Presence Of Competition Research Articles

Invasive non-native species of fish in upper Paraná river Basin, Brazil: variations of caloric content in Cichla kelberi

The allocation of assimilated energy may be influenced by seasonal changes, growth, and reproductive cycle of fish, food consumption and environmental conditions. The objective of this research was to evaluate the energetic variations of Cichla kelberi in the upper Paraná River floodplain, analyzing the caloric content in muscles, gonadosomatic index (GSI), and the condition factor between assessed systems, sex, and stage of gonadal maturation. The results obtained in the present study permit assuring that this is a species that efficiently converts the resources of the environment into energy. Although presenting higher condition factor in the environment where there is a greater ease in getting food (Paraná subsystem), the energy identified in the muscles was the same in both subsystems. During the process of gonadal maturation there is optimization in energy accumulation in the muscles of females, before and after reproductive period, and somatic growth occurs significantly when the individual is not reproducing. Further detailed studies on ecological mechanisms influencing the success of the species, as the presence of competitors and preference for native preys, are needed to implement effective management measures aimed at preventing that the species proliferation in the environment is even more damaging to local biodiversity.

Effects of size and size structure on predation and inter-cohort competition in red-eyed treefrog tadpoles

Individual and relative body size are key determinants of ecological performance, shaping the strength and types of interactions within and among species. Size-dependent performance is particularly important for iteroparous species with overlapping cohorts, determining the ability of new cohorts to invade habitats with older, larger conspecifics. We conducted two mesocosm experiments to examine the role of size and size structure in shaping growth and survival in tadpoles of the red-eyed treefrog (Agalychnis callidryas), a tropical species with a prolonged breeding season. First, we used a response surface design to quantify the competitive effect and response of two tadpole size classes across three competitive environments. Large tadpoles were superior per capita effect competitors, increasing the size difference between cohorts through time at high resource availability. Hatchlings were better per biomass response competitors, and maintained the size difference between cohorts when resource availability was low. However, in contrast to previous studies, small tadpoles never closed the size gap with large tadpoles. Second, we examine the relationship between body size, size structure, and predation by dragonfly nymphs (Anax amazili) on tadpole survival and growth. Hatchlings were more vulnerable to predation; predator and large competitor presence interacted to reduce hatchling growth. Again, the size gap between cohorts increased over time, but increased marginally more with predators present. These findings have implications for understanding how variation in resources and predation over the breeding season will shape population size structure through time and the ability of new cohorts to invade habitats with older conspecifics.

Prey-capture efficiency between juveniles and adults, feeding habitat and abundance of Wattled Jacana foragers in northern Pantanal, Mato Grosso state, Brazil

The choice of foraging strategies implies an attempt at gaining energy by predators. Supposedly, the difference in employing the "sit and wait" or "active foraging" behavior lays in hunter skills, experience and the kind of prey consumed. With the hypothesis that "active foraging" demands no learning, in this study we compared the prey capture efficiency among Wattled Jacana juveniles and adults, and also present descriptive information about feeding habitat and the abundance variation of foragers throughout the day in the northern Pantanal. Prey capture efficiency did not differ significantly among juveniles and adults, corroborating our initial hypothesis that "active foraging" is an instinctive behavior and demands no experience to be effective. However, future work is necessary to compare the energetic quality of consumed items by juveniles and adults, searching for differences explained by adults' experience. Foraging individuals were found at an average distance of 14 m ranging from 2 to 42 m) from the margin of the sampled swamps, however 64% of the foragers were found closer to the margins. The average depth of foraging sites was 17 cm, ranging from 5 to 40 cm, although no preference for specific classes of depth was found (p > 0,05). Despite the accepted general pattern of birds being more active in the early morning, the largest number of individuals foraging was observed between 11:00 and 12:00 AM, but no significant difference was found in the abundance of foraging individuals among different periods of the day. Factors, which were not analyzed, such as food availability and presence of competitors and predators need to be studied to reveal the main factors of the spatial and temporal distribution of the Wattled Jacana.

Populasi Lychas mucronatus (Scorpiones:Buthidae) di Kampus Undip Tembalang Semarang.

Scorpion is an animal that has a high adaptability in various environmental conditions. Lychas mucronatus isone species of scorpion of the Buthidae family, which can be found on Campus Diponegoro University, SemarangTembalang. No data population and the spread of L. mucronatus on the campus of Diponegoro University, SemarangTembalang. This study aims to assess the population of L. mucronatus on the campus of Diponegoro University,Semarang Tembalang. This research was conducted in October-November 2009 in the region Undip TembalangHyderabad campus. Samples were taken by hand collecting techniques directly in the field accompanied by an imagecapture scorpion on its habitat. L. population data mucronatus were analyzed descriptively. The results showed L.mucronatus found on campus Undip Tembalang were 22 specimens consisting of 15 females, 2 males, 1 juvenile,and 4 specimens of unknown gender. L. mucronatus females in this study more likely in because of male mortalityduring mating season. L. mucronatus was found in grassland and shrub habitats, fields, and around the tree, L.mucronatus occupy four types of microhabitat characteristics, namely: leaf litter, rotten wood, in the soil, and understones. L. mucronatus most common in grassland and shrub habitats with sloping contour with microhabitat under arock. The presence of predators and competitors are likely to be a factor not found in L. mucronatus in severallocations on campus Undip Tembalang.

Preference of larvae of Enallagma cyathigerum (Odonata: Coenagrionidae) for habitats of varying structural complexity

In macrophyte-rich lentic ecosystems, higher numbers of damselfly larvae occur in areas where there is structurally complex vegetation than in those where the plant architecture is relatively simple. Biotic interactions rather than morphological constraints are considered to underlie this pattern. We investigated whether the preference of the larvae of the damselfly Enallagma cyathigerum for a particular habitat was retained in absence of prey, predators and/or conspecifics. A series of laboratory choice experiments was conducted in which combinations of sediment and artificial plants differing in structural complexity were offered simultaneously to the larvae. Larvae preferred patches with structurally complex vegetation over patches with simply structured vegetation or lacking vegetation. Patches with simply structured vegetation were preferred over those with bare sediment, but the number of larvae showing a clear choice, which is regarded as an indication of the strength of the preference for a particular habitat, was relatively low compared to the number of individuals responding when complex vegetation was present. Based on the results presented, we conclude that the preference of E. cyathigerum larvae for structurally complex vegetation is independent of the presence of predators, prey or competitors. This suggests that this behaviour of the larvae is either learned or an innate response.

Impact of Competition and Mycorrhizal Fungi on Growth of Centaurea stoebe, an Invasive Plant of Sand Dunes

Soil biota such as arbuscular mycorrhizal fungi (AMF) have been shown to increase invasive plant species success in a wide variety of systems by providing both direct and indirect benefits to the invader. For example, Centaurea stoebe invasion in the western US is at least partially due to AMF networks allowing Centaurea to parasitize some native plant species. Centaurea also invades sand dune systems of the northern Great Lakes region, which often have reduced or altered soil communities compared to other grasslands. In these habitats, AMF may play a different role in invasion success of this species. We conducted a greenhouse experiment to compare effects of soil biota and AMF on competitive interactions between Centaurea and two varieties of Ammophila breviligulata, a dominant native grass of Great Lakes sand dunes. We found that Centaurea growth was slowed by the presence of Ammophila competitors, while AMF had no direct or indirect effect on growth. Both Ammophila varieties were uninhibited by the presence of Centaurea. The commercially available Cape variety of Ammophila had more than twice the inhibitory effect of a native Michigan variety on Centaurea growth. It does not appear that Centaurea takes advantage of AMF networks in this dune system. Indeed, since Centaurea growth is actually reduced in direct competition with Ammophila, we suspect that invasion of dunes by this species is a result of disturbance. For land managers, planting Ammophila in open areas as part of a restoration plan may slow spread of Centaurea in this system.

The Effect of Previous Feeding on Water Hyacinth Leaf Acceptability by Three Water Hyacinth Biological Control Agents Measured with a Simple Y-Tube Olfactometer

The odours released by a plant under herbivory pressure are intercepted by other herbivorous insects and can elicit behavioural changes. The relevant information relayed to the herbivorous insect may include the nutritional quality of the plant, the presence of potential competitors and natural enemies (Dicke 2000; Dicke & van Loon 2000). It may be expected that with this information, a herbivorous insect may be attracted to or repelled by a particular host plant, depending on the apparent costs and benefits associated with that plant (Dicke & van Loon 2000).

Evolution in coyotes (Canis latrans) in response to the megafaunal extinctions.

Living coyotes modify their behavior in the presence of larger carnivores, such as wolves. However, little is known about the effects of competitor presence or absence on morphological change in coyotes or wolves over long periods of time. We examined the evolution of coyotes and wolves through time from the late Pleistocene, during which many large carnivorous species coexisted as predators and competitors, to the Recent; this allowed us to investigate evolutionary changes in these species in response to climate change and megafaunal extinctions at the end of the Pleistocene. We measured postcranial skeletal morphologies of wolves (Canis lupus) and coyotes (C. latrans) from Pleistocene-aged tar deposits, as well as early, mid, and recent Holocene populations of both. We found few morphological differences between Pleistocene and Holocene wolf populations. Conversely, we found many differences in coyotes: Pleistocene coyotes were larger and more robust than Holocene populations. However, within 1,000 y of the megafaunal extinctions, coyotes are morphologically indistinguishable from modern populations. We cannot attribute these differences directly to climate change because modern coyotes do not follow Bergmann's rule, which states body size increases with decreasing temperature. Instead, we suggest that Pleistocene coyotes may have been larger and more robust in response to larger competitors and a larger-bodied prey base. Although we cannot separate competition from predator-prey interactions, this study indicates that the effects of biotic interactions can be detected in the fossil record.

Transforming the nature and scope of new product development

PurposeOver the last several decades, product development efforts have seen unacceptably high new product failure rates. One important factor is the presence of competitors who can interfere with marketing strategy and force changes that sap resources and reduce success. As industries try to improve their success, line extensions, i.e. developing products similar but different to successful products, have become more common. Simultaneously, industries have reacted by refining the new product development (NPD) process to make it more reliable and accurate. The refined development techniques are so helpful in refining product benefits with which firms are familiar that they reinforce the pressure to extend the line. The result is overcrowded markets where destructive competition destroys profitability. A “blue ocean” strategy promises to change the destructive cycle of market crowding. Originally the framework focused on overall market strategy. However, it has a direct application to NPD. Revising the NPD process to incorporate a blue ocean viewpoint before the idea generation stage may reduce the failure rate and create breakthrough products that are not easily emulated. This paper aims to address this issue.Design/methodology/approachThe paper reviews the NPD literature as well as work implementing a blue ocean strategy. It delineates the tools developed for applying blue ocean concepts to strategy. The paper then applies a blue ocean approach to the NPD process with the objective of developing new products and services that are unhindered by competitive offerings. Implementing a blue ocean strategy involves four main actions and may be focused on six targets. The paper integrates the elements into a strategic opportunity product development matrix which may help practitioners. Moreover, it identifies at which stage of the new product development process blue ocean concepts should be introduced.FindingsThe paper reveals that there are no unvarnished panaceas in product development. Applying a blue ocean strategy to avoid competition early in the product life cycle promises to reduce dangerous competition to allow the product to succeed. However, the gains will probably not extend indefinitely. It requires constant improvement and application of the concepts to gain a measure of sustainability. If firms are successful early, they may be able to defend gains in some areas to retain profitability, while seeking new blue oceans.Practical implicationsBlue ocean applied to marketing strategy has seen large gains in success. Integrating efforts to find uncluttered market space holds the promise of increased success. It will also refine the NPD process.Originality/valueBlue ocean strategy has not been applied to the new product development process in the literature. The paper integrates the concepts of the strategy with the elements of product development. The result is a new approach toward success products and product introductions.

Patch exploitation strategies of parasitoids: The role of sex ratio and forager's interference in structuring metapopulations

We use a mathematical model to explore the effects of parasitoid reproductive strategies and foraging behavior in response to spatio-temporal variations in the patch quality of a host–parasitoid metapopulation system. The variations of patch quality over the landscape were measured by the presence of parasitoid competitors and the density of hosts. The parasitoid responses to patch quality are given by three different foraging behaviors: (i) the decision to remain in or leave the current patch; (ii) the control of progeny's sex ratio and (iii) competitive abilities, measured by changes in the potential to attack hosts due to interference from conspecifics in the exploited patch. We study the dynamics of host and parasitoid populations characterized by different levels of density-dependent sex ratio adjustment and interference competition. Our results show that population stability increases when parasitoid growth is correlated with patch conditions. The effect of sex ratio adjustment alone does not account for qualitative changes to system dynamics or to the distribution patterns of species. In contrast, the degree of competitive interference among the parasitoids plays a crucial role in constraining the parasitoids’ potential to reduce host populations and in determining the species’ distribution in the landscape. We found that high levels of interference competition disrupt the population dynamics within a patch and allows hosts to completely dominate the landscape. This study shows that the inclusion of life history traits and the co-evolutionary aspects of host–parasitoid interaction can help researchers to understand species distribution patterns in the landscape.

Foraging speed in staging flocks of semipalmated sandpipers: evidence for scramble competition

Foraging speed is a key determinant of fitness affecting both foraging success and predator attack survival. In a scramble for food, for instance, evolutionary stable strategy models predict that speed should increase with competitor density and decrease when the risk of attack by predators increases. Foraging speed should also decrease in richer food patches where the level of competition is reduced. I tested these predictions in fall staging flocks of semipalmated sandpipers (Calidris pusilla) foraging for an evasive prey. Capture rate of these prey decreased with sandpiper density as the presence of competitors reduced the availability of resources for those behind. Foraging speed was evaluated indirectly by measuring the time needed to cross fixed boundaries on mudflats over 6 years. As predicted, foraging speed increased with sandpiper density and decreased with food density, but, unexpectedly, increased closer to obstructive cover where predation risk was deemed higher. When foraging closer to cover, from where predators launch surprise attacks, the increase in foraging speed may compensate for an increase in false alarms that interrupted foraging. While foraging in denser flocks decreases foraging success, joining such flocks may also increase safety against predators. In semipalmated sandpipers that occupy an intermediate position in the food chain, foraging behavior is influenced simultaneously by the evasive responses of their prey and by the risk of attack from their own predators.

Cyclodextrin Polymer Nanoassemblies: Strategies for Stability Improvement

The main goal of this work was to develop two strategies for stabilization of nanoassemblies made of β-cyclodextrin polymer and amphiphilic dextran associated through host-guest complexes. The first strategy was to coat the nanoassemblies with a dextran derivative bearing adamantyl anchoring groups and hydrophilic poly(ethylene oxide-co-propylene oxide) side chains to increase the steric repulsion between the nanoassemblies. The second strategy developed was to post-reticulate the nanoassemblies upon UV irradiation. Photo-cross-linkable nanoassemblies have been prepared from new host or guest polymers bearing allylether or methacrylate groups. The modified nanoassemblies have been characterized by dynamic light scattering as a function of time and for various salt and competitor concentrations. The results of the first strategy show an improvement of shelf stability and resistance at relatively low concentrations of competitors. The second strategy is the most efficient in providing good shelf stability, much larger than with the first strategy, together with a large resistance to dissociation in presence of competitors.

Daily bursts of biogenic cyanogen bromide (BrCN) control biofilm formation around a marine benthic diatom

The spatial organization of biofilms is strongly regulated by chemical cues released by settling organisms. However, the exact nature of these interactions and the repertoire of chemical cues and signals that micro-organisms produce and exude in response to the presence of competitors remain largely unexplored. Biofilms dominated by microalgae often show remarkable, yet unexplained fine-scale patchy variation in species composition. Because this occurs even in absence of abiotic heterogeneity, antagonistic interactions might play a key role. Here we show that a marine benthic diatom produces chemical cues that cause chloroplast bleaching, a reduced photosynthetic efficiency, growth inhibition and massive cell death in naturally co-occurring competing microalgae. Using headspace solid phase microextraction (HS-SPME)-GC-MS, we demonstrate that this diatom exudes a diverse mixture of volatile iodinated and brominated metabolites including the natural product cyanogen bromide (BrCN), which exhibits pronounced allelopathic activity. Toxin production is light-dependent with a short BrCN burst after sunrise. BrCN acts as a short-term signal, leading to daily "cleaning" events around the algae. We show that allelopathic effects are H(2)O(2) dependent and link BrCN production to haloperoxidase activity. This strategy is a highly effective means of biofilm control and may provide an explanation for the poorly understood role of volatile halocarbons from marine algae, which contribute significantly to the atmospheric halocarbon budget.

Prey habitat selection under shared predation: tradeoffs between risk and competition?

An individual's choice of habitat should optimize amongst conflicting demands in a way that maximizes its fitness. Habitat selection by one species will often be influenced by presence and abundance of competitors that interact directly and indirectly with each other (such as through shared predators). The optimal habitat choice will thus depend on competition for resources by other species that can also modify predation risk. It may be possible to disentangle these two effects with careful analysis of density‐dependent habitat selection by a focal prey species. We tested this conjecture by calculating habitat isodars (graphs of density assuming ideal habitat selection) of chital deer living in two adjoining dry‐forest habitats in Gir National Park and Sanctuary, western India. The habitats differed only in presence (Sanctuary) and absence (National Park) of domestic prey (cattle and buffalo). Both species are preyed on by Asiatic lions. The habitat isodar revealed at low densities, that chital live in small groups and prefer habitat co‐occupied by livestock that reduce food resources, but also reduce predation risk. At higher densities, chital form larger groups and switch their preference toward risky habitat without livestock. The switch in chital habitat use is consistent with theories predicting that prey species should trade off safety in favor of food as population density increases.

Corporate Lobbying: A Review of the Recent Literature

This survey covers recent literature on lobbying, with particular focus on corporate lobbying. Three main research traditions - contests for policy rent, persuasion games, and multiple means models - are analyzed in detail. Various strategic aspects of lobbying a represented in the context of a single unified model that encompasses both strategic communication and monetary contributions. Next, the review investigates into three particular issues in the lobbying literature: Incentive to lobby and the equilibrium amount of lobbying,both in the presence and absence of competitors, strategic substitution and complementarity of lobbying and contributions,and the role of intermediation in lobbying. Recent evidence from corporate lobbying is presented.

Influence of intra- and inter-specific competitions on food hoarding behaviour of buff-breasted rat (Rattus flavipectus)

Food hoarding behavior of sympatric conspecific rodents has been extensively documented during the last decades, while research concerning the influence of intra- and inter-specific competition on hoarding behaviour of rodents is limited. We investigated food hoarding behaviour of buff-breasted rat (Rattus flavipectus) under conditions of semi-natural enclosures in the tropical rain-forest of the Xishuangbanna area (altitude 475–2430 m, 21°09′–22°36′N, 99°58′–101°50′E), Yunnan Province, Southwest China. The main goal of this study was to understand the influence of intra- and inter-specific competition on food hoarding behaviour of rodents. Seeds of Lithocarpus truncatus (Fagaceae), with woody and hard seed coat, were selected and marked as a food item in this experiment. The result showed that: (1) R. flavipectus mainly exhibited food hoarding behaviour in larder form; and (2) the presence of intra-specific competitors significantly increased larder hoarding in R. flavipectus, while an inter-specific competitor, Chinese white-bellied rat (Niviventor confucianus), exerted no significant influence on food hoarding behaviour of subjects. These results indicated that rodent species would adjust their food hoarding behaviour in the presence of competitors, and intra-specific competition has a greater effect than inter-specific competition.

Temporal activity patterns of the swamp rat (Rattus lutreolus) and other rodents in north-eastern New South Wales, Australia

The activity patterns and partitioning of time by four small mammal species, with a focus on the swamp rat (Rattus lutreolus) in north-eastern New South Wales, was investigated using camera trap data from two studies. Analysis was carried out on 1079 camera trap events over 1530 camera trap–nights or 36 720 h of camera trap deployment in the field. The activity patterns of Rattus lutreolus were distinctly diurnal with crepuscular peaks of activity but this differed between sites and when in the presence of competitors. The Hastings River mouse (Pseudomys oralis) and the bush rat (Rattus fuscipes) displayed typical bimodal patterns of nocturnal activity. Antechinus were mostly nocturnal but were occasionally active during the day. These data indicate that where species of Muridae co-occur, diurnal time partitioning by R. lutreolus may reduce competition for food resources. It also confirms the speculation that R. lutreolus displays diurnal behaviour, albeit dependent on the presence of other murids.

Elevational Ranges of Birds on a Tropical Montane Gradient Lag behind Warming Temperatures

BackgroundSpecies may respond to a warming climate by moving to higher latitudes or elevations. Shifts in geographic ranges are common responses in temperate regions. For the tropics, latitudinal temperature gradients are shallow; the only escape for species may be to move to higher elevations. There are few data to suggest that they do. Yet, the greatest loss of species from climate disruption may be for tropical montane species.Methodology/Principal FindingsWe repeat a historical transect in Peru and find an average upward shift of 49 m for 55 bird species over a 41 year interval. This shift is significantly upward, but also significantly smaller than the 152 m one expects from warming in the region. To estimate the expected shift in elevation we first determined the magnitude of warming in the locality from historical data. Then we used the temperature lapse rate to infer the required shift in altitude to compensate for warming. The range shifts in elevation were similar across different trophic guilds.ConclusionsEndothermy may provide birds with some flexibility to temperature changes and allow them to move less than expected. Instead of being directly dependent on temperature, birds may be responding to gradual changes in the nature of the habitat or availability of food resources, and presence of competitors. If so, this has important implications for estimates of mountaintop extinctions from climate change.

Context-dependent male mate choice: the effects of competitor presence and competitor size

Differences in the intensity of male–male competition for high- and low-quality females affect their value as mates. This can favor the evolution of mating preferences that vary with inherent male competitiveness and/or context-dependent mate choice. In the eastern mosquitofish (Gambusia holbrooki) we investigated how a male’s choice of mate is influenced by his absolute size when alone (baseline mating preference) and by the presence and relative size of a competitor (context dependent). In standard 2choice mating trials, we compared the time in association with the larger of 2 females in: 1) the absence of a rival; 2) the presence of a same-sized rival, and 3) the presence of a different-sized rival. We predicted which female the focal male would choose based on his estimated reproductive success. In all 3 social contexts, large and small focal males spent significantly more time with large females, but large males had a stronger association bias, indicating an effect of male size (competitiveness) on male mating preference. In contrast, neither the presence of a competitor nor his relative size affected the time the focal male spent with the large female. There was therefore no evidence that males facultatively adjust mate choice decisions to avoid competitors. This suggests that males do not maximize their expected reproductive success in the context of the current social setting. Key words: eastern mosquitofish, Gambusia holbrooki, male–male competition, mating preferences, sexual selection. [Behav Ecol]

Specialization and Competition in the Venture Capital Industry

An important type of product differentiation in the VC market is industry specialization. We estimate a market structure model to assess competition among differentiated participants in the venture capital (VC) industry. The impacts of competitor presence on profits appear markedly different than in other industries with differentiated competitors. Consistent with the presence of network effects that soften competition, these patterns are concentrated in markets that exhibit dense organizational networks among incumbent VC firms. Markets with sparser incumbent firm networks, by contrast, exhibit competitive patterns that resemble those of other, non-networked industries.