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.