Competitive Identity Research Articles

ANTAGONISTIC INTERACTIONS BETWEEN PLANT COMPETITION AND INSECT HERBIVORY

Interspecific competition between plants and herbivory by specialized insects can have synergistic effects on the growth and performance of the attacked host plant. We tested the hypothesis that competition between plants may also negatively affect the performance of herbivores as well as their top-down effect on the host plant. In such a case, the combined effects of competition and herbivory may be less than expected from a simple multiplicative response. In other words, competition and herbivory may interact antagonistically. In a greenhouse experiment, Poa annua was grown in the presence or absence of a competitor (either Plantago lanceolata or Trifolium repens), as well as with or without a Poa-specialist aphid herbivore. Both competition and herbivory negatively affected Poa growth. Competition also reduced aphid density on Poa. This effect could in part be explained by changes in the biomass and the nitrogen content of Poa shoots. In treatments with competitors, reduced aphid densities alleviated the negative effect of herbivory on above- and belowground Poa biomass. Hence, we were able to demonstrate an antagonistic interaction between plant-plant interspecific competition and herbivory. However, response indices suggested that antagonistic interactions between competition and herbivory were contingent on the identity of the competitor. We found the antagonistic effect only in treatments with T. repens as the competitor. We conclude that both competitor identity and the herbivore's ability to respond with changes in its density or activity to plant competition affect the magnitude and direction (synergistic vs. antagonistic) of the interaction between competition and herbivory on plant growth.

Competitive identity: The new brand management for nations, cities and regions

Competitive identity: The new brand management for nations, cities and regions

Mechanisms of resistance to invasion in a California grassland: the roles of competitor identity, resource availability, and environmental gradients

Resistance to the invasion of exotic plants may sometimes result from the strong effects of a relatively small number of resident species. Understanding the mechanisms by which such species resist invasion could provide important insights for the management of invaded ecosystems. Furthermore, the individualistic responses of community members to resource availability and environmental gradients could drive spatial variation in resistance at the local to landscape scales. We tested the resistance of monoculture plots of three native perennial grasses from the California coastal prairie to the invasion of the European perennial grass Holcus lanatus. We also used a watering treatment that increased early summer water availability and a natural elevational gradient in resource availability and soil texture to evaluate how resident identity interacted with abiotic resistance to affect Holcus establishment. Two native species, Festuca rubra and Calamagrostis nutkaensis, exhibited strong resistance, correlated with their negative effects on light availability. A third native grass, Bromus carinatus var. maritimus, had either no effect or a weakly facultative effect on Holcus performance relative to bare plots. Water addition did not alter the resistance of these species, but the elevation gradient did. Holcus invasion increased with improving abiotic conditions towards the slope bottom in bare and Bromus plots, but invasion decreased towards the bottom in Calamagrostis plots, where better conditions favored competitive residents. These results support the idea that resistance to invasion can sometimes be due to a subset of native species, and that the resistance provided by even a single species is likely to vary across the landscape. Identifying the mechanisms by which species resist invasion could facilitate the selection of management strategies that at best increase, or at worst do not decrease, natural resistance.

Public diplomacy and place branding: Where's the link?

In March 2007, a conference on Public Diplomacy was held at Wilton Park, the conference centre of the United Kingdom’s Foreign and Commonwealth Office. Public Diplomacy practitioners and academics from several different countries attended the event, and a lively discussion emerged around the future of PD. One strand of the debate that particularly interested me centred on the connection between PD and competitive identity.

ORIGINAL ARTICLE: Can Ellenberg's indicator values for Mediterranean plants be used outside their region of definition?

AbstractAim The aims of this study are: (1) to explore the relationships between the Ellenberg indicator values (light, temperature and moisture) recently developed for two Mediterranean regions (Italy and Greece); and (2) to evaluate the possibility of using these values in other Mediterranean areas.Location Southern Greece and the Mediterranean part of Italy.Methods A global matrix containing 966 items of information (161 species × 3 indicator variables × 2 values assigned in each study, one in Italy and one in Greece) was constructed. A test of the accuracy of the values in predicting actual environmental conditions was provided using a detrended correspondence analysis (DCA) on published vegetation relevés from the Mediterranean region. The gamma statistic was used to express relationships of ecological indicator values between the two regions, and pairs of indicator values calculated for each species were compared using Wilcoxon matched pairs tests.Results The results showed that indices developed for Greece and Italy were not similarly correlated to sample scores along DCA axis 1. Species’ indicator values for Italy and for Greece were highly significantly correlated for light and moisture and significantly correlated for temperature, but the correlations were weak (0.20 ≤ gamma ≤ 0.31). Pairwise testing gave significantly different indicator values for the two regions. Discrepancies below or equal to 2 units on 9‐point scales (12 points for moisture) were found for 88%, 70% and 54% of the species respectively for light, temperature and moisture indices. A substantial number of species showed higher discrepancies, from 3 up to 6 units.Main conclusions In the light of the present work, it seems clear that the indicator values developed for Italy and for Greece should not be used outside the region for which they were defined. This constitutes additional evidence that indicator values can be influenced by the identity of potential competitors. It also underlines the need to use standardized methods for calibrating indicator values against measured variables in such a way that indicator systems can serve as general reference systems.

Pilfering ravens, Corvus corax, adjust their behaviour to social context and identity of competitors

Like other corvids, food-storing ravens protect their caches from being pilfered by conspecifics by means of aggression and by re-caching. In the wild and in captivity, potential pilferers rarely approach caches until the storers have left the cache vicinity. When storers are experimentally prevented from leaving, pilferers first search at places other than the cache sites. These behaviours raise the possibility that ravens are capable of withholding intentions and providing false information to avoid provoking the storers' aggression for cache protection. Alternatively, birds may refrain from pilfering to avoid conflicts with dominants. Here we examined whether ravens adjust their pilfer tactics according to social context and type of competitors. We allowed birds that had witnessed a conspecific making caches to pilfer those caches either in private, together with the storer, or together with a conspecific bystander that had not created the caches (non-storer) but had seen them being made. Compared to in-private trials, ravens delayed approaching the caches only in the presence of storers. Furthermore, they quickly engaged in searching away from the caches when together with dominant storers but directly approached the caches when together with dominant non-storers. These findings demonstrate that ravens selectively alter their pilfer behaviour with those individuals that are likely to defend the caches (storers) and support the interpretation that they are deceptively manipulating the others' behaviour.

Understanding the Challenges of African Democratization through Conflict Analysis

This paper discusses the need for increased 'conflict analysis' during democratization attempts in Africa. Through a comparison of both structure and agency, the author highlights how current efforts at democratizing Africa continue to remain solution heavy and analysis light, with donor nations and agencies focusing primarily on top-down institutional and electoral reforms. Without sufficient understanding of how individual and group-level forces shape Africa's sociopolitical landscape, democracy, which is most often advertised as a solution to societal conflict, can actually precipitate conflict conditions. Purely structural reforms can potentially create highly competitive identity struggles within the grassroots, and in many cases, lead to conflict that derails democratization. Furthermore, certain instrumentalist African leaders, who lack sincere commitment to the democratic process, can easily manipulate ethnic divides in order to retain power. Multi-disciplinary and holistic analysis that is inclusive of theories grounded in structure and agency is advocated for increasing the chances of peaceful democratic transition.

Competitive relationships ofAndropogon gerardii(Big Bluestem) from remnant and restored native populations and select cultivated varieties

SummaryAlthough genetic differentiation among plant populations is well known, its relevance for preserving the integrity of native ecosystems has received little attention. In a series of competition experiments withAndropogon gerardiiVitman, a dominant species of the North American Tallgrass Prairie, plant performance was related to seed provenance and restoration activities.Glasshouse experiments showed plant performance to be a function of seed source. Differential target plant performance relative to competitor identity was observed when plant performance was assessed across a range of competitor densities. Local and non‐local plants were larger when competing against non‐local plants relative to the local and cultivar plants, while cultivar plants were consistently larger than local and non‐local plants regardless of competitor identity or density. The consistency of cultivar performance could reflect directional selection during cultivar development for consistently high fecundity, vigorous vegetative growth and resistance to pathogens.In a field experiment, non‐local plants were half the size of local and cultivar plants, supporting recognition of seed provenances ofA. gerardiibased on differences in plant performance among source populations observed in the glasshouse study, and previous genetic analyses of the same populations.This study establishes that seed provenance and restoration activities influence the competitive ability of a dominant species which, in turn, may affect plant community structure and potential ecosystem function.

‘For the honour of the town’: comparison, competition and civic identity in eighteenth-century England

Eighteenth-century England was not merely ‘polite and commercial’; it was also notoriously competitive. This article argues that competition and contrast were not confined to weighing up the comparative status and achievements of individuals but were also fundamental to the development of civic consciousness and identity. Contemporaries developed a wide, comparative frame of reference which encouraged a heightened sense of competition with rival urban centres. However, this process also encouraged elements within urban society to define themselves in opposition to rival ‘communities’ within their own walls.

The importance of competitor identity, morphology and ranking methodology to outcomes in interference competition between sponges

The nature or structure of competition within communities has been a dynamic area of practical and theoretical research for a number of decades. Certain components of some communities have proved hard to incorporate within such studies; in marine benthic work this has included the sponges. In this study, intra- and inter-phyletic interactions involving sponges (7,817 in total) were studied on 125 rocks (ranging in surface area from 10 to 2,438 cm2) at a site experiencing low disturbance levels at Lough Hyne Marine Nature Reserve, Co. Cork, Ireland. The outcomes of sponge-sponge (intra-phyletic) interactions were significantly different in both outcome and structure to those involving sponges and representatives of other phyla. Typically sponge-sponge competition resulted in a much higher number of tied outcomes than did inter-phyletic encounters. Sponges over-grew all groups of organisms with the exception of some cnidarians and ascidians. The morphology of any sponge species (thickness in most cases) was important in determining the outcome of intra-phyletic, but not inter-phyletic, interactions. Sponges which exhibited thick (>2 mm) crusts were, in the majority of interactions, superior competitors compared to the thin (<1 mm) crusts. However, the method used to rank species (i.e. wins:loss or wins:total ratio) made a significant difference to the ranking of sponge competitors. The transitivity of the sponge assemblage investigated was calculated using the index formulated by Tanaka and Nandakumar (1994) as 0.23, indicating the assemblage to be organised as a network rather than a hierarchical system. We suggest this network of principally tied outcomes (due to standoffs) may be maintained in part by chemical interaction. However, in the absence of disturbance, the network is more likely to be mediated through processes of growth and regression of tissues during summer and winter months respectively.

Linking hypercompetition and strategic group theories: strategic maneuvering in the US insurance industry

Focusing on the dynamics of strategic maneuvering, this paper draws parallels between the accumulated perspectives of strategic group theory and ideas drawn from evolutionary economics and from a recent strategy-oriented book on hypercompetition (D'Aveni RA. 1994. Hypercompetition: Managing the Dynamics of Strategic Maneuvering. The Free Press: New York). Using insurance industry data, the paper first uses the methodological framework of strategic groups to define competitive positioning and the identity of close competitors. It then develops a Markovian model to analyse two important aspects of strategic maneuvering over time: the level of firm movement, and the determination of optimal maneuvering paths and their related long-term performance. The results provide insights into industry competitive dynamics and rivalry. First, there is clear evidence of strategic maneuvering over the entire time period studied and a higher level of maneuvering in the long run. Second, for some competitive scenarios, there are optimal maneuvering trajectories that optimize a firm's long-term economic performance. Copyright © 2001 John Wiley & Sons, Ltd.

Linking hypercompetition and strategic group theories: strategic maneuvering in the US insurance industry

AbstractFocusing on the dynamics of strategic maneuvering, this paper draws parallels between the accumulated perspectives of strategic group theory and ideas drawn from evolutionary economics and from a recent strategy‐oriented book on hypercompetition (D'Aveni RA. 1994. Hypercompetition: Managing the Dynamics of Strategic Maneuvering. The Free Press: New York). Using insurance industry data, the paper first uses the methodological framework of strategic groups to define competitive positioning and the identity of close competitors. It then develops a Markovian model to analyse two important aspects of strategic maneuvering over time: the level of firm movement, and the determination of optimal maneuvering paths and their related long‐term performance. The results provide insights into industry competitive dynamics and rivalry. First, there is clear evidence of strategic maneuvering over the entire time period studied and a higher level of maneuvering in the long run. Second, for some competitive scenarios, there are optimal maneuvering trajectories that optimize a firm's long‐term economic performance. Copyright © 2001 John Wiley &amp; Sons, Ltd.

Effects of maternal age on larval competitiveness in house flies.

At advanced ages, many insects lay smaller eggs with reduced viability, but adults produced by different maternal age classes are usually indistinguishable. In most species it is not known if there are any significant differences between hatchlings from smaller, later eggs (i.e. those produced by old females) and those from larger, earlier eggs (i.e. those produced by young females). For many insects, the best way to determine if such differences exist is to rear larvae from different maternal age classes together and compare their success. We tested the effects of maternal age on the competitive ability of house fly larvae, using a modified replacement (substitution) design with pairwise comparisons of two maternal age classes from three electrophoretically marked lines. For each comparison, known numbers of larvae were reared together at five ratios, including pure cultures, at densities high enough to ensure severe competition. We measured the effects of maternal age on hatchling to adult survival, development time, and adult size. In general, older females produced larvae that had higher viability and attained larger sizes, but developed more slowly. Maternal age effects were line-specific, suggesting that they are determined genetically, and there were significant interactions of maternal age effects between pairwise line comparisons. Maternal age effects on performance in pure culture were not predictive of performance in mixed cultures. Competitor identity significantly affected the success of each line and maternal age class, suggesting that use of tester strains to determine relative competitiveness of lines, or maternal age classes, is not generally valid. The results are discussed with respect to the possible adaptive nature of maternal age effects in this species.

Competition between co-dominant plants of the Serengeti plains depends on competitor identity, water, and urine

Kyllinga nervosa (Steud.) and Sporobolus kentrophyllus (K. Schum.) are co-dominant plants of the Serengeti short-grass plains, Tanzania. The plains are characterized by seasonal and sporadic rainfall and currently support in excess of 1.5 million migratory ungulates. The interactive effect of simulated bovine urine and water availability were tested on the competitive interactions of these species in the laboratory.

Plant competition and slug herbivory: Effects on the yield and biomass allocation pattern of Poa annua L

A factorial greenhouse experiment was conducted to examine the overall impact of slug herbivory, plant density and neighbour iden- tity on the yield and allocation pattern of the short-lived grass Pea cmnua. The effects of slug herbivory were compared in experimental plants at two densities in two types of culture: pure and mixed with Arabidopsi.~ thalianu. All the plant parts of P annua showed significantly greater bio- mass in mixed than in pure stands, and in low compared to high density stands. Slug herbivory consistently reduced the biomass of reproductive organs and the percentage of total biomass allocated to reproduction, whereas density had no effect on allocation. In mixed stands, the proportion of biomass allocated to reproductive organs and leaves was greater and lesser, respectively, than in pure stands. There were significant interactions between herbivory and culture for root biomass and for the percentage of biomass allocated to root and shoots, and between herbivory, culture and density for shoot, stem, leaf and total biomass. Slug herbivory reduced root biomass in pure stands, whereas it did the opposite in mixed stands. The root:shoot ratio did not vary between mixed and pure stands in the absence of slugs, while when slugs were present pure stands had lower root/shoot ratio than mixed stands. Except for reproductive structures, all the plant parts showed greater biomass in grazed than in ungrazed low density mixed stands, whereas the general trend in high and low density pure stands, and in high density mixed stands was that herbivory decreased biomass. The study indicates that the competitive ability of plants is conditioned by a variety of factors. Plant density, the identity of competitors, and occurrence of herbivory are all relevant factors, the particular combination of which will alter competitive interactions. 0 Elsevier, Paris

Mechanisms Controlling Invasion of Coastal Plant Communities by the Alien Succulent Carpobrotus Edulis

The South African succulent Carpobrotus edulis has been invading native and non—native plant assemblages in California since its introduction in the early 1900s. This study was designed to determine mechanisms controlling invasion by this species into three different communities: coastal grassland, backdune, and coastal scrub. The communities differed in several factors that influenced invasion by Carpobrotus: soil disturbance, herbivory, and identity of competitors. Disturbances of the soil was required for establishment of Carpobrotus at the grassland site. Soil disturbance did not promote Carpobrotus establishment in the coastal scrub or backdune. Establishment in these sites was restricted by herbivory. The influence of neighboring vegetation on Carpobrotus establishment was site dependent. At the grassland site, Carpobrotus seedling survival was reduced by grasses, and the only surviving seedlings were on gopher mounds. Growth of larger Carpobrotus plants, however, was unaffected by grasses. Proximity to shrubs, the dominant plant type at the backdune and coastal scrub sites, did not affect Carpobrotus seedling survival. It did, however, decrease both root and shoot biomass of seedlings and cuttings. Invasion is expected to occur most rapidly at the grassland site. Although germination and early survival there depend on the occurrence of rodent disturbances, these occur frequently, and seedling recruitment in the grassland was observed during this study. Once established, clonal growth is great and is not affected by herbivory or competition. In contrast, at the coastal growth, intense herbivory prevented successful establishment during this study. Cage experiments suggested that herbivory counteracted the high growth potential of Carpobrotus at this site. At the dune site, even caged plants showed very poor growth. Thus, although seedling recruitment does not occur there, invasion is expected to be slow due to harsh physical conditions that limit both survival and growth. These findings demonstrate strong community differences in the factors governing invasability by Carpobrotus edulis.

Bidding Strategies and Probabilities

Seven competitive bidding strategies for optimizing profits in construction contracting are developed; namely: (1) Lone Bidder Strategy—no competitors; (2) Two Bidders Strategy—one competitor; (3) Many Bidders Strategy—more than one competitor, number and identity of competitors not known; (4) All Bidders Known Strategy—more than one competitor, number and identity of competitors known; (5) Number of Bidders Known Strategy—more than one competitor, number of competitors known but identity of competitors not known; (6) Least Spread Strategy—minimizing money left on the table; and (7) Unbalanced Bidding—maximizing competitive position through quantity change. In addition, the following statistical distributions and applications are investigated: (1) Binomial Distribution—forecasting the frequency of winning; (2) Gaussian Distribution—precision of bidding; and (3) Poisson Distribution—forecasting of number of competitors. Other related topics are examined briefly.

Place of Marketing Agreements in Stabilizing Farm Income

EITHER through direct intervention by government or through combination by sellers, agricultural control programs have manipulated volume or method of production, prices paid for productive resources, levels of demand, and distribution of supplies. Analysis is limited here to manipulation by sellers of average price for already produced supplies. One or more determinants of industry average price are controlled by representatives of the whole industry, for its benefit and at its risk, with formal execution and enforcement of group decisions by government. Participating firms retain competitive identity with respect to scale and method of procurement and production and the uncontrolled determinants of total gross receipts. The primary instruments of these programs are marketing agreements and orders, four attributes of which are considered here: (1) definition, (2) price effects, (3) feasibility of wider use, and (4) necessary statutory changes. Federal programs are emphasized. Agreements and orders are defined in terms of effects upon firm and industry profit policy, control techniques, legal and administrative attributes, limitations, and collateral programs. Price effects are appraised largely in terms of impact upon market structure. Desirability of wider use and of statutory changes is weighed in terms of operational feasibility and effectiveness of control. The basic issue of stabil-