Neurotoxic pesticides, such as neonicotinoids, negatively affect the cognitive capacity and fitness of non-target species, and could also modify interspecific interactions. We tested whether sublethal contamination with neonicotinoid could affect foraging, colony fitness and the outcome of behavioural interactions between a native (Monomorium antarcticum) and an invasive ant species (Linepithema humile). The foraging behaviour of both ants was not affected by neonicotinoid exposure. Colonies of the invasive species exposed to the neonicotinoid produced significantly fewer brood. In interspecific confrontations, individuals of the native species exposed to the neonicotinoid lowered their aggression towards the invasive species, although their survival probability was not affected. Exposed individuals of the invasive species interacting with non-exposed native ants displayed increased aggression and had their survival probability reduced. Nonexposed individuals of the invasive species were less aggressive but more likely to survive when interacting with exposed native ants. These results suggest that non-target exposure of invaders to neonicotinoids could either increase or decrease the probability of survival according to the exposure status of the native species. Given that, in any community, different species have different food preferences, and thus different exposure to pesticides, non-target exposure could potentially change the dynamics of communities and influence invasion success.

Invasive species have an enormous global impact, with international trade being the leading pathway for their introduction. Current multinational trade deals under negotiation will dramatically change trading partnerships and pathways. These changes have considerable potential to influence biological invasions and global biodiversity. Using a database of 47 328 interceptions spanning 10 years, we demonstrate how development and governance socio-economic indicators of trading partners can predict exotic species interceptions. For import pathways associated with vegetable material, a significantly higher risk of exotic species interceptions was associated with countries that are poorly regulated, have more forest cover and have surprisingly low corruption. Corruption and indicators such as political stability or adherence to rule of law were important in vehicle or timber import pathways. These results will be of considerable value to policy makers, primarily by shifting quarantine procedures to focus on countries of high risk based on their socio-economic status. Further, using New Zealand as an example, we demonstrate how a ninefold reduction in incursions could be achieved if socio-economic indicators were used to select trade partners. International trade deals that ignore governance and development indicators may facilitate introductions and biodiversity loss. Development and governance within countries clearly have biodiversity implications beyond borders.

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Biological invasions are a threat to global biodiversity and provide unique opportunities to study ecological processes. Population bottlenecks are a common feature of biological invasions and the severity of these bottlenecks is likely to be compounded as an invasive species spreads from initial invasion sites to additional locations. Despite extensive work on the genetic consequences of bottlenecks, we know little about how they influence microbial communities of the invaders themselves. Due to serial bottlenecks, invasive species may lose microbial symbionts including pathogenic taxa (the enemy release hypothesis) and/or may accumulate natural enemies with increasing time after invasion (the pathogen accumulation and invasive decline hypothesis). We tested these alternate hypotheses by surveying bacterial communities of Argentine ants (Linepithema humile). We found evidence for serial symbiont bottlenecks: the bacterial community richness declined over the invasion pathway from Argentina to New Zealand. The abundance of some genera, such as Lactobacillus, also significantly declined over the invasion pathway. Argentine ants from populations in the United States shared the most genera with ants from their native range in Argentina, while New Zealand shared the least (120 vs. 57, respectively). Nine genera were present in all sites around the globe possibly indicating a core group of obligate microbes. In accordance with the pathogen accumulation and invasive decline hypothesis, Argentine ants acquired genera unique to each specific invaded country. The United States had the most unique genera, though even within New Zealand these ants acquired symbionts. In addition to our biogeographic sampling, we administered antibiotics to Argentine ants to determine if changes in the micro-symbiont community could influence behavior and survival in interspecific interactions. Treatment with the antibiotics spectinomycin and kanamycin only slightly increased Argentine ant interspecific aggression, but this increase significantly decreased survival in interspecific interactions. The survival of the native ant species also decreased when the symbiotic microbial community within Argentine ants was modified by antibiotics. Our work offers support for both the enemy release hypothesis and that invasive species accumulate novel microbial taxa within their invaded range. These changes appear likely to influence invader behavior and survival.

Multiple biotic and abiotic factors influence species coexistence and co‐occurrence patterns. In a competitive environment, for example, temperature and diet variation may modify both foraging behaviour and aggression, thereby changing competitive interactions and species co‐occurrence patterns. In New Zealand, two endemic ant species (Prolasius advenus and Monomorium antarcticum) often form allopatric distributions; though also periodically do co‐occur in the same habitat. Here, we performed a long‐term laboratory experiment in an attempt to understand how diet, colony size and environmental conditions may influence these co‐occurrence patterns. The consequences of temperature and diet variation differed between P. advenus and M. antarcticum. Colonies of P. advenus exhibited increased aggression and foraging activities at higher temperatures. In addition, P. advenus colonies augmented their foraging activities when deprived of a carbohydrate‐rich food source. Conversely, small M. antarcticum colonies exhibited higher aggression than when in large colonies, and increased their foraging activities at lower temperatures. The modulation of aggression and foraging behaviour may influence the likelihood of small P. advenus and M. antarcticum colonies persisting in the long term. Our results are compatible with the hypothesis that the environment is likely to be a strong filter for the negative co‐occurrence patterns we observe between P. advenus and M. antarcticum in New Zealand. Furthermore, this study provides a mechanistic explanation for potential impacts of climate warming on community structure. Environmental modification of aggression and foraging behaviour could potentially alter competitive interactions and influence community assembly.