Islands within islands: a frontier for eco-evolutionary
studies?
The use of simplified subterranean ecosystems as a model allowed us to
disentangle the role of interactions from that of confounding effects,
such as the shift of traits related to ecological successions or
trait-dependent extinction risk that has been described in other types
of island habitats (Karadimou et al. 2018; Gray 2019). Conversely, given
that the subterranean environment through time and across islands
filters for simplified communities bearing a relatively narrow set of
traits, we avoided problems associated with selecting meaningful traits
across a large sample of organisms. However, the main advantage of our
model system is that there is no migration across subterranean habitats
between different islands, warranting that most changes that we observe
in the trait space of each island depends on in-situ processes.
In essence, subterranean habitats in each island are independent and
only linked by the common geological history of the archipelago.
In a sense, including further archipelagos in our analyses would have
increased the number of confounding factors, since different
archipelagos across the world have largely different species pools with
different evolutionary trajectories. Archipelagos consisting of
non-oceanic islands, for example, are expected to follow different
geological evolution generating different age-dependent diversity
patterns (Whittaker et al. 2017). Furthermore, most oceanic archipelagos
in the world are much younger than the Canary Islands and cover a
shorter time span hindering comparability of results (Borregaard et al.
2017). There are few exceptions, such as Cabo Verde and Madeira
(Florencio et al. 2021). However, very fragmentary data exists on the
subterranean animals of Cabo Verde, whereas only non-specialized species
have been found in the Selvagens and Porto Santo, the oldest island in
Madeira (OromÃ, 2004).