云南高原湖泊水葱克隆生长与有性繁殖特征及影响因子

为掌握挺水植物克隆生长与有性繁殖参数的空间分布格局特征及环境因子对植物繁殖的影响路径,该文利用云南高原的立体地形,通过空间替代时间的方法,探讨6个湖泊共有挺水植物水葱(Schoenoplectus tabernaemontani)的克隆生长、有性繁殖的地理差异和变化规律以及对环境变化的响应。结果表明：(1)密度、株高、基径等克隆生长参数,以及结实率、穗生物量及其投资比、种子产量、活性种子数等繁殖参数在不同地理空间上存在显著差异(P<0.05),而地上生物量无显著差异。(2)密度、株高、结实率、穗生物量及其投资比等参数具有显著的经纬度、海拔地带性分布特征,其中密度随纬度和海拔的增加而增加、随经度的增加而减小,而株高、结实率、穗生物量及其投资比随纬度和海拔的增加而减小、随经度的增加逐渐增大。(3)暖月和冷月均温,土壤全氮、全磷是影响水葱克隆生长(密度、株高)的关键因子,其中暖月均温影响最大,年均降水、土壤有机碳是影响水葱有性繁殖的关键因子,其中年均降水影响最大。综上认为,气候因子(暖月均温、冷月均温和年均降水)是影响云南高原湖泊湖滨带植物水葱生长和繁殖的主要因子。     

Between‐species differences in demographic responses to temperature of coexisting cladocerans

Abstract In this work we report on the seasonal trends of abundances in terms of temperature exposure for four coexisting cladoceran species (Daphnia ambigua (Daphniidae), Ceriodaphnia dubia (Daphniidae), Diaphanosoma chilense (Sididae) and Moina micrura (Moinidae)) from a Chilean temperate lake. In order to compare the demographic response to temperature, we used life table experiments to parameterize matrix models for the four species at four fixed temperatures. From these life table response experiments we assessed the effects of temperature, species and their interaction on the variation in growth rate, as well as the contribution of juvenile survival, adult survival, fertility and age at first reproduction to the changes in growth rate. Our results showed interspecific differences in the effect of temperature on the growth rate. Species that present higher field abundance at lower temperature also exhibited, under controlled experiments, higher growth rates at low temperature and lower growth rates at high temperature, relative to the additive model. Conversely, species with higher abundances during the warmer seasons exhibited higher growth rates at higher experimental temperatures and lower growth rates at lower temperatures, relative to the additive model. The vital rates that most contributed to the variation in growth rate were age at first reproduction and fertility. Our growth rate estimates matched predictions of the metabolic ecology model.     

Growth and reproduction of the mosquitofish,Gambusia affinis,in relation to temperature and ration level: consequences for life history

The allocation of energy to growth and reproduction, in relation to temperature and food availability, was investigated in laboratory experiments with the mosquitofish,Gambusia affinis. At constant temperature of 20, 25 and 30°C and ad libitum feeding, specific growth rates increased with increasing temperature at 1.7, 3.1 and 3.4% dry mass day⁻¹, respectively. Growth rates in a cycling temperature regime (20–30°C, ) were faster than in a 25°C constant temperature. As temperature increased from 20 to 30°C, mean age at first reproduction decreased from 191 to 56 days and brood size and mass of offspring increased significantly. Interbrood interval was also temperature dependent; estimates at 25 and 30°C for females >1000 mg were 22.6 and 18.6 days, respectively. Interbrood interval could not be calculated at 20°C. Although fitness was highest at 30°C, females at 25°C invested a greater proportion of surplus energy (growth and reproduction) to reproduction (38%) than at 20 (17%) or 30°C (36%) during the 32-week study. Fish at cooler temperatures began reproduction at a smaller size. Where rations were controlled at low, medium, and ad libitum levels, somatic and gonadal growth increased with increasing temperatures and food availability. The proportion of energy invested in reproduction was highest at 25°C for each comparable ration level. Calculated energy budgets indicated that over the 10-week study, 17–22% of the food energy was invested in growth, 0–7% in reproduction, and 75–83% in respiration and excretory losses, depending on feeding and temperature conditions.     

Temperature response of root‐lesion nematode (Pratylenchus thornei) reproduction on wheat cultivars has implications for resistance screening and wheat production

The root‐lesion nematode Pratylenchus thornei is a major pathogen of wheat and other field crops, particularly in the northern grain region of sub‐tropical eastern Australia. Research was conducted into the temperature requirements of P. thornei for reproduction on wheat to increase the reliability of selection in resistance tests for wheat breeding. Final population densities (P_f) of P. thornei were determined on four wheat cultivars (Gatcher, GS50a, Potam and Suneca) at fortnightly intervals from 8 to 18 weeks at a range of six soil temperatures (15°C, 20°C, 22.5°C, 25°C, 27.5°C and 30°C) in a glasshouse experiment. Pratylenchus thornei had the highest P_f in the temperature range of 20–25°C on all wheat cultivars at all growth times after sowing, with no nematode reproduction measured at 30°C and very little at 15°C. The wheat cv. GS50a consistently produced lower P_f than cvs Gatcher, Potam and Suneca in the optimum temperature range of 20–25°C. In carrot disc cultures, P. thornei had an optimum temperature of 25°C with little reproduction at 17.5°C and none detectable at 30°C. A standard soil temperature of 23°C was chosen to maximise differences in nematode reproduction between resistant and susceptible wheat genotypes for selection in wheat breeding, and to improve reproducibility among successive experiments. The relationships derived from these experiments will be valuable for simulation of P. thornei reproduction in crop growth models. They also indicate that early sowing of wheat into cool soil (≤15°C) in farmers' fields of the northern grain region should favour wheat growth over nematode reproduction and increase grain yield.     

Effects of temperature, light and heterotrophy on the growth rate and budding of the temperate coral Cladocora caespitosa

Recent investigations have shown the temperate scleractinian coral Cladocora caespitosa to be a new potential climate archive for the Mediterranean Sea. Whilst earlier studies have demonstrated a seasonal variation in growth rates, they were unable to distinguish which environmental parameter (light, temperature, or food) was influencing growth. In this study, the effect of these three factors on the coral physiology and calcification rate was characterized to aid the correct interpretation of skeletal trace element variations. Two temperatures (13 and 23°C), irradiances (50 and 120 μmol m⁻² s⁻¹), and feeding regimes (unfed and fed with nauplii of Artemia salina) were tested under controlled laboratory conditions on the growth, zooxanthellae density, chlorophyll (chl) content, and asexual reproduction (budding) of C. caespitosa during a 7-week factorial experiment. Unlike irradiance, which had no effect, high temperature and food supply increased the growth rates of C. caespitosa. The effect of feeding was however higher for corals maintained at low temperature, suggesting that heterotrophy is especially important during the cold season, and that temperature is the predominant factor affecting the coral’s growth. At low temperature, fed samples had higher zooxanthellae density and chl content, possibly for maximizing photosynthetic efficiency. Sexual reproduction investment of C. caespitosa was higher during favourable conditions characterised by high temperatures and zooplankton availability.     

LATITUDINAL TRENDS IN THE GROWTH AND REPRODUCTIVE SEASONALITY OF DELESSERIA SANGUINEA,MEMBRANOPTERA ALATA,AND PHYCODRYS RUBENS (RHODOPHYTA)1

The seasonality of Delesseria sanguinea, Membranoptera alata, and Phycodrys rubens (Rhodophyta) was studied at Helgoland (North Sea, Germany) and Roscoff (Brittany, France). Plants were collected at bimonthly intervals, and growth and reproduction were monitored. Growth of blades was observed mainly in spring, although small blades were found on plants of M. alata and P. rubens all year round. In summer, plants started to degenerate and in autumn they became fertile. The reproductive season of D. sanguinea lasted from October to February/April at both locations, whereas reproductive plants of M. alata and P. rubens were found until April at Helgoland and until June and August, respectively, in Roscoff_: Lower winter temperatures at Helgoland than at Rascoff may have caused these differences in the duration of the reproductive season. Using published data, the seasonal patterns at Helgoland and Roscoff were compared to those found at other locations (e.g. Barents Sea; Maine, USA; Isle of Man, UK) and local temperature/daylength conditions. Blade growth was synchronized across all populations and occurred in spring, when temperatures were usually still suboptimal for growth. Maximum reproduction was generally found in the colder half of the year but started earlier in autumn in the Barents Sea. Adaptive strategies in the seasonal control of growth and reproduction are discussed. Adequate timing of the history events (e.g. appearance of juveniles in spring) appears more important than maximal growth and reproduction of adults during the season with the most favorable temperatures.     

ABIOTIC REGULATION OF INVESTMENT IN SEXUAL VERSUS VEGETATIVE REPRODUCTION IN THE CLONAL KELP LAMINARIA SINCLAIRII (LAMINARIALES,PHAEOPHYCEAE)1

Clonal kelp taxa may reproduce both sexually and vegetatively resulting in a potential trade‐off in the allocation of acquired carbon and nitrogen resources. Such trade‐offs may dictate a different response of clonal kelps to varying environmental conditions relative to aclonal kelp taxa. Laboratory temperature and nutrient manipulation experiments demonstrated that investment in sexual and vegetative reproduction in Laminaria sinclairii (Harv. ex Hook. f. et Harv.) Farl., C. L. Anderson et D. C. Eaton was regulated by different abiotic factors. Sorus production (investment in sexual reproduction) and blade growth were significantly higher at 12°C compared to 17°C, regardless of nutrient concentration. Net carbon storage and depletion in rhizomes were observed in the low‐ and high‐temperature treatments, respectively, suggesting that carbon stores were not responsible for increased growth. Rhizome elongation (investment in vegetative reproduction), on the other hand, was significantly higher in 12 μM NO₃^? than in 2 μM NO₃^?, irrespective of temperature. This increase in rhizome growth was concurrent with elevated rhizome percent tissue nitrogen levels also observed in treatments with higher nutrients, again indicating a growth response to treatment independent of previous nutrient stores. These results suggest that regulation of growth and investment in sexual reproduction in L. sinclairii is similar to that in aclonal kelps (i.e., warmer temperatures result in decreased reproductive output). Additionally, depletion of carbon and nitrogen from rhizomes in suboptimal conditions confirms the role of clonal kelp rhizomes in carbon and nutrient storage.     

Survival and Reproduction Potential of Philodina roseola (Ehrenberg) (Rotatoria,Bdelloida) under Various Temperature Conditions

Survival data, in addition to data on growth and reproduction rate, are necessary to estimate rotifer productivity under various thermal conditions. A method of individual culturing of Philodina roseola helped the authors to obtain data concerning length of life span and realisation of reproduction potential at different temperatures, ranging from 9 to 35 °C. The method also was helpful in revealing the causes of individual deaths. It is shown that at a temperature of 20 °C net reproduction rate (R₀) of Ph. roseola is maximum and is equal to reproduction potential of the individual. The peculiarity of Philodina ontogenetic reaction to temperature beyond optimum is the impairment of reproduction process.     

Modelling Effects of Temperature and Feeding Level on the Life Cycle of the Midge Chironomus Riparius: An Energy-Based Modelling Approach

Survival, growth, emergence and reproduction were monitored during the life cycle of Chironomus riparius in the laboratory at five temperatures from 15 to 27 °C and two feeding diets (ad libitum and limiting). Data were analysed using an energy-based model. Survival was not affected. In ad libitum conditions, growth rate increased linearly with temperature as a consequence of quicker food ingestion. Our model parameterised using the data in ad libitum conditions could account for the data obtained in food limited conditions. Reproduction was not influenced by temperature because the decrease of the duration of the period of energetic investment into reproduction compensated for the increase of the feeding rate when temperature increased. Based on these results, we then built a model describing life cycles in the field which may contribute to the field assessment of the consequences of global warming or pollution.     

Peculiarities of Philodina roseola (Ehrbg.) (Rotatoria,Bdelloida) – Growth and Reproduction under Various Temperature Conditions

Most investigations dealing with rotifer reproduction have been performed with populations and not with individuals. At the same time the variations in the growth and reproduction rates of rotifers are of considerable interest. This paper presents the results of investigations carried out by culturing individuals of Philodina roseola during the lifespan of an individual under different temperature conditions ranging from 9 to 35 °C. The paper presents curves showing the growth in length and weight, the periods of maximum growth rate and the maximum sizes of Philodina as affected by temperature conditions. The reproduction rate is investigated at the same time. The variation in egg evolution duration, in duration of the reproductive period and in the egg laying rate are shown under all the conditions investigated. The data serve as a basis for estimating the effect of temperature on the productivity of Philodina roseola.     

Growing or reproducing in a temperate sea: optimization of resource allocation in a colonial ascidian

Relatively little is known about the life cycles of ascidians in temperate seas. Here, we investigated the biological cycle of the colonial ascidian Didemnum fulgens, a dominant species in some shallow localities of the NW Mediterranean Sea. Growth rates and frequencies of fission/fusion events were calculated over a period of 13 months, and the reproductive cycle determined after 32 months of observation. For analyses of reproduction, zooids were dissected in the laboratory and classified into five reproductive categories; these data were used to calculate a maturity index. For growth analyses, underwater photographs of marked colonies were used to estimate the surface area of D. fulgens colonies, calculate monthly growth rates, and document fusion and fission events. Clear seasonal patterns in reproduction and growth were observed, with distinct periods of investment into each function. Gonad maturation started in winter and larval release occurred in early summer, just before maximal sea temperatures were reached. After reproducing, colonies shrank and aestivated during the warmer summer months. Growth occurred during the cooler months, with maximal and minimal growth rates observed in winter and summer, respectively. Fusions and fissions occurred year‐round, although fissions were more frequent in fall (coincident with high growth rates) and fusions in spring (coincident with reproduction). These results add to the mounting evidence that ascidian life cycles in temperate seas are characterized by a trade‐off between investment in reproduction and growth, triggered by seasonal temperature shifts and constrained by resource availability during summer.     

Field and cultural observations on the growth and reproduction of Polysiphonia denudata from Texas

The life history of an isolate of Polysiphonia denudata (Dillw.) Kütz. from Texas is shown by means of cultural studies to be of the Polysiphonia-type (a sequence of gametophytic, carposporophytic and tetrasporophytic phases in which the former and latter are morphologically similar). The effects of light intensity and temperature on the isolate have been investigated by a cross-gradient culture apparatus; a series of incubators was used to investigate the effects of variations in daylength on the growth and reproduction of the species. Seasonal observations were conducted on growth and reproduction of the species in nature and an attempt is made to explain the observed distribution of the species on the basis of the cultural study.     

PARENTAL EFFECTS IN PLANTAGO LANCEOLATA L. I.: A GROWTH CHAMBER EXPERIMENT TO EXAMINE PRE- AND POSTZYGOTIC TEMPERATURE EFFECTS

In spite of the potential evolutionary importance of parental effects, many aspects of these effects remain inadequately explained. This paper explores both their causes and potential consequences for the evolution of life-history traits in plants. In a growth chamber experiment, I manipulated the pre- and postzygotic temperatures of both parents of controlled crosses of Plantago lanceolata. All offspring traits were affected by parental temperature. On average, low parental temperature increased seed weight, reduced germination and offspring growth rate, and accelerated onset of reproduction by 7%, 50%, 5%, and 47%, respectively, when compared to the effects of high parental temperature. Both pre- and postzygotic parental temperatures (i.e., prior to fertilization vs. during fertilization and seed set, respectively) influenced offspring traits but not always in the same direction. In all cases, however, the postzygotic effect was stronger. The prezygotic effects were more often transmitted paternally than maternally. Growth and onset of reproduction were influenced both directly by parental temperature as well as indirectly via the effects of parental temperature on seed weight and germination. Significant interactions between parental genotypes and prezygotic temperature treatment (G × E interactions) show that genotypes differ in their intergenerational responses to temperature with respect to germination and growth. The data suggest that temperature is involved in both genetically based and environmentally induced parental effects and that parental temperature may accelerate the rate of evolutionary change in flowering time in natural populations of P. lanceolata. The environmentally induced temperature effects, as mediated through G × (prezygotic) E interactions are not likely to affect the rate or direction of evolutionary change in the traits examined because postzygotic temperature effects greatly exceed prezygotic effects.     

The influence of temperature and resource level on the fecundity of a predatory planktonic mite,Piona exigua Viets

Summary Piona exigua Viets is a predaceous freshwater mite that can potentially affect the population densities of its cladoceran prey. As part of a study of the effect of Piona exigua on its prey populations we measured the effects of water temperature and prey density on the lifespan, age at first reproduction and per capita egg production of adult female mites. Mites were raised in the laboratory at five prey (Ceriodaphnia, Daphnia) densities (5, 15, 30, 60, 120/l) at 15° C and at four temperatures (10, 15, 18, 22° C) at c. 60 prey/l. In response to increased food level, mites increased the number of eggs laid to reach a maximum at 60 prey/l, the rate at which they were laid increased and the pre-reproductive period was shorter. Low temperatures prolonged the pre-reproductive period. At temperatures above 10° C, food level and temperature had more influence on the timing of reproductive events (growth rate, oviposition rate, age at first reproduction) than on the size of females at first reproduction. When temperatures exceed 10° C and food levels exceed 5 prey/l the major scope for reproductive plasticity in Piona lies in the timing and duration of egg production.     

Intraspecific competition and light effect on reproduction of Ligularia virgaurea,an invasive native alpine grassland clonal herb

The relationship between sexual reproduction and clonal growth in clonal plants often shows up at the ramet level. However, only a few studies focus on the relationship at the genet level, which could finally account for evolution. The sexual reproduction and clonal growth of Ligularia virgaurea, a perennial herb widely distributed in the alpine grasslands of the Qinghai‐Tibetan Plateau of China, were studied under different competition intensities and light conditions at the genet level through a potted experiment. The results showed that: (1) sexual reproduction did not depend on density or light, and increasing clonal growth with decreasing density and increasing light intensity indicated that intraspecific competition and light intensity may affect the clonal life history of L. virgaurea; (2) both sexual reproduction and clonal growth show a positive linear relationship with genet size under different densities and light conditions; (3) a threshold size is required for sexual reproduction and no evidence of a threshold size for clonal growth under different densities and light conditions; (4) light level affected the allocation of total biomass to clonal and sexual structures, with less allocation to clonal structures and more allocation to sexual structures in full sunlight than in shade; (5) light determined the onset of sexual reproduction, and the genets in the shade required a smaller threshold size for sexual reproduction to occur than the plants in full sunlight; and (6) no evidence was found of trade‐offs between clonal growth and sexual reproduction under different densities and light conditions at the genet level, and the positive correlation between two reproductive modes indicated that these are two integrated processes. Clonal growth in this species may be viewed as a growth strategy that tends to maximize genet fitness.     

Response of green alder (Alnus viridis subsp. fruticosa) patch dynamics and plant community composition to fire and regional temperature in north‐western Canada

Aim Feedbacks between climate warming and fire have the potential to alter Arctic and sub‐Arctic vegetation. In this paper we assess the effects and interactions of temperature and wildfire on plant communities across the transition between the Arctic and sub‐Arctic. Location Mackenzie Delta region, Northwest Territories, Canada. Methods We sampled air temperatures, green alder (Alnus viridis ssp. fruticosa) cover, growth, reproduction and age distributions, and overall plant community composition on burned and unburned sites across a latitudinal gradient. Results Mean summer temperature across the study area decreased by 3 °C per degree of increasing latitude (6 °C across the study area). In the northern part of the study area, where seed viability was low, alder was less dominant than at southern sites where seed viability was high. The age structure of alder populations across the temperature gradient was highly variable, except in the northern part of the forest–tundra transition, where populations were dominated by young individuals. Alder growth and reproduction were significantly greater on burned sites (38–51 years following fire) than on unburned sites. North to south across the temperature gradient, vegetation changed from a community dominated by dwarf shrubs and fruticose lichens to one characterized by black spruce (Picea mariana), alder and willows (Salix spp.). Regardless of the position along the temperature gradient, burned sites were dominated by tall shrubs. Main conclusions Temperature limitation of alder abundance and repro‐duction, combined with evidence of recent recruitment on unburned sites, indicates that alder is likely to respond to increased temperature. Elevated alder growth and reproduction on burned sites shows that wildfire also has an important influence on alder population dynamics. The magnitude of alder’s response to fire, combined with observations that burns at the southern margin of the low Arctic are shrub dominated, suggest that increases in the frequency of wildfire have the potential to alter northern vegetation on decadal scales. By creating new seedbeds, fire provides opportunities for colonization that may facilitate the northward movement of tall shrubs. Feedbacks between the global climate system and low Arctic vegetation make understanding the long‐term impact of increasing fire frequency critical to predicting the response of northern ecosystems to global change.     

Temperature,light, and photoperiod responses of some Northeast American and West European endemic rhodophytes in relation to their geographic distribution

The relationship between distributional boundaries and temperature responses of some Northeast American and West European endemic and amphiatlantic rhodophytes was experimentally determined under varying regimes of temperature, light, and daylength. Potentially critical temperatures, derived from open ocean surface summer and winter isotherms, were inferred from distributional data for each of these algae. On the basis of the distributional data the algae fall within the limits of three phytogeographic groups: (1) the Northeast American tropical-to-temperate group; (2) the warm-temperate Mediterranean Atlantic group; and (3) the amphiatlantic tropical-to-warm temperate group. Experimental evidence suggests that the species belonging to the northeast American tropical-to-temperate group(Grinnellia americana, Lomentaria baileyana, andAgardhiella subulata) have their northern boundaries determined by a minimum summer temperature high enough for sufficient growth and/or reproduction. The possible restriction of 2 species (G. americana andL. baileyana) to the tropical margins may be caused by summer lethal temperatures (between 30 and 35 °C) or because the gradual disintegration of the upright thalli at high temperatures (>30 °C) promotes an ephemeral existence of these algae towards their southern boundaries. Each of the species have a rapid growth and reproductive potential between 15–30 °C with a broad optimum between 20–30 °C. The lower limit of survival of each species was at least 0 °C (tested in short days only). Growth and reproduction data imply that the restrictive distribution of these algae to the Americas may be due to the fact that for adequate growth and/or reproduction water temperatures must exceed 20 °C. At temperatures 15 °C reproduction and growth are limited, and the amphiatlantic distribution through Iceland would not be permitted. On the basis of experimental evidence, the species belonging to the warm-temperate Mediterranean Atlantic group(Halurus equisetifolius), Callophyllis laciniata, andHypoglossum woodwardii), have their northern boundaries determined by winter lethal temperatures. Growth ofH. equisetifolius proceeded from 10–25 °C, that ofC. laciniata andH. woodwardii from 5–25 °C, in each case with a narrow range for optimal growth at ca. 15 °C. Tetrasporelings ofH. woodwardii showed limited survival at 0 °C for up to 4 d. For all members of the group tetrasporangia occurred from 10–20 °C. The southern boundary ofH. equisetifolius andC. laciniata is a summer lethal temperature whereas that ofH. woodwardii possibly is a winter growth and reproduction limit. Since each member of this group has a rather narrow growth and survival potential at temperatures <5 °C and >20 °C, their occurrence in northeast America is unlikely. The (irregular) distribution ofSolieria tenera (amphiatlantic tropical-to-warm temperate) cannot be entirely explained by the experimental data (possibly as a result of taxonomic uncertainties).Paper presented at the Seaweed Biogeography Workshop of the International Working Group on Seaweed Biogeography, held from 3–7 April, 1984 at the Department of Marine Biology, University of Groningen (The Netherlands). Convenor: C. van den Hoek.     

Effects of kinetin and related compounds on growth and sexual reproduction of Saprolegnia australis

Summary An isolate of Saprolegnia australis grew readily and produced abundant sex organs on a chemically defined medium. The optimal temperature for growth was higher (25°) than the optimal temperature for sexual reproduction (20°). Addition of the purines, adenine and hypoxanthine to the medium stimulated production of oogonia while addition of kinetin and 6-benzylaminopurine inhibited this process. When kinetin and adenine were added together, the two purines interacted in affecting oogonial production, and adenine overcame the inhibitory action of kinetin. It is suggested that purines may play some specific role in the synthesis of one or more of the hormones which probably initiate sexual reproduction in S. australis and that kinetin and 6-benzylaminopurine may inhibit hormone synthesis. Two other growth regulators of higher plants, indol-3-ylacetic acid and gibberellic acid, did not affect development of the fungus. No evidence was found to suggest that S. australis was producing any substance with cytokinin activity.     

The relative importance of sexual and clonal reproduction for population growth in the perennial herb Fragaria vesca

The relative importance of sexual and clonal reproduction for population growth in clonal plants is highly variable. Clonal reproduction is often more important than sexual reproduction but there is considerable interspecific variation and the importance of the two reproductive modes can change with environmental conditions. We carried out a demographic study on the woodland strawberry (Fragaria vesca), a widespread clonal herb, at 12 sites in Switzerland during 2 years. Study sites were selected in two different habitats, i.e., forest and forest edge. We used periodic matrix models to estimate annual population growth rates and carried out prospective analyses to identify life cycle components that influence population growth rates most. Retrospective analyses were applied to study how the two different habitats affected population dynamics. Furthermore, we tested whether trade-offs between sexual and clonal reproduction occurred. There were large differences in annual population growth rates between sites and large within-site differences between years. Results of the prospective analyses clearly indicate that clonal reproduction is the dominant reproductive pathway whereas sexual reproduction is rather insignificant for population growth. Compared to forest habitats, forest edge habitats had higher population growth rates in the first year but smaller growth rates in the second year. We attribute these differing habitat effects to different water availabilities during consecutive years. No trade-offs between sexual and clonal reproduction were found. In conclusion, population growth of F. vesca relies heavily on clonal reproduction. Furthermore, reproduction and survival rates of F. vesca depend highly on spatio-temporal variation of environmental conditions.     

Influence of temperature on the infradian growth rhythm in Ulva lactuca (Chlorophyta)

The vegetative growth of Ulva lactuca was studied to determine if the growth rate of the alga is driven by infradian rhythmicity. The influence of temperature on the infradian rhythm of growth was also investigated. Discs of Ulva were grown in controlled laboratory conditions at different combinations of temperature (5, 10, 15, 20°С) and irradiance (40 and 60 μmol photons m^?2 s^?1) under 12 : 12 h light : dark cycles. The growth rates exhibited a rhythmic pattern with one major peak every 2 or 3 days. Growth at 5 or 10°С increased the prevalence of 3-day cycles and maintained U. lactuca in the vegetative growth stage. In contrast, growth at 15 or 20°С provoked a predominance of the 2-day cycle and induced reproduction. The 2- or 3-day cycles were combined in longer cycles having a period close to 6 days. We suppose that the 2-, 3- and 6-day rhythms of physiological processes are related to large-scale Rossby and Kelvin waves, which produce oscillations in the geomagnetic field and seawater temperature with the same periods. The predominance of 2-day or 3-day fluctuations of the geomagnetic field and temperature probably determine the prevalence of reproduction and vegetative growth, respectively, in Ulva.