Phytogeography ofLusitanianMacaronesia: biogeographic affinities in species richness and assemblage composition

Abstract

Analysis of biogeographic affinities is a key tool to establish and improve the resolution of hierarchical biogeographic systems. We describe patterns of species richness of the marine macroalgal flora across Lusitanian Macaronesia (Azores, Madeira, the Salvage Islands and the Canary Islands), and test (i) whether such differences are related to differences in proximity to the nearest continental shore and size among islands. We also explore biogeographic affinities in the composition of macroalgal assemblages (¼ presence/absence of each taxon in multivariate datasets) to determine (ii) whether each archipelago is a biogeographic unit within this ecoregion and (iii) whether patterns in assemblage composition are related to proximity (i.e. distances) among islands. Presence/absence matrices were created to test and visualize multivariate affinities among archipelagos. A total of 872 taxa were compiled. Species richness peaked at the Canary Islands and decreased towards the Azores; the pattern matched a progressive increase in distance from the nearest continental shores, matching the classical island biogeography theory. Intra-archipelago differences in species richness were largely related to variations in island size. Biogeographic similarities among archipelagos were hierarchically structured. Madeira and the Salvage Islands constituted one biogeographic unit. Floras from the Azores, Madeira and the Salvage Islands were barely separable from each other, but were different from those at the Canary Islands. Such biogeographic similarities among islands were negatively correlated with the geographical separation (i.e. distances) among them. Proximity to nearby continental shores, in conjunction with large-and meso-scale oceanographic patterns, seems to interact to create patterns in richness and composition of algal assemblages across Lusitanian Macaronesia.

Island biogeography: patterns of marine shallow‐water organisms in the Atlantic Ocean

“…The decrease of seaweed richness with isolation in the Atlantic, as detected in this study, has been found previously at a smaller scale (Tuya & Haroun, ) and is probably because of the relatively lower dispersal capacity of seaweeds (Kinlan & Gaines, ; Kinlan et al ., ). Although isolation explained seaweed richness, it was a poor predictor of fish and gastropod species richness.…”

“…Islands within oceanic archipelagos in the Atlantic show strong connectivity between their reef communities, although these archipelagos are highly isolated from other reef habitats. This results in a peculiar endemism in each archipelago and in a strong affinity of the reef biota between an archipelago's islands, so that each archipelago can be viewed as a biogeographical unit ( Avila, 2000;Floeter et al, 2008;Tuya & Haroun, 2009). Therefore, when focusing on marine shallow-water systems at an ocean-wide biogeographical scale, each of the Atlantic archipelagos can be treated as an island in studies of reef biota island biogeography.…”

“…However, the prevalence of convex-shaped models indicates that niche availability does not increase linearly with area. The variation in seaweed richness with area seems to be highly scale dependent (Tuya & Haroun, 2009). Previous work found no seaweed SAR between archipelagos of the Macaronesian region; however, this pattern was derived from a study on a much more refined scale, between islands within each Macaronesian archipelago (Tuya & Haroun, 2009).…”

“…The few studies on marine island biogeography have presented evidence of the species–area and species–isolation patterns commonly observed in studies on terrestrial organisms (Mora et al ., ; Sandin et al ., ; Tuya & Haroun, ; Parravicini et al ., ). However, to our knowledge, the relationship between species richness and island geological age (the species–age pattern) has not been investigated in marine systems.…”

Ichthyofauna of the Selvagens Islands. Do small coastal areas show high species richness in the northeastern Atlantic?

“…These results are congruent with the colonization of the Macaronesian Islands through a stepping-stone process, as proposed by Santos et al (1995) and Almada et al (2001). Overall, the high affinity between the ichthyofauna of the Macaronesian Islands and the west African coast parallels the biogeographic patterns found with other taxonomic groups (see Morton & Britton 2000;Tuya & Haroun 2009). …”