Aim Non‐native invasive insects have major impacts on ecosystem function, agricultural production and human health. To predict the geographical distributions of these species, correlative ecological niche models (ENMs) are typically used. Such methods rely on assumptions of niche conservatism, although there is increasing evidence that many species undergo niche shifts during invasions. The magnitude and direction of niche shifts, however, is likely to vary within and between taxonomic groups, highlighting that an assessment of potential niche shifts in such insects is required. Location Global. Time period Current. Major taxa studied Insects. Methods We compile a novel database of 22 globally invasive, non‐native insect species and test for niche expansion and unfilling across this group. We examine if factors such as the native range size, poleward shifts and human influence may be associated with observed niche changes. Finally, we construct ENMs and examine the reliability of their predictions in light of our niche shift results. Results Niche expansion was apparent in 12 of the 22 species, suggesting that altered species–climate relationships during invasion is common for this group. Likewise, niche unfilling occurred in 15 of the species. Increasing human disturbance (combining human population, transport networks and land use) explained 40% of observed niche expansions and 54% of incidents of niche unfilling. Niche metrics and ENM performance were sensitive to the choice of background extents. Main conclusions Many non‐native insects expand into new climates in their invasive ranges. The prevalence of niche unfilling across this group suggests climate disequilibrium and the potential for further range expansion. Non‐native invasive insects tend to invade areas with similar human disturbance to their native range, and habitat accessibility appears important for these species to achieve their full invasion range potential. Ideally, ENMs should not be used in isolation for this group, but should be coupled with other methods or experiments to test for potential niche change.

Aim Predicted distributions of invasive species are often not congruent between their realized native and introduced ranges, but the reasons for this are rarely investigated empirically. We tested for niche shift in an invasive species using a simple framework combining environmental niche models (ENMs) and niche‐limiting thermal tolerance traits. Location Australia and South Africa. Methods The red‐legged earth mite, Halotydeus destructor, native to South Africa, is a major agricultural pest in Australia and has expanded its range to areas not predictable from its native range in the last 40 years. Revisiting recently constructed ENMs for H. destructor, we select populations in both native and invasive ranges that appear to occupy different niches. We characterize thermal tolerance traits and test for acclimation patterns of cold tolerance of these H. destructor populations to test for niche shifts. Results Australian populations had an increased upper thermal threshold for movement and were able to recover from cold stress more rapidly than South African populations. Australian populations also differed in trait means from the likely source population in South Africa. Acclimation patterns were conserved across ranges for most populations, with 10 °C acclimation lowering the onset of and recovery from cold tolerance and 15 °C raising them when compared with field‐acclimated populations. Main conclusions These results support the prediction, based on ENMs, that H. destructor may have undergone a niche shift by adapting to environmental conditions in Australia. The increase in thermal resistance has implications for how this invasive species will respond to future climate change.

Aim  Niche conservatism is key to understanding species responses to environmental stress such as climate change or arriving in new geographical space such as biological invasion. Halotydeus destructor is an important agricultural pest in Australia and has been the focus of extensive surveys that suggest this species has undergone a niche shift to expand its invasive range inland to hotter and drier environments. We employ modern correlative modelling methods to examine niche conservatism in H. destructor and highlight ecological differences between historical and current distributions. Location  Australia and South Africa. Methods  We compile comprehensive distribution data sets for H. destructor, representing the native range in South Africa, its invasive range in Australia in the 1960s (40 yr post‐introduction) and its current range in Australia. Using MAXENT, we build correlative models and reciprocally project them between South Africa and Australia and investigate range expansion with models constructed for historical and current data sets. We use several recently developed model exploration tools to examine the climate similarity between native and invasive ranges and subsequently examine climatic variables that limit distributions. Results  The invasive niche of H. destructor in Australia transgresses the native niche in South Africa, and the species has expanded in Australia beyond what is predicted from the native distribution. Our models support the notion that H. destructor has undergone a more recent range shift into hotter and drier inland areas of Australia since establishing a stable distribution in the 1960s. Main conclusions  Our use of historical and current data highlights that invasion is an ongoing dynamic process and demonstrates that once a species has reached an established range, it may still expand at a later stage. We also show that model exploration tools help understand factors influencing the range of invasive species. The models generate hypotheses about adaptive shifts in H. destructor.

We contend that invasion ecology requires a universal, measurable trait of species and their interactions with resources that predicts key elements of invasibility and ecological impact; here, we advocate that functional responses can help achieve this across taxonomic and trophic groups, among habitats and contexts, and can hence help unify disparate research interests in invasion ecology.Invasion ecology is fragmented and lacks truly unifying principles across taxonomic and trophic groups, with many widely cited invasion hypotheses

BackgroundThe invasive fruit fly, Bactrocera invadens, has expanded its range rapidly over the past 10 years. Here we aimed to determine if the recent range expansion of Bactrocera invadens into southern Africa can be better understood through niche exploration tools, ecological niche models (ENMs), and through incorporating information about Bactrocera dorsalis s.s., a putative conspecific species from Asia. We test for niche overlap of environmental variables between Bactrocera invadens and Bactrocera dorsalis s.s. as well as two other putative conspecific species, Bactrocera philippinensis and B. papayae. We examine overlap and similarity in the geographical expression of each species’ realised niche through reciprocal distribution models between Africa and Asia. We explore different geographical backgrounds, environmental variables and model complexity with multiple and single Bactrocera species hypotheses in an attempt to predict the recent range expansion of B. invadens into northern parts of South Africa.Principal Findings Bactrocera invadens has a high degree of niche overlap with B. dorsalis s.s. (and B. philippinensis and B. papayae). Ecological niche models built for Bactrocera dorsalis s.s. have high transferability to describe the range of B. invadens, and B. invadens is able to project to the core range of B. dorsalis s.s. The ENMs of both Bactrocera dorsalis and B. dorsalis combined with B. philipenesis and B. papayae have significantly higher predictive ability to capture the distribution points in South Africa than for B. invadens alone.Conclusions/SignificanceConsistent with other studies proposing these Bactrocera species as conspecific, niche similarity and overlap between these species is high. Considering these other Bactrocera dorsalis complex species simultaneously better describes the range expansion and invasion potential of B. invadens in South Africa. We suggest that these species should be considered the same–at least functionally–and global quarantine and management strategies applied equally to these Bactrocera species.