Effects of competitive interactions of different life forms submersed plants on biomass allocation in shallow lakes

Plant competition has been recognized as one of the most important factors influencing the soructure and function of lake ecosystems. Competition from plants of dissimilar growth form may have profound effects on shallow lakes＇. An experiment was conducted to investigate the effects of competitive interactions of submersed plants with dis- similar growth forms on the biomass allocations. Hydrilla verticitlata and Vallisneria natans were selected and were planted in a single-species monoculture and a mixed-species pattern, Results showed that the growth of E natans was＇ significantly affected by the tt, verticillata and caused a sharp reduction of biomass, but the root：shoot ratio of E ha- tans was not affected significantly and there was a minimal increase in mixture： while for H. verticillata, the biomass and the root：shoot ratio were not significantly changed by the competitive interactions ore natans, there was minimal increase of biomass and minimal decrease of the root：shoot ratio. These results may indicate that theplant which can develop a dense mat or canopy at the water surface would be a stronger competitor relative to the plant that depends more on light availability near the sediment.

Competitive interactions and coexistence of sympatric flagship carnivores in Asia

Understanding the competition and coexistence of flagship carnivores is key to creating strategies for their conservation in the face of global carnivore declines.Although studies exploring the dynamics and competition between tigers(Panthera tigris)and leopards(P.pardus)span decades,there is a lack of understanding regarding the factors that influence their coexistence mechanisms on a broad scale,as well as the drivers determining their exploitative and interference competition.We gathered a comprehensive list of research papers among which 36 papers explored the interspecific interactions between tigers and leopards and tested the influence of biotic and abiotic factors on the coexistence mechanisms along three dimensions using multiple response variables regression models;we also tested the influence of ecological drivers determining the exploitative or interference competition between tigers and leopards.Elevation and ungulate density were the most important predictors in regulating the coexistence mechanisms.Tigers and leopards exhibited more positive relations/higher overlaps as elevation increased in the spatial niche.In addition,they showed a higher dietary overlap in the prey-rich regions.We determined that interference competition between tigers and leopards was less frequently observed in habitats with dense tree cover and homogeneous vegetation structures.Meanwhile,studies with multiple metrics would promote the detection of interference competition.Our study provides new insight into the competitive interactions and coexistence mechanisms of tigers and leopards on a broad scale.Policy-makers and managers should pay more attention to the factors of elevation,prey abundance,and habitat structures for the conservation of tigers and leopards.

Emergent plant presence and richness alter competitive interactions between two foating plants

Interactions between two plant species can be infuenced by the presence of other plant species and such an effect may change as the diversity of the other species increases.To test these hypotheses,we frst constructed aquatic communities consisting of 1,2 and 4 emergent plant species and then grew ramets of Lemna minor only,ramets of Spirodela polyrhiza only or ramets of both L.minor and S.polyrhiza within these aquatic communities.We also included controls with ramets of L.minor,S.polyrhiza or both but without any emergent plants.Biomass and number of ramets of L.minor and S.polyrhiza were signifcantly smaller with than without the emergent plants,but they did not differ among the three richness levels.The presence of S.polyrhiza did not signifcantly affect the growth of L.minor,and such an effect was not dependent on the richness of the emergent plant species.Without the emergent plant species,the presence of L.minor markedly reduced biomass(-92%)and number of ramets(-88%)of S.polyrhiza.However,such a competitive effect of L.minor on S.polyrhiza became much weaker in the presence of one emergent plant species(-46%biomass and-39%number of ramets)and completely disappeared in the presence of two or four emergent plant species.Therefore,both the presence and richness of emergent plant species can alter competitive interactions between the two duckweed species.These fndings highlight the importance of species diversity in regulating plant-plant interactions.

A size-gradient hypothesis for alpine treeline ecotones

Research on the stress gradient hypothesis recognizes that positive(i.e. facilitative) and negative(i.e. competitive) plant interactions change in intensity and effect relative to abiotic stress experienced on a gradient. Motivated by observations of alpine treeline ecotones, we suggest that this switch in interaction could operate along a gradient of relative size of individual plants. We propose that as neighbors increase in size relative to a focal plant they improve the environment for that plant up to a critical point. After this critical point is surpassed, however, increasing relative size of neighbors will degrade the environment such that the net interaction intensity becomes negative. We developed a conceptual(not site or species specific) individual based model to simulate a single species with recruitment, growth, and mortality dependent on the environment mediated by the relative size of neighbors. Growth and size form a feedback. Simulation results show that the size gradient model produces metrics similar to that of a stress gradient model. Visualizations reveal that the size gradient model produces spatial patterns that are similar to the complex ones observed at alpine treelines. Size-mediated interaction could be a mechanism of the stress gradient hypothesis or it could operate independent of abiotic stress.

Seasonal resource use and niche breadth in an assemblage of coexisting grazers in a fenced Park

Many small Parks inKenyaare being fenced to control human-wildlife conflict. Some of these Parks have a diversity of large herbivores which might increase in density in the wake of fencing and subsequent compression of their home ranges due to closure of their migratory routes. It is important to understand the consequences of such an increase on the structuring of insularised herbivore assemblages in such Parks. We studied seasonal resource segregation and niche breadth variation as mechanisms of coexistence in a high density grazer assemblage inLakeNakuruNational Parkwhich is small and completely fenced. Diet composition and habitat use were considered as variables of resource use. We predicted that overlap in resource use and niche breadth would be the smallest among grazers with similar body weights in the dry season which is the most resource limiting for grazers in East Africa. Our results were contrary to the predictions because of lack of seasonal differentiation in the overlap of diet composition and habitat use, and in niche breadth. Overlaps in resource use were consistently high during both the wet and dry seasons, and niche breadth contraction during the dry season was not possible probably because of lack of species-specific niches during the dry season. Our results suggest that there might be competitive interactions in this grazer assemblage which is an important parameter to consider in the management of the Park.

Dilution Accelerates Crystallization:A Negative-Order Kinetic Coordination Reaction Induced by the Competitive Interplay of Dissociation and Complexation

Chemical reactions in homogenous systems are generally associated with positive-order kinetics;that is,the reaction rate increases with the increased concentration of reactants.In this work,we report a coordination reaction of Cu^(2+)ions,cyanuric acid(CA),and pyridine in aqueous solution which shows negative-order kinetics with respect to the concentration of pyridine.As the pyridine concentration increases,the complexation of CA with pyridine overwhelms its dissociation in water,resulting in the redistribution of CA;that is,CA is sealed in the pyridine phase by forming an unreactive hydrogenbonded complex.As a result,the number of accessible anionic CA for crystallization in water decreases,and thus the crystallization slows down and almost terminates.Further,the crystallization yields two types of crystals with similar structures but disparate colors(red and blue),and the origin is investigated by the ligand field analysis.

Factors affecting the spatial distribution and breeding habitat of an insular cliff-nesting raptor community

The specific spatial distribution and habitat association--strongly influenced by environmental fac- tors or competitive interactions--are major issues in ecology and conservation. We located and georeferenced nesting sites of five cliff-nesting raptors （Egyptian vulture Neophron percnopterus [a locally extinct species], common buzzard Buteo buteo, osprey Pandion haliaetus, common kes- trel Falco tinnunculus, Barbary falcon Falco peregrinus pelegrinoides）, and common raven Corvus corax on one of the most biodiverse hotspot within the Canary Islands （Teno, Tenerife）. We used generalized linear models to evaluate the factors affecting abundance, richness, and intra- and interspecific interactions. Raptor abundance increased with slope, shrub-covered area, and habitat diversity, and decreased with altitude, and forested and grassed areas. Richness increased with slope and decreased with altitude. Threatened species （osprey, Barbary falcon, and raven） occu- pied cliffs farther away from houses and roads, and more rugged areas than the non-threatened species. The models suggested that the probability of cliff occupation by buzzards, falcons, and rav- ens depended only on inter-specific interactions. Buzzard occupation increased with the distance to the nearest raven and kestrel nests, whereas falcons and ravens seek proximity to each other. Teno holds between 75% and 100% of the insular breeding populations of the most endangered species （osprey and raven）, indicating the high conservation value of this area. Our study suggests that the preservation of rugged terrains and areas of low human pressure are key factors for raptor conservation and provide basic knowledge on the community structure and habitat associations to develop appropriated management actions for these fragile island populations.

Using functional trait diversity to infer community assembly mechanisms:an exclosure experiment as an example

Aims The Qinghai-Tibetan Plateau has a mean altitude exceeding 4000 m and covers about 2.5 million km2.More than 60%of this area is alpine grassland.Exclosures have been widely used in this region to study the sustainable use of grassland resources.We used patterns of functional trait diversity to infer the effects of exclosures on com-munity assembly in alpine meadows.Methods We studied functional diversity using five traits under grazing and three enclosed(exclosure)plots(3,8,and 18 years old)in an alpine meadow on the Qinghai-Tibetan Plateau.We quantified the strength of the community assembly processes by comparing the observed functional trait diversity with a null model that assumes random community assembly.Important findings We found evidence for deterministic assembly processes for plant communities in exclosures.The changes in CWM of the five traits from grazing land to 18-year exclosure indicated that environmen-tal filtering occurred due to the exclosures.Multivariate functional diversity(MFDis and MPDses),and functional diversity of individual traits,including that of leaf area,leaf weight and aboveground bio-mass(FDis of leaf area,leaf weight,and aboveground biomass),increased gradually from grazing land to the 18-year exclosure,and the values of the 18-year exclosure were significantly greater than null expectation.This can be interpreted to indicate that exclosures resulted in greater competitive interaction between species.These results suggest that the effect of exclosures on community assembly is more deterministic than stochastic in this meadow.