Different community assembly of ground beetles and spiders in subalpine forests and alpine scoria deserts of a young volcano, Mt. Fuji

Abstract

While the colonization processes of arthropods in new volcanoes have attracted our attention, the arthropod assembly process in sites where vegetation reaches climax forests after the Holocene catastrophic eruption is unknown. In this study, ground beetles and spiders were investigated using pitfall traps in 12 sites from the subalpine and alpine areas of Mt. Fuji, which were shaped about 2300 years ago and where undisturbed subalpine climax forests and alpine deserts are formed. We examined how elevation, canopy and forest floor vegetation affected turnover and nestedness structure of these assemblages. The alpine desert and subalpine forest comprised different species for both beetles and spiders. The species from the alpine desert seemed to have high dispersal ability. In the subalpine forest, the beetle assemblage found at higher elevations was a subset of those at lower elevations. This nested structure was generated by the expansion of flightless species from montane forests to subalpine forests. Species tolerance to harsh weather conditions may decide the upper elevational limit. The spider assemblage was affected by forest floor vegetation, where species turnover was observed between different floor types. Subalpine spiders included both species expanding from the montane area and those probably colonizing from distant subalpine areas by ballooning. These results suggest that the assembly process differed between alpine and subalpine areas, and also between different taxa particularly in subalpine forests. Examining the genetic relationship between Mt. Fuji populations and possible source populations in other mountains will elucidate the detailed community assembly process in Mt. Fuji.