Biogeographic drivers of community assembly on oceanic islands: The importance of archipelago structure and history

Abstract

Aim Accounting for geo‐environmental dynamics is crucial to understand community assembly across islands. Whittaker et al. (J Biogeogr, 35:977–994, 2008)’s General Dynamic Model (GDM) aims towards this goal. Yet, it does not explicitly consider that most islands belong to archipelagos. We examined how island biodiversity dynamics are influenced by the interaction of eco‐evolutionary processes acting at the archipelago level with each island's geo‐environmental dynamics. Location Hypothetical archipelagos. Taxon Any. Methods We used an individual‐based model, ecologically neutral within the archipelago. Several islands emerge in succession with a typical volcanic ontogeny. We considered both mainland and inter‐island dispersal. Geographically isolated lineages diverged over time, possibly speciating. Results We found diversity to be at dynamic equilibrium. In an archipelago, islands hosted more diversity and more endemic species, at both island and archipelago levels, than an equivalently‐sized single isolated island. This was due to an ‘archipelago effect’: inter‐island dispersal increased within‐island diversity through species occurrence on multiple islands; species may undergo anagenetic changes on the colonised islands, eventually speciating, thereby increasing archipelago diversity. Biodiversity dynamics of different islands may differ even on islands with identical geo‐environmental dynamics because the archipelago effect varied over time and affected each island differently (‘history effect’). By accounting for these effects, we predicted detectable deviations from the GDM predictions, which are largest for remote archipelagos, with islands located close together and with an intermediate time of island emergence. In linear stepping‐stone archipelagos, we predicted higher diversity on centrally located islands. Main conclusions Our results demonstrate that analyses of insular biodiversity data would greatly benefit from explicitly accounting for both archipelago and history effects. We suggest incorporating variables characterising the spatio‐temporal structure of the whole archipelago. We discuss possible difficulties in distinguishing between the archipelago effect and equilibrium diversity dynamics.

The robustness of a simple dynamic model of island biodiversity to geological and sea‐level change

“…The island ontogeny with sea‐level changes within this study resembles the histories of such archipelagos, and by extension indicates the reliability of DAISIE's previous findings on dynamic oceanic systems. The simulations to test geodynamics do not account for the fact that islands within an archipelago may have been connected and disconnected (Aguilée et al, 2021). However, under the assumption that the archipelago operates as a single island (Valente et al, 2015; Valente, Illera, et al, 2017) the change in area through time can mimic archipelago dynamics.…”

“…and disconnected (Aguilée et al, 2021). However, under the assumption that the archipelago operates as a single island (Valente et al, 2015;Valente, Illera, et al, 2017) the change in area through time can mimic archipelago dynamics.…”

Intermediate dispersal hypothesis of species diversity: New insights

“…The general dynamic model of oceanic island biogeography (GDM) has added a new perspective to island biogeography, allowing us to recognize that geological processes are essential factors of species diversification and extinction within archipelagic systems (Borregaard et al, 2017). The GDM provides a dynamic and non‐equilibrium framework that generates previously undiscovered predictions of biodiversity in oceanic islands (Aguilée et al, 2021). Depending on the relative speed of evolutionary and tectonic dynamics, speciation and extinction are not balanced, and species accumulation may not be at equilibrium.…”

From bone palaeohistology to insularity: the palaeobiological archive as a witness to insular evolution

“…Le nanisme de ces sauropodes n'a jamais été égalé en valeurs absolues par aucun autre groupe insulaire qui a suivi leurs pas. Ce processus évolutif singulier a été particulièrement soutenu par les hauts niveaux marins du Crétacé supérieur (100-66 Ma) jusqu'à 120 mètres plus haut que l'actuel, isolant les populations locales au sein de l'archipel européen, configuration plus qu'idéale pour l'évolution insulaire (Aguilée et al, 2021). Ce n'est pas pour rien que l'archipel européen a été le témoin d'émergence de nouvelles espèces plutôt originales (Csiki et al, 2010 ;Csiki-Sava et al, 2018) ainsi que d'autres géants et nains insulaires (e.g., Buffetaut et al, 2002 ;Benton et al, 2010 ;Chiarrenza et al, 2021).…”