Chi-Man Leong

Many broad‐scale studies along spatial and habitat gradients show that organisms' traits can strongly influence community assembly by facilitating dispersal and environmental filtering. Nonetheless, how traits structure local faunal communities within habitats remains poorly understood. In particular, the often‐assumed role of traits in affecting the outcome of competition among animal species is rarely tested. We coupled a field study with a mesocosm experiment to explore how arboreal ant species' traits shaped competition and community structure, leveraging a small mangrove ecosystem which conceivably imposed minimal dispersal and environmental filtering effects on ant community assembly. We first surveyed the ant communities inhabiting 115 mangrove trees using >2000 carbohydrate and protein baits, and measured multiple morphological, physiological (critical thermal maximum) and dietary (stable isotope trophic position) traits of all ant species. We then coupled co‐occurrence network analyses with meta‐analytical models to uncover the trait‐based mechanisms structuring species co‐occurrences in the field. Finally, in a mesocosm experiment, we reared 87 colonies of eight ant species from the mangrove over 30 days under different competition treatments to investigate trait‐mediated effects of competition on ant colony performance. Patterns of ant species co‐occurrences and bait recruitment indicated strong competition for limited protein‐rich resources. Accordingly, dissimilarities in three traits—eye size, pronotum width and antennal scape length—consistently explained species co‐occurrences, suggesting that the communities were competitively assembled by a partitioning of resource acquisition strategies among species. Species co‐occurrences were also, to a lesser extent, explained by similarities in critical thermal limits, suggesting mild environmental filtering. In the mesocosm experiment, increasing directional differences in eye size and pronotum width between neighbouring ant colonies exacerbated interspecific competitive effects on colony survival and growth. Our results empirically demonstrate that traits linked to resource acquisition shape both coexistence and exclusion in ants. More broadly, by contrasting field patterns of niche partitioning with experimentally measured competitive effects, we show that the same traits can underpin stabilising processes that promote coexistence through limiting similarity, or equalising processes that drive exclusion through hierarchical differences, with their relative importance shifting across spatial scales and environmental contexts. Read the free Plain Language Summary for this article on the Journal blog.

Urban ecosystems present unique challenges for biodiversity monitoring, demanding efficient methods to document species diversity in rapidly changing environments. This study quantifies insect diversity in Macao SAR — a hyper-urbanised region — by integrating data on 1,339 species documented in expert-led surveys and 1,012 species recorded in citizen-science observations between 2019 and 2023. Striking divergence emerged between the expert and citizen-science datasets: only 462 species (33.5% of total diversity) were detected by both groups, with experts documenting 877 unique taxa often requiring specialised collection or morphological analysis, while citizen scientists contributed 550 distinctive species through spatially explicit, image-based records. Together, these approaches achieved 96.59% estimated species coverage within five years, demonstrating that combining community-driven data with expert methods accelerates comprehensive biodiversity documentation. Citizen-science platforms played a pivotal role by providing high-resolution geotagged imagery which enabled experts to validate records and resolve taxonomic ambiguities. Meanwhile, expert surveys detected cryptic taxa overlooked by citizen scientists. The rapid species coverage achieved through this synergy highlights the transformative potential of integrated frameworks. By mobilizing the scalability of citizen science to fill spatial and taxonomic gaps, while leveraging expert precision to ensure rigour, urban biodiversity monitoring can adapt to the rapid pace of ecological change. These findings advocate for collaborative strategies that harness public participation and scientific validation to optimise conservation efforts in data-deficient and highly-stressed ecosystems.

Under global warming, animal species show shrinking body size responses, cascading deep changes in community structure and ecosystem functions. Although the exact physiological mechanisms behind this phenomenon remain unsolved, smaller individuals may benefit from warming climate more than larger ones. Heat‐coma, a physiological state with severe consequences on locomotion ability, is often considered as an “ecological death” scenario under which individuals are unable to escape and exposed to predation, further heat injury, and other hazards. Species are expected to increasingly encounter heat‐coma temperature thresholds under warming climate, and body size may be an important trait for thermoregulation in particular for ectotherms. The relationship between heat‐coma and shrinking body size remains, however, unclear. Yet, recovery after short‐term heat‐coma is possible, but little is known about its importance in thermal adaptation and how organismal size correlates with post heat‐coma recovery. Here, using ants as a model system, we firstly examined the fate of heat‐comatose individuals under field conditions to quantify the ecological benefits of post heat‐coma recovery. Then, we quantified ants' recovery ability after heat‐coma using a dynamic thermal assay in the laboratory and asked if thermal resilience varies between species with different body mass. Our results confirm that heat‐coma represents an inherent ecological death where individuals failed to recover from coma suffer strong predation pressure. Additionally, following phylogenetic signals inclusion, organisms with small mass were more likely to recover, supporting the temperature‐size rule in thermal adaptation and recent studies showing a decrease in body size composition of ectotherm community under warmer climatic conditions. Body size as a fundamental trait in ecology thus affects ectotherm survival under thermal stress, which may drive species body size adaptations and community composition under future warming scenarios.

Understanding mechanistic processes driving biodiversity change in land‐use transformation is paramount but challenging. Functional trait‐based approach provides a framework to understand the environmental filtering process of species composition shifts. Yet, trait selection bias may affect the results on forecasting species dynamics, subsequent analyses and the scope of conclusions, in particular, if most studies on terrestrial arthropods rely exclusively on the use of a subset of morphological traits. The integration of ecophysiological traits could then provide additional dimensions of environmental filtering caused by land‐use conversion. Our study investigates how land‐use conversion from forest to rubber plantation impacts functional traits distribution and trait space in foraging ant assemblages in tropical Thailand by integrating both physiological and morphological traits. The results showed that both physiological and morphological traits may explain, although unevenly, the differences observed in ant assemblages between forest and rubber plantation. The use of Critical Thermal maximum provided an important and unique role for differentiating assemblages encountered in both habitats and in characterising the niche structure of species assemblage from forest. The use of particular traits can thus improve our perception of species dynamic along land‐use gradient. To advance our knowledge on the species responses and consequences of land‐use changes, the use of different types of functional traits is recommended.

The assumption that differences in species' traits reflect their different niches has long influenced how ecologists infer processes from assemblage patterns. For instance, many assess the importance of environmental filtering versus classical limiting-similarity competition in driving biological invasions by examining whether invaders’ traits are similar or dissimilar to those of residents, respectively. However, mounting evidence suggests that hierarchical differences between species' trait values can distinguish their competitive abilities (e.g. for the same resource) instead of their niches. Whether such trait-mediated hierarchical competition explains invasions and structures assemblages is less explored. We integrate morphological, dietary, physiological and behavioural trait analyses to test whether environmental filtering, limiting-similarity competition or hierarchical competition explain invasions by fire ants on ant assemblages. We detect both competition mechanisms; invasion success is not only explained by limiting similarity in body size and thermal tolerance (presumably allowing the invader to exploit different niches from residents), but also by the invader's superior position in trait hierarchies reflecting competition for common trophic resources. We find that the two mechanisms generate complex assemblage-level functional diversity patterns—overdispersion in some traits, clustering in others—suggesting their effects are likely missed by analyses restricted to a few traits and composite trait diversity measures.

Critical Thermal maximum (CT_max) is often used to characterize the upper thermal limits of organisms and represents a key trait for evaluating the fitness of ectotherms. The lack of standardization in CT_max assays has, however, introduced methodological problems in its measurement, which can lead to questionable estimates of species’ upper thermal limits. Focusing on ants, which are model organisms for research on thermal ecology, we aim to obtain a reliable ramping rate that will yield the most rigorous measures of CT_max for the most species. After identifying three commonly used ramping rates (i.e., 0.2, 0.5 and 1.0°C min^-1) in the literature, we experimentally determine their effects on the CT_max values of 27 species measured using dynamic assays. Next, we use static assays to evaluate the accuracy of these values in function of the time of exposure. Finally, we use field observations of species’ foraging activities across a wide range of ground temperatures to identify the most biologically relevant CT_max values and to develop a standardized method. Our results demonstrate that the use of a 1°C min^-1 ramping rate in dynamic assays yields the most reliable CT_max values for comparing ant species’ upper thermal limits, which are further validated in static assays and field observations. We further illustrate how methodological biases in physiological trait measurements can affect subsequent analyses and conclusions on community comparisons between strata and habitats, and the detection of phylogenetic signal (Pagel’s λ and Bloomberg’s K). Overall, our study presents a methodological framework for identifying a reliable and standardized ramping rate to measure CT_max in ants, which can be applied to other ectotherms. Particular attention should be given to CT_max values obtained with less suitable ramping rates, and the potential biases they may introduce to trait-based research on global warming and habitat conversion, as well as inferences about phylogenetic conservatism.

The continuous increase in urbanization has been perceived as a major threat for biodiversity, particularly within tropical regions. Urban areas, however, may still provide opportunities for conservation. In this study focused on Macao (China), one of the most densely populated regions on Earth, we used a comprehensive approach, targeting all the vertical strata inhabited by ants, to document the diversity of both native and exotic species, and to produce an updated checklist. We then compared these results with 112 studies on urban ants to illustrate the dual roles of cities in sustaining ant diversity and supporting the spread of exotic species. Our study provides the first assessment on the vertical distribution of urban ant communities, allowing the detection of 55 new records in Macao, for a total of 155 ant species (11.5% being exotic); one of the highest species counts reported for a city globally. Overall, our results contrast with the dominant paradigm that urban landscapes have limited conservation value but supports the hypothesis that cities act as gateways for exotic species. Ultimately, we argue for a more comprehensive understanding of ants within cities around the world to understand native and exotic patterns of diversity.

Upper thermal limit (UTL) is a key trait in evaluating ectotherm fitness. Critical Thermal maximum CT _max , often used to characterize the UTL of an organism in laboratory setting, needs to be accurate to characterize this significant and field-relevant threshold. The lack of standardization in CT _max assays has, however, introduce methodological problems in its measurement and incorrect estimation of species upper thermal limit; with potential major implications on the use of CT _max in forecasting community dynamics under climate change. In this study we ask if a satisfactory ramping rate can be identified to produce accurate measures of CT _max for multiple species. We first identified the most commonly used ramping rates (i.e. 0.2, 0.5 and 1.0 °Cmin ⁻¹ ) based on a literature review, and determined the ramping rate effects on CT _max value measurements in 27 ant species (7 arboreal, 16 ground, 4 subterranean species) from eight subfamilies using both dynamic and static assays. In addition, we used field observations on multiple species foraging activity in function of ground temperatures to identify the most biologically relevant CT _max value to ultimately develop a standardized methodological approach. Integrating dynamic and static assays provided a powerful approach to identify a suitable ramping rate for the measurements of CT _max values in ants. Our results also showed that among the values tested the ramping rate of 1 °Cmin ⁻¹ is optimal, with convergent evidences from CT _max values measured in laboratory and from foraging thermal maximum measured in the field. Finally, we illustrate how methodological bias in terms of physiological trait measurements can also affect the detection of phylogenetic signal (Pagel’s λ and Bloomberg’s K ) in subsequent analyses. Overall, this study presents a methodological framework allowing the identification of suitable and standardized ramping rates for the measurement of ant CT _max , which may be used for other ectotherms. Particular attention should be given to CT _max values retrieved from less suitable ramping rate, and the potential biases that functional trait based research may induce on topics such as global warming, habitat conversion or their impacts on analytical interpretations on phylogenetic conservatism.

Ants are a highly diverse group that not only are often strongly associated with certain habitat types, but also can be found on carcasses and, therefore, in crime scenes. In the present study, a survey of the necrophilous ants in Taiwan was conducted and a preliminary species checklist was provided for the first time. The aim of this study was primarily to offer information on Taiwanese ant species of forensic significance. A total of 50 ant species/morphospecies from 26 genera were collected from large scale regions in Taiwan using combination pig liver bait and pitfall traps, bringing the Taiwanese necrophilous ants up to 55 species from 33 genera within the known Taiwanese ant fauna of 288 species from 71 genera. Seventeen species found in this study are tramp or potentially exotic species, which often dominated the baits. Use of pitfall traps increased the diversity of ants collected relative to hand-collecting from the carcass, adding useful data. These necrophilous ants may play important roles in carcass decomposition and can be useful in reconstructing crime scenes, as certain ants are more common in certain habitat types. This checklist and accompanying habitat information of these ants is likely the first such comprehensive data in Taiwan applying ants to the field of forensic entomology.

Despite its small size, Hong Kong hosts a surprising level of ant diversity. Through faunal studies on arthropods conducted in Hong Kong over recent years, a new record and species of the genus Ponera have been discovered, which are introduced here. Poneraguangxiensis Zhou, 2001 is reported for the first time from Hong Kong, and Poneratudigongsp. nov. is here described as a new species, easily distinguishable from other Ponera species and unique within the genus for its four mandibular teeth.