Relative Importance of Seed-Bank and Post-Disturbance Seed Dispersal on Early Gap Regeneration in a Colombian Amazon Forest

Early forest gap regeneration may be generated by postdisturbance seed rain and by seed, seedling or bud banks (i.e., resprouting). The relative importance of each process may depend on several factors (e.g., fruit/seed production, abundance and behavior of seed dispersers, gap characteristics, etc.). We experimentally compared the importance of seed-bank and seed-rain affecting early recruitment of seedlings in an Amazonian forest (Zafire Biological Station, Colombia), using soil transplants from forests to gaps and seed rain enclosures. We found that, during the 8-mo study, the seed-bank contributed with a larger number of individuals and species than seed-rain. The low seedling recruitment rates may be associated with reduced populations of animal seed-dispersers due to hunting and/or low levels of forest fruit production.     

Diel changes in vertical distribution of Oithona similis (Cyclopoida) and Oncaea curvata (Poecilostomatoida) under sea ice in mid-summer near Syowa Station, Antarctica

The diel vertical distributions of two small copepods, Oithona similis and Oncaea curvata, were investigated at 4-h intervals over a 24-h period under fast ice near Syowa Station during continuous daylight conditions in the Antarctic mid-summer, December 1993. Oithona similis and O. curvata exhibited small-scale diel vertical migrations during the study period, in a way opposite to what is expected, i.e., remaining mostly in the upper layer during the day and moving into deeper layers at night. The nighttime descent of both species coincided with the time of disappearance of a high algal concentration at the ice–water interface during the day and an increase of the algal concentration in the mid-water layer at night. This suggests the migration behavior of the copepods was responsible for the change of food availability. The daily grazing impact of these copepods was estimated to remove one-third of the algae daily released from ice during mid-summer at Syowa Station.     

Investigations in plant commonness and rarity: a comparison of seed removal patterns in the widespread Jatropha standleyi and the endemic J. chamelensis (Euphorbiaceae)

During early August to late September 1998 we examined seed dispersal in the tree species Jatropha standleyi (widespread) and J. chamelensis (endemic; Euphorbiaceae) at the Estacion de Biologia Chamela, Jalisco, Mexico. Using general linear models, we found that seed removal from beneath the parental canopy did not differ between the two species and that seed removal was correlated with both seed availability on the ground and rodent predation. We inferred that seed removal was largely mediated by rodents and determined that if a seed was not removed within 4d (approx. 16% chance), it was highly unlikely to be removed at all (approx. 3.5% chance) for both species. We note that although differences in patterns of seed removal may not explain the observed differences in range size, differences between the two species in seed crop size arc similar to patterns found in other endemic/widespread species pairs.     

南极长城站地区土壤微生物生态作用的初步探讨

从南极长城站附近联合采样13个,并进行了土壤微生物的数量统计与种类鉴定。氨化细菌的菌量为10⁴～10⁶cells／g,共7个属：微球菌属（Micrococcus）,葡萄球菌属（Staphylococcus）,假单胞菌属（Pseudomonas）,芽孢杆菌属（Bacillus）,产碱菌属（Alcaligenes）,黄杆菌属（Flavobacterium）,节杆菌属（Arthrobacter）;固氮细菌菌量为10⁵～10⁷cells／g,仅一个固氮菌属（Azotobacter）;硝化细菌一般为10⁴cells／g,分属两个属：硝化杆菌属（Nitrobacter）,硝化球菌属（Nitrococcus）;真菌为10³cells／g,分属5个属：青霉菌属（Penicillium）,金孢霉菌属（Chrysosporium）,枝孢霉菌属（Cladosporium）,曲霉菌属（As-pergillus）,散囊菌属（Eurotium）,反硝化菌为 10²～10⁴cells／g,分属 3个属：假单胞菌属（Pseudomonas）,微球菌属（Micrococcus）,芽孢杆菌属（Bacillus）;放线菌分属3个属：链霉菌属（Streptomyces）,小单孢菌属（Micromonospora）,和诺卡氏菌属（Nocardia）。联采样品12℃培养的出现率主要类群是：假单胞菌属（42％）,芽孢杆菌属（35％）,微球菌属（31％）,节杆菌属（27％）,青霉菌属（58％）,枝孢霉菌属（54％）,硝化杆菌属（81％）,固氮菌属（88％）,反硝化细菌中主要是假单胞菌属（58％）,芽孢杆菌属（38％）。文中还讨论了微生物菌量与土壤总碳、总氮的相关性及其在该地区氮循环中的生态学作用。     

Exudates from Gracilaria chilensis stimulate settlement of epiphytic ulvoids

In the diatom communities of the Vanishing and Ornithologist Creek 74 taxa were found. Most of the taxa have a cosmopolitan range and are resistant to various environmental stresses. For example, Achnanthes lanceolata var. lanceolata, is found in all types of waters and in several ecological conditions. Achnanthes delicatula ssp. delicatula, Nitzschia frustulum, N. capitellata, Navicula mutica, and N. gregaria develop both in fresh and brackish waters. Some of the organisms also settle in terrestrial environments. Navicula atomus, N. mutica, Pinnularia borealis, and Hantzschia amphioxys are common soil algae. Navicula digitulus, N. contenta, N. cohnii and Achnanthes coarctata also live in an aerial environment. Navicula atomus is well developed in eutrophic waters and Nitzschia capitellata can tolerate a high level of pollution, while Nitzschia gracilis, Fragilaria capucina, and F. alpestris appear both in oligotrophic, and enriched waters. Stenotopic ecological features are shown by Achnanthes marginulata and Navicula digitulus — known from the Alps and the North, and Navicula muticopsis characteristic for Antarctic and Subantarctic.The index of diatom biomass, usually of low and medium value, was highest in the area of possible impact by a penguin colony.     

The change of the distribution pattern of the large weevil,Hyposipalus gigas Fabricius (Coleoptera,Rhynchophoridae) within a single generation. A preliminary note

The distribution pattern of adults of the large weevil, Hyposipalus gigas on logs of the Japanese black pine and that of larvae in pine stumps were examined by using the m^*−m method (Iwao , 1968). The distribution of adults on logs was contagious, probably due to their response to local heterogeneity of the environment. The larval distribution was also contagious, but there was no significant correlation between the number of larval bores and the stump size. The mortality of young larvae seemed not to be related with the number of larvae per stump, but it was related with the density per unit area of bark surface. There was some sign of inversely density-dependent or ‘all-or-none’ type mortaltiy in the late larval stage.     

Mechanism for the differential induction of mutation by S9 activated benzo[a]pyrene employing either a glucose-6-phosphate-dependent NADPH-regenerating system or an isocitrate-dependent system

A significant difference in mutation frequency has been observed in CHO cells exposed to benzo[a]pyrene with alternative activation systems. Each system employed rat-liver S9 homogenate with one using isocitrate dehydrogenase to provide reduced NADP, while the other method uses glucose-6-phosphate dehydrogenase. Total aryl hydrocarbon hydroxylase (AHH) activity was greater for the isocitrate dependent system, however, this yielded a lower level of HGPRT mutants. It was ascertained that this reduced mutation frequency may result from sequestering of B[a]P substrate by crystals in the medium, possibly calcium phosphate, which decreased the effective substrate concentration. This sequestration enhances B[a]P internalization, which would explain the dichotomy between the AHH values and the mutation frequency data. The production of specific B[a]P metabolites was also examined by reverse phase HPLC quantitation of extracts of solutions in which the two activation systems were used. The levels of 7,8 dihydroxybenzo[a]pyrene produced by the glucose-6-phosphate protocol were consistently greater than with isocitrate. This may also be a contributing mechanism for elevating the mutation frequency with this procedure. These results demonstrate several interactions between test compound, cells, and metabolizing system which must be considered with in vitro activation systems.