Convergence of dominance and neglect in flying insect diversity

nature ecology & evolution Article https://doi.org/10.1038/s41559-023-02066-0 Convergence of dominance and neglect in flying insect diversity Received: 8 August 2022 Accepted: 6 April 2023 Amrita Srivathsan 1, Yuchen Ang2, John M. Heraty3, Wei Song Hwang 2, Wan F. A. Jusoh 2,4, Sujatha Narayanan Kutty5,6, Jayanthi Puniamoorthy 5, Darren Yeo5, Tomas Roslin 7 & Rudolf Meier 1,5 Published online: 18 May 2023 Check for updates Most of arthropod biodiversity is unknown to science. Consequently, it has been unclear whether insect communities around the world are dominated by the same or different taxa. This question can be answered through standardized sampling of biodiversity followed by estimation of species diversity and community composition with DNA barcodes. Here this approach is applied to flying insects sampled by 39 Malaise traps placed in five biogeographic regions, eight countries and numerous habitats (>225,000 specimens belonging to >25,000 species in 458 families). We find that 20 insect families (10 belonging to Diptera) account for >50% of local species diversity regardless of clade age, continent, climatic region and habitat type. Consistent differences in family-level dominance explain two-thirds of variation in community composition despite massive levels of species turnover, with most species (>97%) in the top 20 families encountered at a single site only. Alarmingly, the same families that dominate insect diversity are ‘dark taxa’ in that they suffer from extreme taxonomic neglect, with little signs of increasing activities in recent years. Taxonomic neglect tends to increase with diversity and decrease with body size. Identifying and tackling the diversity of ‘dark taxa’ with scalable techniques emerge as urgent priorities in biodiversity science. Biodiversity loss is now widely recognized as a major threat to planetary health1–3. Halting the loss requires that the basic building blocks of biodiversity are known, so that changes can be recorded, drivers of change can be identified and appropriate policy actions can be implemented. However, much of the terrestrial animal diversity belongs to hyperdiverse invertebrate clades that are so poorly known4,5 that it is difficult to obtain this critical information. For example, only 0.17 G of the 2.16 G records in the Global Biodiversity Information Facility pertain to arthropods. By comparison, 67% of Global Biodiversity Information Facility records relate to birds, although birds account for only 10,000–20,000 species (0.2%) of the estimated 8–10 million multicellular species worldwide6,7. These numbers alone reveal the size of the knowledge gap for many truly diverse clades that due to their current position in the information shadow have been called ‘dark taxa’8. To allocate resources for discovering and conserving species, it is crucial to establish the relative contribution of different taxa to overall biodiversity. Only in this way can the most diverse and abundant taxa be given adequate attention. Identifying these taxa is furthermore important for understanding the basic structure of the living world, and for gaining insights into how community composition is shaped by evolutionary, biogeographic or ecological factors9. Where such analyses have been carried out—for example, for plants and snakes10—they have Center for Integrative Biodiversity Discovery, Leibniz Institute for Evolution and Biodiversity Science, Museum für Naturkunde, Berlin, Germany. 2Lee Kong Chian Natural History Museum, National University of Singapore, Singapore, Singapore. 3Department of Entomology, University of California, Riverside, CA, USA. 4School of Science, Monash University Malaysia, Subang Jaya, Malaysia. 5Department of Biological Sciences, National University of Singapore, Singapore, Singapore. 6Tropical Marine Science Institute, National University of Singapore, Singapore, Singapore. 7Department of Ecology, Swedish University of Agricultural Sciences, Uppsala, Sweden. e-mail: 1 Nature Ecology & Evolution | Volume 7 | July 2023 | 1012–1021 1012 Article revealed that a few clades dominate communities across the world11. Unfortunately, corresponding information is lacking for arthropods. This is a striking shortcoming, given that arthropods are found worldwide, functionally important12 and currently undergoing major declines in diversity and abundance13,14. In this Article, we analyse the taxonomic patterns among flying insects sampled by Malaise traps in different habitats, climates and biogeographic regions. Malaise traps are widely used in global biomonitoring programmes because they provide standardized and efficient tools for collecting diverse communities of flying insects and semi-aquatic taxa15–17. Similar to all other trap types, they only subsample the insect communities. For example, Malaise traps rely on the passive interception of insect flight paths, and collect those insects that climb towards the highest point of the trap (Supplementary Fig. 1). For this reason, strong and active fliers like dragonflies (which largely avoid the traps) or beetles (which tend to drop to the ground when encountering an obstacle) are under-represented. However, overall, Malaise traps are so effective at sampling flying insects that sample processing is a major challenge due to high specimen and species yields15,18. In addition, most specimens caught in Malaise traps cannot be identified, because many species are undescribed and relevant taxonomic expertise is either non-existent or dwindling6. Fortunately, recent advances in large-scale DNA barcoding with new sequencing technologies allow for processing large numbers of specimens rapidly and cost-effectively19,20. Using molecular species delimitation methods, these data can then be converted into estimates of species diversity without formal description of the component taxa and most species can be assigned to major insect clades for analysis of community structure. We here determine the taxonomic composition of Malaise trap samples21 from five biogeographic regions, eight countries and diverse habitats. In total, our material encompasses >225,000 specimens belonging to >25,000 species living in habitats ranging from temperate meadows to tropical rainforests. We discover surprising congruence with regard to which 20 insect families are dominant components of flying arthropod communities worldwide (accounting for >50% of species and specimens in each sample). When we compare family-specific diversity with taxonomic attention, we find that most of the particularly diverse and abundant taxa are poorly known and suffer from persistent taxonomic neglect. In other words, a very large proportion of terrestrial animal biodiversity is not only unknown to science, but will also remain so for the foreseeable future unless such ‘dark taxa’ become a preferred target for biodiversity science. Results Our study comprises 225,261 barcoded arthropods belonging to 458 families. Th (...truncated)