Professor Leslie Christidis

Taxonomy defines the units that conservationists strive to preserve for future generations. However, the discovery of new species and the taxonomic revision of existing species affect conservation efforts. Despite the importance of taxonomy for a species’ conservation, there is currently no overview of how those leading species extinction risk assessments use taxonomy. To fill this gap, we asked the chairs of the International Union for Conservation of Nature's (IUCN) Species Survival Commission Specialist Groups and other IUCN expert groups that coordinate extinction risk assessments about the state of taxonomy within their taxonomic group of interest, their sources of information, and what taxonomy-related challenges they encounter in conducting assessments. Most experts answered immediately and in detail, reflecting the importance of taxonomy. Approaches to taxonomy were diverse. Although most experts ignored debates about species definitions, for some groups, particularly mammals and birds, there were theoretical differences about what constitutes a species. Governance of species lists varied from individual experts making all decisions, to dedicated committees, to collective decisions for all taxonomic resolutions being made by others outside the group. The extent to which current taxonomy represents the views and consensus of the taxonomic community with an interest in that taxonomic group is not known. However, the taxonomies used in IUCN assessments differ from those used by other species conservation initiatives led by multilateral environmental agreements or the Catalogue of Life. Greater alignment is possible and could be beneficial, though it may constrain the flexibility and adaptability in taxonomic decision-making that informs IUCN Red List assessments. We argue that regardless of the extent to which further alignment is sought, there is potential to enhance taxonomic list governance within the IUCN.

Biodiversity corridors aim to reconnect fragmented habitats and protected areas,yet their impact on landowners varies and requires assessment. In the CentralAnnamite Landscape, Vietnam, initiatives like Payment for Forest EnvironmentServices (PFES) for watershed protection, forest restoration, and non-timber forestproduct development program seek to enhance conservation-based livelihoods. Asurvey of 120 households across four villages was conducted to compare incomeand other livelihood benefits of landholders residing inside and outside the biodi-versity corridors. Findings revealed that landowners within the corridors earnedsignificantly higher incomes (USD 412/ha/year) primarily from PFES paymentsfor watershed protection and participation in restoration activities, while thoseoutside earned less (USD 330/ha/year) from afforestation (Acacia plantations) andforest product harvesting. Households inside corridors also reported greater accessto livelihood support, improved forest governance, and higher participation incommunity-based forest management. To maximize benefits for landowners, localpolicies should expand conservation incentives, including restoration, patrolling,and monitoring. Interventions should leverage local assets to create alternativeincome sources, reducing dependence on forest exploitation. Strengtheningconservation-oriented livelihoods can enhance the economic benefits for land-owners while ensuring the long-term sustainability of biodiversity corridors.

Taxonomic lists, usually of species, have many functions. However, there is currently no reliable and convenient way to determine whether a list contains the information that a user requires other than by reading the list in detail. We therefore developed 24 indicators to characterise list contents. The indicators aim to describe the extent to which the scored list covers their intended class of organisms, the quality of their taxonomic scholarship, and additional information they provide for each taxon. We tested the indicators on 16 lists drawn from a wide range of vertebrates, invertebrates, and plants. A list content score was derived from individual indicator scores after they had been weighted to reflect the preferences that taxonomists had expressed in a global survey. The indicators aim to help list creators provide the details taxonomists and list users consider important. We expect indicators to be refined after public debate.

Taxonomic lists are important tools for efficient communication about biodiversity. The processes by which they are created and maintained need to be robust, scientifically sound, and transparent. Articulating and scoring a set of governance quality indicators provides a way to assess the relative strengths of list management, gives list users a means to assess the quality of this process, augments the information available to list aggregators, and allows patterns to be measured over time and among forms of life. Based on published principles, we created 12 governance quality indicators which we tested on 16 lists spanning a range of taxonomic groups. Independence of taxonomy from nomenclature scored most strongly, but scores for local and regional involvement were lower. The governance quality indicators may eventually provide a rubric for assessing best practice species list governance but now need a period of further testing, review, and refinement before they are institutionalized.

Human-mediated introductions have enabled species to colonize beyond their native ranges, yet the mechanisms underlying successful establishment remain unclear. We combined genomic and ecological analyses to investigate parallel introductions of the Eurasian Tree Sparrow across continents. Our analyses of genetic structure and demography revealed that introduced populations in North America (European origin) and Australia (Chinese origin) experienced founder effects, with resulting bottlenecks, reduced genetic diversity, and increased inbreeding. Despite the genome-wide loss of diversity, we identified conserved regions of high genetic variation in the introduced populations, potentially maintained through balancing selection of ancestral polymorphisms. Genotype-climate association and genetic offset modeling demonstrated that climate-adaptive genetic variants retained similar frequencies across the native and introduced ranges, likely maintaining similar interactions of genetic components with climate niches. Our findings highlight how retention of adaptive polymorphism facilitates establishment success in the introduced populations, providing a framework for predicting invasion potential through genomic signatures of adaptation.

Aim: Range size constitutes a fundamental characteristic of every species and is commonly believed to influence diversification rates. This relationship is potentially dependent on the mode of speciation and other intrinsic factors, including geographic setting and species attributes. Yet, not only the size of the geographic range, but also the heterogeneity of environments it comprises, including its vertical extent (elevational range size) can affect speciation and extinction processes. For instance, mountain species and those whose range encompasses only one ecoregion (specialists) are expected to show higher diversification rates than lowland and generalist species. This study aims to investigate the link between range size, niche specialisation and diversification rates in a speciose bird superfamily that occurs throughout the Americas.
Location: America.
Taxon: The Tyrannoidea superradiation.
Methods: We employed a suite of phylogenetic methods including phylogenetic generalised least squares regressions, ancestral reconstructions and multiple-states speciation-and-extinction models.
Results: We observed a triangular pattern in the relationship between geographic and elevational range size, indicating that while species with a broad elevational range generally also have a large geographic range, the opposite is not necessarily true. The strong support for the BAYAREALIKE + j model, along with the negative association between range size and diversification rates, suggests that the predominant mode of speciation in this system is likely parapatric speciation, where divergence arises due to steep environmental gradients or local adaptation. Species inhabiting only one ecoregion and mountain species exhibited higher diversification rates than generalists and lowland species.
Main Conclusions: Reconstruction of ancestral geographic ranges and habitat supports the idea that the colonisation of open environments that proliferated in the Miocene fueled the diversification of this superfamily. The absence of a positive relationship between range size and diversification may explain the low conservatism observed for the analysed spatial traits in this study, which contrasts with that observed in other avian groups where the process of speciation has been largely allopatric.

Biodiversity corridors can promote wildlife conservation by facilitating movement between habitat patches if carefully planned. The biodiversity corridors in the Central Annamite Landscape, Vietnam, were legally established in 2018. However, there has been no detailed modeling or surface analysis undertaken to assess their effectiveness. If biodiversity corridors are not well planned and rigorously monitored, they could lead to humanwildlife conflicts and create ecological sinks. Here we assessed the potential effectiveness of biodiversity corridors between five protected areas in Quang Nam and Thua Thien Hue provinces with the aim of identifying opportunities for improving connectivity via forest restoration and infrastructure mitigation. The Linkage Mapper toolset in ArcGIS was used for the connectivity modeling process using cost-weighted distances. In the absence of robust empirical biodiversity data for this region, we relied on a panel of local species experts to generate a consensus resistance surface. A total of 152,200 ha was identified as potentially effective biodiversity corridors, primarily consisting of natural forests without roads. Barrier areas were found near roads, emphasizing the importance of linear infrastructure mitigation to promote connectivity. Our results provide a quantitative assessment of opportunities for enhanced corridor effectiveness in the Central Annamite Landscape and demonstrate the application of expert-based approaches as a first step to connectivity conservation in datachallenged biodiversity hotspots. Subsequent studies using species-specific empirical data remains a critical future step to improve our understanding of functional connectivity in the Central Annamite Landscape.

Universally recognized scientific names for organisms are necessary for accurate and efficient communication. Incongruence in taxonomic treatments results in situations where one name is used for different entities or one entity is known by different names, with negative consequences for conservation, science, trade, legislation, law enforcement, and education, leading to discord among stakeholders and confusion among users. Within the ornithological community taxonomic incongruence among four widely adopted global bird checklists has led to calls for the development of a single unified global avian taxonomy or checklist. Here we introduce AviList, a comprehensive, collaborative and evolving effort towards developing a unified global avian taxonomy, spearheaded by representatives of most current global checklists and many major regional authorities, and supported by the International Ornithologists’ Union (IOU), BirdLife International and the Cornell Lab of Ornithology. AviList version 2025, the first version, was officially launched on 11 June 2025 and is available online as a comprehensive, searchable public-access database. It recognizes 11,131 bird species in 2376 genera, 252 families and 46 orders. This global effort has resolved over 1000 species-level taxonomic incongruences among existing checklists.
With AviList’s launch, the IOC World Bird List and the Clements Checklist of Birds of the World have ceased any independent taxonomic updates, while BirdLife International is in the process of total alignment, leading to a harmonization in the classification underpinning a number of major bird projects, including eBird, Macaulay Library, Merlin Bird ID and the IUCN Red List. Adoption of AviList will improve inter-operability across global biodiversity, molecular, ecological and spatial databases (e.g. GBIF). Strong governance of AviList will ensure it is a “living” document that is regularly updated by a global community of bird taxonomists as new scientific advances are made, with positive impacts for conservation, academia and human society. It is hoped that AviList will support and encourage taxonomic science by identifying areas where further research is most needed, and that it will provide a blueprint for taxonomic authorities in other organismic groups endeavoring to achieve taxonomic harmonization.

Aim
Variation in community composition along environmental gradients provides crucial information for identifying zones where species turnover is rapid and to ascertain whether compositional changes occur gradually or rather abruptly. We examined changes in bird community composition along three bioclimatic transects in Australia to test whether drivers of species turnover are consistent, rather than spatially contingent, across biologically contrasting ecosystems. We also detected potential transition zones associated with environmental thresholds and determined whether certain abiotic conditions promote a higher rate of community compositional turnover.

Location
Mainland Australia.

Taxon
Terrestrial birds.

Methods
We applied multivariate community analysis, generalised dissimilarity modelling (GDM) and threshold indicator taxa analysis (TITAN).

Results
We observed that environmental variables are better predictors of community composition than spatial distance, which indicates that species sorting, rather than dispersal, plays a key role in structuring Australian avian communities. Annual precipitation constitutes a key driver of species turnover regardless of the analysed transect. The most humid landscapes and those with a higher tree canopy show lower spatial heterogeneity in community composition compared to those with less benign environmental conditions (e.g., dryer environments). TITAN detected significant transition points and supported the results obtained using GDM, which suggests that bird composition change along the gradients is not monotonic.

Main Conclusions
Our results suggest that avian beta diversity increases with increasing environmental harshness, presumably through changes in the relative importance of stochastic versus deterministic processes. The obtained findings show that open forests and woodlands are extremely important ecosystems on this continent and deserve special attention in terms of conservation due to their vulnerability to global change. Lastly, this study exemplifies the value of combining community- and taxon-based analyses to identify and interpret community thresholds, which can serve to pinpoint targets for preserving biodiversity.

Sexual selection can directly contribute to reproductive isolation and is an important mechanism that can lead to speciation. Lek-mating is one of the most extreme forms of sexual selection, but surprisingly does not seem to preclude occasional hybridization in nature. However, hybridization among lekking species may still be trivial if selection against offspring with intermediate phenotypes prohibits introgression. Here we investigate this further by sequencing the genomes of nearly all bird-of-paradise (Paradisaeidae) species and 10 museum specimens of putative hybrid origin. We find that intergeneric hybridization indeed still takes place despite extreme differentiation in form, plumage, and behavior. In parallel, the genomes of contemporary species contain widespread signatures of past introgression, demonstrating that hybridization has repeatedly resulted in shared genetic variation despite strong sexual isolation. Our study raises important questions about extrinsic factors that modulate hybridization probability and the evolutionary consequences of introgressive hybridization between lekking species.