Effect of light and nutrients on interspecific interactions between submerged macrophytes:implications for restoration of multispecies aquatic vegetation in eutrophic lakes

Constructing multispecies submerged vegetation systems and maintaining stable seasonal succession is crucial for restoring shallow eutrophic lakes.However,little is known about the interactions between successional and existing species of different growth forms,particularly under the low light and high nutrient conditions of eutrophic lakes.We measured the functional traits of mature Vallisneria natans(Lour.)Hara plants and Potamogeton crispus L.shoots in monoculture and mosaic patterns under different light and nutrient conditions.The effect of light on functional traits of the submerged macrophyte species was more significant than that of nutrients,but the reverse was true for P.crispus biomass allocation.Moreover,interspecific interactions affected only the submerged macrophytes under the low light condition and varied with species.Specifically,the interaction of P.crispus to V.natans was biased towards competition,while the interaction of V.natans to P.crispus was converted from facilitation to competition by eutrophication,particularly in the homogenous mosaic growth pattern.This study demonstrates that sufficient light is a prerequisite and patch planting is an effective means to form a multispecies submerged vegetation system.In addition,we emphasize that the coexistence of eutrophication and low light will likely result in a competition between submerged macrophytes thus simplifying the vegetation,even if their growth forms and growing seasons are different.These findings help explain the collapse of multispecies submerged vegetation and guide the restoration of aquatic plants in eutrophic lakes.

TWO-DIMENSIONAL NONLINEAR DYNAMIC SYSTEM MODEL OF INTERSPECIFIC INTERACTION AND NUMERICAL SIMULATION RESEARCH ON IT

The mechanism and the course of two_dimensional nonlinear dynamic system of interspecific interaction were dealt with systematically. By extending the Lotka_Volterra model from the viewpoint of biomechanics, it developed new models of two_dimensional nonlinear autonomous and nonautonomous dynamic systems, with its equilibrium point's stability and the existence and stability of its periodical solutions analyzed, and did numerical simulation experiments on its dynamics course. The results show that efficiency of interaction between two populations, time_varying effort, and change direction of action coefficient and reaction coefficient have important influences on the stability of dynamic system, that too large or too small interspecific interaction efficiency and contrary change direction of action coefficient and reaction coefficient may result in the nonstability of the system, and thus it is difficult for two populations to coexist, and that time_varying active force contributes to system stability.

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.

Replanting of broadleaved trees alters internal nutrient cycles of native and exotic pines in subtropical plantations of China

Background:The replanting of broadleaved trees in pure coniferous plantations is widely implemented,as mixed plantations are generally more stable and functional.However,the effect of interspecific interactions between broadleaved and coniferous trees on internal nutrient cycles of conifers remains unclear.Methods:We selected pure coniferous plantations of a native(Pinus massoniana)and an exotic(P.elliottii)pine species and their corresponding mixed plantations with broadleaved trees(Schima superba)in subtropical China,and measured the nitrogen(N)and phosphorus(P)contents in the rhizosphere soils,fine roots,twigs,needles and needle litter of pines.We calculated the root capture,needle resorption and translocation of N and P by pines to determine the mobility of nutrients in trees.Results:Although the N and P in the rhizosphere soils increased due to the replanting of broadleaved trees,the N and P contents in the aboveground tissues of the two pine species did not increase in mixed plantations.Mixed planting had a negative effect on the N and P capture of native pine and a positive effect on that of exotic pine.The N and P resorption efficiencies increased in native pine but were unchanged in exotic pine after the replanting of S.superba.Native pine preferentially employed an aboveground nutrient resorption strategy,whereas exotic pine tended to adopt a belowground nutrient capture strategy after replanting.Translocation of N and P in trees was detected,which reflected the trade-offs between root nutrient capture and needle nutrient resorption.Conclusions:The effect of mixed planting varied between the species of native and exotic pines,and the internal nutrient cycles of both pine species might be dominated by interspecific interaction effects on nutrients rather than soil nutrients.Our study highlights the importance of selecting suitable broadleaved species for replanting in coniferous plantations.

THE 4C APPROACH AS A WAY TO UNDERSTAND SPECIES INTERACTIONS DETERMINING INTERCROPPING PRODUCTIVITY

Modern agriculture needs to develop transition pathways toward agroecological,resilient and sustainable farming systems.One key pathway for such agroecological intensification is the diversification of cropping systems using intercropping and notably cereal-grain legume mixtures.Such mixtures or intercrops have the potential to increase and stabilize yields and improve cereal grain protein concentration in comparison to sole crops.Species mixtures are complex and the 4C approach is both a pedagogical and scientific way to represent the combination of four joint effects of Competition,Complementarity,Cooperation,and Compensation as processes or effects occurring simultaneously and dynamically between species over the whole cropping cycle.Competition is when plants have fairly similar requirements for abiotic resources in space and time,the result of all processes that occur when one species has a greater ability to use limiting resources(e.g.,nutrients,water,space,light)than others.Complementarity is when plants grown together have different requirements for abiotic resources in space,time or form.Cooperation is when the modification of the environment by one species is beneficial to the other(s).Compensation is when the failure of one species is compensated by the other(s)because they differ in their sensitivity to abiotic stress.The 4C approach allows to assess the performance of arable intercropping versus classical sole cropping through understanding the use of abiotic resources.

Lower marine productivity increases agonistic interactions between sea lions and fur seals in Northern Pacific Patagonia

Interspecific interactions are key drivers of individual and population-level fitness in a wide range of animals.However,in marine ecosystems,it is relatively unknown which biotic and abiotic factors impact behavioral interactions between competing species.We assessed the impact of weather,marine productivity,and population structure on the behavioral agonistic interactions between South American fur seals(SAFSs),Arctocephalus australis,and South American sea lions(SASLs),Otaria byronia,in a breeding colony of SAFS.We hypothesized that agonistic interactions between SAFSs and SASLs respond to biotic and abiotic factors such as SAFS population structure,marine productivity,and weather.We found that SASL and SAFS interactions almost always resulted in negative impacts on the social structure or reproductive success of the SAFS colony.SASL adult males initiated stampedes of SAFS and/or abducted and predated SAFS pups.Adult SAFS males abundance and severe weather events were negatively correlated with agonistic interactions between species.However,proxies for lower marine productivity such as higher sea surface temperature and lower catches of demerso-pelagic fish were the most important predictors of more frequent agonistic interactions between SAFS and SASL.Under the current scenario of decline in marine biomass due to global climate change and overfishing,agonistic interactions between competing marine predators could increase and exacerbate the negative impacts of environmental change in these species.

Enhanced oxidation of benzo[a]pyrene by crude enzyme extracts produced during interspecific fungal interaction of Trametes versicolor and Phanerochaete chrysosporium

The effects of interspecific fungal interactions between Trametes versicolor and Phanerochaete chrysosporium on laccase activity and enzymatic oxidation of polycyclic aromatic hydrocarbons （PAHs） were investigated. A deadlock between the two mycelia rather than replacement of one fungus by another was observed on an agar medium. The laccase activity in crude enzyme extracts from interaction zones reached a maximum after a 5-day incubation, which was significantly higher than that from regions of T. versicolor or P. chrysosporium alone. The enhanced induction of laccase activity lasted longer in half nutrition than in normal nutrition. A higher potential to oxidize benzo[a]pyrene by a crude enzyme preparation extracted from the interaction zones was demonstrated. After a 48 hr incubation period, the oxidation of benzo[a]pyrene by crude enzyme extracts from interaction zones reached 26.2%, while only 9.5% of benzo[a]pyrene was oxidized by crude extracts from T. versicolor. The oxidation was promoted by the co-oxidant 2,2＇-azinobis-3- ethylbenzthiazoline-6-sulphonate diammonium salt （ABTS）. These findings indicate that the application of co-culturing of white-rot fungi in bioremediation is a potential ameliorating technique for the restoration of PAH-contaminated soil.

Numerical Evaluation of External Effects on Interspecific Interacting Populations

In this paper, effects of environmental and hunting parameters on the interspecific interacting populations are considered by applying the Rosenzweig-MacArthur model with the Holling type II functional response. Attenuating functions of the carrying capacity are introduced with a concern on the hunting parameters. We carry out numerical study to investigate how the population densities behave when environmental quantities change. We obtain the Hopf bifurcation diagrams from numerical results.

Same place, different time, head up: Multiple antipredator responses to a recolonizing apex predator

Prey adjust their antipredator behavioral tactics to minimize the risk of an encounter with predators.Spatiotemporal responses of prey to pred-ators have been reported,but the nature of antipredator response is not ubiquitous and it is the object of increasing interest,especially consid-ering the recent recovery of large carnivores in Europe,and the potential for behavioral antipredator responses to elicit consequences at the ecosystem level.We have tested multiple antipredator responses by fallow deer Dama dama to wolf Canis lupus in a Mediterranean protected area recently recolonized by this apex predator.Through intensive camera trapping,we tested for temporal and spatial association between predator and prey,and we have also studied deer vigilance in forest habitats where focal observations are usually impossible.Wolf detection rates were spatially associated with those of fallow deer.Accordingly,no evidence was found for fallow deer avoiding sites with higher predator detection rates.Temporal activity patterns were significantly different between the 2 species,with the wolf being mainly nocturnal whereas fallow deer was active especially during daylight.A comparison with a preliminary study strongly suggests an increase in the diurnal activity of fallow deer along with the stabilization of wolf presence in the area.Both the rate and the duration of vigilance of female fallow deer increased with the local frequency of wolf activity.We suggest an antipredator response based on temporalrather than spatialavoidance,as well as increasedvigilance.

Invasive cichlids(Teleostei:Cichliformes)in the Amacuzac River,Mexico:Implications for the behavioral ecology of the native Mexican mojarra Amphilophus istlanus

The introduction of species is a leading cause of biodiversity loss and habitat alteration.Several species have invaded Mexican freshwater ecosystems,adversely affecting native fishes.Specifically,in the Amacuzac River of the Balsas Basin(Central Mexico),at least four non-native cichlids have been recorded:tilapia Oreochromis sp.,convict cichlid Amatitlania nigrofasciata,spotcheek cichlid Thorichthys maculipinnis,and green terror Andinoacara rivulatus.These species co-occur with the Mexican mojarra Amphilophus istlanus,the only native cichlid in the Basin.Invasive cichlids compete for resources such as shelter and food,and prey on offspring of the Mexican mojarra.In the presence of invasive cichlids,the costs and risks of foraging and finding available shelter increase for the native cichlid.Predation pressure from invasive cichlid fishes on the Mexican mojarra increases the time invested by parents in caring for offspring and their stress levels,potentially contributing to Mexican mojarra population declines.Here,we gathered the best evidence available to discuss some mechanisms and consequences of such co-occurrences in relation to reproductive behaviors,parental care,competition for resources,and dominance hierarchy,and how the four invasive cichlids have negatively affected the Mexican mojarra.

INTERCROPPING:FEED MORE PEOPLE AND BUILD MORE SUSTAINABLE AGROECOSYSTEMS

Intercropping is a traditional farming system that increases crop diversity to strengthen agroecosystem functions while decreasing chemical inputs and minimizing negative environmental effects of crop production.Intercropping is currently considerable interest because of its importance in sustainable agriculture.Here,we synthesize the factors that make intercropping a sustainable means of food production by integrating biodiversity of natural ecosystems and crop diversity.In addition to well-known yield increases,intercropping can also increase yield stability over the long term and increase systemic resistance to plant diseases,pests and other unfavorable factors(e.g.,nutrient deficiencies).The efficient use of resources can save mineral fertilizer inputs,reduce environmental pollution risks and greenhouse gas emissions caused by agriculture,thus mitigating global climate change.Intercropping potentially increases above-and belowground biodiversity of various taxa at field scale,consequently it enhances ecosystem services.Complementarity and selection effects allow a better understanding the mechanisms behind enhanced ecosystem functioning.The development of mechanization is essential for largescale application of intercropping.Agroecosystem multifunctionality and soil health should be priority topics in future research on intercropping.

Competition of insect decomposers over large vertebrate carrion:Necrodes beetles(Silphidae)vs.blow flies(Calliphoridae)

Large carrion is inhabited by highly variable and interactive communities of insects.Positive interactions in carrion insect communities have been recently the focus in carrion ecology.In contrast,competition between carrion insects is rather undervalued.Here we provide evidence that blow flies(Calliphoridae)and Necrodes beetles(Silphidae),dominant decomposers of large carcasses in terrestrial habitats,compete over carrion.By reanalyzing the results from 90 pig carcasses,we demonstrated that the contribution of the flies and the beetles to the decay was negatively related.The greater part of the large carrion pool was monopolized by blow flies,whereas Necrodes beetles abundantly colonized carcasses,on which blow flies were less effective as decomposers.In behavioral assays,we found that adult beetles killed 4 times more frequently feeding than postfeeding third instar larvae of the flies,with the large decrease in the killing frequency after the larvae reached the age of early third instar.Therefore,adult Necrodes beetles preferentially killed the larvae that were before or in their peak feeding.The study provides evidence that the interaction between blow flies and Necrodes beetles is a combination of indirect exploitative effects of the flies and direct interference effects of the beetles(the mixed competition).

Intensity and Importance of Competition for a Grass (Festuca rubra) and a Legume (Trifolium pratense) Vary with Environmental Changes

How plant competition varies across environmental gradients has been a long debate among ecologists. We conducted a growth chamber experiment to determine the intensity and importance of competition for plants grown in changed environmental conditions. Festuca rubra and Trifolium pratense were grown in monoculture and in two- and/or three- species mixtures under three environmental treatments. The measured competitive variations in terms of growth （height and biomass） were species-dependent. Competition intensity for Festuca increased with decreased productivity, whilst competition importance displayed a humpback response. However, significant response was detected in neither competition intensity nor importance for Trifolium. Intensity and importance of competition followed different response patterns, suggesting that they may not be correlated along an environmental gradient. The biological and physiological variables of plants play an important role to determine the interspecific competition associated with competition intensity and importance. However, the competitive feature can be modified by multiple environmental changes which may increase or hinder how competitive a plant is.