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Aim: One of the main goals of functional biogeography is to examine distribution patterns of trait diversity, and islands provide excellent study cases for this emerging field. We tested the hypothesis that multiple dispersals from a common mainland pool would promote functional similarity among island systems when environmental conditions are similar, but also novel phenotypic traits related to colonization history and exploitation of new habitats. Location: Mediterranean Basin and Macaronesian islands. Taxon: Wolfbane (Periploca laevigata) Methods: We used the well‐known biogeographical history of a woody plant complex (P. laevigata s.l.) to examine trait variation and how it relates to climatic conditions of mainland and subtropical island settings. In a common garden experiment, we measured a suite of leaf physiological and anatomical traits tightly related to plant performance in 320 seedlings representing 21 populations of five sublineages—the oldest (2.6 my) island colonization (western Canary Islands) as a reference, three sublineages stemming from independent events of island colonization in the last 0.5 my from NW Africa (Cape Verde, Fuerteventura, Lanzarote) and their widespread Mediterranean mainland counterpart. Results: We observed strong phenotypic divergence between island and mainland sublineages linked to contrasting climatic conditions. Mediterranean mainland populations displayed a very specialized leaf phenotype characteristic of arid plants (i.e. small leaves, amphistomaty, isobilateral mesophyll, high photosynthetic rates). In turn, low seasonality on islands was linked to the recurrent expression of a phenotype characterized by larger leaves and lower photosynthetic rates. Our analyses showed that the high investment in secondary compounds (i.e. tannins) on islands decouples photosynthesis from growth rates. Despite this pattern of parallel differentiation, each island sublineage displayed a distinctive phenotype, with some traits related to colonization time, which resulted in a mosaic of functional variation across island systems. Main conclusions: Our data suggest that the studied subtropical islands promote expression of traits specific to certain sublineages and other common traits that are no longer adaptive in the original mainland pool due to Pleistocene climatic shifts. These findings ultimately extend the role of islands as biodiversity refugia and hotspots of plant functional diversity. [ABSTRACT FROM AUTHOR]

• Sahelian tree species differ in functional traits reflecting resource use strategies. • They also differed in their responses to different levels of water and nutrients. • Plasticity explained the large geographical distribution of some species in Africa. • Environmental changes will affect plant distribution and community structure. • They will also affect the services tree species provide to human populations. Plants experience a fluctuating environment in time and space that affects resource supply. As human impacts on the environment directly and indirectly alter resource availability, it is important to address plant responses to changing resources to be able to anticipate impacts of these changes on plant communities. We analyzed plant traits to assess responses to resource limitation in four Sahelian tree species of wide ecological and socio-economic importance. We used species already adapted to harsh conditions (high temperatures, low rainfall) to anticipate how climate change could affect their growth patterns and, indirectly, their spatial distribution and the services they provide. Seedlings grew under two levels of water and nutrient additions in a factorial design. Our results showed differences among species, watering regimes, and nutrient supply in three key functional traits related to the plant's resource-use strategy, relative growth rate (RGR), root-to-shoot ratio (R/S), and specific leaf area (SLA). On average, RGR was responsive to the amount of water and nutrients, with species with high RGR showing the largest response to resource supply. RGR in the species with a conservative resource-use strategy (evergreen leaves, lowest RGR) remained unchanged with different levels of water and nutrients. Overall, large RGR was supported by large SLA. All species allocated more biomass to roots than to shoots, particularly under low resource supply, reflecting adaptive strategies to keep RGR leveled to resource supply. Not all species showed similar plasticity in their functional traits responses; however, Acacia tortilis and Faidherbia albida showed the greatest plasticity, which may explain their large geographical distribution range in Africa. Our data suggest that the different Sahelian species will respond differently to future environmental changes, likely affecting their geographical distribution, the structure of plant communities, and the services they provide. [ABSTRACT FROM AUTHOR]