Assembly of functional diversity in an oceanic island flora

Abstract

Oceanic island floras are well-known for their morphological peculiarities and exhibit striking examples of trait evolution1,2. These morphological shifts are commonly attributed to insularity and thought to be shaped by biogeographical processes and evolutionary histories of oceanic islands1,3. However, the mechanisms through which biogeography and evolution have shaped the distribution and diversity of plant functional traits remain unclear. Here, we describe the functional trait space of an oceanic island flora (Tenerife, Canary Islands, Spain) using extensive field and laboratory measurements, and relate it to global trade-offs in ecological strategies. We find that the island trait space is concentrated around a functional hotspot dominated by shrubs with a conservative life-history strategy. By dividing the island flora into species groups with distinct biogeographical distributions and diversification histories, our results reveal that long-distance dispersal, and the interplay between inter-island dispersal and archipelago-level speciation processes drive functional divergence and expand trait space. Conversely, speciation via cladogenesis has overall led to functional convergence, densely packing trait space around shrubbiness. Our approach combines ecology, biogeography and evolution and opens avenues for new trait-based insights into how dispersal and speciation shape the assembly of native island floras.