Ground-dwelling beetle community in beech forests of Sado Island, Japan: comparison with the mainland

Abstract

Island ecosystems differ from mainland ecosystems in their long-term isolation. On Sado Island, Japan, cattle grazing in the past gradually changed forests into grasslands, thereby altering the diversity of indigenous insects. We compared ground-dwelling beetle diversity on Sado Island to that on the nearby mainland. Contrary to previous reports, the island isolation effect resulted in lower c and b diversity than on the mainland, because of the low species richness of beetles with low dispersal abilities. Few flightless beetles could invade Sado Island, even when the beech forests on the island were relatively adjacent to those on the mainland. Such a history of ecosystem formation could be the general pattern for continental-island mountain forests that were never connected to those of the mainland. We did not observe low a diversity of ground-dwelling beetles, suggesting that the cattle grazing history of the island has not changed environmental conditions for ground-dwelling beetles enough to reduce their diversity. In addition, cattle grazing increases the abundance of merdivorous insects by increasing the abundance of their food resource.

Macroscale evolutionary patterns of flight muscle dimorphism in the carrion beetle Necrophila japonica

“…Both flight-capable and flightless (i.e., lacking flight muscles) individuals occurred in most parts of the distribution area and in all clades of COI-II haplotypes. Thus, flight dimorphisms in N. japonica , which are likely maintained by inhabiting various habitats ranging from unstable river banks to relatively stable forests ( Nagano and Suzuki 2003 ; Ikeda et al 2008a , 2010 ; Shibuya et al 2008 ), might enable rapid colonization of peripheral territories.…”

“…We were not able to determine the flight muscle status of larvae and some adult beetles of which tissues were rotten due to poor fixation. Samples examined by Ikeda et al (2007 , 2008b) were also included in the analyses. To examine differences in the proportion of beetles with flight muscles between sexes, we conducted a Fisher's exact test using R 2.11.1 ( R Development Core Team 2010 ).…”

“…We have not found any seasonal change in the proportion of the individuals with flight muscles in N. japonica (H. Ikeda unpubl. data), and individuals with flight muscles lay many eggs ( Ikeda et al 2008 ). Thus, histolysis of flight muscles is not likely to occur in this species.…”

“…Thus, histolysis of flight muscles is not likely to occur in this species. N. japonica inhabits various types of habitats ranging from disturbed riparian zones to relatively stable forests and is often numerically dominant in the ground invertebrate community ( Nagano and Suzuki 2003 ; Ikeda et al 2008a , 2010 ; Shibuya et al 2008 ). Flight muscle type does not correlate with diet or reproductive investment ( Ikeda et al 2007 , 2008b ).…”

“…N. japonica inhabits various types of habitats ranging from disturbed riparian zones to relatively stable forests and is often numerically dominant in the ground invertebrate community ( Nagano and Suzuki 2003 ; Ikeda et al 2008a , 2010 ; Shibuya et al 2008 ). Flight muscle type does not correlate with diet or reproductive investment ( Ikeda et al 2007 , 2008b ). Therefore, we have not found any clear relationship of the flight muscle dimorphism with divergent ecological niches or the trade-off between dispersal and reproduction.…”