization
A Contribution of climate variables to the first two axes of the principal component analysis. B Direction of variables with respect to the first two principal components. Direction of arrows indicates increasing values of that variable. The first two principal components represent the environmental space used for further niche analysis. Some variable names are shortened for simplicity: Minimum Precipitation = Precipitation of the driest quarter (BIO17), Maximum Precipitation = Precipitation of the wettest quarter (BIO16), Minimum Temperature = Minimum temperature of the coldest month (BIO6), Maximum Temperature = Maximum temperature of the warmest month (BIO5)
Comparisons of niche overlap in environmental space. Each panel shows a comparison between the native range (Teal) and one of the introduced ranges (New Zealand–Green; North America–Pink; Australia–Orange). The climate space occupied by the species is shown in solid lines and the total available climate space of the respective range is shown with dashed lines. Comparing down columns shows differences between regions whereas comparing across rows shows differences between species in the same region. Increasing values of PC1 broadly correspond to cooler, more variable temperatures, and less seasonal precipitation. Increasing values of PC2 broadly correspond to increased precipitation, and more stable temperatures. Variable correlations with PC1 and PC2 can be seen in full in Fig. 3
Climatic niche shifts occur when species occupy different climates in the introduced range than in their native range. Climatic niche shifts are known to occur across a range of taxa, however we do not currently understand whether climatic niche shifts can consistently be predicted across multiple introduced ranges. Using three congeneric weed species, we investigate whether climatic niche shifts in one introduced range are consistent in other ranges where the species has been introduced. We compared the climatic conditions occupied by Rumex conglomeratus, R. crispus, and R. obtusifolius between their native range (Eurasia) and three different introduced ranges (North America, Australia, New Zealand). We considered metrics of niche overlap, expansion, unfilling, pioneering, and similarity to determine whether climatic niche shifts were consistent across ranges and congeners. We found that the presence and direction of climatic niche shifts was inconsistent between introduced ranges for each species. Within an introduced range, however, niche shifts were qualitatively similar among species. North America and New Zealand experienced diverging niche expansion into drier and wetter climates respectively, whilst the niche was conserved in Australia. This work highlights how unique characteristics of an introduced range and local introduction history can drive different niche shifts, and that comparisons between only the native and one introduced range may misrepresent a species’ capacity for niche shifts. However, predictions of climatic niche shifts could be improved by comparing related species in the introduced range rather than relying on the occupied environments of the native range.
Natural infections of Verticillium spp. (Fungi, Ascomycota) on Ailanthus altissima have suggested to consider the biological control as a promising strategy to counteract this invasive plant, which is otherwise difficult to control by traditional mechanical and chemical treatments. Verticillium wilt is able to lead plants to death, throughout a pathogenic mechanism including vessel occlusions and production of degrading enzymes and phytotoxins. In this study, a 10 weeks open air pot experiment was set to investigate the ecophysiological and biochemical responses of Ailanthus trees artificially inoculated in the trunk with the V. dahliae strain VdGL16, previously isolated in Central Italy from the same host. Inoculated plants showed visible injuries starting from 2 weeks post inoculation (wpi), that progressively developed until a final severe defoliation. The fungal infection rapidly compromised the plant water status, and photosynthesis was impaired due to both stomatal and mesophyll limitations from 4 wpi, with subsequent detrimental effects also on PSII activity. Moreover, the disease altered the translocations of nutrients, as confirmed by cation and carbohydrate contents, probably due to a consumption of simple sugars and starch reserves without replacement of new photosynthesized. An accumulation of osmolytes (abscisic acid and proline) and phenylalanine (a precursor of phenylpropanoids) was also reported at 8 wpi, this being a response mechanism that needs to be further elucidated. However, the activation delay of such defence strategy inevitably did not avoid the premature defoliation of plants and the decline of physiochemical parameters, confirming the key role of Verticillium in Ailanthus decay.
Effects of removal treatments on P. setaceuma plant cover and b number of plants removed. Counts were taken prior to subsequent treatment applications each year starting one year after removals began. Cover data for invaded control is not included for 2021 because P. setaceum was treated in the plots after sampling in 2020. Bars represent one standard error of the mean. Asterisks indicate a year*treatment interaction effect at this p level: ***p < 0.001. Lower case letters represent significant differences among treatments, averaged over season, using sidak post hoc comparisons of means. Plots are 5 m × 5 m
Response of native and nonfocal non-native plant cover to removal treatments over time. Upper case letters represent differences among year, averaged over treatment. Treatment differences were calculated using sidak post hoc comparisons of means. Asterisks indicate a year * treatment interaction effect at these p levels: *p < 0.05. and **p < 0.01. Bars represent one standard error of the mean
Response of native and nonfocal non-native plant richness to removal treatments over time. Upper case letters represent differences among year, averaged over treatment. Treatment differences were calculated using sidak post hoc comparisons of means. An asterisk indicates a year * treatment interaction effect at p < 0.05. Bars represent one standard error of the mean
Pennisetum setaceum standing dead and litter cover by treatment over time. Upper case letters represent differences among year, averaged over treatment. Three asterisks indicates a year * treatment interaction effect at p < 0.001. Bars represent one standard error of the mean
Costs of removal treatments by a mean time conducting treatments in 25 m² plot, b mean measured cost of labor and supplies in 25 m² plot, and c total estimated costs. Total estimated costs include measured costs (based on cost of labor and supplies in plot) plus estimated preparation time (labor per plot and per day) and two-hour round-trip travel to the site. The x and y axes for plot c are on a logarithmic scale. Area of plots was 25 m². Lower case letters represent differences among treatments averaged over year using sidak post hoc comparisons of means. Bars represent one standard error of the mean
Fountain grass ( Pennisetum setaceum ) is a globally pervasive invasive species and a prime example of an escaped horticultural ornamental. In areas where it is not naturally found, it displaces native plant communities and disrupts ecological systems and processes. Cost-effective removal efforts that protect the native plant community are needed for its control. We conducted an experiment from March 2018 to March 2021 in 5 m × 5 m plots to test the efficacy and record costs for common removal techniques (cut and herbicide, herbicide one or two times per year, manual removal) in the Sonoran Desert, Arizona, United States. Each treatment took 2.5 years to achieve control in the plots, and treatments did not negatively affect the native plant community. The response of native plants was mediated by year, such that native cover in treatment plots recovered to similar levels as uninvaded control plots with sufficient rainfall. Plots that received the manual removal treatment had almost five more native plant species than the invaded control treatment (22.7 ± 1.63 compared to 18.1 ± 1.61). Herbicide applied in spring and fall increased efficacy of removals in the first year but was not significantly different from the other treatments averaged over year. Herbicide once per year was most cost effective across different sized areas. Manual removal was also cost effective in small areas (< 0.06 hectares) but was more expensive than herbicide twice a year in larger areas. Our results provide a toolset that enables managers to select removal treatments based on a balance of convenience, resources, and scale of the infestation.
A Holling type-II functional response aV1+aThV\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\frac{aV}{1+a{T}_{h}V}$$\end{document}, with attack rate a\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$a$$\end{document} representing the slope at low prey abundance V\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$V$$\end{document}, and handling time Th\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${T}_{h}$$\end{document} representing the inverse of the asymptotic values at high V\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$V$$\end{document}. Dashed vs normal lines represent 2 different values of handling time, while each of the 3 lines represent different values of attack rate, with thickness proportional to attack rate. B Effect of parameters on prey-predator nullclines and equilibria. Dashed lines represent predator nullclines (where solutions cross horizontally), while dotted lines represent prey nullclines (where solutions cross vertically). The vertical predator nullcline represent the equilibrium prey abundance V∗=μa(β-μTh)\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${V}^{*}=\frac{\mu }{a(\beta -\mu {T}_{h})}$$\end{document}, while the thin vertical dotted line represents the maximum V̲=12K-1aTh\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\underline{V}=\frac{1}{2}\left(K-\frac{1}{a{T}_{h}}\right)$$\end{document} of the nonlinear prey nullcline. Empty dots at V=0\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$V=0$$\end{document} and V=K\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$V=K$$\end{document} represent saddle equilibria (unstable), while the full dot represents the stable coexistence equilibrium. The slope of the nonlinear prey nullcline at this coexistence equilibrium approximates its stability and resilience: negative slope (V∗>V̲\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${V}^{*}>\underline{V}$$\end{document}) means stable, and the larger the absolute value of this negative slope the higher the resilience; otherwise a positive slope (V∗<V̲\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${V}^{*}<\underline{V}$$\end{document}) means unstable coexistence that diverges from the equilibrium and converges to a limit cycle with periodic coexistence. In both panels the effect of parameters is indicated by the arrows, pointing in the direction of an increase in the specified parameters. Functional response parameters (in bold) directly affect both the equilibrium prey abundance and the stability and resilience of prey-predator coexistence. Other predator parameters (conversion efficiency β\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\beta$$\end{document} and mortality μ\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\mu$$\end{document}) only directly affect the equilibrium prey abundance, and through it indirectly affect stability and resilience. Prey carrying capacity K\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$K$$\end{document} only directly affects stability and resilience
A Effect of predator parameter change on the equilibrium prey abundance V∗\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${V}^{*}$$\end{document} and B on the prey-predator coexistence equilibrium stability. Thick lines represent functional response parameters, while normal lines represent other predator parameters. Increasing attack rate a\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$a$$\end{document} and conversion efficiency β\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\beta$$\end{document} in (A) have a negative impact on prey equilibrium abundance, while increasing handling time Th\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${T}_{h}$$\end{document} and mortality μ\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\mu$$\end{document} has a positive effect. Functional response parameters a\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$a$$\end{document} and Th\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${T}_{h}$$\end{document} have in fact a smaller impact on prey equilibrium abundance compared to other predator parameters. Increasing attack rate a\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$a$$\end{document} and conversion efficiency β\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\beta$$\end{document} in (B) have a negative impact on equilibrium stability, increasing mortality μ\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\mu$$\end{document} has a positive effect, while increasing handling time Th\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${T}_{h}$$\end{document} has a non-monotonic effect, increasing stability when sufficiently large but reducing stability when small. Parameter values: a=1.5\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$a=1.5$$\end{document}, Th=1\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${T}_{h}=1$$\end{document}, β=0.5\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\beta =0.5$$\end{document}, and μ=0.25\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\mu =0.25$$\end{document}. Parameter ranges are chosen so that coexistence equilibrium is stable (V̲<V∗<K\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\underline{V}<{V}^{*}<K$$\end{document})
The effect of a higher invasive functional response (both higher attack rate a\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$a$$\end{document} and lower handling time Th\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${T}_{h}$$\end{document}) does not predict the outcome of invasion. The normal line represents prey abundance, the dotted line represents invader predator abundance, and the dashed line represents native predator abundance. Despite an initially faster growth of the invader with respect to the native due to a higher invader functional response, a A lower mortality rate μ\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\mu$$\end{document}, and B a larger conversion efficiency β\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\beta$$\end{document} of the native species can allow long-term resistance to invasion. Invader parameter values: a=1.5\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$a=1.5$$\end{document}, Th=0.5\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${T}_{h}=0.5$$\end{document}, β=0.5\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\beta =0.5$$\end{document}, and μ=0.25\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\mu =0.25$$\end{document}. Native predator parameters: a=1\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$a=1$$\end{document}, Th=1\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${T}_{h}=1$$\end{document}, β=0.5\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\beta =0.5$$\end{document}, and μ=0.125\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\mu =0.125$$\end{document} in (A) and a=1\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$a=1$$\end{document}, Th=1\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${T}_{h}=1$$\end{document}, β=0.82\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\beta =0.82$$\end{document}, and μ=0.25\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\mu =0.25$$\end{document} in (B)
The effect of stability on the transient dynamics to prey-predator coexistence equilibrium driven by different prey carrying capacity K\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$K$$\end{document}. The normal line represents prey abundance and the dotted line represents predator abundance. Despite reaching the same prey equilibrium abundance V∗\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${V}^{*}$$\end{document}, a higher value of prey carrying capacity K\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$K$$\end{document} in (B) with respect to (A) is responsible for a larger predator equilibrium abundance, reached after longer and more pronounced oscillations in prey-predator transient abundances. Parameter values: a=1.5\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$a=1.5$$\end{document}, Th=0.5\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${T}_{h}=0.5$$\end{document}, β=0.5\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\beta =0.5$$\end{document}, μ=0.25\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\mu =0.25$$\end{document}, and K=1\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$K=1$$\end{document} in (A) while K=2\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$K=2$$\end{document} in (B)
The Comparative Functional Response Approach (CFRA) was developed to provide a practical methodology by which short-term experiments can be used to forecast the longer-term impacts of a potential invading consumer. The CFRA makes inferences about potential invader impact based on comparisons of the functional responses of invader and native consumers on native resources in a common experimental venue. Application of the CFRA and derivative approaches have proliferated since it was introduced in 2014. Here we examine the conceptual foundations of the CFRA within the context of basic Lotka–Volterra consumer-resource theory. Our goals are to assess whether core predictions of the CFRA hold within this framework, to consider the relative importance of background mortality and consumer assimilation efficiency in determining predator impact, and to leverage this conceptual framework to expand the discussion regarding stability and long term consumer and resource dynamics. The CFRA assertion that consumers with a higher functional response will have larger impacts on resources only holds as long as all other parameters are equal, but basic theory indicates that predator impacts on prey abundance and stability will depend more on variation in conversion efficiency and background mortality. While examination of the CFRA within this framework highlights limitations about its current application, it also points to potential strengths that are only revealed when a theoretical context is identified, in this case the implications for stability and conceptual links to competition theory.
Current invasive range and ecological niche modelling of the fundamental niche and potential distribution of non-native Pinus radiata in New Zealand. a The national 25 km grid squares containing confirmed occurrences of invasive P. radiata; potential distribution of P. radiata (blue shading) is predicted by the species’ fundamental climatic niche. b The estimated fundamental niche (blue shading) of P. radiata calculated from global native and non-native occurrence data using Mahalanobis niche modelling. For context, contours show the climate space containing 55, 75, and 95% percentiles for the current climatic conditions of New Zealand, and the histograms show the distribution of occurrences for each climate variable
Pinus radiata has invaded a wide range of ecosystems across New Zealand, including successional vegetation and naturally rare ecosystems such as: a geothermal ecosystems (Wairakei, Waikato, photo: Rowan Sprague); b inland basic cliff (Banks Peninsula, Canterbury, photo: Rowan Buxton); c abandoned marginal land undergoing secondary succession (Northland, photo: Peter Bellingham); d gumland heaths (Northland, photo: Ceres Sharp); e inland cliffs (Waikato river, photo: Rowan Sprague); f coastal dunes (Northland, photo: Ceres Sharp)
Tree species in the Pinaceae are some of the most widely introduced non-native tree species globally, especially in the southern hemisphere. In New Zealand, plantations of radiata pine ( Pinus radiata D. Don) occupy c . 1.6 million ha and form 90% of planted forests. Although radiata pine has naturalized since 1904, there is a general view in New Zealand that this species has not invaded widely. We comprehensively review where radiata pine has invaded throughout New Zealand. We used a combination of observational data and climate niche modelling to reveal that invasion has occurred nationally. Climate niche modelling demonstrates that while current occurrences are patchy, up to 76% of the land area (i.e. 211,388 km ² ) is climatically capable of supporting populations. Radiata pine has mainly invaded grasslands and shrublands, but also some forests. Notably, it has invaded lower-statured vegetation, including three classes of naturally uncommon ecosystems, primary successions and secondary successions. Overall, our findings demonstrate pervasive and ongoing invasion of radiata pine outside plantations. The relatively high growth rates and per individual effects of radiata pine may result in strong effects on naturally uncommon ecosystems and may alter successional trajectories. Local and central government currently manage radiata pine invasions while propagule pressure from existing and new plantations grows, hence greater emphasis is warranted both on managing current invasions and proactively preventing future radiata pine invasions. We therefore recommend a levy on new non-native conifer plantations to offset costs of managing invasions, and stricter regulations to protect vulnerable ecosystems. A levy on economic uses of invasive species to offset costs of managing invasions alongside stricter regulations to protect vulnerable ecosystems could be a widely adopted measure to avert future negative impacts.
Study area map indicating landscape vulnerability to tree invasion from roadsides under the three most conservative dispersal estimates. Buffer units are in meters (m). The 1000 m buffer is not shown due to it covering virtually the entire study area and largely obscuring the underlying land cover classes
Percentage of rangeland (solid line) and forest (dotted line) within the 6278-hectare (ha) study area vulnerable to tree invasion, based on four dispersal distance scenarios. Numbered points indicate the hectares of each land cover type impacted by each dispersal scenario
Tree species counts across transects (n = 10)
Roadsides can be vectors for tree invasion within rangelands by bisecting landscapes and facilitating propagule spread to interior habitat. Current invasive tree management in North America’s Great Plains focuses on reducing on-site (i.e., interior habitat) vulnerability through on-site prevention and eradication, but invasive tree management of surrounding areas known to serve as invasion vectors, such as roadsides and public rights-of-ways, is sporadic. We surveyed roadsides for invasive tree propagule sources in a central Great Plains grassland landscape to determine how much of the surrounding landscape is potentially vulnerable to roadside invasion, and by which species, and thereby provide insights into the locations and forms of future landcover change. Invasive tree species were widespread in roadsides. Given modest seed dispersal distances of 100–200 m, our results show that roadsides have potential to serve as major sources of rangeland exposure to tree invasion, compromising up to 44% of rangelands in the study area. Under these dispersal distances, funds spent removing trees on rangeland properties may have little impact on the landscape’s overall vulnerability, due to exposure driven by roadside propagule sources. A key implication from this study is that roadsides, while often neglected from management, represent an important component of integrated management strategies for reducing rangeland vulnerability to tree invasion.
Location of the Pandeiros River basin and the sampled sites. Sites with occurrence of Corbicula fluminea are marked in red
Values of the metrics used to determine which physical habitat variables are most important for the distribution of Corbicula fluminea in streams of the Pandeiros River basin
Corbicula fluminea is one of the most successful invasive species in neotropical freshwater ecosystems. As alien species’ distribution in invaded regions is often facilitated by the presence of anthropogenic altered ecosystems, such as artificial channels and reservoirs. The present study is part of a larger joint scientific assessment of the ecological effects of a run-of-river dam in the Pandeiros River Basin, Brazil, aiming at supporting decision making regarding its possible decommissioning. Our focus was to determine which in-stream physical habitat metrics are most important for the distribution of C. fluminea in Pandeiros river basin, a Neotropical dammed Savanna-river basin. We found that its occurrence was linked positively with sheltered margins and pipes in the riparian zone, and negatively with the distance from the Pandeiros River dam. These results show that C. fluminea distribution is closely linked to anthropogenic alterations in the physical habitat and, due to the dam influence in enhancing this invasive species distribution, we could recommend the decommissioning of the Pandeiros River dam, built in 1957, but whose economic activities, including electrical power generation, have been totally deactivated since 2007.
Kruger National Park is situated in the north-eastern corner of South Africa and borders Mozambique in the east and Zimbabwe in the north. Camps that were surveyed for alien ornamental plants during this study and/or that of Foxcroft et al. (2008) are shown
A selection of alien plants recorded in 35 camps in the Kruger National Park during 2020. Food plants: A a patch of Cucurbita moschata (butternut squash) cultivated between solar panels; B a stand of Abelmoschus esculentus (okra); and C seedlings of Mangifera indica (mango). Populations starting to spread: D seedlings (marked by white circles) of Kalanchoe beharensis spreading outside a camp fence; EAgave angustifolia 'variegata' plantlets growing outside a garden fence; and FTradescantia pallida spreading beyond a garden fence into natural vegetation. Extralimital species: GChlorophytum comosum is one of the most widely cultivated garden species, HAloidendron ramosissimum cultivated in a pot (potted plant in the centre), and I one of South Africa’s flagship plant species, Strelitzia reginae, is considered native by many people irrespective of where in South Africa it is cultivated, despite being native only to the Eastern Cape.
Numbers of ornamental alien plant species recorded in 35 camps in the Kruger National Park in two separate surveys, in 1999–2003 and 2020. Arrows in the middle show changes in species richness, in terms of the total number, nationally regulated, locally regulated, and unregulated species. Change in alien species richness between 2003 and 2020 is indicated as either increase (red), decrease (light green), or no change (=); categories absent in both surveys are indicated with “−”. Camps are arranged in terms of overall change (largest absolute decrease: top; largest absolute increase: bottom). Note: three camps (Boulders, Roodewal, Tamboti) did not have any alien plants in the surveys and are not shown on this figure; Shangoni is not shown as it was not resurveyed in 2020.
Number of camps in which each ornamental alien species was found in the Kruger National Park in surveys conducted in 1999–2003 and 2020. Scatterplot top panels A, B show regulated versus unregulated alien species; the bottom panels C, D show unregulated alien species as separated into alien and extralimital categories. Species that occur on the “zero-difference” lines (slope = 1) were found in the same number of camps in both surveys; species below the line showed reduced distribution, while those above showed increased distribution. E Turnover between surveys (shared and unique species). Jitter was added to reduce overplotting.
Regulations provide the legal basis for managing biological invasions, but assessments of their effectiveness are rare. To assess the influence of national and local regulations on alien plant species richness and composition in a large protected area (Kruger National Park [KNP], South Africa) we surveyed tourist camps and staff villages for alien ornamental plants. We compared our survey results in 2020 with a previous survey carried out between 1999 and 2003, in the context of national regulations on alien plants promulgated in 2001 and 2014. The number of alien plant species recorded in KNP has almost doubled since the first survey (from 231 to 438), although there has been significant species turnover (93% average replacement across all camps). Importantly, however, both the number of listed and regulated alien plant species found in KNP, and their species richness per camp, have declined (by 38% overall and by 56% per camp). This suggests that regulations are effective. In contrast, the number of unregulated ornamental alien species recorded has increased (by 157% overall). This is likely partly due to an increase in survey effort. Alien species regulations provide clear guidance for conservation managers, and there are promising signs of their effectiveness in directing management in KNP. However, converting alien species lists into priorities for control or regulation will continue to require risk analyses sensitive to park user needs. We advocate for better monitoring of the effectiveness of the regulations, and for the results of such monitoring to be interpreted based on local management needs and concerns.
The content of sodium, potassium, water and the Na/K ratio in the body of Elodea canadensis depending on the salinity of the environment. The horizontal lines relative to the abscissa axis reflect the boundaries of the ranges of regulation of the content of sodium, potassium, water and the Na/K ratio in the body in the tolerant salinity range. The inclined line reflects the isonatremia. The blue line parallel to the ordinate axis reflects the salinity at which the sodium concentration in the body and the environment are equal to each other (the state of isonatremia). The red dotted line parallel to the ordinate axis reflects the upper limit of the tolerant salinity range
A submerged aquatic plant Elodea canadensis is highly invasive in Eurasia and has a very high ability to spread within the water ecosystems. There is currently no data on the tolerance range of salinity in which E. canadensis can survive. This makes it difficult to assess the possible distribution range of this important invasive species under natural conditions and to predict the possibility of its introduction into new water bodies. The aim of the study is to evaluate the tolerance salinity range for E. canadensis by the parameters of water-salt homeostasis. Here we show that the tolerance range of salinity for E. canadensis is 0.0001–6 g/L NaCl. Within the tolerance salinity range E. canadensis maintains the parameters of water-salt homeostasis within physiological limits, as well as carries out photosynthesis and growth. The upper limit of the salinity tolerance range is determined by the pattern of regulation of the potassium concentration in the body. At salinities above 6 g/L NaCl, a decrease in the concentration of potassium in the body below physiological values is observed, along with a sharp violation of the ratio of Na/K concentration, lack of growth and photosynthesis, and loss of green color of leaves. The optimal salinity range for E. canadensis is 0.009 (fresh water)—1.2 g/L NaCl, at which an increase in dry mass and the largest growth were observed. The critical salinity zone for elodea is 2.4–6 g/L NaCl, at which a decrease in the growth rate of the main and lateral shoots is observed. E. canadensis can inhabit and develop only in those water bodies where the salinity of the water is within the tolerance range. Based on the obtained results and the availability of data on salinity in various water bodies, it is possible to estimate the boundaries of areal of E. canadensis in natural conditions, and to make a prediction about the possibilities of its introduction into brackish lakes, river estuaries, coastal brackish waters of the seas, which is especially important in the current conditions of the ongoing salinization of water bodies due to various factors.
Many important wetland functions are tied to sediment dynamics, which are influenced by infaunal invertebrate communities. These communities are sensitive to changes in sediment structure and to colonization by non-native species. In a southern California salt marsh, the non-native isopod Sphaeroma quoianum has created dense networks of burrows within the marsh banks. Since this isopod increases erosion in many areas and can change local invertebrate communities, its possible contribution to habitat loss in this already-scarce southern California ecosystem is an important issue. To determine the relationship of S. quoianum to invertebrate community and sediment characteristics, three burrowed transects and one unburrowed transect were surveyed and sampled for invertebrate and sediment cores. This study tested the association between burrows and grain size distribution, sediment carbon content, respiration rates, and invertebrate community composition. Sphaeroma quoianum burrows were correlated with altered invertebrate community composition, decreased carbon content, and steep marsh bluffs. These results highlight the potential susceptibility of salt marsh habitat with steep edges to invasion by non-native species. These results also suggest that S. quoianum invasion of salt marsh habitats can alter native communities and ecosystem functions; thus, incipient invasions should be of concern to managers and ecologists alike.
Sampling map of Trachycarpus fortunei in Canton Ticino (southern Switzerland), Lombardy and Piedmont provinces (northern Italy) for both types of markers (microsatellites and SNPs). Historical naturalised populations were defined based on literature and are indicated with an asterisk
Synthesis and comparison of the two types of markers (microsatellites and SNPs) in Trachycarpus fortunei. White circles: Hardy–Weinberg equilibrium (both markers); Blue circles: Significant excess of heterozygotes: Manno (both markers), Intragna and Pianezzo (SNPs); Red circles: Significant excess of homozygotes: Isole di Brissago and Verscio (microsatellites); Red squares: Highest mean pairwise Fst indices: Cannobio, Intragna, Isola Madre and Manno (both markers), Tegna (microsatellites) and Gandria (SNPs); LD: More than one pair of loci in significant in linkage disequilibrium (microsatellites): Cannobio, Caslano, Gandria, Ghiffa and Manno; *: Significant signs of bottlenecks (microsatellites): Gandria, Intragna, Maccagno, Melano and Ronco s. Ascona. Historical naturalised populations were defined based on literature and are indicated with an asterisk
Genetic analyses in Trachycarpus fortunei: PCA Plots on microsatellites (A) and SNP markers (B) on 200 and 199 individuals, respectively. The individuals are named according to their population (abbreviations) and coloured according to the two regions (Lake Maggiore in blue and Lake Lugano in purple). The ellipsoids represent the 95% confidence intervals of each region centroid
Genetic analyses in Trachycarpus fortunei: structure Plots mapped on geography with microsatellites (A) and SNP markers (B) on the 21 analysed populations with individuals coloured according to Structure and FastStructure results into two or seven panmictic populations, respectively. Historical naturalised populations were defined based on literature and are indicated with an asterisk
Trachycarpus fortunei (Arecaceae: Coryphoideae) is an Asian palm that was introduced during the nineteenth century in southern Switzerland and northern Italy as an ornamental plant. In the recent decades, the palm has become an aggressive invasive species in the region. Before this study, the genetic structure and diversity of the naturalised populations were unknown. We aimed at understanding the dynamics of invasion and at comparing the results obtained with two types of markers. This genetic approach aimed at tracing back as far as possible the source of invasive populations comparing historical information found in literature and invasive genetic patterns. The genetic diversity was analysed using eight microsatellites (five were developed for that purpose) and 31′000 SNPs identified through GBS analyses. Genetic analyses were carried out for 200 naturalised individuals sampled from 21 populations in the Canton Ticino (Switzerland) and the provinces of Lombardy and Piedmont (Italy). The observed general panmixia indicates that the expansion of T. fortunei is active in its naturalised areas. The genetic pattern found for both SNPs and microsatellites appears to be related to the colonisation process, with a lack of geographic structure and bottleneck signatures occurring at the colonisation front, distantly from historical sites. This study gives a better understanding of the expansion of T. fortunei and adds new insights to its ecology.
Sample completeness curve depicting sample coverage per interpolated and extrapolated number of sampled individuals from native and invasive ranges
Neighbor Joining, unrooted phylogenetic tree based on Maximum Likelihood analysis under the GTR + G + I substitution model. Nodes are named by Haplotype number (H); GenBank accession number; Country of origin for accession (abbreviations as follows: Vi: Vietnam; Ch: China; Ha: Hawaii; Th: Thailand; Ta: Taiwan; Ja: Japan; So: South Africa; US: California; Is: Israel)
The ambrosia beetle Euwallacea fornicatus (Polyphagous Shot Hole Borer; PSHB), native to Asia, was documented in South Africa for the first time in 2012. Death of susceptible host trees is caused by blocking of xylem tissues by the mutualistic plant-pathogenic fungus, Fusarium euwallaceae and extensive tunnelling by the beetles into the sapwood. Within a few years, PSHB has spread from its putative entrance point in the coastal province of KwaZulu-Natal to nearly every other province in South Africa. This study serves as a preliminary assessment of dispersal pathways and population genetic relationships of PSHB in South Africa. PSHB individuals were collected from five provinces across South Africa. In addition, data on PSHB from three provinces in its native range in China and invasive PSHB from California were also generated here and supplemented by sequence data of PSHB available from GenBank. Comparisons of Cytochrome Oxidase Subunit I (COI) sequences of PSHB in South Africa revealed a nearly homogenous population. The majority of individuals have the same haplotype as is present in California, Israel and Vietnam (H33). A second haplotype was present in only two localities in KwaZulu-Natal and the Western Cape. This haplotype is also present in Vietnam and China (H38). The placement of the two haplotypes identified within South Africa, into different haplogroups suggests more than one invasion event. This pilot project justifies the use of more comprehensive genomic tools to finely map the relationships, global invasion pathways and within-country dispersal patterns of PSHB to better inform management of this invasive species.
Invasion curves for common myna (Acridotheres tristis) invasion in the Kruger National Park, South Africa. First records stand for observations that were made in a given location within KNP for the first time, i.e., repeated observations from the same locations were excluded–these are considered in the cumulative number of all records. The cumulative number of birds refers to all birds recorded in KNP during observations that are displayed as all records
Frequency distribution of the number of common myna birds recorded during individual observations
Current distribution map with years of first sightings. Only first records for a given location are shown. Most of the earliest records (before 2001) come from urban areas outside the park, except for the very first record at Talamati and Lower Sabie camps (white dots). The majority of the records come from the most recent time interval (2016–2020), with mynas appearing to establish more frequently in the northern part of KNP
Common myna (Acridotheres tristis) is a passerine bird native to south-east Asia, established as an alien in many parts of the world including South Africa, where it is invasive. Common mynas are synanthropic birds with a strong preference for urban areas that usually do not expand into natural areas. However, as we document here, since the first records in Kruger National Park in 2000 when the birds started to spread from outside the park, the rate of spread has recently dramatically increased, with last three years accounting for 66% of the total number of 128 sightings. Thirty-two birds were observed to be nesting or breeding. This data suggests that the common myna in Kruger National Park is in the initial phase of establishment. Although the impacts on native birds at a population level are unlikely to be severe in a large natural savanna area with little human influence, the species is scored as having moderate impact in the EICAT IUCN scheme. Thus, we suggest that the population of common myna needs to be monitored and controlled to prevent it from further increase and spread.
Understanding the origins and genetic relationships of invasive, non-native species is critical to informing conservation and management practices. Pistia stratiotes is one such species—a pantropical floating plant that is problematic in many regions of the world, including Florida, USA. Questions surrounding the origins of P. stratiotes populations in Florida and elsewhere prompted a molecular investigation using five chloroplast and one mitochondrial DNA sequences. A total of 154 samples were collected from 14 countries. The sequence data was analyzed using haplotype network analysis, maximum likelihood phylogenetics and species delimitation tools. These data show that P. stratiotes comprises a minimum of seven distinct haplotypic clades worldwide, three of which differ enough to likely represent different species. Florida, which was more heavily sampled than other regions of the world, contains four of the clades—one of which shows evidence of being pan-Caribbean with sufficient variation to suggest regional (including Florida) nativity. A second clade, present in the U.S. Gulf States and California, may be native within this range, however more sampling is needed to fully describe its distribution and nativity. Another clade, predominant in southern Florida and the St. Johns River, likely originated in South America. Results are discussed in the broader context of the effects of cryptic species on weed management, including biological control efforts.
An updated checklist of the Calabrian alien vascular flora is presented. By way of field, bibliographic, and herbarium research, we recorded 382 alien taxa (representing almost 14% of all regional flora), of which 371 are angiosperms, nine gymnosperms, and two ferns. In relation to the state of spread, the majority of alien species are casual (207 taxa; 54%), followed by naturalized (127; 33%) and invasive (48; 13%), these last include four on the list of Union Concern, sensu Regulation (EU) no. 1143/2014. The most represented families are Asteraceae (39 taxa) and Poaceae (39). Among genera, Amaranthus (nine taxa), Prunus , Euphorbia , and Oxalis (seven taxa) make up those with the greatest number of taxa. A total of 21 taxa were reported for the first time, three of them are new to the European flora ( Camptosema rubicundum, Musa ×paradisiaca and, only for continental Europe, Ipomoea hederacea ), two to the Italian peninsula ( Pelargonium graveolens, Schinus terebinthifolia ) and 16 to the Calabrian flora ( Aeonium arboreum, Asparagus asparagoides, Aspidistra elatior, Bidens sulphurea, Catalpa bignonioides, Citrus ×aurantium, Crassula ovata, Cucurbita ficifolia, Dimorphotheca ecklonis, Graptopetalum paraguayense subsp. paraguayense, Kalanchoë laxiflora, Nicotiana tabacum, Phytolacca dioica , Portulaca umbraticola, Talinum paniculatum, Tecomaria capensis ). In terms of residence status, there are 291 neophytes (76%), 73 archaeophytes (19%), and 18 regional aliens (5%); neophytes are the most represented group (45 out of 48) among invasive taxa. Concerning life forms, the two most abundant groups are therophytes (30.1%, 115 taxa) and phanerophytes (29.6%, 113 taxa). Regarding habitats, 72% of alien taxa occur in artificial (199 taxa, 52%) and agricultural habitats (75 taxa, 20%). The majority of alien taxa are native to the Americas (159; 41.6%), numerous aliens also originated in Asia (76; 19.9%) and Africa (56; 14.7%). The majority of taxa were introduced for ornamental purposes (55%). Over the past decade, alien taxa in the flora in Calabria have increased from 190 to the current 382 taxa. While this trend could be linked to some extent to increasing awareness of the problem of alien species and the increasing intensity of research over recent decades, it is also most probably due to new introductions resulting from the globalization that relentlessly affects the whole planet.
Global climate change could alter the range, abundance, and interactions of species, potentially favouring invasive species and harming endemics. Ship rats ( Rattus rattus ) are one of the world's worst invasive predators but are typically absent from Aotearoa New Zealand's native Fuscospora cliffortioides (mountain beech) forest above 1000 m. Stoats ( Mustela erminea ) are another damaging invasive predator in Aotearoa New Zealand and prey on ship rats. We analyse community trapping records 2007–2020 to investigate the spatial and temporal distribution of ship rats and their key predator stoats at Craigieburn Forest Park. We document an invasion of ship rats after 2010 at Craigieburn and hypothesised two drivers of the increase in rat abundance: (1) more frequent mountain beech high-seed years providing more food for rats; and (2) warming winter temperatures allowing rats to invade areas that were previously too cold. We were unable to test a third possible driver (stoat trapping resulting in top-down meso-predator release) due to the nature of the data available. Rats were more common at low altitudes near streams, and stoats were more common at higher-altitudes on forest edges. Average winter temperature, but not seedfall, increased significantly at Craigieburn mid-elevations since 1972. The best predictor of annual rat catch was higher average winter temperatures interacting with high seedfall. This shows a key interaction between two global change drivers: warming temperatures have allowed exotic ship rats to expand into areas where they were previously absent, increasing the resultant "thermal squeeze" of predation on sensitive endemic birds at higher-altitude sites.
Map of the study area with focal watersheds highlighted in grey. White points indicate locations of quantitative surveys and excretion measurements. Black triangles indicate USGS gages used to estimate volumetric excretion rates. Pies represent the proportional biomass or density of mussels grouped into phylogenetic tribes and Corbicula fluminea. Numbers correspond to site identifiers used in the text
Length frequency distributions (5 mm bins) for Corbicula and five phylogenetic tribes for mussels. Sites are numbered consecutively from upstream to downstream for each river. Note this analysis is exploratory and mean to illustrate body size differences between broadly classified mussels and Corbicula
Effect size of biomass, density, aggregate areal N excretionrates, aggregate areal P excretion rates, and aggregate areal excretion N:P from four mussel bed reaches in the Cahaba and Duck Rivers, USA. Dotted lines in each panel indicate net zero of each taxonomic group’s effect such that positive values indicate greater mussel biomass, density, excretion rate, and N:P and negative values indicate greater Corbicula biomass, density, excretion, and N:P at a reach. Separate boxplots of each response variable are available as Online Resources 8–1
Volumetric excretion (EV) of nitrogen (N) during 01 May 2020 to 31 August 2020 in relation to discharge (shown on second y‐axis, with blue dashed line) at two Cahaba River reaches and two Duck River reaches. Percentage of each group’s contribution to aggregate volumetric N excretion is presented as text on each panel
Animal-mediated nutrient cycling research tends to emphasize either native or invasive fauna, yet communities comprising both groups are common, and biogeochemical control may shift from native to invasive species, altering local nutrient regimes. In North American rivers, co-occurring native mussels (Unionidae) and the invasive clam, Corbicula fluminea, have strong nutrient cycling effects through filter-feeding and bioturbation. When these two groups co-occur, the degree to which their nutrient cycling effects differ remains unclear. We quantified bivalve density, biomass, and nutrient excretion rates at four reaches in each of two rivers once during the same year to test whether differences in density and biomass led to different spatial and temporal nutrient cycling and stoichiometry patterns for co-occurring mussels and Corbicula. We hypothesized high densities, coupled with small body size would elevate Corbicula population-level nutrient cycling rates above those of less dense assemblages of larger-bodied mussels. Corbicula occurred at all mussel beds and their densities generally exceeded mussel densities, but Corbicula biomass was consistently lower. High densities and greater mass-specific excretion rates led to Corbicula population-level excretion rates that were greater than or equal to mussel aggregate rates at half the reaches. Abiotic conditions limited bivalve nutrient supply relative to ambient concentrations, but their contributions increased during low flows and are likely concentrated at finer spatial scales. Our results suggest spatial variation in invasive and native trait distribution associated with phylogenetic tribes influences the potential for animal-mediated nutrient cycling to shift from native to invasive species control. Overall, our study highlights the need for new management paradigms that account for nutrient cycling by invasive species.
Overview of the experimental designs of the leaching experiment (top), and the seed germination and seedling growth experiments (bottom)
Total glyphosate and aminomethylphosphonic acid (AMPA) leached out of Phragmites australis and Typha × glauca plant material treated with either 5 or 8% glyphosate over the course of 21 days (sampling times: 1 h, 1 day, 3 days, 7 days, and 21 days post-introduction of plant material in water). Each treatment was replicated three times per plant. Grey shading illustrates the 95% confidence bounds of the linear mixed-effects models. Dashed horizontal lines indicate average measured glyphosate or AMPA residues in plant material pre-introduction (n = 1 for 5% treatment for each plant, n = 2 for 8% treatment for each plant)
The proportion of Ammannia robusta seeds that germinated (left panels) and sprouted (right panels) over the course of ten days (assessments on days 2, 3, 4, 5, 7, and 10) in the field leachate and garden leachate experiments. Field leachate treatments included a control treatment (leachate = none; tap water), and leachate treatments from either Phragmites australis or Typha spp. material treated with either tap water (0% glyphosate) or 5% glyphosate. Garden leachate treatments included a control treatment (leachate = none; tap water), and leachate treatments from Typha × glauca material treated with either tap water (0% glyphosate), 5% glyphosate, or 8% glyphosate. The experiments included five independent replicates per treatment and assessment day
The proportion of Typha latifolia seeds that germinated (left panels) and seedling length (right panels) over the course of ten days for the field leachate experiment (assessments on days 2, 3, 4, 5, 7, and 10) and 12 days for the garden leachate experiment (assessments on days 2, 3, 5, 7, 10, and 12). Field leachate treatments included a control treatment (leachate = none; tap water), and leachate treatments from either Phragmites australis or Typha spp. material treated with either tap water (0% glyphosate) or 5% glyphosate. Garden leachate treatments included a control treatment (leachate = none; tap water), and leachate treatments from Typha × glauca material treated with either tap water (0% glyphosate), 5% glyphosate, or 8% glyphosate. The experiments included five independent replicates per treatment and assessment day
Invasive plant management can support the restoration of native plant communities. Glyphosate-based herbicides are commonly used for management because glyphosate does not persist at toxic concentrations in water and soil; however, glyphosate can accumulate in the tissues of treated plants. This study investigated whether glyphosate-treated plants can release glyphosate in their leachate, and if so, whether leachate from glyphosate-treated versus untreated plants affects the germination and seedling growth of native plants. We sprayed industry-standard concentrations of glyphosate (Roundup WeatherMAX®) on two macrophyte taxa that are invasive in North America: Phragmites australis and Typha × glauca. Nine weeks after spraying, we submerged sprayed and unsprayed plant tissues in water to create leachate. We quantified glyphosate and the degradation product aminomethylphosphonic acid (AMPA) in leachate over 21 days, and assessed the effects of leachate from sprayed and unsprayed plants on the germination and growth of two co-occurring native macrophytes, Typha latifolia and Ammannia robusta. Leachate from both treated invasive plant taxa contained glyphosate and AMPA, with P. australis leaching more glyphosate on average than T. × glauca. Typha latifolia germination and growth was stimulated by leachate with and without glyphosate. Ammannia robusta exhibited mixed responses, with some indication that leachate and glyphosate residues exert temporary inhibitory effects. Our study demonstrated that glyphosate-sprayed plants can release glyphosate into the environment, but negative impacts from this leachate on the germination and growth of at least some native macrophytes are short-term (< 10 days). Nevertheless, early-stage growth can be important to successful establishment, and we therefore recommend that invasive plant managers consider species-specific effects of both glyphosate and leachate when planning restoration activities.
Within many populations, some individuals may be more apt to move, and these individuals can substantially impact population dynamics. Invasive Silver Carp (Hypophthalmichthys molitrix) have spread throughout much of the Mississippi River Basin, and their presence has resulted in multiple negative ecosystem effects. Silver Carp are known to move hundreds of km, which has likely contributed to their rapid spread. Our study examined movement patterns and environmental cues for movement in Silver Carp based on acoustic telemetry of tagged fish that ranged widely (i.e., mobile) and those that did not range far from the site of their original capture and tagging (i.e., sedentary) in the Wabash River, USA. Sedentary and mobile designations were made based on observed extremes of mean annual ranges, and these designations were consistent within seasons and among years. Both movement groups displayed seasonal variation in movements, with mobile Silver Carp consistently moving greater distances within each season and sedentary Silver Carp exhibiting lower variability in distances moved than mobile individuals. Discharge (change in discharge) and temperature were significant predictors of mobile and sedentary individuals’ movements. Additional environmental variables (i.e., cumulative growing degree day, day of year, and change in temperature) also related to movement likelihood of sedentary individuals, whereas total length was the only additional variable that influenced movement likelihood of mobile individuals. Total length was significantly related to movement distance for both groups of Silver Carp, but the relationship was negative for sedentary fish and positive for mobile fish. Results point to differences in behavior that may require targeted management strategies to achieve agency goals to interrupt mobile individual movements that can result in range expansion. Such strategies may also limit introductions and invasions by other aquatic invasive species that exhibit similar behaviors.
Box plots of the leaf morphological traits and Carbon/Nitrogen contents and stable isotopes. A Leaf area (LA), B leaf thickness (LT), C leaf mass per area (LMA), D mass-based carbon content (Cmass), E mass-based nitrogen content (Nmass), F carbon:nitrogen ratio (C:N), G carbon isotope ratios (δ¹³C), and H nitrogen isotope ratios (δ¹⁵N) for native (in yellow) and non-native (in green) plant species studied. *Denotes statistically significant difference at p < 0.05 and *** p < 0.001
Box plots of the leaf physiological traits. A net CO2 assimilation (A), B maximum net assimilation rate per unit dry mass (Amass), C electron transport rate (ETR), D stomatal conductance (gs), E mesophyll conductance (gm), F intrinsic water-use efficiency (WUE), G photosynthetic nitrogen-use efficiency (PNUE), H respiration (Rd), and I photosynthetic CO2 assimilation over respiration (A/Rd), J stomatal limitation (ls), K mesophyll conductance limitation (lm) and L biochemical limitation (lb) for native (in yellow) and non-native (in green) plant species studied. *Denotes statistically significant difference at p < 0.05 and *** p < 0.001
Principal Component Analysis (PCA) of the significant variables for the leaf morphological traits, Carbon/Nitrogen contents and stable isotopes, and leaf physiological traits between for native (in yellow) and non-native (in green) plant species studied. The 2 big points represent the centroids of both native and non-native plant species
Relationship between the maximum net assimilation rate per unit dry mass (Amass) versus leaf mass per area (LMA) (A), mass-based nitrogen content (Nmass) (B), and net CO2 assimilation (A) versus respiration (Rd) (C) for native (in yellow) and non-native (in green) plant species studied
Islands tend to be more prone to plant invasions than mainland regions, with the Mediterranean ones not being an exception. So far, a large number of studies on comparing leaf morphological and physiological traits between native and non-native plants in Mediterranean environments have been performed, although none of them on Mediterranean islands. To fill this gap, this study focuses on 14 plant species grown in a controlled growth chamber in the absence of stress. The goal was (1) to differentiate leaf morpho-physiological traits between native and non-native plants on a Mediterranean island and (2) to deepen in the underlying causes of the differential photosynthetic traits displayed by non-native species. Results showed that in Mediterranean islands, non-native plant species show on average larger values of net CO2 assimilation, stomatal conductance (gm), photosynthetic nitrogen-use efficiency, among others, and lower leaf mass per area (LMA) and leaf thickness, compared to the native species. Among the assessed traits, this study reports for the first time larger gm, and lower mesophyll conductance limitation in non-native species, which seems to be linked to their lower LMA. These novel traits need to be added to the ‘leaf physiological trait invasive syndrome’. It was also found that on a Mediterranean island, native and non-native species are placed on opposite sides of the leaf economics spectrum, with non-native species being placed on the ‘‘fast-return’’ end. In conclusion, this study demonstrates that non-native species inhabiting a Mediterranean island possess distinct leaf morphological and physiological traits compared to co-occurring native species, at least during the favorable growth season, which increases the chances of a successful invasion.
Invasions of alien plants pose a serious threat to native biodiversity and ecosystem processes. Forests are considered more resistant to invasion due to limited light availability in understories. However, disturbance and abiotic stress may open tree canopies and promote invasion. Their combined effects together with the resistance of resident species may determine the numbers and abundances of invasive species. Here we explore how canopy openness, water stress, and taxonomic and functional properties of resident communities affect the invasion by a frequent single invasive species (Aster lanceolatus and Impatiens parviflora) compared to that by multiple invaders in Central European lowland forests. Different abiotic factors and species-specific mechanisms of invasiveness determined the success of single versus multiple invaders. The massive spread of A. lanceolatus was associated with the long-distance seed dispersal and exploitation of available resources by fast growth resulting in formations of compact clonal patches in disturbed, open-canopy floodplain forests. The success of I. parviflora was caused by avoiding competition via tolerating less favorable conditions under the dense tree canopy on drier sandy soils. A. lanceolatus thus suppressed resident species richness, while I. parviflora spread in communities of higher functional and phylogenetic diversity. Multiple invasive species, mostly represented by subordinate species with low cover, colonized forests that were rich in resident species. We conclude that a combination of intense disturbance and stress favor the invasion of single dominant species that act as drivers of changes in native communities. Multiple invasive species colonize forests with less extreme conditions acting more as passengers who increase rather than decrease forest diversity.
Mean dry mass of leaf litter in the mesocosm experiment for each earthworm treatment group (Amynthas presence/absence and Lumbricus presence/absence). 460 g wet mass of leaf litter was originally added to each tank, and the experiment was run from July to September 2019. Error bars represent the standard error of each treatment mean
Mean percentage of American toad metamorphs (Anaxyrus americanus) surviving in the mesocosm experiment at each sample date (Aug 31 and Sep 25, 2019) for each earthworm treatment group. Error bars represent the standard error of each treatment mean
of attack data from feeding trial experiments showing a mean total number of attacks by toads per trial on crickets (Acheta), Amynthas, and Lumbricus in Exp. 1., b mean total number of attacks by toads per trial on Amynthas and Lumbricus in Exp. 2., c mean attack success (number of successful attacks/number of total attacks) by toads per trial for each prey type in Exp. 1, and d mean attack success by toads per trial for each prey type in Exp. 2. Error bars represent the standard error of each treatment mean
a Boxplot showing prey movement time (time moving/total trial time) for Amynthas and Lumbricus prey in Exp. 2. The center lines represent the median percentages. b Linear model of log-transformed prey detection time (time at which toad was observed to first detect prey) predicted by logit-transformed prey movement time in Exp. 2. The grey area represents a 95% confidence interval
Invasive species can affect native communities through multiple mechanisms, including habitat modification and trophic interactions. In North America, invasive jumping worms (Amynthas spp.) may alter microhabitats used by native herpetofauna or serve as a novel prey resource for herpetofauna predators. We investigated effects of recently introduced Amynthas and previously established Lumbricus spp. earthworms on leaf litter microhabitat and trophic interactions of native herpetofauna using an outdoor mesocosm experiment, laboratory feeding trials, and field surveys of predator stomach contents in southern Wisconsin, USA. In mesocosms, Amynthas and Lumbricus reduced leaf litter biomass but did not have strong effects on soil conditions (pH, moisture, and temperature) or survival of American toad metamorphs (Anaxyrus americanus). In laboratory trials, American toads preyed on Amynthas but were less successful at capturing Amynthas than Lumbricus or crickets (Acheta domesticus). Attack success differences were likely due to unique defensive behaviors of Amynthas. Amynthas spent less time moving than Lumbricus, which was a behavior associated with delayed prey detection times by toads. In our diet surveys, we found novel evidence of Amynthas consumption by common garter snakes (Thamnophis sirtalis). We did not find Amynthas in stomach contents of American toads or red-bellied snakes (Storeria occipitomaculata), though additional surveys would help definitively determine whether these taxa are consuming Amynthas. Our findings highlight the importance of studying multiple mechanisms by which invasive species affect native communities and suggest that unique anti-predator behaviors may influence how Amynthas are incorporated into food webs as a novel prey resource.
Top-cited authors
James Byers
  • University of Georgia
Ingrid M Parker
  • University of California, Santa Cruz
Daniel Simberloff
  • University of Tennessee
Peter B Moyle
  • University of California, Davis
Karen Goodell
  • The Ohio State University