Ryo O. Suzuki

Morphological adaptation of a palatable plant to long-term grazing can shift interactions with an unpalatable plant from facilitative to competitive

Unpalatable plants can protect palatable neighbor plants from grazing pressure, but morphological evolution of a palatable species might change its interactions with unpalatable plants. We predicted that when a palatable species has locally adapted to grazing by expressing a dwarf phenotype that reduces grazer accessibility, the dwarf plants experience relatively more competitive effects than facilitative effects from large, well-defended, unpalatable species. We used a transplant experiment, in which both dwarf and large ecotypes of a palatable annual species, Persicaria longiseta, were transplanted outside and inside the canopy of an unpalatable nettle, Urtica thunbergiana, in a long-term deer grazing habitat of Nara Park, Japan. The dwarf ecotype of Persicaria has adapted to the grazing environments of the park by exhibiting inherently short shoots and small leaves, whereas the large ecotype is found in habitats with no grazing history. A previous common-garden study suggested that the phenotypic differences were genetically based and that phenotypic plasticity contributed little to the morphological difference. The large-phenotype of Persicaria experienced significantly increased morphological size, survival, and reproductive output under the Urtica canopy compared to outside the canopy, whereas these traits of the dwarf phenotype were reduced under the Urtica canopy compared to outside. These results indicate that the net effects of Urtica on Persicaria were positive for the large ecotype and negative for the dwarf ecotype. Thus, the morphological adaptation of a palatable species to avoid grazing altered its interactions with a large, well-defended neighbor.

Geographical Pattern and Environmental Correlates of Regional-Scale General Flowering in Peninsular Malaysia

In South-East Asian dipterocarp forests, many trees synchronize their reproduction at the community level, but irregularly, in a phenomenon known as general flowering (GF). Several proximate cues have been proposed as triggers for the synchronization of Southeast Asian GF, but the debate continues, as many studies have not considered geographical variation in climate and flora. We hypothesized that the spatial pattern of GF forests is explained by previously proposed climatic cues if there are common cues for GF among regions. During the study, GF episodes occurred every year, but the spatial occurrence varied considerably from just a few forests to the whole of Peninsular Malaysia. In 2001, 2002 and 2005, minor and major GF occurred widely throughout Peninsular Malaysia (GF2001, GF2002, and GF2005), and the geographical patterns of GF varied between the episodes. In the three regional-scale GF episodes, most major events occurred in regions where prolonged drought (PD) had been recorded prior, and significant associations between GF scores and PD were found in GF2001 and GF2002. However, the frequency of PD was higher than that of GF throughout the peninsula. In contrast, low temperature (LT) was observed during the study period only before GF2002 and GF2005, but there was no clear spatial relationship between GF and LT in the regional-scale episodes. There was also no evidence that last GF condition influenced the magnitude of GF. Thus, our results suggest that PD would be essential to trigger regional-scale GF in the peninsula, but also that PD does not fully explain the spatial and temporal patterns of GF. The coarse relationships between GF and the proposed climatic cues may be due to the geographical variation in proximate cues for GF, and the climatic and floristic geographical variations should be considered to understand the proximate factors of GF.

Fruiting behavior of dipterocarps in two consecutive episodes of general flowering in a Malaysian lowland rain forest

We examined fruiting behaviors of 24 dipterocarp species in a lowland rain forest of Peninsular Malaysia during two consecutive episodes of general flowering (GF). The first GF episode (GF2001) occurred from August 2001 to February 2002, and the second GF episode (GF2002) followed immediately, from March to September 2002. The magnitude of GF2002 was greater than that of GF2001 at the community level. Significant positive size dependence of fruiting behavior at the community level was found in both GF2001 and GF2002, but there was no significant association between the fruiting behaviors in GF2001 and GF2002 except for one species. These results imply that tree size was one of the explanatory factors for fruiting behavior of dipterocarp species, but there was no evidence that adjacent reproduction caused the absence of reproduction and decreased fecundity in the subsequent fruiting event. In contrast, strong spatial aggregation of fruiting trees was found in GF2001, suggesting that external factors may affect fruiting behavior of dipterocarps in a minor GF episode. Among the 12 study species, there were large variations in fruiting behavior, but growth type (e.g., fast-growing or slow-growing) did not simply explain the inter-specific pattern of fruiting behavior. Thus, tree size may account for fruiting behavior of dipterocarps during the consecutive GF episodes through species-specific differences in phonological responses to internal and external conditions.

Facilitative and competitive effects of a large species with defensive traits on a grazing-adapted, small species in a long-term deer grazing habitat

Plants can adapt to grazing environments by developing defensive traits, such as spines and toxins, or having a small phenotype, such as short and prostrate growth forms. This study examined facilitative and competitive interactions between species with different types of grazing adaptation. We predicted that large species with defensive traits sometimes protect grazing-adapted species without defensive traits from herbivores, but competitively suppress them overall. We conducted an experiment using fences and removals of an unpalatable plant in the long-term deer grazing habitat of Nara Park in Nara, Japan. We evaluated the seasonal variations in the facilitative and competitive effects of a defensive perennial, Urtica thunbergiana, on the growth, survival, reproduction, and final fitness of a small palatable annual species, Persicaria longiseta, during a growing season. The populations of the two species in the park have adapted to the grazed habitat by increasing the density of stinging hairs (Urtica) and developing inherently short shoots and small leaves (Persicaria). We found that Urtica individuals had facilitative effects on the growth of Persicaria individuals under grazing during a few periods of the growing season, but had neutral effects on survival and plant fitness throughout the season. In the fenced plots, Urtica had negative effects on the growth, survival, and reproduction of Persicaria. These results suggest that the relative importance of the facilitative and competitive effects of Urtica on Persicaria fluctuated due to seasonal variations in grazing pressure and vegetative productivity. Although well-defended plants often facilitate less-defended species, we conclude that the facilitative effects of Urtica on Persicaria are limited in a plant community with a long history of intensive grazing.

Seasonal Habitat Partitioning between Sympatric Terrestrial and Semi-Arboreal Japanese Wood Mice, Apodemus speciosus and A. argenteus in Spatially Heterogeneous Environment

Abstract. Habitat partitioning can maintain the coexistence of species with very similar ecological traits. We studied habitat partitioning between terrestrial and semi-arboreal congeneric rodents (Apodemus speciosus and A. argenteus) that often coexist despite asymmetry in their competitive abilities. To understand seasonal and habitat variation in their partitioning, we evaluated seasonal variation in food resources, habitat use, and habitat similarity between the species in a site comprising a mixture of grassland, pine forest, and mixed forest. Food resources were available on the ground in all vegetation types in spring and autumn, but were severe in summer. Apodemus speciosus was observed in all types of vegetation on the ground. In contrast, A. argenteus was observed on the ground and on trees in pine forest, especially areas where the understory is covered by dwarf bamboo. Habitat similarity tests revealed that habitat partitioning between two Apodemus species may vary seasonally, and the relationship depends on habitat structure. This study suggests that the mechanism of habitat partitioning between terrestrial and semi-arboreal rodents in temperate forest is more complex than previously recognized.

Fracture Strength of CuCrZr in High Temperature Environment

ABSTRACT The fracture strength was estimated for copper-alloy CuCrZr, and their HIPed joints with SS316L and CuCrZr, which were the candidate materials consisting of the First Wall of ITER. Fracture toughness and fatigue crack propagation ratio of those materials were superior to those of copper-alloy DS-Cu and its HIPed joint with SS316. It was confirmed that the cracks near the CuCrZr/SS316L HIPed boundary was propagated in copper-alloy along the interface at a distance of about 10μm from the interface. The lost of ductility of all materials caused the decrement of fracture toughness and increment of crack propagation ratio in high temperature (573K).

Warming can enhance the detrimental effect of pathogens on a host plant, Miscanthus sinensis, in a cool-temperate montane grassland in Nagano, Japan

ABSTRACT This study investigated the effects of two fungal pathogens, the smut fungus Sporisorium kusanoi and the discomycete Naemacyclus culmigenus, on the Japanese pampas grass Miscanthus sinensis, under experimental warming. In a cool-temperate grassland in a montane region, a field experiment was conducted with two treatments: 1) warming plots in open-top chambers (OTC); and 2) control plots with ambient temperature. Mean air temperature was 1.1°C higher in OTC than control. The fate, length, number of leaves, and aboveground biomass of uninfected and infected shoots of M. sinensis naturally established within the plots were recorded during the 2014 growing season. Disease symptoms emerged earlier in OTC. Infected shoots were shorter and had fewer leaves in OTC, whereas uninfected shoots were similar between OTC and control. Shoot biomass tended to be higher for uninfected shoots than infected shoots, but similar between OTC and control. Finally, shoot survival tended to be lower in OTC than control, as well as in infected than uninfected shoots. These results indicated that survival and growth of M. sinensis shoots were reduced following pathogen infection and that the detrimental effects of pathogens were more apparent under the warming condition.

Effects of local densities and abiotic microenvironments on reproductive outputs of a biennial, Lysimachia mauritiana var. rubida

To understand the relative importance of density-dependent and density-independent factors on plant fitness, we examined the effects of local densities and surrounding ground surface conditions on the reproductive output of a monocarpic biennial plant, Lysimachia mauritiana var. rubida in a natural population. Observations were conducted during five successive years in open dry habitats on rocky coastal cliffs of the subtropical Bonin (Ogasawara) Islands, Japan. Local density and ground surface conditions, categorized by gravel size, were remarkably heterogeneous in the study population. Therefore, we hypothesized that number of flowers per plant was affected by local density, ground surface condition, and their interaction. During 3 of 5 years, the number of flowers per individual L. mauritiana var. rubida plant was only negatively affected by the local density around the plant. The interaction effects of local density and ground surface conditions were observed in two years. Taken together with the results of previous studies, these results suggest that density effects are dominated survival in the early growing season and reproduction, while the effects of ground conditions are important for seedling recruitment and survival in the late growing season. Thus, interactive effects between density-dependent and density-independent factors on the life cycle from germination to reproduction regulate populations of L. mauritiana var. rubida in spatially heterogeneous habitats.