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41.
José A. Mejías 《Plant Systematics and Evolution》1994,191(3-4):147-160
Sexual reproduction is the main reproduction mechanism among the 14 wild Iberian taxa ofLactuca, Prenanthes, Cicerbita, andMycelis. High levels of self-fertilization occur inLactuca, as well as facultative and obligate xenogamy. Xenogamy is strongly correlated with large capitula having blue or bright yellow colouration, high P/O ratios, and long anthesis, whereas self-fertilization is correlated with smaller capitula having pale yellow colouration, small P/O ratios, and short anthesis. Large variations occur in P/O index among taxa showing similar fertilization mechanism, probably in relation to the number of florets included in flower heads. Interesting differences in reproductive systems have been detected between subspecies ofLactuca viminea. 相似文献
42.
A 2-year study of three natural populations of the distylousJasminum fruticans showed that mean fruit and seed production were significantly greater in shortstyled plants (thrums) than in long-styled
plants (pins). In this study, we investigated the role of four sequential factors which may differentially influence fruit
and seed set in the two floral morphs: (1) differences in flowering phenology, (2) a limitation of pollen transfer towards
pins, (3) a differential capacity of the two morphs to act through famale and male function and (4) differential fruit abortion
in the two morphs. Fruit set was significantly influenced by differences in flowering phenology although there were no differences
in flowering time between the two morphs. supplementary pollinations in a natural population significantly increased fruit
set and reduced the difference in fruit set between the two morphs in relation to controls, indicating a limitation on pollen
transfer which was most severe towards pin stigmas. In reciprocal crosses, seed set was significantly dependent on the paternal
and maternal identity of the pin parent. There was no significant variation among thrums for their performance as male or
female parent. Furthermore, individual pin plants with relatively high percentage seed set as female parents gave poor seed
set as male parents and vice-versa. Whereas fruit removal had no effect on seed number in thrum plants, a greater proportion
of viable seeds were produced on pin plants which were left to naturally mature their fruits than on pins which had fruits
artificially removed, suggesting the occurrence of selective fruit abortion in pins but not in thrums. The initially greater
maternal fitness of thrums due to their greater success as pollen recipients may thus be opposed by increased viable seed
set in the pins due to factors acting after the pollination stage. The relative reproductive success of floral morphs in the
distylousJ. fruticans is thus differentially influenced by ecological factors occurring at different stages of the reproductive process. 相似文献
43.
《Journal of Asia》2023,26(1):102018
Heavy metals are known to modulate the life history traits of spider species. This study aimed to explore the divergence in life-history traits, including survival, growth, development, and reproduction, in Pardosa birmanica and Lycosa terrestris housed on artificial soil or fed artificial food containing10mM of CuSO4 and10mM of PbCl2 either separately or in a binary mixture(i.e., 10 mM CuSO4 + 10 mM PbCl2) from 4thto 8th instars under laboratory conditions. The results revealed that all metals treatments caused developmental delays, and reduced growth rate. Metals treated females laid lower number of eggs with high hatching success but prolonged hatching time. The co-exposure of metals had great potential to affect the life-history traits of spiders than did Cu or Pb alone, specially by dietary uptake. This study demonstrated that the lifehistory traits of spider’s species provided sensitive endpoints and biomarkers for ecotoxicological risk assessments. Spiders are beneficial sentinel species and bioindicators because they help us monitor the risk to the organisms themselves and the ecosystem. 相似文献
44.
45.
The effects of salinity on the reproduction of coastal submerged macrophyte species were studied on samples of communities from six seasonal marshes in two outdoor experiments performed in autumn and in spring. The submerged macrophyte communities were submitted to five different salinity levels (0, 1, 2, 4 and 6 g/1 Cl?1). In a companion paper (Grillas, van Wijck & Bonis 1993) three groups of species were distinguished on the basis of their biomass production over the salinity range 0 to 6 g/1 Cl?1: (1) glycophytes (non-salt-tolerant species), (2) salt-tolerant species and (3) halo-phytes. This part of the study describes the impact of salinity on the reproduction of the individual species during the two experiments. The species differ in their capacity to reproduce in the autumn; only Zannichelliapedunculata and Tolypella hispánica were able to produce fruits in that season. For all species reproduction was greater in spring and strongly correlated with biomass, except for Chara canescens. Differences in reproductive effort over the salinity range amplified the halophytic nature of Ruppia marítima and Chara canescens and the intolerance of Callitriche truncata and Chara contraria. For the other species, reproductive effort did not differ significantly over the salinity range. Regarding the effect of salinity on biomass and reproductive effort of individual species, there were large differences in the total weight of propagules produced at the community level and in the relative contribution of individual species. The resulting quantitative changes in the species composition of the seed bank could affect the structure of the communities by their effects on the establishment and survival of species populations. 相似文献
46.
为比较山美水库两种入侵齐氏罗非鱼(Coptodon zillii)和伽利略罗非鱼(Sarotherodon galilaeus)种群的繁殖生物学特征,于2021年3—10月份在山美水库逐月采样,分析了繁殖时间、性比、绝对繁殖力、相对繁殖力和成熟卵径等特征。结果表明,两种罗非鱼均于4月份开始繁殖,齐氏罗非鱼繁殖高峰为7月, 10月结束繁殖;伽利略罗非鱼繁殖高峰为6月, 9月结束繁殖。齐氏罗非鱼平均绝对繁殖力为(4009.85±1305.69)粒、平均体重相对繁殖力为(67.32±15.63)粒/g、平均体长相对繁殖力为(31.31±5.03)粒/mm;伽利略罗非鱼平均绝对繁殖力为(1701.85±591.29)粒、平均体重相对繁殖力为(6.46±0.87)粒/g、平均体长相对繁殖力为(8.22±2.33)粒/mm;齐氏罗非鱼的绝对繁殖力、体重相对繁殖力和体长相对繁殖力均显著高于伽利略罗非鱼,平均成熟卵径则显著小于伽利略罗非鱼。齐氏罗非鱼和伽利略罗非鱼繁殖群体的雌雄性比分别为1.59和1.83,两个种群的雌雄性比无显著差异,但均显著偏离1﹕1。研究表明两种共同入侵的罗非鱼种群具有不同的繁殖... 相似文献
47.
J. Bastow Wilson Mick J. Crawley Mike E. Dodd Jonathan Silvertown 《Plant Ecology》1996,124(2):183-190
Repeated patterns, of a type that would be expected to result from limitations to species coexistence (i.e. assembly rules) were sought in the Park Grass experiment. This classical grassland experiment was sampled in two years, using replicated biomass samples. Variance in a number of measures was examined, and compared to the variance expected under appropriate null models, the latter based on assumptions of no interactions between species. In each case, an assembly rule would result in low variance. Examining variance in species richness between quadrats within a treatment, there was no indication of constraint on species co-occurrences; variance in richness was actually greater than expected under the null model, attributable to environmental variation or perhaps positive interactions between species. However, there was control on biomass, evidenced by variance in total biomass (i.e. over all species) within a treatment being significantly lower than expected under the null model. There was no indication of community structure based on guilds (i.e. functional types). Although there was in 1991 some, non-significant, indication of a constant proportion of species from the legume guild, there was no sign of such an effect in 1992. Searches for intrinsic guilds failed to converge. There was no indication at all of constancy in the proportional representation of guilds by biomass. Thus, there is good evidence for competitive control on plant growth, but none for control of species occurrences. There is no convincing evidence for guild structure in this community at the scale sampled. Possible conflict is discussed between the existence of evidence for temporal stability but the absence of evidence for spatial uniformity. It is concluded that most of the mechanisms proposed for temporal stability will not necessarily lead to control on spatial variation. For many mechanisms, this would depend on the spatial scale examined. 相似文献
48.
Akio Mori 《Primates; journal of primatology》1995,36(1):11-26
The feeding process of Japanese monkeys on soy beans which were scattered over a sandy beach on Koshima islet was studied.
Younger monkeys were able to pick up more beans when 8 kg of beans were divided and given two times (“two times feeding”)
than when the whole amount (8 kg) of beans was given at one time (“one time feeding”). The effect of saturation of the food
intake capacity in younger monkeys at the first feeding in “two times feeding” did not appear at the second feeding one hour
later. The minutely intake of soy beans (feeding speed) for each age class was analyzed. The decline of feeding speed in adult
females after the peak in “one time feeding” was not related to the decline in density of beans on the ground, and this decline
was caused by saturation of their food intake capacity.
Adult females were divided into four classes according to their dominance rank order: high, lower-high, higher-low, and low
classes. The total amount of intake in “one time feeding” was far larger in the high class than in any of the other classes.
The total amount of feeding in the first feeding of “two times feeding” increased in accordance with rise in the dominance
rank class, and there was no relation to rank and total feeding amount in the second feeding of “two times feeding.” Differences
existed in the process of feeding between the rank classes. The feeding speed of the low class was as high as that of the
high class on the curve of minutely intake, while the low class stopped feeding much earlier than the high class. The lower-high
class displayed a low feeding speed, and stopped feeding the latest. The order of the duration to stay and to feed in the
feeding area was lower-high > high > higher-low > low, and this order did not change under the three different feeding conditions,
“one time feeding,” and the first and second feedings of “two times feeding.” Adolescent females tended to stay the longest
duration in the feeding area among all age classes. Both the lower-high class females and adolescent females had an unstable
social status in the Koshima group, and their social status affected their feeding behaviors. The feeding behaviors were similar
in attitude depending on social status, and are considered to be maintained for a fairly long time.
The feeding strategy of the lower-high class, in staying a longer duration in the artificial feeding area, and departing later,
may be effective under the artificial feeding conditions, but it may be a bad strategy in a natural habitat where the food
is not so clumped as in artificial feeding, and where choice of other food patches is possible. The above results agree well
with previous reports for the Koshima group, indicating that the rank of the lower-high class females was unstable (Mori et al., 1989), and that their reproductive success was low (Watanabe et al., 1992). 相似文献
49.
Summary
Rhamnus alaternus L. is a dioecious, fleshy-fruited shrub, typical of Mediterranean vegetation, which has been recorded from the region since the tropical Tertiary. Reproductive biology of this species has been studied in Southern Italy over a period of 4 years with both field and laboratory experiments. In all the studied populations male plants predominate over the females, have a higher flower density and flower regularly every year while females are usually alternate-bearing. A strong negative association between fruit formation and vegetative growth has been found indicating that the presence of fruits on a branch reduces the growth of new shoots. This phenomenon, together with alternate-bearing, is evidence of a strong competition between vegetative growth and reproductive activity and indicates resource limitation. Flower morphology and quantity of pollen produced are typical of insect pollinated species, and flies of the Empididae and Muscidae were trapped bearing pollen at female plants but pollen is also dispersed by wind. Field experiments on pollination success showed that the exclusion of insects as pollen vectors produces a significant decrease in fruit development. Excess pollen provided by hand-pollination increases fruit set over open-pollination and reproductive success in the field is therefore pollen limited. The variability of sex expression, male fitness, fruit production, regrowth and pollination presented here suggests that these predispersal characteristics ofR. alaternus have been subject to evolutionary change since the tropical Tertiary climate was replaced by a Mediterranean one. This points to the possibility that reproductive, as well as morphological and physiological characteristics, may be equally selected for in extreme environments such as the Mediterranean. 相似文献
50.
This study examines the annual energetics of a small folivorous marsupial, Pseudocheirus peregrinus. Particular attention was given to the energy and time allocated to reproduction by the females. Daily energy expenditure was measured directly using the doubly labelled water technique. Energy transferred to the young via the milk was estimated from information on milk composition and production. There was no significant seasonal variation in the energy expenditure or water influx of males or females. The mean daily energy expenditure of a 1-kg non-lactating adult ringtail possum was 615 kJ day–1 or 2.2 times standard metabolic rate. Females showed significant changes in daily energy expenditure according to their reproductive status. Without the burden of lactation the total annual energy expenditure of an adult female was estimated as 212.4 MJ kg–1 year–1. The total annual energy expenditure of a female rearing two young was 247.5 MJ kg–1 year–1, with the late stage of lactation constituting the most energetically expensive period accounting for 30% of the total yearly energy expenditure during 24% of the time. Total metabolisable energy allocation during reproduction (22 MJ kg) was similar to estimates available for other herbivores, although, the peak metabolisable energy allocation during lactation (759 kJ day–1) was lower than values available for other herbivores. The total energy requirement for reproduction (metabolisable energy plus potential energy exported to young via milk) suggests that the ringtail possum also has a relatively low overall energy investment in reproduction. It is suggested that the lactational strategy of the ringtail possum has been selected in order to spread the energy demands of reproduction over time due to constraints on the rate of energy intake imposed by a leaf diet and/or to prolong the mother-young bond. The strategies a female ringtail possum may employ to achieve energy balance when faced with the energy demands of reproduction are discussed. 相似文献