Summary Ecological theory attempts to predict how impacts for native species arise from biological invasions. A fundamental question centres on the feeding interactions of invasive and native species: whether invasion will result in increased interspecific competition, which would result in negative consequences for the competing species, or trophic niche divergence, which would facilitate the invader's integration into the community and their coexistence with native species.Here, the feeding interactions of a highly invasive fish, topmouth gudgeon Pseudorasbora parva, with three native and functionally similar fishes were studied to determine whether patterns of either niche overlap or divergence detected in mesocosm experiments were apparent between the species at larger spatial scales. Using stable isotope analysis, their feeding relationships were assessed initially in the mesocosms (1000 L) and then in small ponds (<400 m2) and large ponds (>600 m2).In the mesocosms, a consistent pattern of trophic niche divergence was evident between the sympatric fishes, with niches shifting further apart in isotopic space than suggested in allopatry, revealing that sharing of food resources was limited. Sympatric P. parva also had a smaller niche than their allopatric populations.In eight small ponds where P. parva had coexisted for several years with at least one of the fish species used in the mesocosms, strong patterns of niche differentiation were also apparent, with P. parva always at a lower trophic position than the other fishes, as also occurred in the mesocosms. Where these fishes were sympatric within more complex fish communities in the large ponds, similar patterns were also apparent, with strong evidence of trophic niche differentiation.Aspects of the ecological impacts of P. parva invasion for native communities in larger ponds were consistent with those in the mesocosm experiments. Their invasion resulted in divergence in trophic niches, partly due to their reduced niche widths when in sympatry with other species, facilitating their coexistence in invaded ecosystems. Our study highlights the utility of controlled mesocosm studies for predicting the trophic relationships that can develop from introductions of non‐native species into more complex ecosystems and at larger spatial scales.

2. Two fully-factorial mesocosm experiments (one for each crayfish pair) were used to investigate crayfish diet, and their impact on benthic invertebrate community structure, benthic algal standing stock and leaf litter decomposition rates, in allopatric and sympatric populations, compared to a crayfish free control. We used stable isotope analysis to examine crayfish diet in the mesocosms and in allopatric populations of each species in the Thames catchment.3. Isotopic niche width did not vary significantly between allopatric and sympatric populations of crayfish pairs in the mesocosms and isotopic niche partitioning in all the wild populations suggests the invaders can coexist.4. All four species altered benthic invertebrate community structure but with differing functional effects, often mediated via trophic cascades. Red swamp crayfish predation upon snails evidently promoted benthic algal standing stock via reduction in grazing pressure. However, a trophic cascade whereby the crayfish consumed native invertebrate shredders, causing a reduction in net leaf litter decomposition, was decoupled by red swamp and signal crayfish since they consumed leaf litter directly and thus moderated the cascade to a trickle when in sympatry with Turkish or virile crayfish, respectively. 6. Our results suggest that the combined effect of multiple invasions on the ecosystem can reflect either an additive effect of their independent impacts, or an amplified effect, which is greater than the sum of their independent impacts. A lack of general pattern in their effects makes any potential management strategy more complex.

When non-native species are introduced into a new range, their parasites can also be introduced, with these potentially spilling-over into native hosts. However, in general, evidence suggests that a high proportion of their native parasites are lost during introduction and infections by some new parasites from the native range might occur, potentially resulting in parasite spill-back to native species. These processes were investigated here using parasite surveys and literature review on seven non-native freshwater fishes introduced into England and Wales. Comparison of the mean numbers of parasite species and genera per population for each fish species England and Wales with their native ranges revealed\9 % of the native parasite fauna were present in their populations in England and Wales. There was no evidence suggesting these introduced parasites had spilled over into sympatric native fishes. The non-native fishes did acquire parasites following their introduction, providing potential for parasite spill-back to sympatric fishes, and resulted in non-significant differences in overall mean numbers of parasites per populations between the two ranges. Through this acquisition, the non-native fishes also had mean numbers of parasite species and genera per population that were not significantly different to sympatric native fishes. Thus, the non-native fishes in England and Wales showed evidence of enemy release, acquired new parasites following introduction providing potential for spill-back, but showed no evidence of parasite spill-over.

Forced migration is likely to continue to grow in the coming years due to climate change, disease outbreaks, conflict, and other factors. There are a huge number of challenges to maintaining good health, and specifically good mental health, among migrants at all stages of migration. It is vital to fully understand these diverse challenges so that we can work towards overcoming them. In 2017, as a response to the growing health challenges faced by migrants and refugees, the M8 Alliance created an expert group focussing on migrant and refugee health. The group meets annually at the Sapienza University of Rome, Italy, and this article is based on the discussions that took place at the third annual meeting (6–7 June 2019) and a special session on “Protecting the Mental Health of Refugees and Migrants,” which took place on 27 October at the World Health Summit 2019 in Berlin. Our discussions are also supported by supplementary literature to present the diverse and complex challenges to the mental health of migrants and refugees. We conclude with some lessons learned and hope for the future.

Throughout recent years, we have witnessed an increase in human migration as a result of conflict, political instability and changes in the climate. Despite the growing number of migrants and refugees, provisions to address their health needs remain inadequate and often unmet. Whilst a variety of instruments exist to assert and emphasise the importance for migrant and refugee health, the lack of shared priorities between partners and stakeholders results in poor access to healthcare and essential medicines.In response to the growing health challenges faced by migrants and refugees, members of the M8 Alliance launched an annual Expert Meeting on Migrants’ and Refugees’ Health. This report is shaped by discussions from the second M8 Alliance Expert Meeting (Sapienza University of Rome, Italy, 15–16 June 2018) and is supported by supplementing literature to develop a framework addressing critical reflections, challenges and solutions of and for migrant and refugee health. This report aims to inform decision-making fostering a humanitarian, ethics and rights-based approach. Through a series of country-specific case studies and discussions, this report captures the most prominent themes and recommendations such as mental health, tuberculosis (TB) and best practices for increased access.

were that the invaders would have significantly higher consumption rates for 34 chironomids than the native fishes, but not for G. pulex. Mean consumption rates for 35 chironomids were significantly lower for both invaders than B. barbus and S. 36 cephalus, but were similar to T. tinca. Barbus barbus had a significantly lower 37 consumption rate of G. pulex than both invaders, but there were no significant 38 differences between S. cephalus, T. tinca and the invaders. All FRs were type II, with 39 functional response curves for the invaders preying upon chironomids never being 40 significantly higher than the native fishes, contrary to predictions. For G. pulex, some 41 significant differences were apparent between the invaders and native fishes, but 42 again were contrary to predictions. These results indicated that when predation 43 impacts of invasive fishes could also be a function of their population density and 44 body sizes, these parameters should be incorporated into FR models to improve 45 impact predictions. 46

Understanding how ecological communities are structured is a major goal in ecology. Ecological networks representing interaction patterns among species have become a powerful tool to capture the mechanisms underlying plant-animal assemblages. However, these networks largely do not account for inter-individual variability and thus may be limiting our development of a clear mechanistic understanding of community structure. In this study, we develop a new individual-trait based approach to examine the importance of individual plant and pollinator functional size traits (pollinator thorax width and plant nectar holder depth) in mutualistic networks. We performed hierarchical cluster analyses to group interacting individuals into classes, according to their similarity in functional size. We then compared the structure of bee-flower networks where nodes represented either species identity or trait sets. The individual trait-based network was almost twice as nested as its species-based equivalent and it had a more symmetric linkage pattern resulting from of a high degree of size-matching. In conclusion, we show that by constructing individual trait-based networks we can reveal important patterns otherwise difficult to observe in species-based networks and thus improve our understanding of community structure. We therefore recommend using both trait-based and species-based approaches together to develop a clearer understanding of the properties of ecological networks.

Globally, inland waters emit over 2 Pg of carbon per year as carbon dioxide, of which the majority originates from streams and rivers. Despite the global significance of fluvial carbon dioxide emissions, little is known about their diel dynamics. Here we present a large-scale assessment of day- and night-time carbon dioxide fluxes at the water-air interface across 34 European streams. We directly measured fluxes four times between October 2016 and July 2017 using drifting chambers. Median fluxes are 1.4 and 2.1 mmol m−2 h−1 at midday and midnight, respectively, with night fluxes exceeding those during the day by 39%. We attribute diel carbon dioxide flux variability mainly to changes in the water partial pressure of carbon dioxide. However, no consistent drivers could be identified across sites. Our findings highlight widespread day-night changes in fluvial carbon dioxide fluxes and suggest that the time of day greatly influences measured carbon dioxide fluxes across European streams.