bluuebunny/crossref_metadata_2025 huggingface dataset:
Measurement of the intracellular pH threshold for sperm aster formation in sea urchin eggs
Authors: Hamaguchi Miyako S. , Hamaguchi Yukihisa
Published: March 2003

In the fertilization of sea urchin eggs, intracellular [Ca2+] (Cai) increases transiently and intracellular pH (pHi) elevates accordingly. Unlinking these two activating factors experimentally, the requirement of the increase in pHi for sperm aster formation in the sea urchin, Clypeaster japonicus, was investigated. When the eggs were injected with an EGTA or BAPTA solution, they incorporated sperm but did not organize the sperm aster. Using these sperm‐incorporated eggs under the condition that an increase in Cai was blocked, pHi was regulated by two methods: (i) perfusing ammonium acetate‐containing seawater; and (ii) injecting pH buffer solutions of various pH values. By either of the two methods, the sperm aster formed at pHi 7.0 or more and functioned in female pronuclear migration when the sperm aster reached the female pronucleus. Hence, the step of the transient increase in Cai at fertilization can be bypassed. In contrast, a pHi increase is indispensably required for sperm aster formation in sea urchin eggs. Moreover, under the condition that there was the transient increase in Cai, the threshold pHi value for sperm aster formation was pHi 7.0 or more. Consequently, whether a Cai increase on fertilization occurs or not, the threshold pHi value for sperm aster formation is constant in sea urchin eggs.
Developmental fates of the first four blastomeres of the chaetognath Paraspadella gotoi: Relationship to protostomes
Authors: Shimotori Taishin , Goto Taichiro
Published: March 2003

Experimental analysis of the development of chaetognaths is virtually lacking. To elucidate developmental fates, single blastomeres of the 2‐cell and 4‐cell embryos of Paraspadella gotoi were injected with a lineage‐tracing dye (Fluoro‐Ruby or DiI). The distribution of the labels was observed in the hatchlings. In a previous study, embryos were injected at the 2‐cell stage with Fluoro‐Ruby and two sets of complementary labeling patterns (DL and VR, and DR and VL) were found. The same results were obtained when DiI was used as a tracer dye. The 4‐cell embryo consists of the animal and vegetal cross‐furrow cells in a tetrahedral arrangement and one of the vegetal cross‐furrow cells typically contains the germ plasm. When single cells were injected at the 4‐cell stage, four labeling patterns were observed (D, V, L and R). These four patterns represent subsets of the four patterns observed in the hatchling injected at the 2‐cell stage. The V pattern is probably generated from the blastomere containing the germ plasm. It was found that the positions of the blastomeres at the 4‐cell stage corresponded to the future body axes, similar to classic spiralians and modified spiralians such as crustaceans. Furthermore, it was confirmed that second cleavage occurs in a leiotropic fashion, which is seen in the second cleavage of the classic spiralians. Chaetognaths may have some similarities to protostomes in their developmental program.
βFTZ‐F1 dependent and independent activation of Edg78E, a pupal cuticle gene, during the early metamorphic period in Drosophila melanogaster
Authors: Kawasaki Haruhisa , Hirose Susumu , Ueda Hitoshi
Published: March 2003

Insect metamorphosis is a developmentally important event for formation of adult structures from larval imaginal cells, and it is controlled by the ecdysteroid hormone. At the onset of metamorphosis, both the cuticle gene Edg78E and the transcription factor βFTZ‐F1 are expressed during the mid‐ to late prepupal period after a large ecdysteroid pulse. Edg78E mRNA is inducible by premature expression of βFTZ‐F1 and the Edg78E expression level is reduced in an ftz‐f1 mutant. Using a transgenic fly reporter assay, a 1.2 kb promoter region of the Edg78E gene has been identified, which was sufficient for appropriate temporally and spatially specific expression of the reporter gene LacZ. Within the promoter region, two βFTZ‐F1 binding sites are present and disruption of these sites reduced the expression level of the reporter gene. LacZ expression levels were dramatically reduced in the head and thorax regions but not affected in the abdominal region, suggesting that βFTZ‐F1 is required for high‐level Edg78E expression specifically in the head and thorax regions. The findings suggest that βFTZ‐F1 is a regulator for temporal gene expression at the onset of metamorphosis, and that complex mechanisms regulate the temporal and spatial regulation of gene expression during metamorphosis.
Localization of γ‐tubulin and cyclin B during early cleavage in physiologically polyspermic newt eggs
Authors: Iwao Yasuhiro , Murakawa Tomomi , Yamaguchi Junko , Yamashita Masakane
Published: March 2003

To understand the mechanism of the very slow block to polyspermy in physiologically polyspermic eggs of the newt Cynops pyrrhogaster, we used confocal laser microscopy to determine the distribution of γ‐tubulin and cyclin B1 in fertilized eggs. More γ‐tubulin was localized in the animal hemisphere than in the vegetal. The centrosomes of the principal sperm nucleus and the zygote nucleus had much accumulated γ‐tubulin, but little γ‐tubulin was associated with the centrosomes of the accessory sperm nuclei. These results are consistent with observations that the largest sperm aster is associated with the principal sperm nucleus. More cyclin B1 appeared in the animal hemisphere than in the vegetal at the end of interphase. The zygote nucleus had much accumulated cyclin B1, but little cyclin B1 was associated with the accessory sperm nuclei. Cyclin B1 disappeared earlier around the zygote nucleus at metaphase than around the accessory sperm nuclei. These findings correspond well with the earlier entry and exit into metaphase in the zygote nucleus than in the accessory sperm nuclei in newt eggs, supporting our maturation‐promoting factor (MPF) model that accounts for the mechanism of nuclear degeneration in physiologically polyspermic eggs. Cyclin B1 began to accumulate in the nucleus during interphase in synchronous cleavage, and its greatest expression was in the centrosomes and the nucleus at prometaphase.
Knockdown of connexin43‐mediated regulation of the zone of polarizing activity in the developing chick limb leads to digit truncation
Authors: Law Lee Yong , Lin Jun Sheng , Becker David L. , Green Colin R.
Published: March 2003

In the developing chick wing, the use of antisense oligodeoxynucleotides to transiently knock down the expression of the gap junction protein, connexin43 (Cx43), results in limb patterning defects, including deletion of the anterior digits. To understand more about how such defects arise, the effects of transient Cx43 knockdown on the expression patterns of several genes known to play pivotal roles in limb formation were examined. Sonic hedgehog (Shh), which is normally expressed in the zone of polarizing activity (ZPA) and is required to maintain both the ZPA and the apical ectodermal ridge (AER), was found to be downregulated in treated limbs within 30 h. Bone morphogenetic protein‐2 (Bmp‐2), a gene downstream of Shh, was similarly downregulated. Fibroblast growth factor‐8 expression, however, was unaltered 30 h after treatment but was greatly reduced at 48 h post‐treatment, when the AER begins to regress. Expressions of Bmp‐4 and Muscle segment homeobox‐like gene (Msx‐1) were not affected at any of the time points examined. Cx43 expression is therefore involved in some, but not all patterning cascades, and appears to play a role in the regulation of ZPA activity.
Effects of outbreak of the train millipedeParafontaria laminata armigeraVerhoeff (Diplopoda: Xystodesmidae) on litter decomposition in a natural beech forest in Central Japan. 1. Density and biomass of soil invertebrates
Authors: Niijima Keiko
Published: March 2003

Soil invertebrates were studied to determine the animals important in litter decomposition and soil formation in a natural forest ofFagus crenataBlume mixed withQuercus mongolicavar.grosseserrataREHD. et WILS., where outbreak of the adult train millipede,Parafontaria laminata armigeraVERHOEFFwas recorded in 1980. The density and biomass of soil invertebrates, and their distribution in soil, were surveyed largely by hand sorting and also using Tullgren and Baermann apparatuses. The densities of soil macroinvertebrates were 102–103individuals/m2. Diplopoda was the most abundant among them, 87.3% of which was the train millipede. The total biomass in wet weight of soil macro‐invertebrates was 34.9–70.5 g/m2in 1980–1981, when the millipede was pre‐adult or adult, and it decreased to 3.5–6.7 g/m2in 1982–1984, when it was young. The density of soil invertebrates extracted by apparatuses was 104–106individuals/m2. The total biomass of these was estimated to be 5.8–10.8 g/m2. The majority of soil invertebrates lived in the A0horizon, whereas the train millipede lived in soil of the A1 + A2horizon. These results suggest that the train millipede is one of the most important soil invertebrates affecting soil properties. For evaluating the importance of the species, more than 8 years' survey of hand‐sorting together with the Tullgren apparatus was necessary, as the train millipede grew synchronously and had an 8‐year life span and young stages of 1.5–3.5 mm long.
Study of changes in life zone distribution in north‐east China by climate–vegetation classification
Authors: Liu Qi‐Jing , Kondoh Akihiko , Takeuchi Nobuo
Published: March 2003

Life zones and their changes in distribution in north‐east China were studied based on climate–vegetation relationships. The warmth index (WI) and aridity index (the ratio of evaporation [evaporation rate, ER] to precipitation) were used to represent the site condition. The typical site condition of each vegetation type was determined as the classification criterion. The boundaries of the four potential vegetation zones were estimated based on the combinations of WI and ER in relation to vegetation (i.e. cold‐temperate conifer forest zone, temperate broad‐leaved conifer mixed forest zone, warm‐temperate deciduous forest zone, and temperate steppe zone). The distribution changes in vegetation zone caused by human activities were estimated by comparing the potential vegetation with the actual one. The percentage cover of forest has shrunk from about 70% to the present 27%. About 23% of the study area was replaced by agricultural vegetation and industrial use. Nearly half of the region could have been covered by broad‐leaved conifer mixed forest which was shrunk to a small area, less than 5% of the region. The broad‐leaved deciduous forest zone in the southern part could have occupied about 7% of the area, and had almost no virgin stand.
Diurnal changes in leaf gas exchange and chlorophyll fluorescence in tropical tree species with contrasting light requirements
Authors: Ishida Atsushi , Nakano Takashi , Matsumoto Yoosuke , Sakoda Mutsumi , Ang Lai Hoe
Published: March 2003

Interspecific ecophysiological differences in response to different light environments are important to consider in regeneration behavior and forest dynamics. The diurnal changes in leaf gas exchange and chlorophyll fluorescence of two dipterocarps, Shorea leprosula (a high light‐requiring) and Neobalanocarpus heimii (a low light‐requiring), and a pioneer tree species (Macaranga gigantea) growing in open and gap sites were examined. In the open site, the maximum net photosynthetic rate (Pn), photosystem II (PSII) quantum yield (Δ; F/Fm′), and relative electron transport rate (r‐ETR) through PSII at a given photosynthetic photon flux density (PPFD) was higher in S. leprosula and M. gigantea than in N. heimii, while non‐photochemical quenching (NPQ) at a given PPFD was higher in N. heimii. The maximum values of net photosynthetic rate (Pn) in M. gigantea and S. leprosula was higher in the open site (8–11 μmol m−2 s−1) than in the gap site (5 μmol m−2 s−1), whereas that in N. heimii was lower in the open site (2 μmol m−2 s−1) than in the gap site (4 μmol m−2 s−1), indicating that N. heimii was less favorable to the open site. These data provide evidence to support the hypothesis that ecophysiological characteristics link with plant’s regeneration behavior and successional status. Although Pn and stomatal conductance decreased at midday in M. gigantea and S. leprosula in the open site, both r‐ETR and leaf temperature remained unchanged. This indicates that stomatal closure rather than reduced photochemical capacity limited Pn in the daytime. Conversely, there was reduced r‐ETR under high PPFD conditions in N. heimii in the open site, indicating reduced photochemical capacity. In the gap site, Pn increased in all leaves in the morning before exposure to direct sunlight, suggesting a relatively high use of diffuse light in the morning.
Intrapopulation variation in carbon and nitrogen stable isotope ratios in the earthwormAporrectodea longa
Authors: Schmidt Olaf
Published: March 2003

The natural abundance variations in carbon and nitrogen stable isotope ratios in a population of the earthwormAporrectodea longa, a species known to feed on both soil and plant litter, is reported in this paper. Worms were collected from a small land area of an old white clover field and body tissue and mucus were analyzed separately. The range of isotopic values was small, but patterns of variation were not random. Tissue carbon and nitrogen isotope ratios were significantly higher in adult than in juvenileA. longaand tissue nitrogen isotope ratios tended to increase with increasing biomass of individuals. Further, carbon and nitrogen isotope ratios were positively correlated in both tissue and mucus. Possible causes of the observed patterns, including physiological effects, body composition and assimilation of C and N from different plant, soil and microbial sources are discussed. It is concluded that the causes of natural variability in isotopic composition must be understood and validated experimentally before natural abundance stable isotope methods can be used for the analysis of trophic relations among detritivorous soil invertebrates.
Density effect, self‐thinning and size distribution in Pinus densiflora Sieb. et Zucc. stands
Authors: XUE LI , HAGIHARA AKIO
Published: March 2003

The competition‐density (C‐D) effect for given times and self‐thinning over time in even‐aged, natural, pure stands of Pinus densiflora Sieb. et Zucc. were analyzed with the reciprocal equation of the C‐D effect in self‐thinning stands, and the equation describing the time‐trajectory of mean stem volume and stand density. The C‐D effect and self‐thinning were consistently well explained by the two equations. Differences in mean stem volume and in stand density among the stands tended to merge with increasing stand age. The self‐thinning line with a slope of approximately –3/2 was reached by the higher density stand prior to the medium and lower density stands. The skewness of tree height distribution showed positive values, which means that the distribution is more or less L‐shaped, and in addition the skewness decreased with increasing mean tree height, which indicates that smaller trees died as the stands grew. This trend is consistent with the asymmetric (one‐sided) competition hypothesis that self‐thinning is driven by competition for light. The tree height distribution was analyzed using the Weibull distribution. The location parameter hmin of the Weibull distribution increased with increasing stand age, and the scale parameter a tended to increase slightly with increasing stand age. The range of the shape parameter b of the Weibull distribution corresponded to that of the skewness.
Feeding rates and energy deficits of juvenile and adult Japanese monkeys in a cool temperate area with snow coverage
Authors: Nakayama Yuri , Matsuoka Shiro , Watanuki Yutaka
Published: March 2003

Japanese monkeys, Macaca fuscata, living in a cool temperate forest experienced energy crises in winter. We measured feeding times and feeding rates (mass of foods eaten per unit time of feeding) in six different‐sized, age–sex classes (1.2–12.6 kg body mass) in autumn and winter. One‐, 2‐ and 3~4‐year‐olds spent 34–35% and 44–46% of the day feeding in autumn and winter, respectively. Monkeys less than 0 years old spent less time feeding (16–28%) than average in winter and autumn; adult females spent less (41%) in winter; and adult males spent less (25%) in autumn. All age–sex classes ate mainly fruits in autumn and the heavier classes fed more on tree bark than buds in winter. The feeding rate for fruits (2.3–53.5 g min−1) was nine to 12 times faster than those for buds (1.0– 4.8 g min−1) and bark (0.5–4.4 g min−1), and energy content did not differ among fruits (22.1 kJ g−1 dry mass), buds (19.9 kJ g−1 dry mass) and bark (23.2 kJ g−1 dry mass). Energy base feeding rates increased with body mass where the body mass exponent for buds (0.29) was smaller than those for bark (0.64) and fruits (0.63), which might be attributable to the unit size of food items and mass dependency of masticatory apparatus. Our monkeys obtained two to five times more energy in autumn (1567–1150 kJ day−1) than in winter (604–3020 kJ day−1). Adult females obtained 60% of expected energy expenditure and other classes obtained 77–88% of that in winter.
Terrestrial gastropods and experimental climate change: A field study in a calcareous grassland
Authors: Sternberg Marcelo
Published: March 2003

The impact of field manipulations of local climate on terrestrial gastropod populations and how they may affect the dynamics of the plant community were studied in a calcareous grassland. The experimental site was located in a grassland at the Wytham estate, Oxfordshire, UK. Manipulations representing two climate change scenarios in a factorial combination were used, these were warmer winters with increased summer rainfall, and warmer winters with summer drought. The climate manipulations had a significant effect on the relative abundance of molluscs. However, no important changes in species composition were found. Distribution and densities of snails and slugs were affected because of changes in the physical environment and the vegetation in the grassland. The responses of different species to the climate manipulations were strongly influenced by their phenological traits and food preferences. Potential responses of mollusc populations to a changing climate are discussed.
Effects of food distribution on the habitat usage of a female brown bear Ursus arctos yesoensis in a beech‐forest zone of northernmost Japan
Authors: Nomura Fuyuki , Higashi Seigo
Published: March 2003

The habitat usage of a female brown bear, Ursus arctos yesoensis L., was studied in relation to the distribution of food plants in a beech‐forest zone of Hokkaido, Japan. The bear’s habitat usage was correlated with the distribution of the plant Angelica ursina (Rupt.) Maxim. in summer. In spring the bear preferred Petasites japonicus (Sieb. et Zucc.) Maxim. and Heracleum dulce Fisch., whose abundance did not differ significantly between Sasa–beech forests and coniferous forests. However, the bear spent more time in coniferous forests where its den site was located. In autumn, this bear preferred the plant Actinidia arguta (Sieb. et Zucc.) Planch. ex Mig., which was abundant in maple–linden forests, however, the bear’s habitat usage was not correlated with the distribution of A. arguta because it frequently returned to an overlapping area where A. arguta was scarce. Thus, the bear’s habitat usage depended on food distribution as well as on the location of the den site and the behavioral core area.
Contribution of root respiration to total soil respiration in a Japanese cedar (Cryptomeria japonica D. Don) artificial forest
Authors: Ohashi Mizue , Gyokusen Koichiro , Saito Akira
Published: March 2003

Soil respiration was measured for 2 years in an artificial gap and in an undisturbed area in a Japanese cedar (Cryptomeria japonica D. Don) forest to estimate the contribution of root respiration to total soil respiration. Measurement plots were set up at the center of the gap, the edge of the gap, the edge of the surrounding stand and within the stand. Using a small gap (2.5 m × 2.5 m) enabled us to maintain the same soil temperature and soil moisture as found in the stand. Seasonal fluctuations in soil respiration, increasing in summer and decreasing in winter, corresponded to changes in the soil surface temperature. Soil respiration in the gap site did not differ significantly from those in the stand in the first year of gap formation. However, in the second year, the minimum CO2 flux was observed at the center of the gap and the maximum at the edge of the surrounding stand. Assuming that the differences between soil respiration in the center of the gap and that in the stand were equal to the root respiration, the root respiration rate was calculated from the relationship between the root respiration rates (Rr) and the soil surface temperature (Ts) by Ln(Rr) = 0.07Ts + 3.48. The average contribution of root respiration to total soil respiration, as estimated from the soil surface temperature in the stand by using the above equation, was 49%. After taking root decomposition into consideration, the contribution of root respiration to soil respiration increased from 49 to 57%.
Dynamic steady state of patch‐mosaic tree size structure of a mixed dipterocarp forest regulated by local crowding
Authors: Kohyama Takashi , Suzuki Eizi , Partomihardjo Tukirin , Yamada Toshihiro
Published: March 2003

A patch age‐ and tree size‐structured simulator was applied to demonstrate the landscape dynamics of a lowland mixed dipterocarp forest, using census data over a 3 year interval from two 1 ha plots in northern West Kalimantan, Indonesia (Western Borneo). Tree growth rate and recruitment rate were estimated as functions of tree size and local crowding. The effect of local crowding was assumed to be one‐sided through light competition, where the basal area for all trees larger than a target tree inside the circle of 10 m radius around the target was employed as the index of crowding. Estimated parameters were similar between the two plots. Tree mortality was expressed by descending function of tree size with asymptotic mortality for large trees corresponding to the gap formation rate. One parameter specifying the survival of trees at gap formation, which was required for the landscape‐level simulation of a shifting‐gap mosaic, was left undetermined from plot census data. Through simulation, this parameter was estimated so as to best fit the observed among‐patch variation in terms of local basal area. The overall time course of simulation and tree size structure were not sensitive to this parameter, suggesting that one‐sided competition along the vertical forest profile is a stronger determinant of average forest structure than among‐patch horizontal heterogeneity in this forest. Simulated dynamic steady state successfully reproduced the observed forest architecture in the gap‐dynamic landscape. It took about 400 years for a vacant landscape to be replaced by a steady‐state architecture of forest. Sensitivity analysis suggests that steady‐state basal area and biomass are most sensitive to changing gap formation rate and intrinsic size growth rate.
Within‐tree variation in density and survival of leafminers on oak Quercus dentata
Authors: Shibata Satoshi , Ishida Takahide A. , Soeya Fumika , Morino Naho , Yoshida Kunikichi , Sato Hiroaki , Kimura Masahito T.
Published: March 2003

The density and survival of leafminers were examined on 50 sun leaves from each of 65 Quercus dentata Thunb. individuals in northern Japan in 1997 and 1998. Phyllonorycter (two species), Caloptilia (one species) and Stigmella (three species) were abundant or common on this oak in the study area. These leafminers appeared after mid‐June, whereas most externally feeding caterpillars occurred from late May to early June when the water content and nitrogen concentration of leaves were high. The density of these leafminers was about four times higher in 1998 than in 1997. A negative correlation was more often observed between mine density and leaf size, leaf wet weight per area or leaf toughness in the Phyllonorycter species, but the opposite correlation was more frequent for Caloptilia and Stigmella species. Conversely, no clear relation was observed between the survival of Phyllonorycter larvae and leaf traits. In all leafminers except the gregarious Stigmella species, the mine density was more often positively correlated with leaf damage by chewing insects, and also the survival of Phyllonorycter larvae was often positively correlated with leaf damage. In the Phyllonorycter species, the survival of larvae tended to increase with the increase in density at the autumn generation. The correlation in the densities of mines between the summer and autumn generations was more frequently positive in the Phyllonorycter and Caloptilia species. In addition, the densities of different leafminers were often positively correlated. Thus, relations among leafminers, between leafminers and externally feeding caterpillars, and also between herbivores and host plants are complicated.
The color of noise and the evolution of dispersal
Authors: Travis Justin M. J.
Published: March 2003

The process of dispersal is vital for the long‐term persistence of all species and hence is a ubiquitous characteristic of living organisms. A present challenge is to increase our understanding of the factors that govern the dispersal rate of individuals. Here I extend previous work by incorporating both spatial and temporal heterogeneity in terms of patch quality into a spatially explicit lattice model. The spatial heterogeneity is modeled as a two‐dimensional fractal landscape, while temporal heterogeneity is included by using one‐dimensional noise. It was found that the color of both the spatial and temporal variability influences the rate of dispersal selected as reddening of the temporal noise leads to a reduction in dispersal, while reddening of spatial variability results in an increase in the dispersal rate. These results demonstrate that the color of environmental noise should be considered in future studies looking at the evolution of life history characteristics.
Mutualistic relationships between phytoplankton and bacteria caused by carbon excretion from phytoplankton
Authors: Aota Yasuaki , Nakajima Hisao
Published: March 2003

For the competition system of phytoplankton and bacteria through inorganic phosphorus, our mathematical model showed that mutualistic relationships between them could occur due to production and consumption of extracellular organic carbon by phytoplankton and bacteria. In our model, phytoplankton are limited in their growth by light and phosphorus, and bacteria are limited in their growth by phosphorus and carbon released from phytoplankton. We adopted ‘permanence’ as a criterion of the coexistence in mathematical analysis, and led necessary conditions of permanence in the model. Under these coexistence conditions, we estimated the strength of total effects of interactions between phytoplankton and bacteria at the steady state by press perturbation method. The results of this estimation indicated the mutualistic interactions between phytoplankton and bacteria. This suggests that mutualistic situation could occur due to the introduction of carbon flow from phytoplankton to bacteria, even if phytoplankton and bacteria compete with each other through common resource, inorganic phosphorus.
Effects of snow cover on the social and foraging behavior of the great tit Parus major
Authors: Nakamura Masahiko , Shindo Noriko
Published: March 2003

In the Joetsu region of central Honshu, Japan, snow lies on the ground 2–3 m deep from January to February every year. To test the effects of snow cover on the social and foraging behaviors of the great tit (Parus major Linnaeus) in the region, the following parameters were compared between the pre‐snowy period (November and December) and the snowy period (January and February) at the individual level: population size, monospecific flock size and the stability of its membership, home range size, attendance rate with mixed‐species flocks, and foraging height. Great tits lived alone or in pairs, but often joined mixed‐species flocks. Throughout the study period, individuals exhibited strong site fidelity, which resulted in a stable population size. Neither the size of a monospecific flock nor its membership was affected by snow cover. The home range expanded when birds joined mixed‐species flocks during both periods. Birds more frequently joined mixed‐species flocks during the snowy period, and the size of mixed‐species flocks was significantly larger than during the pre‐snowy period. During the snowy period, birds shifted their foraging position from the ground to the upper parts of trees. They also used the upper parts of trees when they joined mixed‐species flocks. These results suggest that the intraspecific sociality of great tits is relatively insensitive to snow cover, but that the home range size and foraging positions are affected by joining mixed‐species flocks, rather than by snow cover.
Coupling of two competitive systems via density dependent migration
Authors: Nishimura Kinya , Kishida Osamu
Published: March 2003

Coupling of two Lotka–Volterra type competition systems with density‐dependent migration was surveyed. We assumed that species x and y are each exclusively superior in subhabitat 1 and subhabitat 2, respectively, and that population densities that exert intra‐and interspecific competitive effects also impose pressures for migration of individuals from a subhabitat. If the two species are, respectively, abundant in the subhabitats in which either species is competitively superior, and the migration has a mixing effect, then, it would be intuitively expected that, as potential migration rates increase, the two species are mixed well and coexist in the whole habitat. An analysis of this competitive situation using our model under the assumption of linear diffusion predicted that, even though weak mixing maintains coexistence in the whole habitat, strong mixing collapses coexistence and leads to the exclusion of one species. The assumption that migrations occur due to self‐ and cross‐population pressures provides different predictions: (i) weak dominance and strong mixing destabilize the coexistence state and lead to a monopolizing equilibrium of either species (bi‐stability of monopolizing equiliblia); (ii) conspicuous weakness of the inferior species makes the mixing equilibrium stable, regardless of the potential migration rate; and (iii) tri‐stability exists in between situations (i) and (ii). In the third case, the attainable state is the mixing equilibrium or either of the monopolizing equilibria, depending on the initial state. Migration mechanisms with self‐ and cross‐population pressures tends to mediate spatial segregation and makes coexistence possible, even with strong mixing.
Trophic cascading effects of predatory fish on leaf litter processing in a Japanese stream
Authors: Konishi Motoharu , Nakano Shigeru , Iwata Tomoya
Published: March 2003

A manipulative field experiment to test for trophic cascading effects of predatory fish on detritus processing by benthic invertebrates was performed in stream channels running through a wetland forest in northern Japan. To control for fish effects on benthic invertebrates, two simple treatments (fish‐present and fish‐absent) were established for 4 weeks, with two common predatory fish, rainbow trout (Oncorhynchus mykiss) and freshwater sculpin (Cottus nozawae), being introduced into and excluded from stream cages. At the end of experiment, the biomass of the dominant detritivore, an amphipod (Jesogammarus jezoensis), was significantly less in the fish‐present treatment (0.56 g m–2 in dry mass on average) than that in the fish‐absent treatment (1.32 g m–2), there being no significant treatment effect evident for the second‐dominant detritivore, coleopteran larvae (Optioservus kubotai). The loss of oak leaves (Quercus crispla) from litter bags in the fish‐present treatment (0.31 g week−1 in dry mass on average) was significantly less than in the fish‐absent treatment (0.54 g week−1). Predator‐induced lower biomass and likely lowered foraging activities of the J. jezoensis were responsible for the suppression of litter processing efficiency. In contrast, the standing crop of fine particulate organic matter did not differ significantly between the treatments. The experimental results revealed that the predatory fish had an indirect but significant effect on leaf litter processing in the stream.
Spatial heterogeneity in a grassland community: Use of power law
Authors: Shiyomi Masae , Takahashi Shigeo , Yoshimura Jin , Yasuda Taisuke , Tsutsumi Michio , Tsuiki Mikinori , Hori Yoshimichi
Published: March 2003

A new regression analysis was proposed to evaluate the degree of spatial heterogeneity for individual species comprising a plant grassland community. The weighted average of the heterogeneity value of all the species comprising the community provides a measure of community‐level heterogeneity. A field survey was carried out, as an example, in order to analyze the spatial heterogeneity of a pasture with grazing cows, using 100 quadrats 50 cm × 50 cm, each of which was divided into four smaller quadrats 25 cm × 25 cm, on a 50 m long line‐transect. The frequency of occurrence for all the species in each small quadrat was recorded. The regression associated with the ratio of the theoretical and observed variances of occurence counts was used to analyse the frequency distribution of species in a pasture community. A good fit to the regression for the whole community was obtained. These results indicate that (i) each species in the example was distributed more heterogeneously than a random pattern; and (ii) the regression could well describe the spatial heterogeneity of the grassland plant community. In most of the observed species, spatial heterogeneity is often characterized by species‐specific propagation traits and the architecture of plant bodies. Thus, the spatial patterns of a grassland community can be evaluated in detail by this power‐law approach. This measure is suitable for field surveys and comparative studies of grassland communities, and for other plant communities that are generally short in height.
Growth and reproductive characteristics of an aquatic macrophyte Ottelia alismoides (L.) Pers. (Hydrocharitaceae)
Authors: Jiang Meiyi , Kadono Yasuro
Published: March 2003

Life history and reproductive traits of a submerged aquatic weed, Ottelia alismoides (L.) Pers., were studied in irrigation ponds in southwestern Japan. In addition, growth and seed production were investigated in relation to nutrient condition and water depth. The size of plants was very variable but reproductive allocation was nearly constant irrespective of the plant size at reproductive stage, amounting to more than 30% at maximum. Bagging experiments confirmed autogamy of the species. Ottelia alismoides grew best in nutrient‐rich water with mud substratum. The optimal water depth for the growth of the species was approximately 50 cm compared with 20 and 90 cm. However, the reproductive allocation and seed set rate did not change much in different nutrient and water depth conditions. The seeds were produced by cleistogamous flowers in a depth of 90 cm. Morphological and ecological plasticity revealed in the present study was considered to be adapted to unstable environments such as rice fields and irrigation ponds liable to water‐level fluctuation. The conditions required for the restoration of the populations of O. alismoides are discussed based on the present results.
Assessing the functional implications of soil biodiversity in ecosystems
Authors: Jones Thomas Hefin , Bradford Mark Alexander
Published: March 2003

Soil communities are among the most species‐rich components of terrestrial ecosystems. A major challenge for soil ecologists is to formulate feasible research strategies that will preserve and capitalize on the biodiversity resources of the soil. This article considers the role of soil organism diversity by concentrating on: (i) the relationship between soil biodiversity and ecosystem function; (ii) what issues need to be explored; (iii) studies carried out in the Ecotron controlled environment facility; and (iv) how stable isotope techniques can improve our understanding of the relationship between soil biodiversity and ecosystem function. It is advocated that: (i) the objective of any soil biodiversity study should always be the generation of general concepts, rather than local, system‐specific observations; and (ii) any empirical study can be properly interpreted only within a quantitative ecological framework.
Successional diversity and forest ecosystem function
Authors: Caspersen John P. , Pacala Stephen W.
Published: March 2003

Forest inventory data was used to examine the relationship between successional diversity and forest ecosytem function. The inventory data show that stands composed of early successional species are more productive than stands composed of late successional species, whereas stands composed of late successsional species have lower turnover than stands composed of early successional species. Taken alone, these results would suggest that forests should be managed in a way that favors the most productive early successional species or longest‐lived late successional species, depending on whether the goal is to maximize productivity or maximize carbon storage. However, the inventory data also show that stands with low successional diversity fix and store less carbon than stands with high successional diversity. This result suggests that forests should be managed in such a way as to retain species diversity while also favoring species that maximize the ecosystem function of interest.
Inter‐hemispheric comparison of bottom‐up effects on community structure: Insights revealed using the comparative‐experimental approach
Authors: Menge Bruce A. , Sanford Eric , Daley Bryon A. , Freidenburg Tess L. , Hudson Gregory , Lubchenco Jane
Published: March 2003

The comparative‐experimental approach uses identically designed, replicated experiments at different sites along environmental gradients in order to gain insight into the changing dynamics of communities with changing environmental conditions. Such studies reveal how ecological processes vary in intensity and interact to produce community structure. Early emphases were on the community consequences of shifting top‐down impacts, competition and disturbance with environmental stress. Recent advances include the more precise quantification of gradients and thus a better understanding of species responses to the environment, and the revelation that bottom‐up forces can vary significantly on within‐region scales, with major consequences for the impact of top‐down forces and thus community dynamics. Here the use of the method to examine the role of geographic location (coastal ecosystems in different hemispheres) and oceanographic conditions (upwelling vs downwelling) on these bottom‐up/top‐down linkages is advanced. We show that a bottom‐up factor (prey recruitment) and a top‐down effect (predation rate) vary consistently with oceanographic conditions within each coastal ecosystem, and also between geographic locations (New Zealand, Oregon). In general, both recruitment and predation rates are higher in Oregon. It is postulated that these differences are common responses to oceanographic variation, and that between‐hemisphere differences result from the stronger and more persistent upwelling in the California Current ecosystem.
Host plant suitability of a recently naturalized thistle Cirsium vulgare (Asteraceae) for a phytophagous ladybird beetle, Epilachna pustulosa (Coleoptera: Coccinellidae)
Authors: Fujiyama Naoyuki , Katakura Haruo
Published: March 2003

The phytophagous ladybird beetle, Epilachna pustulosa Kôno occurs mainly on the thistle Cirsium kamtschaticum Ledeb. In recent years, we have confirmed feeding and oviposition by E. pustulosa, and some degree of larval development of this beetle, on a naturalized congeneric thistle, Cirsium vulgare (Savi) Tenore. In this study, we assessed the host suitability of C. vulgare for E. pustulosa, using larval rearing and simple food choice tests, by comparing the performance on, and preference for, their legitimate host C. kamtschaticum. All experiments were initiated in July, when the utilization of C. vulgare by E. pustulosa became obvious. For larval performance, E. pustulosa showed a lower eclosion rate, shorter developmental duration and smaller body size when reared on C. vulgare than on C. kamtschaticum. Cirsium vulgare appeared to be a less adequate larval food than C. kamtschaticum. Adult feeding preference was altered seasonally; females preferred C. kamtschaticum to C. vulgare in a food choice test conducted in early July, whereas they showed the opposite preference in tests conducted in mid and late July. The utilization of C. vulgare by E. pustulosa appeared to be induced by qualitative deterioration of C. kamtschaticum leaves in July, which resulted in increased dispersion of adult beetles.
Diverse visitors with various pollinator importance and temporal change in the important pollinators of Geranium thunbergii (Geraniaceae)
Authors: Kandori Ikuo
Published: March 2003

Assessing pollinator importance of each floral visitor to a plant species is a key to understanding plant–pollinator interaction. The present study examined visitation frequency, pollination efficiency, and pollinator importance of the full range of floral visitors to Geranium thunbergii natural population, by measuring seed‐set. During 2 years of observations, the flowers were visited by at least 45 insect species belonging to four orders. Among the main 22 visitor species, 11 species belonging to three orders (Hymenoptera, Diptera, and Lepidoptera) acted as the efficient pollinators. In both years, Hymenoptera, especially bees, was the most important pollinator to G. thunbergii. Thus, the flowers could be considered as bee‐pollinated. However, the most important species were not constant between years. The study also documented that the efficient pollinators have larger body sizes. The dish‐shaped floral morphology, taxonomically diverse pollinators, and temporal change in the most important pollinators indicate that G. thunbergii–pollinator interaction is a rather generalized system. The results suggest that casual observations of visitation, or even precise measurement of pollinator importance in a single season is insufficient to identify important pollinators.
Influence of the red fox (Vulpes vulpes, Linnaeus 1758) on the distribution and number of breeding birds in an intensively used farmland
Authors: Tryjanowski Piotr , Gołdyn Bartłomiej , Surmacki Adrian
Published: March 2003

This study tested the hypothesis that small birds at their nest sites avoid areas around dens of the red fox (Vulpes vulpes,Linneaus 1758) in an intensively used farmland. Birds were counted at 18 points (radius 100 m) located near dens, as well as at 18 control points that were located at least 600 m away from the nearest den. These two types of points did not differ with respect to the number of recorded bird species. However, a negative effect of the proximity of fox dens on the total density of the bird community was observed. This effect was also recorded for the most abundant bird species, the skylark (Alauda arvensis, Linneaus 1758). In agreement with our expectations, these results indicate a negative impact of fox presence on a breeding bird community in an open farmland.
Factors affecting seedling recruitment and survivorship of the Japanese subalpine stone pine,Pinus pumila, after seed dispersal by nutcrackers
Authors: Kajimoto Takuya
Published: March 2003

To clarify the factors affecting the seedling establishment of the subalpine stone pine (Pinus pumilaRegl.) from nutcracker‐cached seeds, subsequently emerged seedlings were examined in two plots on Mt Akitakomagadake, northern Japan. The survivorship of older seedlings (2–20 years old) was also monitored during six seasons at nine different sites. In one plot with 18 caches, seed germination occurred between June and mid‐July. During this period, nutcracker’s retrieved the stored pine seeds from 16 caches and ate some seeds immediately. Simultaneously, this nutcracker behavior caused mechanical damage to newly emerging seedlings (e.g. uprooting and tearing off cotyledons). Such initial loss to in situ harvesting and mechanical damage accounted for 75% of the total seeds remaining in the caches. The number of established current seedlings sharply declined during the first 2 years, and the survival rate was 4.4% over four winters. Two major mortality factors were identified: uprooting by frost‐heave soil disturbance in the spring of the second year and standing death by drought or other physiological stresses in early summer. In another plot with 13 caches, survivorship of newly emerged seedlings was also low (4.2%), but mortality was mostly due to summer drought, indicating that the frost‐heave event was a site‐specific disturbance factor. For older seedlings, survival rates reached approximately 90% even after six seasons and summer drought stress was a major mortality factor. My findings suggest that seedling recruitment ofP. pumilawas largely limited by both nutcracker disturbance and external disturbance (and/or stresses) at an early stage. However, after the critical first few years, pine seedlings were highly likely to survive and grow to the sapling stage despite the harsh environment of the high mountains.
Functional domains in soils
Authors: Lavelle Patrick
Published: March 2003

Soil processes are significantly regulated by biological activities. Soil ecosystem engineers (predominantly termites, earthworms and ants) and roots produce biogenic structures, aggregates or pores that determine the structure and architecture of soil. The sum of structures produced by a population or community of invertebrate engineers creates a specific environment defined here as a functional domain. Functional domains are characterized by (i) the nature and spatial array of the biogenic structures, solid aggregates, mounds or constructs and pores of different shapes or sizes; (ii) the specific communities of smaller organisms from the meso‐ and microfauna and micro‐organisms that they host; and (iii) the spatial and temporal scales at which soil processes operate. The regulation of processes caused by the physical organization of the soil environment and the redistribution of organic resources have been described and quantified in several studies. In soil, the relative importance of regulation imposed by ecosystem engineering is likely to be greater than regulation by trophic relationships because of the specific ecological constraints observed in this environment when compared to above‐ground conditions.