Michimasa Yamasaki

Temporal and spatial variations in leaf herbivory within a canopy of Fagus crenata

This study investigated spatio-temporal variation in the leaf area consumed by insect herbivores within a canopy of Fagus crenata, with reference to the light conditions of leaf clusters. There was no clear relationship between photosynthetic photon flux density (PPFD) and consumed leaf area (CLA) in May, immediately after leaf flush, but CLA decreased with an increase in PPFD after June. Leaf mass per area, carbon concentration, C/N ratio, concentration of total phenolics, and condensed tannin concentration were higher in leaves under high light intensity than those of leaves under low light. On the other hand, the nitrogen concentration of leaves decreased as light availability increased. Consequently, within-tree variation in light availability affects the consumption of leaves by insect herbivores through temporal changes in leaf characteristics.

Climate oscillation during the Quaternary associated with landscape heterogeneity promoted allopatric lineage divergence of a temperate tree Kalopanax septemlobus (Araliaceae) in East Asia

We investigated the biogeographic history of Kalopanax septemlobus, one of the most widespread temperate tree species in East Asia, using a combined phylogeographic and palaeodistribution modelling approach. Range‐wide genetic differentiation at nuclear microsatellites (G′ST = 0.709; 2205 samples genotyped at five loci) and chloroplast DNA (GST = 0.697; 576 samples sequenced for 2055 bp at three fragments) was high. A major phylogeographic break in Central China corresponded with those of other temperate species and the spatial delineation of the two temperate forest subkingdoms of East Asia, consistent with the forests having been isolated within both East and West China for multiple glacial–interglacial cycles. Evidence for multiple glacial refugia was found in most of its current range in China, South Japan and the southernmost part of the Korean Peninsula. In contrast, lineage admixture and absence of private alleles and haplotypes in Hokkaido and the northern Korean Peninsula support a postglacial origin of northernmost populations. Although palaeodistribution modelling predicted suitable climate across a land‐bridge extending from South Japan to East China during the Last Glacial Maximum, the genetic differentiation of regional populations indicated a limited role of the exposed sea floor as a dispersal corridor at that time. Overall, this study provides evidence that differential impacts of Quaternary climate oscillation associated with landscape heterogeneity have shaped the genetic structure of a wide‐ranging temperate tree in East Asia.

How did the exposed seafloor function in postglacial northward range expansion of Kalopanax septemlobus? Evidence from ecological niche modelling

We attempted to clarify how coastal lands temporarily exposed during the last glacial maximum (LGM) contributed to the northward colonisation of Kalopanax septemlobus (Thunb. ex Murray) Koidzumi during the postglacial period in the Japanese Archipelago. Distribution records in 30-arc-s pixels were related to bioclimate variables using the maximum entropy technique to model the ecological niche of this species. Bioclimatic conditions in the exposed coastal lands during the LGM were reconstructed based on simulated palaeoclimate and fine-resolution marine topography. Potential distribution ranges were then estimated under the climatic conditions during the LGM, mid-Holocene and the present. The ecological niche of this species was influenced mainly by the temperature component of the bioclimates, leading to northward range shift after the LGM as the climate warmed. On average, 26% of the potential range of K. septemlobus during the LGM was located on the exposed seafloor. The northern edges of the species range on both sides of Honshu Island were estimated by up to several hundred kilometres farther north, when compared to the prediction assuming no sea level change. Application of ecological niche modelling provided new insight into the role of exposed seafloor as cryptic glacial refugia for this species, which has never been evidenced by fossil records. In a temperate island system characterised by long coastlines, the northern exposed seafloor would have been more important in terms of harbouring the putative source populations for northward directional colonisation during the postglacial period.

Effect of fungus inoculation on the number of Bursaphelenchus xylophilus (Nematoda: Aphelenchoididae) carried by Monochamus alternatus (Coleoptera: Cerambycidae)

Blue-stain fungi were mainly isolated from the wood of pine wilt-killed Pinus densiflora. Intense blue-stain on the pupal chamber walls of the Japanese pine sawyer (Monochamus alternatus) increased the number of pinewood nematodes (Bursaphelenchus xylophilus) aggregating around such chambers and the number carried by the beetles that emerged from the chambers. There were differences in the numbers of nematodes carried by beetles among individual trees from which the beetles emerged. The beetles emerging from dry chambers carried relatively few nematodes.

An exotic herbivorous insect drives the evolution of resistance in the exotic perennial herb Solidago altissima

Invasive plants often experience rapid changes in biological interactions by escaping from their original herbivores at their new habitats, and sometimes re-associating with those herbivores afterwards. However, little is known about whether the temporal changes in herbivorous impact work as a selective agent for defensive traits of invaded plants. Solidago altissima (goldenrod) is a North American perennial that has widely invaded abandoned fields in Japan. Recently, an herbivorous insect Corythucha marmorata (lace bug), an exotic insect also from North America, which was first recorded in 2000 in Japan, has been expanding its habitat on S. altissima populations in Japan. In this study, we investigated whether the invasion of C. marmorata had a selective impact on the defensive traits of S. altissima, by conducting a field survey, a common garden experiment and microsatellite analysis. We compared quantitative genetic differentiation of traits (resistance, growth, and reproduction) and neutral molecular ...

Effects of water management, connectivity, and surrounding land use on habitat use by frogs in rice paddies in Japan.

In Japan, rice paddies play an important role as a substitute habitat for wetland species, and support rich indigenous ecosystems. However, since the 1950s, agricultural modernization has altered the rice paddy environment, and many previously common species are now endangered. It is urgently necessary to evaluate rice paddies as habitats for conservation. Among the species living in rice paddies, frogs are representative and are good indicator species, so we focused on frog species and analyzed the influence of environmental factors on their habitat use. We found four frog species and one subspecies (Hyla japonica, Pelophylax nigromaculatus, Glandirana rugosa, Lithobates catesbeianus, and Pelophylax porosa brevipoda) at our study sites in Shiga prefecture. For all but L. catesbeianus, we analyzed the influence of environmental factors related to rice paddy structure, water management and availability, agrochemical use, connectivity, and land use on breeding and non-breeding habitat use. We constructed generalized additive mixed models with survey date as the smooth term and applied Akaikes information criterion to choose the bestranked model. Because life histories and biological characteristics vary among species, the factors affecting habitat use by frogs are also expected to differ by species. We found that both breeding and non-breeding habitat uses of each studied species were influenced by different combinations of environmental factors and that in most cases, habitat use showed seasonality. For frog conservation in rice paddies, we need to choose favorable rice paddy in relation to surrounding land use and apply suitable management for target species.

Does community‐level floral abundance affect the pollination success of a rewardless orchid, Calanthe reflexa Maxim.?

Decreases in pollinator abundance may particularly constrain plants that lack floral rewards, since they are poor competitors for pollinators in the plant community. Here, we documented the pollination ecology of a rewardless orchid, Calanthe reflexa Maxim., and examined effects of forest understory degradation by deer browsing on pollination success of the species in the light of a change in the abundance of neighboring flowering plants in 2010 and 2011. Bombus species were the only pollinators at each site and the flowering phenology of C. reflexa did not overlap with that of other rewarding plants. Pollinator visit rates (assessed by time-lapse photography), and pollinia removal rate were higher in the undegraded understory site than the degraded site in both years, while the fruit set ratio did not differ between the sites in 2011. Coverage by neighboring flowering plants was extremely low in the degraded site. Our results suggest that, although its flowering phenology and consequently lower interspecific competition of C. reflexa with rewarding plants for attracting bumblebees, neighboring flowering plants may play an important role for maintaining the visitation frequency of bumblebees of C. reflexa and contribute to its pollination success.

Ambrosia beetles (Curculionidae: Scolytinae and Platypodinae) on Fagus crenata Blume: community structure, seasonal population trends and resource utilization patterns

Ambrosia beetles (many Scolytinae and all Platypodinae) are one of the most important insect pests for forestry worldwide, but little is known about the community structure of ambrosia beetles in terms of their vertical variations and resource utilization. We clarified the community structure and seasonal population trends of ambrosia beetles on 11 living and three newly dead Fagus crenata Blume trees using individual tube traps placed up to 10 m high from May to November in 2007 and 2008. We captured seven scolytine species (Ambrosiodmus lewisi (Blandford), Euwallacea validus (Eichhoff), Trypodendron proximum (Niisima), Xyleborinus saxeseni (Ratzeburg), Xyleborus atratus Eichhoff, Xylosandrus brevis (Eichhoff) and Xylosandrus germanus (Blandford)) and three platypodine species (Crossotarsus niponicus Blandford, Platypus hamatus Blandford and Platypus severini Blandford). The ambrosia beetles were suggested to breed at species‐specific height ranges, with the equal host resource use per individual among the species. Of the three major species, C. niponicus, P. hamatus and P. severini, two (C. niponicus and P. hamatus) had male‐biased sex ratios, which is considered a reproductive strategy to increase maternal fitness. Morphological characteristics of the mandibles may play an important role in the difference of sex roles on reproduction in the three major species.

A low Platypus quercivorus hole density does not necessarily indicate a small flying population

The ambrosia beetle Platypus quercivorus causes mass mortality of Fagaceae trees in Japan, and tree species differ in their susceptibility to P. quercivorus. We hypothesized that interspecific differences in susceptibility are caused by differences in beetle infestation patterns, that is, how many beetles fly to a tree and how many of those arriving bore holes. To examine how tree susceptibility is related to these parameters, two tree species with different degrees of susceptibility were studied (highly susceptible Quercus crispula and less susceptible Q. salicina). Specifically, we measured the number of male beetles per unit area that flew to the host trees (NFM) and the density of holes bored by male beetles (DH). From these two values, we calculated the proportion of male beetles flying to a host tree that bored holes (PBM). These parameters were compared for the two Quercus species. Although the two species did not differ in NFM in 2003, PBM was markedly lower for Q. salicina than for Q. crispula and DH was significantly lower for Q. salicina than for Q. crispula. Thus, the lower susceptibility of Q. salicina is partly explained by its low PBM.

Urban landscape and forest vegetation regulate the range expansion of an exotic lace bug Corythucha marmorata (Hemiptera: Tingidae)

Landscapes and vegetation are critical factors in dispersion of exotic insects and expansion of their range. However, few studies have addressed how the surrounding landscape affects the establishment of exotic insects. We assessed the relationship between establishment of an exotic lace bug Corythucha marmorata (Uhler) and the surrounding landscape in the northern edge of the lace bugs expanded range. We found that the lace bugs showed variability in their density among populations. Urban areas had a positive effect, while the natural forest vegetation had a negative effect on lace bug density, with a buffer range of 1–2 km. Moreover, their abundance decreased with distance from the source population. Our results suggest that natural forest landscapes in urban areas may inhibit the range expansion of invasive insects that feed on exotic plants growing in human‐disturbed habitats.