Scaling species richness and endemism of tropical dry forests on oceanic islands

Abstract

Aim We examine variation in woody plant species richness and endemism within tropical dry forest on oceanic islands and determine what climatic and biogeographic metrics best explain native species richness and endemism across archipelagos, islands and plots. Location Oceanic islands in the Pacific. Methods Stand‐level sampling (0.1 ha) at 35 different dry forest sites across 16 islands, and five archipelagos (New Caledonia, Fiji, Marquesas, Marianas and Hawaii). Descriptors of native species richness and endemism were calculated at the plot, island and archipelago level. Biogeographic and climate metrics at the archipelago, island and plot level were drawn from the literature and computer databases. The effects of biogeographic and climate metrics were investigated using linear mixed‐effects models. Results Dry forests of New Caledonia and Fiji had the highest native species richness, while New Caledonia and Hawaii had the highest endemism. Native species richness and endemism within tropical dry forests on oceanic islands are primarily influenced by biogeographic metrics, especially isolation of the archipelago, and not climatic metrics. Most variance in native species richness and endemism (60% and 64%) is at the archipelago level compared with the island (8%, 16%) and plot (32%, 15%) level. At the island level, species richness in tropical dry forest is affected by precipitation, while island area significantly affects endemism. The area of forest fragments is an important predictor of native species richness and endemism in plots. Main conclusions Although dry forests in the Pacific have been exceptionally deforested and degraded, high native species richness and endemism remains in a number of forest fragments. Biogeographic metrics explain most of the variance in native species richness and endemism across scales, while climatic metrics are important at the island level. First‐order assessments of native richness and endemism at the archipelago, island and stand‐level are possible for forest types on oceanic archipelagos.

Eco-geographical factors affecting richness and phylogenetic diversity patterns of high-mountain flora in the Iberian Peninsula

“…Several studies have shown the relationship between species richness and isolation, both in island ecosystems (Gillespie et al 2013;Karger et al 2014) and mountains (Gehrke and Linder 2014;Sklenář et al 2014). In our case, this relationship is only significant for the endemic element, where high species richness is a result of allopatric speciation after immigration, and suggests that the general patterns can change according to different evolutionary histories.…”

Regional forcing explains local species diversity and turnover on tropical islands

“…The number of species living in a small, ecologically homogeneous area (local or alpha diversity, Ricklefs, ) is the product of local (e.g., local climate, competition, topography, resources) and regional (e.g., regional climate, dispersal, species pool) forcing (Harrison & Cornell, ; Lortie et al, ; Ricklefs, ). On islands, regional forcing operating among archipelagos (the archipelago‐scale) or islands within an archipelago (island‐scale) seems important, as it can explain a considerable proportion of the variation in species diversity at these levels (Gillespie et al, ; Keppel, Gillespie, Ormerod, & Fricker, ). Island or archipelago area may influence local diversity through its effect on the regional species pool or gamma diversity (Ricklefs, ; Rosenzweig & Ziv, ), described as the ‘echo pattern’ by Rosenzweig and Ziv ().…”

“…Climate affects both species diversity and composition of vegetation (Bellard, Bertelsmeier, Leadley, Thuiller, & Courchamp, ; Cabral, Weigelt, Kissling, & Kreft, ; Feeley, Hurtado, Saatchi, Silman, & Clark, ) within and among islands (Gillespie et al, ). On islands, the effects of climate on species diversity are presumed to be less pronounced compared to the mainlands because of area and isolation effects (Field et al, ).…”

“…On islands, the effects of climate on species diversity are presumed to be less pronounced compared to the mainlands because of area and isolation effects (Field et al, ). At the local‐ or plot‐scale, climate can have important effects on species diversity (Gillespie et al, ). However, it should have even stronger impacts on taxonomic composition because species tend to retain their ancestral ecological characteristics (i.e., niches), a phenomenon known as niche conservatism (Wiens & Graham, ).…”

Saving rainforests in the South Pacific: challenges in ex situ conservation

“…The influence of these key sources varies among locations and ecosystems, with the Gondwanan influence being more pronounced in south-eastern Australia, New Caledonia and New Zealand, while the Asian influence is more pronounced in New Guinea and the Solomon Islands (Burbidge 1960;Keppel et al 2009;Sniderman and Jordan 2011). The number and variety of species present on a given island has been influenced by the age of the island, its size, the complexity of its habitats, and its proximity to the key source points (Keppel et al 2010;Gillespie et al 2013;Keppel et al 2016).…”