What drives plant richness and endemicity in east Asian islands?
Submitted by editor on 21 November 2014.
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The role of climate and geohistorical factors in driving plant richness patterns and endemicity on the East Asian continental islands
Written by: Kubota Yasuhiro (Associate Professor), Shiono Takayuki (Postdoctoral Fellow), Kusumoto Buntarou (Postdoctoral Fellow). All at Faculty of Science, Univ. of Ryukyus, Japan.
Background of this study
The Japanese archipelago represents one of the 34 biodiversity hotspots in the world that are characterized by high endemicity. Therefore, the floras in this region provide ideal conditions to study the relationship between biodiversity patterns and biogeographical processes. Kubota et al. (2014) constructed a fine-resolution map of vascular plant diversity (5614 species) by compiling over 2.5 million occurrence records, and identified the importance of historical constraints in the formation of geographical areas with high species richness and endemicity (see Figures).
Findings of this study
Kubota et al. (2014) identified plant diversity hotspots in Japan. The central regions of the Pacific coast of the archipelago and the Ryukyu archipelago exhibited higher diversity than other areas. Mountainous areas and islands that are geographically isolated also harbored many endemic species. Using this plant diversity map, Kubota et al. (2014) analyzed environmental factors in relation to patterns of plant diversity and tested three hypotheses that could explain the formation of biodiversity hotspots.
Isolation, by distance from the continent or by elevation, plays a role in the spatial heterogeneity of species distributions and endemicity. During the Pliocene and Pleistocene, geographical processes in the Japanese archipelago intermittently divided one large regional biota into insular local communities, with periodic connections reforming through land bridge corridors (see Figures). Kubota et al. (2014) suggest that allopatric speciation, caused by dispersal limitation, was partly responsible for species richness patterns, especially the locations of centers of endemicity.
Historical changes in climate may also influence biotic diversification. Although the Japanese archipelago may not have been glaciated during the recent ice ages, climatic cooling and aridity were intensified at various sites according to their exposure to harsh continental climates. In particular, the severity of ice age environments depends on the connection patterns of land bridges and the path of warm ocean currents flowing into the Japan Sea (see Figures). In this study, Kubota et al. (2014) confirm that plant species richness is significantly correlated with palaeoclimatic oscillations and also suggest that historical temperature stability over geological time scales has contributed to species survival and radiation in refugia habitats in Japan.
Geological habitat stability is also an important factor that affects species diversification through the balance between extinction and speciation. There are more than 200 volcanoes on the Japanese islands, and Quaternary volcanism has generated major pyroclastic flows across the archipelago. Kubota et al. (2014) identified a significant decrease in species richness in areas exposed to pyroclastic flows and suggested that Quaternary volcanic activity had effects, to some extent, on species accumulation and diversification.
Contribution to biodiversity conservation
The findings of this study illustrate that diverse geographical conditions, which are characteristics of the Japanese archipelago, led to the various historical drivers responsible for biodiversity patterns. Because the pattern of modern biodiversity is a product of historical processes, the restoration of plant biodiversity hotspots degraded by anthropogenic impacts will be an overwhelming task, considering the geological time scales involved in the generation of biodiversity hotspots in Japan. This study contributes to accomplishing the Aichi targets adopted in the Convention of Biological Diversity 2010 that tackles biodiversity loss, such as the identification of priority areas for biodiversity conservation.
Read full article here: http://onlinelibrary.wiley.com/doi/10.1111/ecog.00981/abstract