Growth and reproduction of the non‐native icefish Neosalanx taihuensis Chen, 1956 (Salangidae) in a plateau lake,southwestern China

Growth, reproduction and abundance traits of the invasive icefish Neosalanx taihuensis Chen, 1956 were investigated monthly from July 2009 to May 2011 in Lake Erhai on the Yunnan‐Guizhou Plateau, south‐western China, in order to explore the changes in life‐history traits after translocation. The results indicated that the icefish exhibited obvious plasticity in growth and reproduction traits. Growth of the fish in Lake Erhai was faster than that in native waters and in other translocated reservoirs. By fitting the von Bertalanffy growth model to the data, it was estimated that icefish obtain an asymptotic size of 96.12 mm, a K of 1.61, and a t₀ of ‐0.26; the calculated overall growth performance index φ′ was 4.17. The strategy of reproduction changed from multiple‐ to single‐spawning. The spawning period was from October to December with the absolute and relative fecundities of 1250 ± 169 eggs per ind and 2557 ± 245 eggs per g, respectively. Plasticity in icefish growth and reproduction in Lake Erhai greatly facilitated its population establishment, making it one of the most abundant fish species. The icefish invasion in the lake may be one of the reasons for the decrease or extinction of native fish species populations, and some measures for the control of this invasive fish are suggested.     

Changes in abundance of the icefish Neosalanx pseudotaihuensis Zhang (Salangidae) and the impact on the zooplankton community of Xujiahe Reservoir,central China

The icefish Neosalanx pseudotaihuensis Zhang is a small and commercially exploited zooplanktivorous fish in Xujiahe Reservoir (central China). Data of catch per unit effort (CPUE) from June 1995 to December 1997 show that the abundance of the icefish varied dramatically, which is reflected in the populations of the dominant cladocerans. The densities of Leptodora kindti, Daphnia galeata and Diaphanosoma dubia were the highest in 1997 when the abundance of the icefish was the lowest, and the reverse was the case for Boimina spp. These results document that the population of this annual fish is very variable and high biomass of the fish could exert a pronounced effect on the zooplankton community.     

银鱼的产量能预报吗

将离散Ｌogistic模型应用于银鱼种群数量变动研究,通过对滇池等４个典型湖泊或水库的银鱼年产量变动的初步分析和模拟,发现现的有的湖泊或水库银鱼产量的参数值都落入了混沌区间,在自然生态系统中找到了混沌行为的证据。同时指出：（１）混沌行为使银鱼产量长期预报不可能实现,只有短期预报才能保证必要的精度。（２）严格控制捕劳对尚未繁殖的亲鱼的影响,保留足够的繁殖亲鱼,才能保证资源的持续利用。另一方面,如谷获得相对稳定的产量,可能控制捕捞死亡率Ｆ来改变增增长率参数μ,防止银鱼产量剧烈波动。（３）水域污染和其他破坏水域饵料生物种群结构的因素能导致银鱼的内禀自然增长率γ值和最大种群数量Ｎmax发生变化,从而引起种群的数量变动。     

Productivity of high and low density populations ofJaponaria laminata armigera (Diplopoda) in a warm-temperate forest ecosystem

The productivity of the final larval and adult populations of a large sized diplopod, Japonaria laminata armigera were studied at a warm temperate ever-green broad leaf forest in Chiba Japan. The population density was about 200/m² in May 1962, and 7/m² in May 1966, the former being about 30 times as much as the latter. A remarkable growth of animals was seen from June to November, and the growth pattern of individuals in both populations was very similar. The growth and mortality were calculated by the following formulae, where G is growth, M mortality, N_t number at the time t,W_t−1 mean body weight of animals at the time t−1, ΔN decrease in number during the period of time from t−1 to t, ΔW growth in mean body weight during the time from t−1 to t. The constant b in the formula R=aW^b representing the relation between body weight and oxygen consumption of Japonaria laminata was determined at 0.81, and Q₁₀ was estimated at about 2. The amounts of growth and assimilation were calculated. The pattern of dynamics in terms of productivity of the population in the two periods were very similar. But, the amounts of assimilation were computed at 57.8 kcal/m²/from May 1962 to April 1963, and 3.01 kcal from May 1966 to April 1967. The former is 20 times as much as the latter. The growth or ecological efficiencies for the populations were similar.     

Phenological features in relation to growth forms and biomass accumulation in an alpine meadow of the Central Himalaya

Phenological records of 50 plant species were made during 1988–89 in an alpine meadow (30° 10-30° 13 N lat. and 79° 39-79°-41 E long.) of Central Himalaya located between 3100–3750 m elevation. The growth initiation occurred when temperature began to rise continuously and the resulting in snowmelt. The peaks of the various phenophases succeeded one after another in time, within a period of about four months (from May to September) which is longer than the period reported for the alpine sites of higher latitudes. The period of growth initiation appeared to be related to growth form, the species showing earlier growth initiation (when temperatures were lower) deployed leaves to lower heights, close to the ground. A majority of forbs completed growth cycle earlier than the grasses. For example, one group represented by Trachydium roylei reached peak growth a few weeks before did another group of species, represented by Danthonia cachemyriana, which is indicative of niche separation of the respective group of species. Activities of accumulation of live and dead shoot biomass were clearly separated in time in most communities, the former occurring from May to August, and the latter mainly in September. Nomenclature: Osmaston (1926).     

The influence of position on genet growth: a simulation of a population of bracken (Pteridium aquilinum (L.) Kuhn) genets under grazing

In a spatially explicit simulation model of vegetation dynamics (VegeTate), I labelled the initial mass of Pteridium aquilinum in each of 225 cells as a single, unique genet or clone. The physical environment was homogeneous and all genets shared the same phenotype. The aim was to discover whether and how the success of each genet was affected by its initial position relative to other genets and a competing grass species. In a scenario in which grazing generated a grass-bracken mosaic with complex spatial dynamics, the amount of growth of each genet ranged widely, from frequent extinction to mass increase by over 300 times. The main factor in the impact of position on genet growth was shown to be a benefit from the initial presence or proximity of a large mass of P. aquilinum. This was because a high density of P. aquilinum reduced local grazing intensity, allowing plant mass to accumulate and shifting the balance of competition in favour of P. aquilinum. Thus variations between cells in initial mass of P. aquilinum were greatly amplified. The implications of this amplification of initial differences between sites for population genetics are briefly discussed. Qualitative features of the spatial distribution of genets at the end of simulations matched reported observations on patchily distributed field populations of P. aquilinum. These features included dominance of a large population by a small minority of genets, widespread mixtures of a dominant genet and one or more subordinate genets, and the presence of patches of P. aquilinum formed both by agglomeration from neighbouring foci and by spread of dominant genets. Under less intense grazing, which allowed little or no development of vegetation mosaics, genet growth varied relatively little and initial variations in relative mass between genets were little changed. Based on this study, I hypothesize that any processes that generate non-linear spatial dynamics will also generate complex genet dynamics.     

Microsatellite analysis reveals genetic differentiation between year-classes in the icefish <Emphasis Type="Italic">Chaenocephalus aceratus</Emphasis> at South Shetlands and Elephant Island

Chaenocephalus aceratus is one of the most abundant Antarctic icefish species in the Atlantic sector and has been a by-catch species in the fishery for mackerel icefish, Champsocephalus gunnari, between the mid-1970s and mid-1980s at South Georgia, South Orkney, and South Shetland Islands. The species became the target of the fishery in particular seasons, such as at South Georgia in 1977/78. In our paper, we report results on genetic differentiation for 11 microsatellite loci in C. aceratus samples collected at the South Shetlands and Elephant Island. This study represents the first report on microsatellite variability of an icefish species. Our results support the evidence from previous studies on differences in infestation patterns of parasites that a single panmictic population of C. aceratus exists, spanning the two sampling sites separated by about 100 km. Moreover, our study indicates the presence of a significant genetic differentiation between individual year-classes pointing out the existence of dynamic processes acting at the population genetic level, according to recent results for broadly distributed marine species. Both small effective population size and immigration from unsampled differentiated stocks may be at the base of the differentiation found in C. aceratus. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Growth,length–weight relationship and biological information on the clearhead icefish (Protosalanx hyalocranius Abbott, 1901) in Lake Khanka (Xingkai)

This paper reports the growth pattern and length‐weight relationship and summarizes biological data for the clearhead icefish (Protosalanx hyalocranius) in Lake Khanka (Xingkai), on the border between China and Russia. The von Bertalanffy growth was estimated as SL = 20.3(1 ? e^{?2.93 (t ? 0.21)}). The length‐weight relationship was W = 0.00448 SL^2.99 for juveniles, and W = 0.000896 SL^3.59 for adults. P. hyalocranius mature in December and spawn in January, when the lake is still covered with ice, then die after spawning. The larvae hatch in March. Juveniles feed mainly on zooplankton whereas adults also feed on other fishes.     

Influence of shade timing on an Equisetum arvense L. population

Equisetum arvense L. is a perennial pteridophyte that grows in open sites. In Tokyo, the plant has photosynthetic shoots from late March to November. However, in some populations, these shoots are lost before summer because of shading by taller plants. To investigate the contribution of shoots that remain on the plant for a certain duration, in terms of the maintenance of the E.arvense population, tubers were cultivated under different light conditions and the dry weight of growth, photosynthetic rates and respiration rates were measured. Individual growth was simulated on the basis of matter production and its partitioning. Biomass at the start of the next growing season (the initial size) was seriously decreased by shading before July. However, shading after July had little effect on the initial size of the next season plants. Thus, E.arvense can maintain its population if its shoots are retained until summer.     

Accidental altruism in insular pit-vipers (Gloydius shedaoensis, Viperidae)

Darwinian theory predicts that organisms will display traits that benefit themselves rather than other individuals; exceptions to this rule usually are explicable by kin selection. Our studies on an insular population of venomous snakes in north-eastern China reveal a different situation. Only one species of snake (Gloydius shedaoensis, Viperidae) occurs on the island of Shedao, and displays altruism between size (age) classes. First, small snakes frequently kill prey items larger than they can swallow themselves. This behaviour enhances rates of feeding of larger conspecifics, which scavenge the birds' carcasses. Second, large snakes kill raptorial birds (sparrowhawks Accipiter nisus) that pose little or no threat to themselves. This behaviour reduces predation risk for smaller snakes. These effects are presumably accidental consequences of the high venom toxicity of the pit-vipers, which enable them to kill inedible prey and non-threatening predators at little cost. Nonetheless, this accidental altruism may have significant ecological consequences. For example, these behaviours may contribute to the remarkably high population densities of snakes on Shedao.     

Genetic analysis of novel intra-species unilateral incompatibility in Brassica rapa (syn. campestris) L.

Plants have evolved many systems to prevent inappropriate fertilization. Among them, incompatibility is a well-organized system in which pollen germination or pollen-tube growth is inhibited in pistils. Self-incompatibility (SI), rejecting self-pollen, promotes outbreeding in flowering plants. On the other hand, inter-species incompatibility, preventing gene flow among species to restrict outbreeding, usually occurs unilaterally, and is known as unilateral incompatibility (UI). In Brassicaceae, little is known about the molecular mechanism of UI, although S-locus genes involved in recognition of self-pollen have been characterized in the SI system. In the present study, we characterized novel UI observed between members of the same species, Brassica rapa; pollen of Turkish SI lines was specifically rejected by pistils of the Japanese commercial SI variety Osome. The incompatible phenotype of this intra-species UI closely resembled that of SI. Segregation analysis revealed that the pollen factor of this UI was not linked to the S-locus.The revised version was published online in December 2004 with corrections to figure 1.     

Do Herbivore-Induced Plant Volatiles Influence Predator Migration and Local Dynamics of Herbivorous and Predatory Mites?

If predators lack information on the prey's position, prey have more chance to escape predation and will therefore reach higher population densities. One of the many possible cues that predators may use to find their prey are herbivore-induced plant volatiles. Although their effects on the behaviour of foraging predators have been well studied, little is known about how these prey-related odours affect predator–prey dynamics on a plant. We hypothesise that herbivore-induced plant volatiles provide the major cue eliciting predator arrestment on prey-infested leaves and that the response to these volatiles ultimately leads to lower prey densities. To test this hypothesis experimentally, we created two types of odour-saturated environments: one with herbivore-induced plant volatiles (treatment), and one with green-leaf volatiles (control). An odour-free environment could not be tested because herbivores require plants for population growth. We measured the rate at which predatory mites (Phytoseiulus persimilis) immigrate, emigrate and exploit a single leaf infested by two-spotted spider mites (Tetranychus urticae). The experiments did not show a significant difference between treatment and control. At best, there was a somewhat higher rate of predator (and possibly also prey) emigration in the treatment. The lack of a pronounced difference between treatment and control indicates that at the spatial scale of the experiments random searching for prey was as effective as directional searching. Alternatively, predators were arrested in the prey patch by responding not merely to herbivore-induced plant volatiles, but also to other prey-related cues, such as web and faeces. Based on our current experience we advocate to increase the spatial scale of the experiment (>1m²) and we provide other suggestions for improving the set-up.     

Strong “bottom‐up” influences on small mammal populations: State‐space model analyses from long‐term studies

“Bottom‐up” influences, that is, masting, plus population density and climate, commonly influence woodland rodent demography. However, “top‐down” influences (predation) also intervene. Here, we assess the impacts of masting, climate, and density on rodent populations placed in the context of what is known about “top‐down” influences. To explain between‐year variations in bank vole Myodes glareolus and wood mouse Apodemus sylvaticus population demography, we applied a state‐space model to 33 years of catch‐mark‐release live‐trapping, winter temperature, and precise mast‐collection data. Experimental mast additions aided interpretation. Rodent numbers in European ash Fraxinus excelsior woodland were estimated (May/June, November/December). December–March mean minimum daily temperature represented winter severity. Total marked adult mice/voles (and juveniles in May/June) provided density indices validated against a model‐generated population estimate; this allowed estimation of the structure of a time‐series model and the demographic impacts of the climatic/biological variables. During two winters of insignificant fruit‐fall, 6.79 g/m² sterilized ash seed (as fruit) was distributed over an equivalent woodland similarly live‐trapped. September–March fruit‐fall strongly increased bank vole spring reproductive rate and winter and summer population growth rates; colder winters weakly reduced winter population growth. September–March fruit‐fall and warmer winters marginally increased wood mouse spring reproductive rate and September–December fruit‐fall weakly elevated summer population growth. Density dependence significantly reduced both species' population growth. Fruit‐fall impacts on demography still appeared after a year. Experimental ash fruit addition confirmed its positive influence on bank vole winter population growth with probable moderation by colder temperatures. The models show the strong impact of masting as a “bottom‐up” influence on rodent demography, emphasizing independent masting and weather influences; delayed effects of masting; and the importance of density dependence and its interaction with masting. We conclude that these rodents show strong “bottom‐up” and density‐dependent influences on demography moderated by winter temperature. “Top‐down” influences appear weak and need further investigation.     

The physiological ecology of two populations of Mytilus edulis L.

Summary Seasonal cycles in the rates of oxygen consumption, feeding, absorption efficiency and ammonia-nitrogen excretion in two populations of Mytilus edulis were measured in the field under ambient conditions and related to body size, the gametogenic cycle, the concentration of suspended particulate matter in the water and temperature. Relationships between the various physiological variables are also considered and protein and energy budgets estimated. Both the scope for growth and the relative maintenance cost were seasonally variable, demonstrating a minimum capacity for growth in the winter and a maximum capacity in the summer. In one population subjected to abnormally high temperatures in the winter the scope for growth was negative for four or five months between January and May. These population differences are discussed and the potential for using physiological integrations in intra-specific comparisons of fitness is identified.     

Seasonal Abundance and Reproduction of the Fourwing Flyingfish, Hirundichthys affinis, off Barbados

The seasonal abundance and reproductive cycle of the flyingfish Hirundichthys affinis was studied near Barbados. H. affinis shows large seasonal variation in abundance. They are common between December and June and scarce from July to November. The population size structure of H. affinis was determined by fishing with four different mesh sizes throughout one year. There appear to be two cohorts of H. affinis present in May and June, one of immature fish with a mean size of 19.8cm FL, and one of mature fish with a mean size of 21.7cm FL. From September to April there is only a single cohort of maturing fish with a mean size that increases from 20.4cm FL in September to 22.0cm FL in April. H. affinis spawns throughout the fishing-season (December–June) and shows a peak in spawning activity from March to June. Immature fish are present in Barbados waters from July to November but in very low abundance. Surface water temperature, wind speed and swell height are the only environmental factors with which catch rate of H. affinis showed significant correlation. Catch rate appears to be negatively correlated with temperature, whereas for wind speed and swell height there are optima. Three hypotheses for the seasonal variation in abundance of H. affinis were examined. The hypothesis that this species remains dispersed near Barbados during the off-season was rejected. The other hypotheses were refined. Both post-spawning mortality, resulting in an interval of low abundance between cohorts (non-overlapping generations), and migration of fish away from Barbados at the end of the fishing season, remain possible explanations for the observed seasonal variation in abundance of this species.     

Population structure and dynamics of an evergreen shade herb, Ainsliaea apiculata (Asteraceae), with special reference to herbivore effects

The population structure and dynamics of Ainsliaea apiculata, a forest understory evergreen herb widely distributed in Japan, was examined in a Chamaecyparis obtusa forest in Ibaraki Prefecture, central Japan (36°51N, 140°33E; 750 m a.s.l.). The mean population growth rate () calculated from the transition matrices for 4 years was 0.69 per year, predicting that the population size will decrease remarkably. There was a significant positive correlation between the survival of old leaves and the growth of new shoots in the following year. The shoots, especially new leaves, were damaged severely by herbivores (caterpillars of Leioptilus sp.). The survival rate of leaves formed in the previous spring to the next spring was remarkably low (41–54%). The growth of new shoots depended mainly on the reserves contained in old shoots, especially those in old leaves. New shoots of A. apiculata began to develop in spring, even though they were formed in autumn of the previous year. A defoliation experiment also showed that the removal of old shoots at the beginning of the growing season significantly inhibited the growth of new shoots. Damage to old shoots by herbivores severely influenced the growth and population dynamics of A. apiculata.     

Origins of H-2 polymorphism in the house mouse. II. characterization of a model population and evidence for heterozygous advantage

Comparison of the rate of synonymous and nonsynonymous nucleotide substitutions suggests that certain regions of the functional H-2 genes, which are part of the mouse major histocompatibility complex (Mhc), are under strong positive selection pressure. Thus far, however, little evidence has been provided for the existence of such pressure in natural mouse populations. We have, therefore, initiated experiments designed to test the hypothesis of positive selection acting on H-2 loci. The experiments are being carried out on two natural mouse populations in Jerusalem, Israel. One population occupies a space of about 100 m² in a chicken coop, the other lives in a nearby field in which mouse stations providing food and shelter have been set up. Extensive typing of these two populations revealed the presence of only four H-2 haplotypes. Mice in the two populations breed continually all year around, yet population size varies seasonally, with population maxima in winter and minima in summer. The population in the chicken coop contains a relatively stable nucleus which may be organized in demes with an excess of females over males and limited territorial mobility. The rest of the mice stay in the population for a short time only and then either die or emigrate. The field population is smaller and more loosely organized than the chicken-coop population, with demes probably forming only during population maxima. For the rest of the time breeding in this population is probably panmictic. At a population minimum in the summer of 1984, H-2 homozygotes happened to predominate over heterozygotes. This situation, however, lasted for a short time only and thereafter there was a continuous, statistically highly significant increase in the proportion of H-2 heterozygotes of one or two types. The increase occurred in both populations but was more apparent in the chicken-coop population. This observation provides the first experimental evidence that heterozygous advantage might be one of the mechanisms maintaining high H-2 polymorphism in natural populations of the house mouse.     

Growth and maturation of the 'autumn-fruiting type' of Sargassum horneri (Fucales, Phaeophyta) and comparisons with the 'spring-fruiting type'

The growth and maturation period of the autumn-fruiting population ot Sargassum horneri C. Agardh (Phaeophyta) was investigated in Hiroshima Bay, Seto Inland Sea. Surveyed traits were compared to those of the spring-fruiting type and ecological features of this species were discussed. The annual lifetime of the autumn-fruiting population could be divided into four phases according to the daily increase in thalius length:phase I from December to May (increase in length < 0.1 mm/ day), phase II from May to September (= 0.3–1.0 mm/ day), phase Ml (from September to December > 10 mm/day) and phase IV which was the senescence phase from December to March. Receptacle formation‘as observed in November and gamete release from November to February. Conversely, the spring-fruiting type germinated in April and exhibited swifter growth in its early stage of development than the autumn-fruiting type. Rapid increase in thalius iength in autumn was common in both fruiting types, although the spring-fruiting type continued to grow during winter. Receptacle formation of the spring-fruiting type started in February but gamete release was not observed until April and May. The difference in life-history patterns of both types of S. horneri was in the overwintering period. The autumn-fruiting type spent that season as germi-ings or as young plants exhibiting slow-paced growth, while the spring-fruiting type overvwintered as adult thal-li preparing for gamete release in spring.