## 4 Discussion
Nevertheless, a key difference between disturbed and undisturbed habitats lies within their species composition instead of in the number of species they harbor, and a significant part of Macao's fauna consists of non-native species. The previous survey reported several new records of exotic species in Macao [53], which are here completed with the additions of four exotic and three tramp species (Figure 1), totaling in 18 exotic species and representing 11.5% of the Macanese ant fauna. The most notable newly reported exotic is _Brachymyr mex patagonicus_, a major pest in south-east USA [215]. This represents the second record of _B. patagonicus_ in continental Asia, with the first report from Hong Kong [216]. Its presence in Macao is worrisome, and clear plans to determine the extent of its distribution, with programs to destroy established populations, should be developed quickly. We also report the spread of several alien and potentially harmful species. We found the three exotic species _Anoploplepis gracilipes, Monomorium pharaonis_, and _Paratredina Ionigcornis_ in five, seven, and six forested sites, respectively. They can, thus, establish populations and persist in forested habitats, where their effects on native ants are unknown. Through our standardized sampling, we also found the notorious invasive species _Solenopsis invica_ and _Pheidole megacphala_ but, interestingly, rarely found it in Coloane's forested sites. Despite finding several workers and queens of _S. invica_ through hand collection in open and urban habitats, we found this species in only one forested site near a hiking trail: one individual was found in a leaf litter sample and several workers colonized two ground baits at that site. This reflects previous findings that the distribution of _S. invica_ is mainly restricted to disturbed habitats [217; 218; 219]. Similarly, while we found a high abundance of workers of _P. megacphala_ on one golf course, we collected only two individuals in forested sites. For both of these species, notorious for their destructive impacts on native communities [220; 221; 222], this would indicate that, for now, they are mainly restricted to more open and disturbed habitats. This suggests that forested habitats may help preserve local biodiversity while simultaneously limiting the distribution of some invasive ant species, reflecting results from Hong Kong and Hainan, where less disturbed habitats harbored relatively fewer exotic species than did more disturbed ones [223]. Nonetheless, the occurrence of exotic species in Macao is high. In comparison, the checklist of the ants of Yunnan reports that only 2% of its species are introduced [224], a proportion 5.75 times lower than in Macao. Based on current knowledge, Macao appears to have one of the highest numbers and proportions of exotic species encountered within cities (Table 1). Alas, we also report the presence of 17 tramp species, some of which may very well be introduced, as our biogeographic understanding and the region of origin for several species remains limited; thus, the overall number may be even higher. The high proportion of exotic and tramp species in Macao supports the hypothesis that coastal cities act as gateways for the introduction of exotic species through high propagule pressure [225]. In addition, since the occurrence of non-native species is an indicator of reduced ecological integrity [226], the high proportion of non-native species we found in Macao suggests these habitats have suffered substantial damage. It is, thus, crucial to make periodical biodiversity surveys in Macao and other cities to monitor their habitats' health through time, as well as to identify new arrivals of exotics and prevent their further spread. An historic baseline is lacking for Macao's ant assemblages, but we suspect there may be substantial differences compared to the ant assemblages before urbanization. Indeed, several genera known to occur in southern China and within neighboring cities of the Greater Bay Area, such as Hong Kong, are missing from Macao.