Genetically-and environmentally-dependent processes drive interspecific and intraspecific divergence in the Chinese relict endemic genus Dipteronia

China is a hotspot of relict plant species that were once widespread throughout the Northern Hemisphere.Recent research has demonstrated that the occurrence of long-term stable refugia in the mountainous regions of central and south-western China allowed their persistence through the late Neogene climate fluctuations.One of these relict lineages is Dipteronia,an oligotypic tree genus with a fossil record extending to the Paleocene.Here,we investigated the genetic variability,demographic dynamics and diversification patterns of the two currently recognized Dipteronia species(Dipteronia sinensis and D.dyeriana).Molecular data were obtained from 45 populations of Dipteronia by genotyping three cpDNA regions,two single copy nuclear genes and 15 simple sequence repeat loci.The genetic study was combined with niche comparison analyses on the environmental space,ecological niche modeling,and landscape connectivity analysis.We found that the two Dipteronia species have highly diverged both in genetic and ecological terms.Despite the incipient speciation processes that can be observed in D.sinensis,the occurrence of long-term stable refugia and,particularly,a dispersal corridor along Daba Shan-west Qinling,likely ensured its genetic and ecological integrity to date.Our study will not only help us to understand how populations of Dipteronia species responded to the tectonic and climatic changes of the Cenozoic,but also provide insight into how Arcto-Tertiary relict plants in East Asia survived,evolved,and diversified.

Effects of Interspecific Competition on the Population Dynamics of Four Stored Grain Insect Pests

The effects of interspecific competition on the population dynamics of four insect grain Insecp pests （ Sitophilus zeamais, Rhizopertha dominica, Tribolium castaneum and Cryptolestes ferrugineus ） was studied at 30℃, 75% relative humidity. A regression analysis of the population dynamics was conducted. The results showed that population growth of S. zeamais , R. dominica, T. castaneum and C. ferrugineus was restrained under mixed rearing. Population growth of T. castaneum and C. ferrugineus was remarkably accelerated when they coexisted with S. zeamais or R. dominica, while that of S. zeamais and R. dominica was restrained to some extent. Regression analysis results showed that the population growth potential of S. zeamais was the largest and that of C. ferrugineus was the smallest, and the changing trends of population growth rates were not distinct.

Evaluation and analysis of intraspecific competition in maize: A case study on plant density experiment

Intraspecific competition is a common phenomenon in agricultural production,and maize is one of the most sensitive grass species to intraspecific competition due to its low tillering ability.This study evaluated and analyzed intraspecific competition in maize,and screened competitive indices that could be used to evaluate intraspecific competition in a maize population.A 2-year field experiment was conducted using the maize hybrid Zhongdan 2 at 12 plant densities ranging from 1.5 to 18.0 plants（pl）m-2.The results showed that the response of single-plant grain yield and dry matter at harvest to increased plant density decreased exponentially and that the harvest index decreased linearly.The response of population-level grain yield to plant density was curvilinear,producing a maximum value at the optimum population density.However,the yielddensity equation agreed well with the Steinhart-Hart equation curves,but not with the quadratic equation curves reported by most previous studies.Competitive indices are used to evaluate competition in a plant population or plant species.The present results show that competitive intensity（CI）and absolute severity of competition（ASC）increased with increasing plant density;however,relative yield（RY）and relative reproductive efficiency（RReff）decreased.The different responses of these indices reflect different aspects of competition.According to the analysis of CI,ASC,RY,and RReff,higher CI and ASC values indicate higher intraspecific competition,whereas higher RY and RReff values indirectly reflect lower intraspecific competition.These competitive indices evaluate not only the intraspecific competitive intensity under different plant densities of the same cultivar but also those of different cultivars under the same plant density.However,some overlap exists in the calculations of ASC,CI,and RY,so one could simply select any one of these indices to evaluate intraspecific competition in a maize population.In conclusion,the present study provides a method to evaluate intraspecific competition in maize populations,which may be beneficial for breeding high-yield maize varieties in the future.

The effect of UV-B radiation enhancement on the interspecific competition between Skeletonema costatum and Heterosigma akashiwo

The responses of the interspecific competition between Skeletonema costatum and Heterosigma akashiwo to UV-B radiation enhancement were studied by the co-culture method. The results showed that Heterosigma akashiwo exhibited inhibition on the growth of Skeletonema costatum, and with the increase of initial inoculation density of Heterosigma akashiwo, heavier inhibition on Skeletonema costatum appeared. Under different inoculation proportions, Heterosigma akashiwo could always be in predominance in competition with Skeletonema costatum. The UV-B radiation treatment could change the competition relationship between Skeletonema costatum and Heterosigma akashiwo, which could increase the competitive dominance of Skeletonema costatum and decrease the competitive dominance of Heterosigma akashiwo. When the inoculation proportions of Heterosigma akashiwo and Skeletonema costatum were H∶S=1∶4 and H∶S=1∶1,Skeletonema costatum was in predominance in this competition; however, Heterosigma akashiwo was in predominance when the inoculation proportion was H∶S=4∶1.

Potential tradeoffs between intraspecific and interspecific trait variations along an environmental gradient in a subtropical forest

There has been growing attention to intraspecific variation in trait-based plant ecology. However, studies on these changes across ontogenetic stages and the potential trade-offs with interspecific traits along environmental gradients are rare. In this study, we measured six wood and bark traits of 1030 trees of six species(Castanopsis nigrescens; C. carlesii; Lithocarpus polystachyus; L. synbalanos; Ormosia glaberrima; O. pachycarpa) from a10-ha plot in a subtropical forest. Mean intraspecific variation in bark thickness and bark percentage to DBH was more than twice that for wood density and bark density.Bark thickness and bark percentage showed a consistent trend with increasing tree size. Small-tree traits were more variable than the same traits in larger trees. Altitude,convexity and soil nutrients explained the majority of the variations in the six traits, while sibling species had similar relationships between traits and environmental variables.Trees with dense wood and thin bark were usually found on steep slopes at lower altitudes. Our findings show intraspecific trait variability has different spatial patterns compared with interspecific variabilities along an environmental gradient.

Effects of elevated CO_2 on sensitivity of six species of algae and interspecific competition of three species of algae

Effects of elevated CO, （5000 μl/L） on sensitivity comparison of six species of algae and interspecific competition of three species of algae were investigated. The results showed that, the cell densities of six species of algae grown in elevated CO2 significantly increased compared to those in ambient CO2 （360 μl/L）, and with the time prolonged, the increasing extent increased. Therefore, elevated CO2 can promote the growth of six species of algae. However, there were differences in sensitivity between six species of algae. Based on the effects of elevated CO2 on biomass, the sensitive order （from high to low） was Platymanas sp., Platymanas subcordiformis, Nitzschia closterium, Isochrysis golbana Parke 8701, Dunoliella salina, Chlorella sp., on the condition of solitary cultivation. Compared to ambient CO2, elevated CO2 promoted the growth of three species of algae, Platymanas subcordiformis, Nitzschia closterium and Isochrysis galbana Parke 8701 under the condition of mixed cultivation. The sensitivity of the three species to elevated CO2 in mixed cultivation changed a lot compared to the condition of solitary cultivation. When grown in elevated CO2 under the condition of mixed cultivation, the sensitive order from high to low were Nitzschia clostertium, Platymonas subcordiformis; and Isochrysis galbana Parke 8701. However, under the condition of solitary cultivation, the sensitive order in elevated CO2 was Isochrysis galbana Parke 8701, Nitzschia clostertium, Platymonas subcordiformis, from sensitive to less sensitive. On the day 21, the dominant algae, the sub-dominant algae and inferior algae grown in elevated CO2 did not change. However, the population increasing dynamic and composition proportion of three algal species have significantly changed.

Effects of Mixture Sowing on Forage Yield and Interspecific Competition of Alfalfa and Orchard Grass

[ Objective] To explore the mixture sowing effects and optimal mixture ratio of alfalfa and orchard grass. [ Method] The alfalfa and orchard grass were sowed at different ratios （1 ： 0, 3： 1, 1 ： 1, 1 ： 3 and 0：1 ）. They were grouped and named as CK1, A1, A2, A3 and CK2., respectively. The forage yield, relative yield total （RYT） and the competition rate （CR） of alfalfa and orchard grass in each group were determined, respectively. [ Result] In the A3 treatment group, the total forage yield was the highest （4 827.67 kg/hm2） and significantly different from that of other treatment groups （ P 〈 0.01 ）. In every treatment group, the RYT was higher than 1, and the alfalfa was more competitive than the orchard grass in the mixed-seeding pasture. [ Conclusion] Our studies may provide a basis for the establishment of high yield and high quality artificial mixture pasture.

Effect of UV-B irradiation on interspecific competition between Ulva pertusa and Grateloupia filicina

We report the effect of UVoB irradiation （9.6 kJ m-2 day^-） on interspecific competition between two species of macroalgae, Ulva pertusa （U） and Grateloupiafilicina （G）, in co-culture. Growth of U. pertusa and G. filicina was inhibited by UV-B irradiation in mono-culture and specific growth rate （μ） declined as a result. Interspecific competition between U. pertusa and G filicina was closely related to the initial weights when co-cultured. When initial ratios of U. pertusa （U） to G filicina （G） were U：G=I.2：I and 1：1, U. pertusa was the dominant algae. When the initial U：G ratio was 1：1.2, G. filicina was competitively dominant in the earlier stage, but U. pertusa grew faster, superseding G. filicina in the later stage. At initial ration U：G = 1：1.4, G. filicina was predominant. Under UV-B irradiation, the competitive ability of G filicina was weakened and the interspecific competitive balance favored U. pertusa, which suggests that G. filicina was more sensitive to UV-B irradiation. We also probed the potential allelopathic effects between the two species, which led to mutual growth inhibition.

Interspecific Competition Between Levanderina fissa(Dinophyceae) and the Other Three Microalgal Species in Co-Cultures

Growth interactions between the dinoflagellate Levanderina fissa (=Gyrodinium instriatum) and the other three algal bloom species Skeletonema costatum (Bacillariophyceae), Prorocentrum micans (Dinophyceae), and Chattonella marina (Raphido- phyceae) were studied using bi- or tri-algal co-cultures under laboratory conditions. The Lotka-Volterra model was applied to esti- mate the interspecific competition between them. Results showed that the growth of L. fissa was significantly suppressed in both bi-algal and tri-algal cultures, and the maximum cell densities in co-cultures were only between 21% and 69% of that in mono-cul- ture. L. fissa outcompeted P. micans;however, its effects on S. costatum and C. marina were generally less than the effects of their intraspecific competitions based on the competition coefficients. Contrarily, the inhibitory effects of S. costatum and C. marina on L. fissa were much greater. S. costatum outcompeted the other three species in all co-cultures, and its competition coefficients on the other species were more than 10000 times higher than the opposite. The growth of C. marina was suppressed by S. costatum;how- ever, it outcompeted L. fissa and P. micans. The growth of P. micans was most strongly inhibited in co-cultures, and the maximum cell densities in co-cultures were less than 15% of that in mono-species culture. The results suggested that L. fissa had few advan- tages in the interspecific competition. The adaptation to low salinity and the utilization of organic phosphorus might be the important reasons for L. fissa to take the competitive predominance in brackish estuarine environments.

Experimental approaches to select tree species for forest restoration:effects of light,water availability and interspecific competition in degraded areas

Knowing what native trees can recr uit on degraded areas allows selecting the best species to restore these sites.However,as this information is not often available,experimentation is required before large-scale planting.This study used ex situ experiments to make these decisions on recruitment.Competition with r-strategist plants,excessive solar radiation and water shortage commonly impair tree recruitment in open habitats.The experiments focused on the interactions among these factors and were conducted with three pioneer species from seasonally dry forests of northwest Argentina,Anadenanthera colubrina,Ceiba chodatii and Jacaranda mimosifolia.Seeds of each species were sown at two light levels(sunlight/shade),two rainfall levels(full/reduced)and two levels of interspecific competition(with/without competitor)in a tree nursery.Seedling emergence and survival were monitored over a year and the results indicate that species differentially respond to varying levels of light and water.Seedlings of A.colubrina tolerated water shortages under elevated solar radiation,which are desirable features for forest restoration.Seedlings of C.chodatii tolerated shade and drought,suggesting that they require shading for establishing in open areas.However,J.mimosifolia seedlings neither tolerated full sunlight nor water shortages,suggesting that this species requires shading and regular watering if used in reforestation.Regardless of the effects of light and water,the survival of all species was reduced by interspecific competition.These results highlight the importance of experimentation for selecting the best species for forest restoration and can enhance the cost/benefit ratios of these actions.

Role of intraspecific competition in intrinsic growth rate regulation in an Oikopleura dioica(Tunicata)population

Planktonic Oikopleura dioica respond almost instantly to opportunistic algal blooms,but it is unknown whether the population increase can change from an exponential to a logistic model to avoid a final sudden collapse.To test the hypothesis that intraspecific competition regulates the intrinsic rate of natural increase(r),density-dependent effects on growth and reproduction performance were investigated in O.dioica via laboratory incubations.Over a large food concentration range,batch maturation was observed above the per capita food supply(PFS)of 8.1µgC/ind.in 4.5 d.Somatic growth was saturated beyond this PFS value,whereas gonad length increased continuously.Below this threshold,individuals reached small body and gonad lengths,and maturation was rarely observed during the incubation period.The gonad/body volume and maturation ratios also increased with the PFS.Instead of the food concentration,the r values were regulated by competition pressure via variability in maturation duration and the proportion of mature individuals in the cohorts.When the minimum food demand was satisfied in the designated generation time,the r value tended to be regulated by the spawning proportion in the population.Otherwise,prolonged development duration and decreased r values were expected.

Interspecific Competition and Grain-Hosts Selection of Maize Weevil, <i>Sitophilus zeamais</i>(Motsch.) (Coleoptera;Dryophtoridae) and Larger Grain Borer, <i>Prostephanus truncatus</i>(Horn) (Coleoptera;Bostrichidae)

Laboratory interspecific competition and grain-hosts selection experiments involving maize weevil (MW), Sitophilus zeamais (Motsch.) and larger grain borer (LGB), Prostephanus truncatus (Horn) were performed under ambient temperature and relative humidity (25°C - 35°C and 70% - 80% relative humidity) in their major host cereal, maize grains. The species reproductive rate and grain-hosts preference were evaluated by a number of emerged adults. In combined infestation, both species competed intensively by simultaneously increasing their individuals’ emergence, 9-fold or greater than when reared alone. Even though both species simultaneously increased their progeny, S. zeamais was the dominant competitor and had a significant suppressant effect on P. truncatus. The selection result of grain-hosts showed that P. truncatus placed in the environment containing both uninfested maize grains and grains previously infested by S. zeamais, the insect prefers uninfested grains. Indeed, P. truncatus individuals’ emergences were significantly more important to uninfested grains than to infested grains. The weevil-infested grains seemed to have deterrent and detrimental effects on P. truncatus. Conversely, S. zeamais selection of grain-hosts was significantly (P = 0.0001) more attracted by P. truncatus infested grains than to uninfested grains. Sitophilus zeamais individuals’ emergences were significantly (P = 0.0008) more important to infested grains than to uninfested grains. The S. zeamais preference on grains previously infested would be stimulated by P. truncatus larval vibrations in grain.

Competitive interactions between invasive fall armyworm and Asian corn borer at intraspecific and interspecific level on the same feeding guild

Interspecific competition is an important factor in the population dynamics and geographical distribution of insect populations.Fall armyworm(FAW),Spodoptera frugiperda,an invasive species,and the Asian corn borer(ACB),Ostrinia furnacalis,a native pest species are major pests on maize in China,posing a threat to maize yield and grain quality.A series of laboratory,greenhouse,and field experiments were conducted to elucidate the competitive interactions between FAW and ACB.In the laboratory experiments,FAW exhibited aggressive behaviors more frequently when compared with ACB,while the latter species exhibited defense behaviors more frequently.Higher intraspecific competition was recorded in the FAW conspecific rather than in ACB,particularly in the 6th larval stage.FAW had a higher interspecific competitive advantage through intraguild predation over ACB,resulting in partial or complete displacement ACB when initially the ratio of the 2 species was 1:1.The interspecific competition also had significantly influenced on the population parameters,defensive enzymes,and nutrient of these 2 species.Competitive interaction proved that the response of superoxide,catalase,and soluble protein in FAW were significantly increased,whereas the total sugar content in both species was substantially decreased.Survival rate,and the plant damage that co-infested by both species varied significantly among the sequential combinations under greenhouse and field conditions.FAW consistently exhibited stronger intraspecific aggression than ACB under laboratory and field conditions when co-existing on the same feeding guild.These findings contribute to efforts toward the improvement of integrated pest management programs for FAW,in decision making for invasive and native pests’management strategies to reduce the high risks of FAW and ACB outbreaks.

The importance of aboveground and belowground interspecific interactions in determining crop growth and advantages of peanut/maize intercropping

Intercropping of maize(Zea mays L.) and peanut(Arachis hypogaea L.) often results in greater yields than the respective sole crops. However, there is limited knowledge of aboveground and belowground interspecific interactions between maize and peanut in field. A two-year field experiment was conducted to investigate the effects of interspecific interactions on plant growth and grain yield for a peanut/maize intercropping system under different nitrogen(N) and phosphorus(P) levels. The method of root separation was employed to differentiate belowground from aboveground interspecific interactions. We observed that the global interspecific interaction effect on the shoot biomass of the intercropping system decreased with the coexistence period, and belowground interaction contributed more than aboveground interaction to advantages of the intercropping in terms of shoot biomass and grain yield. There was a positive effect from aboveground and belowground interspecific interactions on crop plant growth in the intercropping system, except that aboveground interaction had a negative effect on peanut during the late coexistence period. The advantage of intercropping on grain came mainly from increased maize yield(means 95%) due to aboveground interspecific competition for light and belowground interaction(61%–72% vs. 28%–39% in fertilizer treatments). There was a negative effect on grain yield from aboveground interaction for peanut, but belowground interspecific interaction positively affected peanut grain yield.The supply of N, P, or N + P increased grain yield of intercropped maize and the contribution from aboveground interspecific interaction. Our study suggests that the advantages of peanut/maize intercropping for yield mainly comes from aboveground interspecific competition for maize and belowground interspecific facilitation for peanut, and their respective yield can be enhanced by N and P. These findings are important for managing the intercropping system and optimizing the benefits from using this system.

The interspecific competition presents greater nutrient facilitation compared with intraspecific competition through AM fungi interacting with litter for two host plants in karst soil

Litter is the crucial carrier of soil nutrition transformation.The influence of arbuscular mycorrhizal(AM)fungi on nutrient acquisition in plants has been widely recognized.However,in nutrient-deficient karst habitat,how competitive plants utilize nutrients regulated by AM fungi via litter remain largely unknown.The experimental treatments included the inoculation with or without Glomus etunicatum,the litter addition by the mixed leaves of Broussonetia papyrifera and Carpinus pubescens or no addition,and the competition through the intraspecific competition of B.papyrifera and C.pubescens,respectively,and the interspecific competition mixed both plants.AM fungi differently affected plant on nutrient acquisition,increasing nutrients acquisitions of B.papyrifera in intra-and interspecific competitions while decreasing for C.pubescens.Litter presented opposite influences on N acquisitions of both plants in interspecific competition with AM fungi,being positive for C.pubescens and negative for B.papyrifera,respectively.Under the interaction of AM fungi and litter,nitrogen(N),phosphorus(P)and potassium(K)acquisitions by B.papyrifera and N acquisition by C.pubescens in interspecific competition were all greater than intraspecific competition.In the interspecific competition,the competitive ability of plants on nutrient absorption presented significant species difference,which of B.papyrifera on P and K was significantly increased,while was converse for C.pubescens on K.In conclusion,these results suggest that the interspecific competition presents greater nutrient facilitation compared with intraspecific competition through AM fungi interacting with litter for plants in karst soil.

COMPETITION IN OLD GROWTH KOREAN PINE FOREST

Korean pine(Pinus koraiensis) interspecilic competition and intraspecifie companioned with other species competition in old growth Korean pine forest in northeast China were studied using Hegyi's competition index model for individual tree.The results show that differences of competitive intensity exist in interspecific and intraspecific for Korean pine with an order of intraspecific ＞Abies nephrolepis Picea koraiensis Tilia amurensis Betula costat＞Acer mono ＞Ulnuts propinqua＞Populus davidiana,and that relationship of competitive index to indivdual size (in DBH) of objective tree follows closely multiplieate eqtuation and that competitive intensity gradually reduces with inereasing of individual size of objective tree, but it is tending towards stability after individual of objective tree inerease to specified size (DBH about 20 cm).It provided a serviceable approach for researches of intraspecific relationship in population ecology.

QUANTITATIVE ANALYSIS FOR INTERSPECIFIC RELATIONSHIP OF LARCH STAND MIXED WITH ASH

Permanent sample plots were set up for researching interspecific relationship of the artificia1 larch stand mixed with natural ash in the slash site in Maoershan Experiment Forestry Farm of Northeast Forestry University. All trees in the plots were taken as objective trees and tree number,DBH, distance between trees and that of crown diameter were measured in range of 1-6m from every objective tree. Then study by Alemdag competition index, variance analysis and quantitation method were made. The result showed that the intraspecific competition was more intensive than the interspecific competition. Especially the competition between larch and ash was least relatively. For these kinds of site, the suitable mixture at 20-30 ages should be 2800 Ind/hm2 in density and 2 larch;1 ash in mixed ratio, which might improve site condition to promote stand produetivity.

Impacts of competition and nitrogen addition on plant stoichiometry and non-structural carbohydrates in two larch species

Previous research has shown that competition between plants can have differential effects on leaf stoichiometry and non-structural carbohydrate(NSC)in different environments.However,little attention has been given to understanding these effects on non-photosynthetic organs,particularly of deciduous tree species.Here we assess the impact of competition on below and aboveground biomass,stoichiometry,nutrient composition and NSC in pure and mixed forests of two Larch species,Larix kaempferi and L.olgensis under nitrogen(N)addition.Nitrogen enrichment did not result in stronger intraspecific competition for both species and L.olgensis benefited from the presence of L.kaempferi under different N levels.Stems kept relatively stable C/N compared to roots and branches in response to competition,while N addition imposed stronger impacts on N/P of different organs rather than competition.In contrast to stable C concentrations,starch and soluble sugar concentrations were more easily impacted by competition and the addition of nitrogen.Competition forced L.kaempferi and L.olgensis to allocate more carbon into storage by increasing their starch concentration and starch/soluble sugar of stems under competition.However,no significant differences in stoichiometry and NSC concentration between intra-and interspecific competition were found.NSC and nutrient pools of L.kaempferi stems,branches and coarse roots consistently declined due to competition regardless of N addition.Coarse and fine roots of L.kaempferi accumulated more N when in competition with L.olgensis than with a conspecific neighbor under N addition.Our results show that NSC was more sensitive to competition relative to stoichiometric traits(N and P)of non-photosynthetic organs.

Behavioural and energetic consequences of competition among three overwintering swan(Cygnus spp.)species

Background:Winter numbers of the northwest European population of Bewick's Swans(Cygnus columbianus bewickii)declined recently by c.40%.During the same period,numbers of two sympatric and ecologically-similar congeners,the Mute Swan(Cygnus olor)and Whooper Swan(Cygnus cygnus)showed increases or stability.It has been suggested that these opposing population trends could have a causal relationship,as Mute and Whooper Swans are larger and competitively dominant to Bewick's Swans in foraging situations.If so,effects of competition of Mute and Whooper Swans on Bewick's Swans should be detectable as measurable impacts on behaviour and energetics.Methods:Here,we studied the diurnal behaviour and energetics of 1083 focal adults and first-winter juveniles("cygnets")of the three swan species on their winter grounds in eastern England.We analysed video recordings to derive time-activity budgets and these,together with estimates of energy gain and expenditure,were analysed to determine whether individual Bewick's Swans altered the time spent on key behaviours when sharing feeding habitat with other swan species,and any consequences for their energy expenditure and net energy gain.Results:All three swan species spent a small proportion of their total time(0.011)on aggressive interactions,and these were predominantly intraspecific(≥0.714).Mixed-effects models indicated that sharing feeding habitat with higher densities of Mute and Whooper Swans increased the likelihood of engaging in aggression for cygnet Bewick's Swans,but not for adults.Higher levels of interspecific competition decreased the time spent by Bewick's Swan cygnets on foraging,whilst adults showed the opposite pattern.When among low densities of conspecifics(<c.200 individuals/km^(2)),individual Bewick's Swans spent more time on vigilance in the presence of higher densities of Mute and Whooper Swans,whilst individuals within higher density Bewick's Swan flocks showed the opposite pattern.Crucially,we found no evidence that greater numbers of interspecific competitors affected the net energy gain of either adult or cygnet Bewick's Swans.Conclusions:We found no evidence that Bewick's Swan net energy gain was affected by sharing agricultural feeding habitat with larger congeners during winter.This was despite some impacts on the aggression,foraging and vigilance behaviours of Bewick's Swans,especially among cygnets.It is unlikely therefore that competition between Bewick's Swans and either Mute or Whooper Swans at arable sites in winter has contributed to the observed decline in Bewick's Swan numbers.Further research is needed,however,to test for competition in other parts of the flyway,including migratory stopover sites and breeding areas.

Open Mass Cultures of Marine Microalgae for Biodiesel Production: Laboratory Approach to Study Species Competition in Mixed Cultures

Since the interspecific competition represents a critical issue for biodiesel production in open mass cultures of microalgae, laboratory studies aimed to select competitive species receive significant interest. In this work, a laboratory approach based on the method of multisizing cell counting was developed to monitor the competition course of single algal species grown in mixed cultures. Two marine microalgae, Dunaliella tertiolecta and Phaeodactylum tricornutum, were used to set-up an induced-contamination assay, with the aim to test their competitive capabilities. The evaluation of the oil production by dried biomass extraction was coupled to the growth assay to investigate the effect of competition on oil yield. The adopted experimental approach revealed effective as a method to selectively measure the algal growth of single species in mixed cultures, enabling to evaluate the competitive properties of Dunaliella outgrowing the contaminant species Phaeodactylum. At the end of the experiment the dominant species contributed more than 90% to the total biomass, while no loss of oil production was observed, the oil yield in the mixed being even higher than in the unialgal culture (3.15 vs. 2.28 mg). The outcomes of the induced competition suggest the use of Dunaliella as a competitive oil-producer species and especially support the potential of the experimental approach to be used for preliminary screening to drive species selection for open mass cultures.