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 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.

As humans accelerate global environmental change, extreme climatic events are increasing in frequency, duration, and intensity. In marine environments, extreme events of particular concern are marine heatwaves (MHWs). Previous reviews synthesising subsets of field-based research examining the ecological effects of these short-term warming events have found they could drive important changes to ecosystems. Here, we reviewed the traits of published literature that has used field, laboratory, and modelling approaches to examine the biotic effects of MHWs, and highlight some of the key findings. Since its first use in this context in 2013, the term “marine heatwave” has generally been used in field-based literature primarily documenting changes in abundance, biodiversity, species distributions, and mortality, primarily in fish and molluscs. Research is increasingly also conducted in laboratory settings, with these investigations focussing on changes in mechanistic processes such as growth and biochemical responses, often in smaller or less motile organisms including seagrasses, algae, molluscs, and crustaceans. Given their different applications, these complementary approaches will provide a more complete understanding when used to consider the same taxonomic groups. Moreover, those manipulating MHWs in laboratory experiments could benefit from the consideration of a range of MHW traits (intensity, duration, and their combination), for species in both isolation and combination, and in the presence of additional abiotic stressors. As such, where future research into MHWs use varied approaches and treatment settings, they will contribute to a more holistic understanding of the biological and ecological effects of future short-term warming events in our ocean.

The ecological impacts of invasive species can be severe, but are generally viewed as highly unpredictable. Recent methods combiningper capitafeeding rates, population abundances and environmental contexts have shown great utility in predicting invader impacts. Here, clearance rates of the invasive Pacific oyster,Crassostreagigas, and native mussel,Mytilusedulis, were investigated in a laboratory experiment where oscillatory water flow and algal food concentrations were manipulated. Invasive oysters had lower clearance rates than native mussels in all experimental groups and did not differ among flow velocities or food concentrations. Native mussel clearance rates were higher at 5 cm s^-1compared to 0 and 15 cm s^-1flow velocities and increased with increasing food concentration. The Relative Impact Potential (RIP) metric was used to assess (i) the influence of flow velocity and food concentration on potential impacts ofC.gigason plankton resources and, (ii) the impacts of coexisting reefs, containing both species, on resources compared to monospecific native mussel beds. Greatest Relative Impact Potential of invasive oysters was seen at the lowest flow velocity, but became reduced with increasing flow velocity and food concentration. Relative Impact Potentials of coexisting reefs were generally greater than monospecific native mussel beds, with greatest impacts predicted at lowest flow velocity. We suggest that the greatest ecological impacts and competition potential ofC.gigaswill occur in areas with low flow velocity, but that increased flow will mediate co-existence between the two species.

Invasive alien species continue to proliferate and cause severe ecological impacts. Functional responses (FRs) have shown excellent utility in predicting invasive predator success, however, their use in predicting invasive prey success is limited. Here, we assessed invader success by quantifying FRs and prey switching patterns of two native predators, the common sea star, Asterias rubens, and the green crab, Carcinus maenas, towards native blue mussels, Mytilus edulis, and invasive Pacific oysters, Crassostrea gigas. Asterias displayed destabilising type II FRs, whereas Carcinus displayed stabilising type III FRs towards both prey species. Both predators exhibited greater search efficiencies and maximum feeding rates towards native compared to invasive prey. Both predators disproportionately consumed native mussels over invasive oysters when presented simultaneously, even when native mussels were rare in the environment, therefore indicating negligible prey switching. We demonstrate that invasion success may be mediated through differential levels of biotic resistance exerted by native predators.