Introduction
Islands have long been a focus for evolutionary and ecological understanding (Warren et al., 2015), largely due to their limited geographic extent, long-term isolation, replicated nature, simplified biota relative to continental settings, high levels of endemism, and diverse ecological settings. At the same time, their flora and fauna are increasingly at risk from global change relative to continental settings for some of the very same reasons that have attracted scientific interest. Depauperate communities that have evolved in isolation may be more susceptible to invasive species (Bellard, Rysman, Leroy, Claud, & Mace, 2017; Spatz et al., 2017; Borges et al. 2020). Within the context of ongoing climate change, island biodiversity requires specific attention because of its increased vulnerability for multiple reasons (see e.g. Manes et al., 2021; Veron, Mouchet, Govaerts, Haevermans, & Pellens, 2019). When climate change is combined with other impacts of increasing human population size and economic development, such as habitat modification and degradation, the challenge for managing and conserving insular biodiversity presents itself as being immediate and large-scale (Russell & Kueffer, 2019). It is not only the loss of species and their interactions that is particularly relevant on islands, but also the loss of unique evolutionary history (phylogenetic and functional diversity), reflecting the loss of unique adaptations to the environment (Sayol et al., 2021; Soares, de Lima, Palmeirim, Cardoso, & Rodrigues, 2021).
Given the above, there are pure and applied scientific reasons for scaling up our understanding of island biodiversity. Scientifically, there is still much to be gained from the investigation of insular biotas (Warren et al., 2015; Patiño et al., 2017; Whittaker, Fernández-Palacios, Matthews, Borregaard, & Triantis, 2017), but with many questions remaining open due to limited arthropod data (Table 1). Our current understanding of ecological and evolutionary processes within islands, and most of the proposed island biodiversity patterns, rules and models, largely derive from empirical data on plants and birds (e.g. Matthews, Rigal, Triantis, & Whittaker, 2019; Valente et al., 2020; Veron, Haevermans, Govaerts, Mouchet, & Pellens, 2019). While invertebrates played a key role in the early developments of island biology (MacArthur & Wilson, 1963; MacArthur & Wilson, 1967; E. Wilson, 1961; E. O. Wilson, 1959), and typically represent the vast majority of insular biodiversity, invertebrate data pertaining to range size and co-occurrence remain under-represented in existing datasets. This can be explained, in part, by the relative difficulty of obtaining such data. It is recognised that invertebrates play a fundamental role in ecosystem processes and services (Dangles & Casas, 2019), and the potential negative impacts of introduced invertebrate species are also well appreciated, with an estimated annual cost of more than 20k million US$ (Diagne et al., 2021). However, understanding of the contribution of invertebrate species to ecosystem resilience, and their vulnerabilities, remain strongly data-limited (Cardoso, Erwin, Borges, & New, 2011; Cardoso & Leather, 2019; Harvey et al., 2020).
A recent initiative calling for the integration of arthropods within the monitoring of insular forest biodiversity also highlights the potentially prohibitive workload for this, even for a limited subset of arthropod biodiversity (Borges et al., 2018). The broad characterisation of invertebrate communities is a universal challenge, largely caused by logistical constraints associated with both the sorting of large volumes of invertebrate material, and its classification to species. However, addressing these challenges through the application of genome-based sampling and taxonomic assignment is an area of intense activity (e.g. Arribas et al., 2021; Kennedy et al., 2020; Piper et al., 2019), currently only paralleled by recent advances in the application of machine learning for the identification of taxa from image processing (Wührl et al., 2021; Ärje et al., 2020; Valan, Makonyi, Maki, Vondráček, & Ronquist, 2019). Both DNA-based and image-based automated identification have the potential to exponentially accelerate arthropod diversity quantification in the near future (Høye et al., 2021; Wührl, et al., 2021). It is now timely to consider how these developments might be integrated to advance the understanding, management and conservation of insular biotas (Fig. 1, Table 1). Here, we focus on the arthropod fraction of terrestrial invertebrate biodiversity to provide a collective opinion of how, as a community, we might most effectively exploit new technologies and techniques to inventory and monitor insular arthropod biodiversity.