Reconstructing biological invasions using public surveys: a new approach to retrospectively assess spatio-temporal changes in invasive spread

Forecasting potential invaders to prevent future biological invasions worldwide

The ever-increasing and expanding globalisation of trade and transport underpins the escalating global problem of biological invasions. Developing biosecurity infrastructures is crucial to anticipate and prevent the transport and introduction of invasive alien species. Still, robust and defensible forecasts of potential invaders are rare, especially for species without known invasion history. Here, we aim to support decision-making by developing a quantitative invasion risk assessment tool based on invasion syndromes (i.e., generalising typical attributes of invasive alien species). We implemented a workflow based on 'Multiple Imputation with Chain Equation' to estimate invasion syndromes from imputed datasets of species' life-history and ecological traits and macroecological patterns. Importantly, our models disentangle the factors explaining (i) transport and introduction and (ii) establishment. We showcase our tool by modelling the invasion syndromes of 466 amphibians and reptile species with invasion history. Then, we project these models to amphibians and reptiles worldwide (16,236 species [c.76% global coverage]) to identify species with a risk of being unintentionally transported and introduced, and risk of establishing alien populations. Our invasion syndrome models showed high predictive accuracy with a good balance between specificity and generality. Unintentionally transported and introduced species tend to be common and thrive well in human-disturbed habitats. In contrast, those with established alien populations tend to be large-sized, are habitat generalists, thrive well in human-disturbed habitats, and have large native geographic ranges. We forecast that 160 amphibians and reptiles without known invasion history could be unintentionally transported and introduced in the future. Among them, 57 species have a high risk of establishing alien populations. Our reliable, reproducible, transferable, statistically robust and scientifically defensible quantitative invasion risk assessment tool is a significant new addition to the suite of decision-support tools needed for developing a future-proof preventative biosecurity globally.

Biological invasions in France: Alarming costs and even more alarming knowledge gaps

The ever-increasing number of introduced species profoundly threatens global biodiversity. While the ecological and evolutionary consequences of invasive alien species are receiving increasing attention, their economic impacts have largely remained understudied, especially in France. Here, we aimed at providing a general overview of the monetary losses (damages caused by) and expenditures (management of) associated with invasive alien species in France. This country has a long history of alien species presence, partly due to its long-standing global trade activities, highly developed tourism, and presence of overseas territories in different regions of the globe, resulting in a conservative minimum of 2,750 introduced and invasive alien species. By synthesizing for the first time the monetary losses and expenditures incurred by invasive alien species in Metropolitan France and French overseas territories, we obtained 1,583 cost records for 98 invasive alien species. We found that they caused a conservative total amount ranging between US$ 1,280 million and 11,535 million in costs over the period 1993–2018. We extrapolated costs for species invading France, for which costs were reported in other countries but not in France, which yielded an additional cost ranging from US$ 151 to 3,030 millions. Damage costs were nearly eight times higher than management expenditure. Insects, and in particular the Asian tiger mosquito Aedes albopictus and the yellow fever mosquito Ae. aegypti, totalled very high economic costs, followed by non-graminoid terrestrial flowering and aquatic plants (Ambrosia artemisiifolia, Ludwigia sp. and Lagarosiphon major). Over 90% of alien species currently recorded in France had no costs reported in the literature, resulting in high biases in taxonomic, regional and activity sector coverages. To conclude, we report alarming costs and even more alarming knowledge gaps. Our results should raise awareness of the importance of biosecurity and biosurveillance in France, and beyond, as well as the crucial need for better reporting and documentation of cost data.

The cost and complexity of assessing impact

The environmental and socio-economic impacts of invasive species have long been recognised to be unequal, with some species being benign while others are disastrous. Until recently there was no recognised standard impact scoring framework with which to compare impacts of species from very different taxa. The advent of the Environmental Impact Classification for Alien Taxa (EICAT) and Socio‐Economic Impact Classification of Alien Taxa (SEICAT) schemes allows for the possibility of assessing impact through a standard approach. However, both these schemes are still in their infancy and the associated costs of the research that informs them is unknown. We aimed to determine the study costs and complexity associated with assessing invasive species’ socio-economic and environmental impacts. We used amphibians as a model group to investigate papers from which EICAT and SEICAT scores could be drawn up to 2019. Our analysis shows that studies that resulted in higher impact scores were more costly. Furthermore, the costs of studies were best predicted by their complexity and the time taken to complete them. If impact scores from EICAT and SEICAT are allowed to inform policy, then we need to carefully consider whether species with low scores represent true impact, or require more research investment and time. Policy makers needing accurate assessments will need to finance larger, more complex, and rigorous studies. Assessing impacts in low and middle income countries may need investment using international research collaborations and capacity building with scientists from high income areas.

Integrated Methods for Monitoring the Invasive Potential and Management of Heracleum mantegazzianum (giant hogweed) in Switzerland

Biological invasions are a major driver of human-induced global environmental change. This makes monitoring of potential spread, population changes and control measures necessary for guiding management. We illustrate the value of integrated methods (species distribution modelling (SDM), plant population monitoring and questionnaires) for monitoring and assessing invasions of Heracleum mantegazzianum (giant hogweed) over time in Switzerland. SDMs highlighted the potential spread of the species, uncovered ecological mechanisms underlying invasions and guided monitoring at a regional level. We used adaptive and repeat plant sampling to monitor invasive population status and changes, and assess the effectiveness of H. mantegazzianum management over three periods (2005, 2013 and 2018) within the pre-Alps, Vaud. We also conducted questionnaire surveys with managers and the public. Multiscale modelling, and integrating global and regional SDMs, provided the best predictions, showing that H. mantegazzianum can potentially invade large parts of Switzerland, especially below 2 000 m a.s.l. Over time, populations of invasive H. mantegazzianum in the Vaud pre-Alps have declined, which is most likely due to a sharp rise in management uptake post 2007 (7% of municipalities before 2007 to 86% in 2018). The level of known invasive populations has decreased by 54% over time. Some municipalities have even successfully eradicated H. mantegazzianum within their borders. However, a few areas, particularly in the rural, higher-altitude municipalities, where management was not implemented effectively, populations have expanded, which could hamper control efforts at lower altitudes. We provide encouraging evidence that control measures can be effective in reducing plant invasions with long-term commitment, as well as a good template for using integrated methodological approaches to better study and monitor invasive alien species.

Invasion syndromes: a systematic approach for predicting biological invasions and facilitating effective management

Our ability to predict invasions has been hindered by the seemingly idiosyncratic context-dependency of individual invasions. However, we argue that robust and useful generalisations in invasion science can be made by considering “invasion syndromes” which we define as “a combination of pathways, alien species traits, and characteristics of the recipient ecosystem which collectively result in predictable dynamics and impacts, and that can be managed effectively using specific policy and management actions”. We describe this approach and outline examples that highlight its utility, including: cacti with clonal fragmentation in arid ecosystems; small aquatic organisms introduced through ballast water in harbours; large ranid frogs with frequent secondary transfers; piscivorous freshwater fishes in connected aquatic ecosystems; plant invasions in high-elevation areas; tall-statured grasses; and tree-feeding insects in forests with suitable hosts. We propose a systematic method for identifying and delimiting invasion syndromes. We argue that invasion syndromes can account for the context-dependency of biological invasions while incorporating insights from comparative studies. Adopting this approach will help to structure thinking, identify transferrable risk assessment and management lessons, and highlight similarities among events that were previously considered disparate invasion phenomena.

What's for dinner? Diet and potential trophic impact of an invasive anuran Hoplobatrachus tigerinus on the Andaman archipelago

Amphibian invasions have considerable detrimental impacts on recipient ecosystems. However, reliable risk analysis of invasive amphibians still requires research on more non-native amphibian species. An invasive population of the Indian bullfrog, Hoplobatrachus tigerinus, is currently spreading on the Andaman archipelago and may have significant trophic impacts on native anurans through competition and predation. We carried out diet analyses of the invasive H. tigerinus and native anurans, across four habitat types and two seasons; we hypothesized that (i) small vertebrates constitute a majority of the H. tigerinus diet, particularly by volume and (ii) the diet of H. tigerinus significantly overlaps with the diet of native anurans, thereby, leading to potential competition. We assessed the diet of the invasive H. tigerinus (n = 358), and individuals of the genera Limnonectes (n = 375) and Fejervarya (n = 65) and found a significant dietary overlap of H. tigerinus with only Limnonectes. Small vertebrates, including several endemic species, constituted the majority of H. tigerinus, diet by volume, suggesting potential impact by predation. Prey consumption and electivity of the three anurans indicated a positive relationship between predator-prey body sizes. Individuals of H. tigerinus and Fejervarya chose evasive prey, suggesting that these two taxa are mostly ambush predators; individuals of Limnonectes chose a mixture of sedentary and evasive prey indicating that the species employs a combination of ‘active search’ and ‘sit and wait’ foraging strategies. All three species of anurans mostly consumed terrestrial prey. This intensive study on a genus of newly invasive amphibian contributes to knowledge of the impact of amphibian invasions, and elucidates the feeding ecology of H. tigerinus, and species of the genera Limnonectes and Fejervarya. We also stress the necessity to evaluate prey availability and volume in future studies for meaningful insights into diet of amphibians.