Spatial pattern of trees in kerangas forest,Sarawak

The 64 most abundant species (10 cm dbh) in a 400×480 m plot of predominantly kerangas forest in Sarawak were individually investigated for two-dimensional pattern by spectral analysis using the basal areas of trees in 20×20 m contiguous quadrats. All species had individuals in the upper canopy.30 species showed pattern with clumps. The most frequent scales of clump size were between 35 and 55 m across. Patterned species were less abundant in the plot, had a greater proportion of smaller (10–20 cm dbh) trees and had a lower ratio of upper to lower canopy trees than species without pattern.Trend across the plot between dipterocarp and kerangas forest types matched the change in soil from red-yellow podzol (oxisol and ultisol) to medium gleyic and bleached sand podzols (spodosol). However, soil differences and small scale (ca. 50 m) changes in topography did not account for patterns.The scale of pattern matches the size of gaps produced by windthrow. It is suggested that patterned species are light-demanding and grow from seeds in gaps, whereas non-patterned species are shade tolerant, growing within closed forest to sapling size and eventually maturing by filling smaller single tree gaps.D. McC. N. thanks the Deutsche Akademische Austauschdienst for a scholarship and the British Council for travel funds to work at Hamburg. We are grateful to A. Weiscke for entry of the 1963 field records on the computer, T. W. Schneider for helpful discussions and T. C. Whitmore for commenting on earlier drafts.Nomenclature for three species follows Whitmore (1972, 1973), Ng (1978) and Ashton (1982).     

4,5-dihydroxypipecolic acids in the seed of Julbernardia,Isoberlinia and Brachystegia

2(S)-carboxy-4(R),5(R),-dihydroxypiperidine has been isolated from seed of Julbernardia paniculata. The distribution of non-protein amino acids in the genera Julbernardia, Isoberlinia, Brachystegia and Cryptosepalum is also reported.     

鼎湖山人工马尾松第1代与自然更新代生长动态比较

应用年轮分析法研究马尾松栽种的第1代和自然更新代的动态。结果表明,本区域马尾松第1代在贫瘠土壤上能正常生长,并在成熟期有较高的生长量,因此不失为较好的造林绿化的先锋树种。从经济利用的角度出发,应在生长量高峰期后采伐最为合理,在本区域采伐期可选择在树龄40年左右。但马尾松的更新代严重退化,表明本区域在土地利用上不能连续栽种马尾松,最佳方式是在35年林龄左右进行林分改造。     

Abundance,growth and grazing loss rates of picophytoplankton in Barguzin Bay,Lake Baikal

The abundance, growth, and grazing loss rates of picophytoplankton were investigated in August 2002 in Barguzin Bay, Lake Baikal. Water samples for incubation were taken once at a near-shore station and twice at an offshore station. Contributions of picophytoplankton to total phytoplankton were high (56.9–83.9%) at the offshore station and low (5.8–6.8%) at the near-shore station. The picophytoplankton community in the offshore station comprised mainly phycoerythrin (PE)-rich cyanobacteria, with eukaryotic picophytoplankton being less abundant. In contrast, as well as PE-rich cyanobacteria and eukaryotic picophytoplankton, phycocyanin (PC)-rich cyanobacteria were found in the near-shore station. At the offshore station, growth and grazing loss rates on 25 August were 0.56 and 0.43 day⁻¹, respectively, and on 29 August, 0.69 and 0.83 day⁻¹, respectively. At the near-shore station, growth and grazing loss rates were 1.61 and 0.70 day⁻¹, respectively. These results show that there is a difference in the abundance, composition, and ecological role in the microbial food web of picophytoplankton between the near-shore and the offshore areas in Barguzin Bay.     

森林更新与空间异质性

森林更换是一个重要的生态学过程,一直是森林生态系统动态研究中的主要领域之一。森林更新受物理环境、自然干扰、人为干扰、更新树种特性、树种对干扰的反应等因素及其相互作用的影响。这些生物和非生物的因素随空间和时间而不断变化,构成了森林的空间异质性和时间异质性,使森林更新具有空间和时间上的变化特点,表现在异质性的格局和过程中。探索森林更新与空间异质性的内在规律,可揭示空间格局对更新的生态学过程的潜在作用机制。本文主要综述了近年来有关森林更新与空间异质性研究的主要内容和一些观点,分析了更新中空间异质性的来源,着重评述了空间异质性的生境及更新树种的反应、小尺度的空间异质性与更新动态、林分中光有效性的空间异质性与更新格局以及土壤和更新的空间异质性尺度的关联性等方面的研究。     

Comparative investigations of niche,growth rates and reproduction between the native moss Campylopus pilifer and the invasive C. introflexus

The invasive Campylopus introflexus (Hedw.) Brid. is suspected to outcompete native bryophytes but we know very little about the mechanisms involved in its success. We used extensive mixed-stands of Campylopus introflexus and the indigenous C. pilifer Brid. in a French Nature Reserve to study comparative ecological niches, growth rates, density and reproduction between the two mosses. A re-evaluation of the discriminant morphological characters was first undertaken to allow a straightforward separation of both species in the field. Sporophytes were never encountered on Campylopus pilifer, whereas they are produced in great profusion by C. introflexus, implying a massive sporal investment. In contrast, Campylopus pilifer can produce deciduous shoot-tips in mature colonies whereas C. introflexus is apparently unable to do so, the propagules being restricted to immature developmental stages. Campylopus pilifer does not occupy exactly the same niche as C. introflexus. Only Campylopus pilifer occupies the harsher microhabitats whereas only C. introflexus occurs in moister ones. The mixed-stands are restricted to medium-dry environments. The success of the alien Campylopus introflexus may be largely attributed to its growth response which is, on average across habitats, about twice that of C. pilifer. The combination of faster growth and higher branch frequency contribute to the competitive advantage of Campylopus introflexus, which is able to aggressively overtop and laterally penetrate adjacent cushions of Campylopus pilifer. Removal of trees as soon as their crown begins to cast some shade and soil scraping should be tested in order to lower the negative impacts of Campylopus introflexus in the study site.     

Differences in growth,pigment composition and photosynthetic rates of two phenotypes Microcystis aeruginosa strains under high and low iron conditions

This paper provided insight into the influence of iron on the growth of Microcystis aeruginosa strains related to different phenotypes of this species. In this research it was intended to compare the growth, pigment composition, photosynthetic efficiency and extracellular polysaccharides production of unicellular and colonial strains of M. aeruginosa. A significantly growth inhibition under iron-limited condition on unicellular M. aeruginosa was noted, whereas the colonial strain could maintain a steady growth along with the culture time. This observation was reconfirmed by the content of chlorophyll a. Compared with unicellular strain; the colonial strain exhibited a higher PSII maximum light energy transformation, photosynthetic oxygen evolution and extracellular polysaccharides (EPS) production in iron-limited condition. Further, in order to gain more information about the accessibility of iron in the two phenotypic Microcystis, we found the two strains could produce hydroxamate-type siderophores, the content of siderophores produced by the colonial strain was more than those in unicellular strain under the iron-limited condition. It was interpreted as an adaptation to the dilute environment. Our results demonstrated that the colonial phenotypes possessed stronger ability to endure iron-limited condition than unicellular strain by higher pigment contents, higher photosynthetic activities, higher EPS production and higher siderophores secretion. It might elucidate that the colonial M. aeruginosa bloom can sustain in eutrophic reservoirs and lakes.     

Effect of wound size on the growth and regeneration of two temperate subtidal sponges

Physical and biological disturbances can damage and remove biomass from marine invertebrates such as sponges. To determine the effect of wound size on sponge recovery, individuals of the Demospongiae Latrunculia wellingtonensis (Alvarez, Berqguist and Battershill) and Polymastia croceus (Kelly-Borges and Bergquist) had 50%, 75%, 90% or none (control) of their volume removed. Regeneration (measured by oscule development), growth (percent and volume change), biofouling and survival were monitored often over 203 days using in situ photographs. The rate of regeneration and growth varied between the two sponges, being greatest for L. wellingtonensis. Interspecific variation may result from differences in choanosome structure: the choanosome in L. wellingtonensis is poorly differentiated but is well developed in P. croceus. For each species, recovery rates were similar between 50%, 75% and 90% removed sponges. All damaged L. wellingtonensis and P. croceus survived, demonstrating the remarkable ability of some sponge species to recovery from massive injuries. L. wellingtonensis and P. croceus are often found in exposed habitats. Good recovery after injury may therefore be an adaptation to reduce the damaging effects of storms and strong water movement.     

神农架天然针阔混交林乔木更新的空间格局

为深入了解神农架天然针阔混交林群落乔木树种的更新特征,于神农架国家公园设置1 hm²森林动态监测样地对树种更新进行调查,利用Ripley的L函数分析优势更新树种的空间分布格局、种间空间关联性以及与大树的空间分布关系。结果显示：（1）更新个体共有35 752株,隶属于19科29属45种。更新优势种基本是乔木层优势树种,物种更新数量表现为：巴山冷杉（Abies fargesii Franch.） > 华山松（Pinus armandii Franch.） > 四蕊槭（Acer stachyophyllum subsp.tetramerum（Pax）A.E.） > 华中山楂（Crataegus wilsonii Sarg.）,混交林群落更新良好。（2）随着尺度增加,巴山冷杉、华山松更新空间格局由聚集分布向随机分布和均匀分布发展;华中山楂、四蕊槭更新的空间格局在整个尺度上均为聚集分布,表明针叶、阔叶树种更新在空间生态利用策略上出现分化。（3）巴山冷杉与其余3个优势更新树种、华山松与华中山楂更新呈显著正相关,表现出对微生境的共同喜好;四蕊槭分别与华山松、华中山楂更新的空间关系表现为显著负相关,种间竞争激烈。（4）巴山冷杉、华中山楂、四蕊槭的更新个体与大树的空间分布总体为显著正相关,这可能与种子传播限制相关;华山松幼苗、幼树与大树的空间分布在小尺度上呈负相关,存在资源不对称竞争。     

Isolation and growth rates of methanol utilizing rhodospirillaceae

38 pure culture strains belonging to seven species of the Rhodospirillaceae were isolated from 39 methanol enrichment cultures inoculated with water and mud samples of different habitats. None of the strains exhibited doubling times shorter than 10 h in methanol-bicarbonate media.     

Application of a changing field of growth rates to a description of root apex formation

Based on the growth tensor method an unsteady field of growth rates for developing root apex is presented. Maps of growth rates distribution as well as simulations in which the field was applied to initially uniform grid of points are presented. In the simulations, the grid undergoes deformation that resembles new root formation in its axial plane. Four variants of field operation on the grid are shown.     

Variable evolutionary rates in the molecular evolution of mammalian growth hormones

In mammals pituitary growth hormone (GH) shows a slow basal rate of evolution (0.22 ± 0.03 × 10^–9 substitutions/amino acid site/year) which appears to have increased by at least 25–50-fold on two occasions, during the evolution of primates (to at least 10.8 ± 1.3 X 10^–9 substitutions/amino acid site/year) and artiodactyl ruminants (to at least 5.6 ± 1.3 X 10^–9 substitutions/amino acid site/year). That these rate increases are real, and not due to inadvertent comparison of nonorthologous genes, was established by showing that features of the GH gene sequences that are not expressed as mature hormone do not show corresponding changes in evolutionary rate. Thus, analysis of nonsynonymous substitutions in the coding sequence for the mature protein confirmed the rate increases seen in the primate and ruminant GHs, but analysis of nonsynonymous substitutions in the signal peptide sequence, synonymous substitutions in the coding sequence for signal peptide or mature protein, and 5 and 3 untranslated sequences showed no statistically significant changes in evolutionary rate. Evidence that the increases in evolutionary rate are probably due to positive selection is provided by the observation that in the cases of both ruminant and primate GHs the periods of rapid evolution were followed by a return to a slow rate similar to the basal rate seen in other mammalian GHs. Differences between the biological properties of GHs have been identified which may relate to these periods of rapid adaptive molecular evolution. On the basis of sequence data currently available (but excluding rodent GHs which show an intermediate rate, the basis of which is not clear) for most (90%) of evolutionary time mammalian GHs have been in the slow phase of evolution, with possibly most of the few amino acid substitutions that have occurred being neutral in nature. But most (80%) of the amino acid substitutions that have been introduced into GH during the course of mammalian evolution have been accepted during the rapid phases and were adaptive in nature.     

Spatial pattern of Quercus regeneration limitation and Acer rubrum invasion in a Piedmont forest

Abstract. Across eastern North America, there is a temporal trend from open Quercus forests to closed forests with increased Acer rubrum in the understory. We used a series of Ripley's K(d) analyses to examine changes in the spatial pattern of Quercus and Acer rubrum stems greater than 2.5 cm DBH over 45 yr in a 2‐ha mapped stand. Specifically, we asked whether changes over time were consistent with the hypothesis that Quercus is being competitively replaced by Acer rubrum. Both Acer rubrum and Quercus stems are spatially clumped, but have become less clumped over time. Stem mortality from Hurricane Fran (1996) was more clumped in all strata of the forest, at all spatial scales, than expected if damage had occurred to stems at random. Acer rubrum ingrowth occurred more often near established trees (all species) in the midstory, whereas Quercus ingrowth occurred less often near established trees in the midstory. The specific hypothesis that stems of Acer rubrum in the midstory of the forest are associated with a lack of Quercus regeneration was strongly supported. This effect occurred at all spatial scales tested, including scales larger than that at which direct competition for light can occur. Edaphic gradients in the plot are correlated with many of the observed trends at large spatial scales, and our results suggest that the presence of such gradients can generate complex spatial patterns over time.     

Stem cell-based growth, regeneration, and remodeling of the planarian intestine

Although some animals are capable of regenerating organs, the mechanisms by which this is achieved are poorly understood. In planarians, pluripotent somatic stem cells called neoblasts supply new cells for growth, replenish tissues in response to cellular turnover, and regenerate tissues after injury. For most tissues and organs, however, the spatiotemporal dynamics of stem cell differentiation and the fate of tissue that existed prior to injury have not been characterized systematically. Utilizing in vivo imaging and bromodeoxyuridine pulse-chase experiments, we have analyzed growth and regeneration of the planarian intestine, the organ responsible for digestion and nutrient distribution. During growth, we observe that new gut branches are added along the entire anteroposterior axis. We find that new enterocytes differentiate throughout the intestine rather than in specific growth zones, suggesting that branching morphogenesis is achieved primarily by remodeling of differentiated intestinal tissues. During regeneration, we also demonstrate a previously unappreciated degree of intestinal remodeling, in which pre-existing posterior gut tissue contributes extensively to the newly formed anterior gut, and vice versa. By contrast to growing animals, differentiation of new intestinal cells occurs at preferential locations, including within newly generated tissue (the blastema), and along pre-existing intestinal branches undergoing remodeling. Our results indicate that growth and regeneration of the planarian intestine are achieved by co-ordinated differentiation of stem cells and the remodeling of pre-existing tissues. Elucidation of the mechanisms by which these processes are integrated will be critical for understanding organogenesis in a post-embryonic context.     

Demographic changes and the development of competition in a native Australian eucalypt forest invaded by exotic pines

Data from the second half of a 14-year study of a eucalypt dry sclerophyll forest invaded by Pinus radiata D. Don shows further progress in the development of a mixed eucalypt-pine stand. Earlier (Chilvers and Burdon 1983) it was clear that pines invading from an adjacent commercial plantation were starting to contribute their own progeny to the mixed stand. Initially the recruitment of established pines (> 1 m high) from these seedlings was very slow. However, since 1984, increasing numbers of seedlings have survived beyond their first year, suggesting the possibility of another wave of successful establishment in the near future. The established fraction of the pine population continued to grow rapidly and incurred no mortality. Many of these plants have now emerged through the top of the eucalypt canopy. In contrast, both juvenile and adult eucalypt numbers continued to decline. Despite these demographic and visual changes, comparative analysis of the growth of established pines over two consecutive 7-year periods (1974–1981; 1981–1988) showed that competition between neighbouring plants, especially pines, is beginning to affect individual growth rates. Growth rates of pines having other pines as nearest neighbours declined 40% between 1974–1981 and 1981–1988, while that of pines with eucalypts as nearest neighbours fell by 28%. In pine-pine nearest neighbour (NN) pairs, growth rates were significantly affected by the size (diameter) of the nearest neighbour. In pine-eucalypt NN pairs growth rates of the pines were not affected by the size of the eucalypt, but these were significantly negatively correlated with the inverse of the distance to the eucalypt. More broad-based assessment of 43 pines showed a significant relationship between their growth rates and the summed competitive effect of other pines within a 5-m radius. No such relationship was found between growth rate and the summed competitive effect of eucalypts in the 5-m zone.     

Relationships between larval nutritional experience, larval growth rates, juvenile growth rates, and juvenile feeding rates in the prosobranch gastropod Crepidula fornicata

Planktonic larvae experiencing short periods of starvation or reduced food supply often grow and develop more slowly, have poor survival, fail to metamorphose, metamorphose at smaller sizes, or grow slowly as juveniles. In this study, we examined the impact of short periods of food limitation at various stages of larval development on larval and juvenile growth in Crepidula fornicata. In addition, we considered whether juveniles that were stressed as larvae grew poorly because of reduced rates of food collection due to impaired gill function. For 5 experiments, larvae were either starved for several days beginning within 12 h of hatching or were starved for the same number of days following 1 or more days of feeding at full ration (cells of the naked flagellate Isochrysis galbana, clone T-ISO, at 18×10⁴ cells ml⁻¹). In one experiment, larvae were transferred for 2 or 4 days to seawater with extremely low phytoplankton concentration (1×10⁴ cells ml⁻¹). In all experiments, larvae were returned to full ration following treatment. Control larvae were fed full ration from hatching to metamorphosis. When larvae reached shell lengths of about 900 μm they were induced to metamorphose and then reared individually at full ration in glass bowls, with phytoplankton suspension replenished daily. Larval and juvenile growth rates were determined by measuring changes in shell length (longest dimension) over time. Juvenile feeding rates were determined by monitoring changes in phytoplankton concentration over 2–3 h at the end of the growth rate determinations. In general, larval growth rates for the first 2 days after the resumption of feeding were inversely proportional to the length of time that larvae were starved. However, larval growth rates ultimately recovered to control levels in most treatments. Starving the larvae caused a significant reduction in initial juvenile growth rates (first 3–4 days post-metamorphosis) in most experiments even when larval growth rates had recovered to control levels prior to metamorphosis. Juvenile growth rates were not significantly reduced when larvae were subjected to reduced food availability (1×10⁴ cells ml⁻¹), even for treatments in which larval growth rates were compromised. Mean weight-specific filtration rates for juveniles were significantly reduced (p<0.05) following larval feeding experience in only one or possibly 2 of the 4 experiments conducted. Our data suggest that although larvae of C. fornicata may fully recover from early nutritional stress, the resulting juveniles may exhibit poor initial growth due to impaired gill function, reduced digestive capability, or reduced assimilation efficiency.     

Improved Deschampsia cespitosa growth by nitrogen fertilization jeopardizes Quercus petraea regeneration through intensification of competition

Plant–plant interactions show differential responses to different combinations of available resources that has been under-explored.The short-term functional response of Quercus petraea seedlings and Deschampsia cespitosa tufts grown alone or in mixture was monitored in contrasting combinations of soil inorganic nitrogen × light availabilities in a greenhouse experiment. Growth, biomass allocation, functional traits and resource acquisition were quantified. Intensity and importance of interactions were calculated by organ biomass-based indices.Competition exerted by D. cespitosa on oak was primarily driven by light availability and secondly, for each light level, by nitrogen supply, leading to a strong hierarchy of resource combinations for each considered plant organ. Under high light, oak preferentially allocated biomass to the roots, underlining the indirect role of light on the belowground compartment. Unexpectedly, Deschampsia cespitosa grew better in the presence of oak seedlings under high nitrogen supply whatever the light availability.Oak short-term nitrogen storage instead of investment in growth might be a long-term strategy to survive D. cespitosa competition. Why Deschampsia had a higher biomass in the presence of oak under nitrogen fertilization is an intriguing question. The role of root exudates or change in balance between intra- vs interspecific interactions may hold the answer. There may be an active mechanism of competition rather than only competitive resource exploitation.Forest managers sometimes practice adding nitrogen fertilizer to improve oak seedling growth in plantations or natural regeneration. Here, the higher biomass in mixture to the benefit of the competitor clearly questions this practice: oak may provide extra nitrogen to competitors during the early period of plant–plant interaction or it may influence the balance between intra- vs interspecific interactions. The identification and quantification of active competition may result in new practices for a broad diversity of plant–plant interactions such as tree regeneration, intercrop management and weed control in agriculture.     

Ingestion rates and dietary lipids affect growth and fatty acid composition of Dendraster excentricus larvae

This study investigated the effect of single and mixed algal diets on growth, fatty acid composition and ingestion rates for Dendraster excentricus larvae. Larvae were assigned to three single algal diet treatments Isochrysis galbana, Dunaliella tertiolecta or Rhodomonas sp. and four mixed algal diet treatments D. tertiolecta and Rhodomonas, I. galbana and D. tertiolecta, I. galbana and Rhodomonas, D. tertiolecta, Isochrysis galbana and Rhodomonas sp. Small amounts (0.36-0.6%) of stearic acid (18:0) were seen in the three algae used but a relatively large percentage (7-25%) of this SAFA was found in Dendraster larvae. The alga D. tertiolecta had the highest percentage (51.7%) of the short chain polyunsaturated fatty acid (PUFA) linolenic acid 18:3(n-3) and trace amounts (0.02-0.14%) of the long chain PUFAs eicosapentanoic (EPA, 20:5(n-3) and docosahexanoic acids (DHA, 22:6(n-3)). However, sand dollar larvae demonstrated the ability to elongate and desaturate shorter chain (18 carbon) polyunsaturated fatty acids (PUFA) to longer chain (20 carbon) n-3 PUFA. Thus high levels of 18:3(n-3) in D. tertiolecta led to high levels of EPA and low levels of 18:3(n-3) in Dendraster larvae fed this diet. Rhodomonas sp. had the highest percentage of stearidonic acid (18:4(n-3), 38.14%) and EPA (10.6%). Despite high levels of 18:4(n-3) in Rhodomonas sp. this acid was absent or found at very low levels in larvae fed this alga, or any combination of this alga. I. galbana had the highest percentage of DHA(14.3%) but was almost devoid of EPA (0.43%). Although Rhodomonas sp. and I. galbana had high levels of EPA and DHA sand dollar larvae did not incorporate higher levels of these long chain PUFAs into their lipids compared to those fed the alga D. tertiolecta. Dendraster larvae synthesized a number of 20 and 22 carbon non-methylene interrupted dienes (NMID), with levels increasing with larval stage. Higher ingestion rates were observed for Dendraster larvae fed single algal diets (Rhodomonas sp. or D. tertiolecta) and lower ingestion rates for those fed mixed algal diets. The highest ingestion rates were for 8-arm Dendraster larvae fed the large alga Rhodomonas sp. presented as a single algal diet. When fed a combination of three algae, selection of particles varied slightly depending on stage with 8-arm larvae ingesting slightly more of the larger algal cell in the mixture than 6-arm larvae. The present study suggests that regardless of the ratios given larvae might have an optimum ratio of different sized particles at which they can feed. The mixed algal diet of I. galbana and D. tertiolecta was the best algal diet leading to significantly larger larvae with high survival and development to metamorphosis. The single algal diets of Rhodomonas sp. or Dunaliella tertiolecta were the second and third best algal diets based on growth and survival to metamorphosis.     

Exceptional growth rates of captive loggerhead sea turtles,Caretta caretta

Twelve loggerhead sea turtle hatchlings (Caretta caretta) were removed from a nest site (A) at the Back Bay National Wildlife Refuge (U.S. Fish and Wildlife Service), Virginia Beach, VA. Hatchlings were distributed among study participants, and raised in captivity for a period of two years. Growth of the loggerheads was recorded weekly by straight-line caliper measurements of carapace lengths as well as measurements of total weights. Growth rates from the present study were much greater than those measured in previous studies. Mean weights for Nest A turtles at 1.5 years ranged from 10.3 to 17.6 kg, with one exceptional individual reaching 20.0 kg. The data from this study provide new insights into the early growth potential of loggerhead sea turtles. How this accelerated development may affect sexual maturity and post-release viability remain to be determined. © 1993 Wiley-Liss, Inc.