Does island ontogeny dictate the accumulation of both species richness and functional diversity?

Aim The accumulation of functional diversity in communities is poorly understood. Conveniently, the general dynamic model of island biogeography (GDM) makes predictions for how such diversity might accumulate over time. In this multiscale study of land snail communities on 10 oceanic archipelagos located in various regions of the globe, we test hypotheses of community assembly in systems where islands serve as chronosequences along island ontogeny. Location Ten volcanic archipelagos. Time period From 23 Ma to the present. Major taxa studied Endemic land snails. Methods Initially, we assembled geological island characteristics of area, isolation and ontogeny for all studied islands. We then characterized island-scale biotic variables, including the species diversity and functional diversity of snail communities. From these data, we assessed relationships between island and snail community variables as predicted by the GDM, focusing initially on the islands of the Galapagos archipelago and thereafter with a broader analysis of 10 archipelagoes. Results As in other studies of island assemblages, in Galapagos we find a hump-shaped curve of species richness, with depauperate snail faunas on early-ontogeny islands, increasing species richness on mid-ontogeny islands and low species richness on islands in late ontogeny. We find exceptionally low functional diversity on early-ontogeny islands that increases through mid-ontogeny, whereas late-ontogeny islands exhibit a range of functional diversity. The analysis including all 10 archipelagos indicates a major role of archipelago-specific factors. In both sets of analyses, functional diversity is exceptionally low on early-ontogeny islands, and island ontogeny is a significant predictor of morphology. Main conclusions Consistent patterns of functional diversity across island ontogeny on all examined archipelagos indicate a common role for habitat filtering, ecological opportunity and competition in a diversity of systems, leading to predictable changes in functional diversity and average morphology through island ontogeny, whereas patterns of species richness appear subject to archipelago-specific factors.

Automated summary

The accumulation of functional diversity in communities is investigated in a multiscale study of land snail communities on 10 oceanic archipelagos. Consistent patterns of functional diversity across island ontogeny on all examined archipelagos indicate a common role for habitat filtering, ecological opportunity, and competition in diverse systems, leading to predictable changes in functional diversity and average morphology through island ontogeny.