The Functional Response (FR) has been identified as a powerful predictive tool to forecast the ecological impacts of existing, emerging and future invasive alien species. In particular, the parameters of attack rate a and handling time h may be predictive of the ecological impacts of invaders when utilised in comparison with trophically analogous natives. However, researchers in many cases face somewhat contradictory impact predictions based on the use of one parameter or the other. Here, we thus propose a new metric, the Functional Response Ratio (FRR), which is simply a divided by h: that is, FRR = a/h. Given that high values of a and low values of h should associate with high impact, and vice versa, the FRR metric balances the information from both parameters. This also resolves contradictions when one parameter gives opposite predictions to the other. Using multiple examples obtained from the literature, we find that the FRR indeed resolves such contradictions and that values of FRR of invaders are consistently higher than those of natives, irrespective of experimental or environmental context. Accordingly, the use of FRR provides a novel and reliable metric for scientists, stakeholders and practitioners to predict the ecological impacts of existing, emerging and future invasive alien species across taxa and trophic groups.

Invasive alien species (IAS) are a significant and growing problem worldwide. In Europe, some aspects of IAS have been\ud addressed through existing legal instruments, but these are far from sufficient to tackle the problem comprehensively. The\ud FINS II Conference considered the relevance of Top 20 IAS issues (Top 10 threats and opportunities) for Europe determined\ud at the 1st Freshwater Invasiveness – Networking for Strategy (FINS I) conference held in Ireland in 2013. Using a similar\ud format of sequential group voting, threats from FINS I (lack of funding, of awareness and education; poor communication)\ud and several new threats (lack of lead agencies, of standardized management and of common approach; insufficient monitoring\ud and management on private property) were identified by 80 academics, applied scientists, policy makers and stakeholders\ud from 14 EU and three non-EU countries (including 10 invited speakers) during four workshop break-out sessions (legislation\ud remit in both EU/non-EU countries; best management and biosecurity practice for control; data management and early warning;\ud pathways of introductions and citizen science). Identified opportunities include improved cooperation and communication,\ud education and leadership to enhance public awareness and stakeholder participation, systems establishment for early detection,\ud rapid response, monitoring and management of IAS using standardised methods of data collection, storage and usage. The\ud sets of threats and opportunities identified underline the importance of international cooperation on IAS issues in\ud communication, education and funding as priorities, as well as in standardization of legislation, control methods and best\ud practise of research

Shorebirds (Charadriiformes) undergo rapid migrations with potential for long‐distance dispersal (LDD) of plants. We studied the frequency of endozoochory by shorebirds in different parts of Europe covering a broad latitudinal range and different seasons. We assessed whether plants dispersed conformed to morphological dispersal syndromes. A total of 409 excreta samples (271 faeces and 138 pellets) were collected from redshank Tringa totanus , black‐winged stilt Himantopus himantopus , pied avocet Recurvirostra avosetta , northern lapwing Vanellus vanellus , Eurasian curlew Numenius arquata and black‐tailed godwit Limosa limosa in south‐west Spain, north‐west England, southern Ireland and Iceland in 2005 and 2016, and intact seeds were extracted and identified. Godwits were sampled just before or after migratory movements between England and Iceland. The germinability of seeds was tested. Intact diaspores were recovered from all bird species and study areas, and were present in 13% of samples overall. Thirteen plant families were represented, including Charophyceae and 26 angiosperm taxa. Only four species had an ‘endozoochory syndrome’. Four alien species were recorded. Ellenberg values classified three species as aquatic and 20 as terrestrial. Overall, 89% of seeds were from terrestrial plants, and 11% from aquatic plants. Average seed length was higher in redshank pellets than in their faeces. Six species were germinated, none of which had an endozoochory syndrome. Seeds were recorded during spring and autumn migration. Plant species recorded have broad latitudinal ranges consistent with LDD via shorebirds. Crucially, morphological syndromes do not adequately predict LDD potential, and more empirical work is required to identify which plants are dispersed by shorebirds. Incorporating endozoochory by shorebirds and other migratory waterbirds into plant distribution models would allow us to better understand the natural processes that facilitated colonization of oceanic islands, or to improve predictions of how plants will respond to climate change, or how alien species spread.

Invasive alien species continue to arrive in new locations with no abatement in rate, and thus greater predictive powers surrounding their ecological impacts are required. In particular, we need improved means of quantifying the ecological impacts of new invasive species under different contexts. Here, we develop a suite of metrics based upon the novel Relative Impact Potential (RIP) metric, combining the functional response (consumer per capita effect), with proxies for the numerical response (consumer population response), providing quantification of invasive species ecological impact. These metrics are comparative in relation to the eco-evolutionary baseline of trophically analogous natives, as well as other invasive species and across multiple populations. Crucially, the metrics also reveal how impacts of invasive species change under abiotic and biotic contexts. While studies focused solely on functional responses have been successful in predictive invasion ecology, RIP retains these advantages while adding vital other predictive elements, principally consumer abundance. RIP can also be combined with propagule pressure to quantify overall invasion risk. By highlighting functional response and numerical response proxies, we outline a user-friendly method for assessing the impacts of invaders of all trophic levels and taxonomic groups. We apply the metric to impact assessment in the face of climate change by taking account of both changing predator consumption rates and prey reproduction rates. We proceed to outline the application of RIP to assess biotic resistance against incoming invasive species, the effect of evolution on invasive species impacts, application to interspecific competition, changing spatio-temporal patterns of invasion, and how RIP can inform biological control. We propose that RIP provides scientists and practitioners with a user-friendly, customisable and, crucially, powerful technique to inform invasive species policy and management.