2. Island community assembly of arthropod biodiversity
Understanding how biological communities form, and why they differ
spatially and temporally, is a key objective in ecology. The integration
of phylogeny into the analysis of community ecology has provided new
dimensions for comparing and contrasting communities, within which
insular environments have proven to be useful sampling frameworks
(Emerson & Gillespie, 2008; Shaw & Gillespie, 2016). Island systems
can yield significant arthropod structuring and turnover over relatively
limited spatial scales and across entire assemblages (e.g.
Salces-Castellano et al., 2021). Such limited spatial dimensions allow
for fine-scale but geographically representative community-level
sampling to characterise the community assembly process. When executed
across multiple islands and coupled with remote sensing data, there is
much potential for an improved understanding of the factors that shape
such patterns (Bush et al., 2017).
Community-scale investigation to describe patterns and infer processes
for island biodiversity requires multiple site-based characterisations
of communities, which is a clear bottleneck in the case of the arthropod
biodiversity. Existing studies in this area have been limited to
specific arthropod lineages, such as beetles or spiders, for which
conventional taxonomical and molecular processing is time-consuming
(e.g. Malumbres‐Olarte et al., 2021; Antonia Salces-Castellano et al.,
2020). HTS barcoding provides an opportunity to increase both the
taxonomic and geographic scale of arthropod community sampling. When
combined with distribution data across gradients (e.g. elevation,
disturbance, island age) or trait data (e.g. dispersal ability, body
size), the opportunities for macroevolutionary and macroecological
unification become tangible. As a proof of concept, Lim et al. (2021)
applied wocDNA metabarcoding to characterise complete arthropod
communities across elevational gradients within the island of Hawaii.
They revealed that climatic niche conservatism is an important factor
shaping ecological assembly across elevation, thus implicating
topographic complexity as an important driver of diversification.
Similarly, wocDNA metabarcoding approaches to characterise soil
arthropod assemblages on the islands of Tenerife and Cyprus have
revealed strong habitat filtering and dispersal limitations as drivers
of community assembly within islands (Andújar et al., 2022; Noguerales
et al., 2022 this issue).
Islands, particularly remote islands, offer much potential for
integrating intraspecific-scale analyses together with phylogenetic
sampling for the investigation of community assembly. Speciation
represents an important contribution to both the origin and evolution of
community structure on remote islands (Shaw & Gillespie, 2016), thus
providing opportunities to link diversification patterns within species
to patterns of speciation at higher levels. Community-level
intraspecific sampling on islands has seen less implementation, and it
is here that HTS barcoding can play an important role. As well as
recording species presence, HTS barcoding provides a measure of
haplotype variation within and across communities, thus addressing the
traditional Darwinian shortfall (defined as the lack of knowledge
regarding the evolution of lineages, species, and traits; Diniz-Filho,
Loyola, Raia, Mooers, & Bini, 2013) for arthropod island faunas. Thus,
alpha and beta diversity can be analysed for hyperdiverse arthropod
communities from genetic to different levels of taxonomic hierarchy to
understand how community-level processes drive macroecological and
macroevolutionary patterns. Processes that can be characterised include
the relative importance of stochasticity, isolation by distance, and
habitat or host-associated differentiation (e.g., see Andújar et al.,
2022; Noguerales et al., 2022; Arribas, Andújar, Salces-Castellano,
Emerson, & Vogler, 2021). Additionally, the extent to which species
diversity and genetic diversity covary can be derived from such data
(Vellend et al., 2014; Vellend, 2010). Overcast, Emerson, & Hickerson,
(2019) have recently described a mechanistic model of community assembly
that can generate linked patterns of abundance and genetic diversity
under an assumption of joint ecological and evolutionary neutrality,
allowing for the estimation of community abundance structure using only
intraspecific genetic variation. As proof of concept, this study
demonstrated that the abundance structure of spiders on the island of
Reunion could be accurately estimated from intraspecific variation from
barcode data (Emerson et al., 2017). Further theoretical developments
will be needed to fully exploit the potential of genetic community-level
data for unifying macroevolution and microevolution, together with
macroecology and microecology, and thus further advance island
biogeography theory (see Overcast et al., 2022, for a review).