Direct Evidence Of Competition Research Articles

Influence of temperature and volume ratio of Cu:Ni exchange solutions on the chemical properties of the guest metals in prepared CuNi–mordenite materials: Evidence of direct competition between copper and nickel ions

Mordenite-type zeolites with a SiO2/Al2O3 ratio of 13 in sodium form were subjected to ion exchange using 0.1 N solutions of Ni(NO3)2 and CuSO4, or mixtures thereof with variable ratio of components at two different temperatures, 20 and 90 °C, varying the volume of Cu:Ni ratio in solution. The diffraction patterns revealed the preservation of the zeolite structure after the ion exchange process. Further ICP–AES measurements showed that the ions exchanged percentage depended on the volume ratio of the components added to the exchange solution. The electronic and chemical states of the species in zeolite were studied by diffuse UV–Vis spectroscopy, TPD–NO, and TPR–H2 methods. According to the UV–Vis DRS spectra, absorption increased in the charge transference region (200–350 nm) as the ion exchange temperature increased from 20 to 90 °C. On the other hand, evidence for changes in the chemical state was obtained from TPR and TPD–NO profiles. In the TPR experiments, we observed differences in reductivity with increasing ion exchange temperature. Meanwhile by TPD–NO experiments, all materials showed a capacity to desorb NO molecule at low temperature (<350 °C) and changes in the types of present species as was related with the variation in the ion-exchange temperature. The composition and properties of the Ni:Cu/mordenite bimetallic system were affected by the ion–exchange temperature and the volume ratio of Cu:Ni metal solutions.

Population level interactions between an invasive woodwasp, an invasive nematode and a community of native parasitoids

Parasitic nematodes and hymenopteran parasitoids have been introduced and used extensively to control invasive Eurasian Sirex noctilio woodwasps in pine plantations in the Southern Hemisphere where no members of this community are native. Sirex noctilio has more recently invaded North America where Sirex-associated communities are native. Sirex noctilio and its parasitic nematode, Deladenus siricidicola, plus six native hymenopteran woodwasp parasitoids in New York and Pennsylvania, were sampled from 204 pines in 2011–2019. Sirex noctilio had become the most common woodwasp in this region and the native parasitoids associated with the native woodwasps had expanded their host ranges to use this invader. We investigated the distributions of these species among occupied trees and the interactions between S. noctilio and natural enemies as well as among the natural enemies. Sirex noctilio were strongly aggregated, with a few of the occupied trees hosting hundreds of woodwasps. Nematode parasitism was positively associated with S. noctilio density, and negatively associated with the density of rhyssine parasitoids. Parasitism by the parasitoid Ibalia leucospoides was positively associated with host (S. noctilio) density, while parasitism by the rhyssine parasitoids was negatively associated with density of S. noctilio. Thus, most S. noctilio come from a few attacked trees in a forest, and S. noctilio from those high-density trees experienced high parasitism by both the invasive nematode and the most abundant native parasitoid, I. l. ensiger. There is little evidence for direct competition between the nematodes and parasitoids. The negative association occurring between rhyssine parasitoids and I. l. ensiger suggests rhyssines may suffer from competition with I. l. ensiger which parasitize the host at an earlier life stage. In addition to direct competition with the native woodwasp Sirex nigricornis for suitable larval habitat within weakened trees, the large S. noctilio population increases the parasitoid and nematode populations, which may increase parasitism of S. nigricornis.

Competitive dominance and broad environmental tolerance favour invasive success of Nile tilapia

Invasive species cause substantial changes to the biodiversity of freshwater systems. The African Nile tilapia (Oreochromis niloticus) is now widely distributed in tropical freshwaters globally. Despite indications that feral populations can influence native species through competitive effects, direct evidence of competition between Nile tilapia and native species is rare. Moreover, it is not clear if environmental variables such as temperature and oxygen concentration modulate competition. Here, interactions between Nile tilapia and the native Mayan cichlid (Mayaheros urophthalmus) were studied in experimental mesocosms in south-eastern Mexico. We found that Nile tilapia was the more active and aggressive of the two species, and their movement was only weakly influenced by temperature and oxygen concentration. By contrast, movement of the Mayan cichlid was strongly predicted by the movement and aggression of Nile tilapia, and the Mayan cichlid showed a steep decline in behaviours with increased water temperature and reduced oxygen. Our results suggest that broad environmental tolerance of the intrinsically aggressive Nile tilapia provides it with an advantage over native species. Collectively these traits may help to exacerbate its invasive success as those environmental conditions become more commonplace in a changing world.

Exercise Reduces Competition between Procedural and Declarative Memory Systems.

The neural systems that govern declarative and procedural memory processing do not always operate independently. Direct evidence of competition between these two memory systems in humans is supported by studies showing that performing a declarative learning task immediately after motor skill learning can disrupt procedural memory and abolish the off-line gains in skill performance obtained during consolidation. The aim of the present study was to extend recent investigations demonstrating that the exposure to a brief bout of cardiovascular exercise can protect procedural memory by enhancing postpractice consolidation. We used an experimental paradigm designed to assess whether exercise can also protect procedural memory consolidation from interference induced with declarative learning. The implicit acquisition of a serial reaction time task (SRTT) was tested after a 6-h waked-filled period. Participants who were exposed to a non-learning vowel counting (VC) task following the practice of the SRTT exhibited successful procedural memory consolidation and significant off-line gains in skill performance. Confirming that declarative memory processes can interfere with procedural memory consolidation, off-line gains in motor skill performance were suppressed when the performance of the VC task was replaced with a word list (WL) task requiring declarative learning. Performing a bout of cardiovascular exercise after the SRTT protected the newly formed procedural memory from the interference produced by the WL task. Protection was evidenced by a return of significant off-line gains in skill performance after the waked-filled period. Exercise optimizes the utilization of neural resources reducing interference between procedural and declarative memory systems.

Belowground competition among invading detritivores.

The factors regulating soil animal communities are poorly understood. Current theory favors niche complementarity and facilitation over competition as the primary forms of non-trophic interspecific interaction in soil fauna; however, competition has frequently been suggested as an important community-structuring factor in earthworms, ecosystem engineers that influence belowground processes. To date, direct evidence of competition in earthworms is lacking due to the difficulty inherent in identifying a limiting resource for saprophagous animals. In the present study, we offer the first direct evidence of interspecific competition for food in this dominant soil detritivore group by combining field observations with laboratory mesocosm experiments using 13C and 15N double-enriched leaf litter to track consumption patterns. In our experiments, the Asian invasive species Amynthas hilgendorfi was a dominant competitor for leaf litter against two European species currently invading the temperate deciduous forests in North America. This competitive advantage may account for recent invasion success of A. hilgendorfi in forests with established populations of European species, and we hypothesize that specific phenological differences play an important role in determining the outcome of the belowground competition. In contrast, Eisenoides lonnbergi, a common native species in the Eastern United States, occupied a unique trophic position with limited interactions with other species, which may contribute to its persistence in habitats dominated by invasive species. Furthermore, our results supported neither the hypothesis that facilitation occurs between species of different functional groups nor the hypothesis that species in the same group exhibit functional equivalency in C and N translocation in the soil. We propose that species identity is a more powerful approach to understand earthworm invasion and its impacts on belowground processes.

Direct evidence for competition between metastable ω and equilibrium α phases in aged β-type Ti alloys

Precipitation response of a recently developed β-type Ti–25Nb–2Mo–4Sn alloy (wt%) during aging was investigated in detail. Experimental results indicate that the metastable ω or equilibrium α phase can form alternatively even under the same aging condition, depending on the condition prior to the aging, i.e., solution treatment or severe cold rolling. This provides, for the first time, the direct evidence for the competition between ω and α in aged β-type Ti alloys. This peculiar aging response is found to be closely related to high-density dislocations and grain boundaries which suppress the formation of ω but favor the precipitation of fine α phase.

Demography and population biology of the invasive kelp Undaria pinnatifida on shallow reefs in southern New Zealand

The ability of alien species to gain traction in native communities and expand along coastlines depends on their life histories interacting with local environments. This includes their demographies and formation of viable populations. Here we assess the patterns of recruitment, growth, reproduction and survival of the invasive kelp Undaria pinnatifida in the low intertidal zone of four sites in two areas of southern New Zealand. All populations produced two overlapping cohorts annually, with maximum recruitment in early autumn and the following spring. The autumn cohort largely died off by late spring and it was therefore likely that it was the spring cohort that produced the following years' recruits. There were few visible sporophytes remaining during the hot summer months and so it was the microscopic life stages that persisted over summer to produce populations in the following year. Maximum lengths of >1.5m occurred in late winter, and maximum erosion rates of laminae in spring and early summer. Potential reproductive output was very large, ranging from 2.6−7.0×108 spores per plant among populations at four sites. The effective dispersal distance of spores settling on the substratum in quiescent conditions was less than 20cm from source sporophylls. Undaria showed strong seasonal and annual cycles, fast growth, high reproductive output and, despite being an annual, an ability to persist among years in local populations as it slowly expands along coastlines. There was no evidence of direct competition with native species but instead it acted as a fugitive species with an ability to recruit into almost any available small patch and, unlike the fucoids in surrounding populations, particularly those inhabited by short turfing coralline algae. The expansion of Undaria along the coastline is clearly aided by its ability to take advantage of patches in the native canopies and to find refuge for its microscopic stages in habitats unsuited to most of the dominant fucoids.

Inter-firm rivalry and firm growth: is there any evidence of direct competition between firms?

Inter-firm competition has received much attention in the theoretical literature, but recent empirical work suggests that the growth rates of rival firms are uncorrelated, and that firm growth can be taken as an essentially independent process. We begin by investigating the correlations of the growth rates of competing firms (i.e. the largest and second-largest firms in the same industry) and observe that, surprisingly, the growth of these firms can be taken as independent. Nevertheless, peer-effect regressions, that take into account the simultaneous interdependence of growth rates of rival firms, are able to identify significant negative effects of rivals' growth on a firm's growth.

Axons Compete for Neuromuscular Junctions

​DuringDuring development, motor neurons in the spinal cord send out axons to connect with muscle. Each axon creates a profusion of branches, each with the potential to innervate the muscle fiber at its neuromuscular junction (NMJ). There are so many excess branches that in the immature animal, axon terminals from multiple neurons crowd each junction. But in short order, the excess is pared away, and each NMJ is left with only one terminal, promoting efficient and fine-tuned communication between muscle and brain. Direct evidence for competition between axons at a developing neuromuscular junction. Three mutually exclusive mechanisms have been proposed as drivers of that pruning process: 1) random removal of all but one terminal, 2) predetermined removal based on factors intrinsic to the neuron and muscle, and 3) competition among terminals, with the victor strengthening its connection while the losers retract. In this issue of PLoS Biology, Stephen Turney and Jeff Lichtman use in vivo imaging to show that axons compete for access to the NMJ, and that would-be winners that temporarily vacate their territory can quickly lose out to others waiting to take their place. The authors studied transgenic mice whose axons expressed fluorescent proteins, making them easy to visualize. They studied a neck muscle of one-week old pups, when NMJs are still multiply innervated, and focused on NMJs that still had two different axon terminals in place. Previous studies have shown that the axon whose terminals occupy the largest fraction of the NMJ at this stage usually remains in control, while those that occupy less eventually withdraw. To test the loser's ability to reinnervate at this stage, they used a laser to ablate the dominant axon's innervating branch, leading the terminal to fragment and quickly disappear. Even when the remaining axon initially occupied less than 5% of the NMJ, within 24 hours it had extended new branches and taken over virtually the entire junction. The resulting NMJ appeared normal, and identical to those created during normal development. Even after an axon had entirely withdrawn from an NMJ, it retained the ability to regrow into it, for up to 2 days. These results clearly showed that withdrawing axons can take over NMJs when the winner is damaged, but what about during normal development? Do axons ever withdraw on their own from an NMJ they have innervated, leaving the junction available to another? Or are they displaced only by a more aggressive axon invading the territory? This is more difficult to determine than it may sound, but through meticulous observation, the authors found a rare case of withdrawal, vacancy, and reinnervation by a second axon. The signal for growth of the second axon was not likely to be due to inactivity of the muscle fiber (a phenomenon observed in large-scale motor neuron damage), since the junction remained mostly innervated. Instead, they argue that the regrowth is likely triggered from a highly local signal from the unoccupied portion of the junction and picked up by nearby axonal branches, which grow into the unoccupied portion. In support of this mechanism, they showed that microscopic ablation of only some of an axon's terminals at a single NMJ led to resprouting and regrowth of that axon to fill the unoccupied portions of the NMJ. Together, these results indicate that the final structure of the NMJ is determined by competition among axons, with withdrawal playing a key role in that competition. The authors suggest contact between axon terminals and NMJs are in flux during development, with individual branches of terminals withdrawing at random. This triggers others, especially those nearby, to fill their spot, leading in short order to an NMJ occupied by a terminal from a single axon. Whether the same competitive process occurs at neuron-to-neuron synapses during development in the central nervous system remains to be seen, but some evidence suggests it does. Further, the same competition may also play a role in the synaptic plasticity underlying learning throughout life. Turney SG, Lichtman JW (2012) Reversing the Outcome of Synapse Elimination at Developing Neuromuscular Junctions In Vivo: Evidence for Synaptic Competition and Its Mechanism. doi:10.1371/journal.pbio.1001352

Hunting for a Bogeyman? In Search of Statistical Evidence of Direct Competition between Firms

Although inter-firm competition is frequently mentioned in industrial organization discussions, it has received limited empirical support. Recently, however, Sutton (2007) has shown that the growth rates of the largest and second largest firms in an industry are essentially statistically independent. This seems incompatible with claims of intense inter-firm competition. We begin by computing correlation coefficients for the growth profiles of firms, but the highest correlation coefficients appear to have random rather than economic explanations. We then present scatterplots of the growth rates of the largest vs. second largest firms in specific industries, but observe that the growth dynamics of these firms are largely independent. Finally, for each industry we calculate a correlation coefficient between the annual growth rates of the two largest firms over 9 years, and observe a bimodal shape in the distribution of these correlation coefficients (one positive mode and one negative mode). This suggests that firms either share common fates (positive correlation), or experience different fates (negative correlation).

Spatial segregation of pines and oaks under different fire regimes in the Sierra Madre Occidental

Surface fire can modify spatial patterns and self-thinning in pine-oak ecosystems. Spatial pattern analyses were used to compare pattern development and interspecific spatial interactions in trees and seedlings in five Madrean pine-oak stands with different recent fire histories. Interspecific and intraspecific patterns were compared in small (< 15 cm dbh) and large (< 15 cm dbh) diameter classes of the pines (Pinus durangensis, P. teocote, and P. leiophylla) and oaks (Quercus sideroxylla, Q. crassifolia, and Q. laeta) that collectively dominated the five stands. Numbers of juvenile trees in 2.5 × 2.5 m subplots were correlated with cumulative distances to adult trees. Small pine and oak trees were intraspecifically clustered at all scales, irrespective of fire regime. Large pines were strongly clustered only in stands with longer fire-free intervals, and patterns of large versus small pine trees were regular or random in frequent fire stands. These patterns were consistent with fire-induced mortality of maturing trees under frequent fire. Large and small pines were segregated from small oaks at short and long distances in one stand with a 32-year fire-free interval, implying that two or more dynamic factors had produced regular patterns at different scales. Such regular spatial patterns at short distances were not seen in other stands. Therefore, there was little evidence for direct competition between oaks and pines. The results reported here are consistent with studies from other pine-oak ecosystems showing that different fire regime and site factors interact to influence stand development processes and relative dominance of pines and oaks. In some stands, the continued absence of fire could foster increasing tree densities and an intensification of local neighborhood effects, producing segregation of pine and oak species at longer distances.

Direct and indirect species interactions influencing within-season dynamics of apple rust mite, Aculus schlechtendali (Acari: Eriophyidae).

We conducted a series of path analyses to determine which direct and indirect species interactions were most important in determining the within-season dynamics of apple rust mite (Aculus schlechtendali) (Eriophyidae) in a series of Nova Scotian (Canada) apple orchards. Typhlodromus pyri (Phytoseiidae) was usually more important than Zetzellia mali (Stigmaeidae) in the direct reduction of the apple rust mite population growth rate. When both predators contributed to lowering apple rust mite growth, T. pyri acted earlier in the season than did Z. mali. Predation by T. pyri was not affected by plant quality (nitrogen content or cultivar), but predation by Z. mali was enhanced by high nitrogen levels and was influenced by cultivar. There was little evidence of direct competition between Panonychus ulmi and apple rust mite in these orchards, possibly due to the low densities of P. ulmi. The indirect effects were generally smaller than the direct effects, but were occasionally important. Apparent competition between P. ulmi and apple rust mite was observed at times in some orchards, more often mediated by Z. mali than by T. pyri. Interference between the predator species was only occasionally strong enough to affect apple rust mite population dynamics.

One hundred million years of competitive interactions between bryozoan clades: asymmetrical but not escalating

Direct evidence of competition is seldom available from the fossil record. Overgrowth relationships of encrusting marine organisms constitute an exception but have previously been reported in only temporally and geographically local occurrences. Results of overgrowths between members of two bryozoan clades, the Cyclostomata and the Cheilostomata, have been compiled for faunas distributed through the past 100 Myr. The cheilostomes have consistendy out-competed the cyclostomes, with approximately 66% overgrowdi success through the entire interval. This difference in success in direct interactions along with the Mid-Cretaceous rapid radiation of cheilostomes is interpreted as a factor in the Mid- to Late Cretaceous reversal from the previous diversification to stasis or gradual decline of cyclostome diversity.

One hundred million years of competitive interactions between bryozoan clades: asymmetrical but not escalating

Direct evidence of competition is seldom available from the fossil record. Overgrowth relationships of encrusting marine organisms constitute an exception but have previously been reported in only temporally and geographically local occurrences. Results of overgrowths between members of two bryozoan clades, the Cyclostomata and the Cheilostomata, have been compiled for faunas distributed through the past 100 Myr. The cheilostomes have consistently out-competed the cyclostomes, with approximately 66% overgrowth success through the entire interval. This difference in success in direct interactions along with the Mid-Cretaceous rapid radiation of cheilostomes is interpreted as a factor in the Mid- to Late Cretaceous reversal from the previous diversification to stasis or gradual decline of cyclostome diversity.

The mechanism of the unimolecular dissociation of trichloroethylene CHCl=CCl2 in the ground electronic state

The unimolecular dissociation of trichloroethylene in its electronic ground state has been investigated using an infrared multiphoton dissociation combined with photofragmentation translational spectroscopy to measure product translational energies. The main reaction channel was found to be HCl elimination on the basis of observed product time-of-flight (TOF) spectra. A center-of-mass translational energy distribution for this channel provides direct evidence for competition between two channels, three- and four-centered HCl eliminations. Cl elimination was found to be a minor but significant channel from observed Cl+ and C2HCl+TOF spectra. The branching ratios were determined as 0.28, 0.55, and 0.17 for the three- and four-centered HCl eliminations and the Cl elimination, respectively. The three-centered channel exhibits a ‘‘statistical’’ translational energy distribution which is typical for a reaction with no potential energy barrier in the reverse reaction, that is to say, no exit barrier reaction. In contrast, the four-centered channel exhibits a ‘‘nonstatistical’’ translational energy distribution having a peak at around 2 kcal/mol in energy, indicating that a significant exit barrier exists in the channel. The fraction of potential energy converted to translational energy was estimated to be around 10%. Ab initio calculations at the QCISD(T)/6-311+G**//MP2(FC)/6-31G* level were employed to confirm the reaction mechanism. The agreement in the energetics is quite good.

Relationship between corticotropin-releasing factor and interleukin-2: Evolutionary evidence

The addition of corticotropin-releasing factor (CRF) to molluscan hemocytes induces the release of biogenic amines (norepinephrine, epinephrine, dopamine), a phenomenon we have considered as an ancestral type of stress response [(1992) Gen. Comp. Endocrinol. 87, 354-360]. A similar but less significant response was observed following the addition of interleukin-2 (IL-2). Pre-incubation of hemocytes with IL-2 or anti-IL-2 monoclonal antibody significantly reduced or completely eliminated the CRF-induced release of biogenic amines. Further direct evidence of competition between CRF and IL-2 was revealed by immunocytochemical and cytofluorimetric analysis. The data are compatible with the presence of a unique (ancestral?) receptor on molluscan hemocytes, capable of binding both CRF and IL-2, two key molecules of the neuroendocrine and immune system, respectively.

Direct evidence for competition between local and global mechanisms of two-dimensional orientation illusions.

Orientation illusions induced by two-dimensional stimuli, such as square outline frames or plaids, have been more or less adequately accounted for in terms of repulsion of the vertical test stimulus from the axis of symmetry nearest vertical of the inducing stimulus, whether that axis is real or virtual. Recently, data have been obtained which directly suggest a more complex mechanism: one in which the observed illusion is the sum of all effects--complementary and antagonistic--induced by all axes flanking vertical which are sufficiently close to vertical to exert a significant effect. Experiments are reported in which this latter hypothesis was directly tested by using nonorthogonal plaid component gratings and varying the real-axis orientations while a virtual plaid axis remained fixed in orientation at 10 degrees from vertical. The data indicate that the real component gratings modulate the virtual-axis effect.

Comparative Population Dynamics of Daphnia rosea and Holopedium gibberum in Four Oligotrophic Lakes

Seasonal abundance patterns of Daphnia rosea and Holopedium gibberum showed great variability over the period 1974–83 in four coastal montane lakes of British Columbia. Though the lakes differed considerably in size, depth, and history of experimental disturbance (fish introductions, fertilization, plankton harvesting}, these differences apparently had much less influence on seasonal abundance patterns than did interannual variation in environmental factors shared by all the lakes. Spring rates of population increase differed strongly among years and were positively correlated between the two species. The timing and magnitude of summer population maxima also differed significantly among years, but were not correlated between the species. Adult mortality rates tended to increase through each season for both species, but showed no clear correlations either between the species or between years. Annual differences in growth and mortality rates and peak abundances were not associated with any obvious differences in environmental factors (insolation, rainfall, water temperature). There was no evidence of direct competition between the species, in terms of negative correlations in abundance. This is surprising in view of their similar life histories and feeding ecologies.

Inhibition of L-[18F]fluorodopa uptake into human brain by amino acids demonstrated by positron emission tomography.

The brain uptake of L-[18F]fluorodopa was measured by positron emission tomography in a healthy male volunteer both under fasting conditions and during intravenous amino acid loading. A significant reduction of tracer uptake into the brain was demonstrated with amino acid loading. This finding represents the first direct evidence for competition between L-dopa and other amino acids for uptake across the blood-brain barrier obtained in vivo in a human subject. It underlines the possible importance of interference by dietary amino acids with the therapeutic actions of L-dopa in Parkinson's disease.

Predation, apparent competition, and the structure of prey communities

It is argued that alternate prey species in the diet of a food-limited generalist predator should reduce each other's equilibrial abundances, whether or not they directly compete. Such indirect, interspecific interactions are labeled apparent competition. Two examples are discussed in which an observed pattern of habitat segregation was at first interpreted as evidence for direct competition, but later interpreted as apparent competition resulting from shared predation. In order to study the consequences of predator-mediated apparent competition in isolation from other complicating factors, a model community is analyzed in which there is no direct interspecific competition among the prey. An explicit necessary condition for prey species coexistence is derived for the case of one predator feeding on many prey species. This model community has several interesting properties: (1) Prey species with high relative values for a parameter r a are “keystone” species in the community; (2) prey species can be excluded from the community by “diffuse” apparent competition; (3) large changes in the niche breadth of the predator need not correspond to large changes in predator density; (4) the prey trophic level as a whole is regulated by the predator, yet each of its constituent species is regulated by both the predator and available resources; (5) increased productivity may either increase, decrease, or leave unchanged the number of species in the community; (6) a decrease in density-independent mortality may decrease species diversity. These conclusions seem to be robust to changes in the prey growth equations and to the incorporation of predator satiation. By contrast, adding prey refugia or predator switching to the model weakens these conclusions. If the predator can be satiated or switched, the elements a ij comprising the community matrix may have signs opposite the long-term effect of j upon i. The effect of natural selection upon prey species coexistence is discussed. Unless r i , K i , and a i are tightly coupled, natural selection within prey species i will tend to decrease the equilibrial abundance of species j.