## 4 Discussion  
A common perception of urban biodiversity is that it is characterized by low species richness and dominated by exotic species [12]. This perception may be induced by the excess of local scale studies (\(\alpha\) diversity) compared to the limited number of studies at larger scale (\(\gamma\) diversity) encompassing the full diversity encountered within of a city (Table 1). Here, our results contrast with the former assumption but agree with the latter. Indeed, we found that Macao hosts a diverse ant fauna, but that a high number of that fauna consists of exotic and tramp species. Figure 5: Species diversity in relation to sampling coverage for each standardized technique used in Macao in 2019. Values in the legend represent the number of species collected, and, in brackets, the estimated number of species that would be collected by this method if sampling coverage would reach 100% (asymptotic estimates of order q = 0 obtained using the function ChaoRichness in the package iNEXT). The dotted line shows the extrapolation for the predicted number of new records if sampling completeness would reach 100% (i.e., a value of 1.00 on the graph). Shaded areas represent the 95% confidence intervals of each curve. Calculation method used species incidence frequency. Leaf litter samples were considered as four units of 1 m\({}^{2}\) per Winkler sack (which pooled 4 m\({}^{2}\) of leaf litter). Abbreviations are (LLSP) leaf litter extraction with the species pool technique and (LLSA) leaf litter extraction with the standard area technique. Macao's ant fauna presents one the highest known ant richness reported for an urban region (Table 1). Our results indicate that, while there are few comprehensive studies for tropical regions--most studies on urban ants have been conducted within temperate regions where species diversity is usually much lower than in tropical and subtropical regions [202]-- several cities, including Macao, offer potential conservation values for ants. For instance, a study limited to the botanical garden of Bogor (Java), a small green oasis within an urban area, captured 216 ant species [69]. Similarly, ecological studies in Abidjan (Ivory Coast, 176 species) and Uberlandia (Brazil, 143 species), among others, also presented high ant species richness [62; 155]. Altogether, these results highlight the potential conservation value of urban habitats, but also their potential to increase the biogeographic and taxonomic knowledge on ants. Indeed, contrary to most natural habitats, urban habitats are characterized by their easy access, which facilitates continuous and thorough sampling. As for tropical forests, the vertical stratification of ants within cities does exist, and, as a result, researchers should consider diversifying their sampling approach to include subterranean and arboreal communities as well as epipeic ants. Ant assemblages are known to be highly structured along a vertical gradient ranging from the top soil layer (first 50 cm) to the tree canopy [203; 204], but such stratification had not been shown for urban environments prior to this study. Our results show that ignoring these strata may lead to an underestimation of species richness estimates. Indeed, although most of the new species records were collected within the ground stratum, we found several previously unrecorded arboreal and subterranean specialists. In particular, of the 35 species collected with our subterranean trapping, 10 were found only within that stratum, nine of which were new records, and three represented undescribed species. Remarkably, this parallels the results of previous surveys focusing on multiple strata but conducted within natural ecosystems [205]. For instance, in Ecuador, [PERSON] and collaborators collected 47 species in subterranean probes, nine of which were exclusively subterranean, and two were undescribed [205]. It is also worth noting that 14 species collected during the 2019 survey were unique to the arboreal stratum, nine of which were new records, and one was an undescribed species.