Differences In Competitive Ability Research Articles

Root Competition between Three Upland Grasses

1 Deschampsia flexuosa (L.) Trin., Festuca ovina L. and Nardus stricta L. were grown alone and in root association in all three possible pairs, at two levels of nitrogen application. 2 Root interference was found with all three combinations of species, attributable to competition for nutrients. Nardus was the least competitive species, and Festuca was the most competitive species, even though Nardus and Festuca showed comparable production in monocultures. 3 A mutualistic interaction occurred between Deschampsia and Festuca, when grown together, in which Festuca took up more nutrients and Deschampsia less; this led to an increased growth of each. 4 In species pairs where straightforward competition occurred, the species showed considerable differences in competitive ability, contrary to the theory of equivalence of competitors. Since they coexist naturally, this implies the presence of a powerful force for coexistence. Key-words: Competition, coexistence, mutalism, nutrients, selection, upland grasses, Festuca ovina, Deschampsia flexuosa, Nardus stricta

Territory acquisition and loss in male song sparrows

Male song sparrows, Melospiza melodia, contested for territories year-round in a non-migratory population. Over 5 years, most settlers were yearlings, but many were older floaters that had previously owned a territory. Most turnovers occurred when floaters evicted territory owners from all or part of their territories. This finding contrasts with the assumptions of most models of dispersal and habitat settlement, i.e. that owners are always dominant to floaters, and that floaters gain territories only after an owner's death. Territory owners often evicted neighbours in the breeding period, when they were also likely to gain access to additional females. Floaters usually gained territories just prior to breeding and as breeding began. These patterns are consistent with the idea that male territory defence primarily serves to provide access to females. Middle-aged males more often expanded their territories and regained them after being evicted than 1- or 4-year-old males. Birds that floated as yearlings were more likely to float after owning a territory as an adult than were birds that gained a territory before April of their first breeding season. Individual differences in competitive ability persist throughout life, but vary with age. Factors that affect patterns of aggressive versus passive territory acquisition between populations include: migratory tendency, habitat saturation, length of the breeding period, the potential to breed outside the natal population, the relative survival rates of territory owners versus floaters, and the mortality rate of territory owners in the absence of challenges by floaters. An understanding of the territorial system is crucial to predicting patterns of dispersal and habitat distribution.

Overgrowth competition in an assemblage of encrusting bryozoans settled on artificial substrata

Overgrowth competition in an assemblage of encrusting bryozoans settled on artificial substrata

Games fish play: Making decisions as a social forager

Suppose a customer wishes to buy a bag of fruit in a market hall during his lunch break and has the choice between two crowded fruiterers' shops. The complexity of problems inherent in such a situation has been increasingly appreciated by behavioural ecologists interested in social foraging of animals. The recognition of consistent individual differences in competitive ability and their incorporation into classical game theoretical models has recently facilitated a step forward in our understanding of social foraging. Here I review theoretical developments in connection with experiments on resource sharing in foraging fish.

Competitive interactions in Drosophila melanogaster IV. Chromosome assay

The technique of chromosome assay, using chromosome substitution lines, has been refined in Drosophila melanogaster to provide a powerful method of investigating the distribution, amongst the chromosomes, of the underlying genetical determinants, particularly in relation to chaeta characters. In the present study this technique is extended to investigate differences in competitive ability. The genotypes used were two inbred lines chosen as showing differences in competitive ability based on a survey of such lines derived from a large laboratory population. The character followed was pa, the proportion (transformed into angles) of eggs which successfully developed into adults. It was found that chromosome III carried gene differences affecting both aggression and response but showing no good evidence of interaction with one another or with genes on other chromosomes. The gene differences on chromosome I, on the other hand, showed no main effect on either aggression or response but a clear interaction with chromosome II in affecting response. Chromosome II also showed a main effect on aggression, though only when associated with one of the two genetically marked lines with which the substitution lines were compared. The implications of these findings are discussed.

Studies on Intergenotypic Competition in a Wheat Multiline Using Alternative Row Design

AbstractDifferences between the isolines in a multiline may result in differences in competitive ability and lead to changes in the frequency of the components after a few cycles of multiplication. Alternative‐row design of Hanson et al. (1961) was used to detect and characterize the presence of intergenotypic interactions among eight isolines of a multiline of bread‐wheat‘Kalyansona’. The material was grown in 1.5 meter row plots using a unique sequence of arrangement. The observations were recorded with respect to plant height and grain yield per plan:. The results of the analysis showed the components of variance for average competitive ability and specific combination to be highly significant, indicating the existence of intergenotypic interactions. Significant genotypic differences between isolines revealed that the genotype of the recurrent parent had not been fully reconstituted. On the basis of the effect of the border genotype averaged over all the genotypes (Ck.), the genotypes were classified into four groups, viz. a) highly depressive, b) mildly depressive, c) mildly cooperative and d) highly cooperative. Categories c and d were indicated as useful for the synthesis of multilines.

Green, bluegreen and diatom algae: Taxonomie differences in competitive ability for phosphorus, silicon and nitrogen

Green, bluegreen and diatom algae: Taxonomie differences in competitive ability for phosphorus, silicon and nitrogen

Communal testing, a method of testing the growth of different genetic groups of common carp in earthen ponds

Communal testing consists of stocking the different genetic groups to be tested into the same (communal) pond. In this system, genetic differences between groups of fish and differences in pond productivity are not confounded, as they are in separate testing. Communal testing reduces the number of replications required and enables larger numbers of groups to be tested in a smaller number of ponds. Growth testing in communal ponds means that the testing environment and the commercial production environment in which the results of genetic investigations are to be applied are not identical. This difference is due to the mutual competitive interactions between test groups in communal ponds, which cannot occur when they are stocked separately. Interactions may be due to differences in initial weight between the groups, or to differences in competitive ability not associated with differences in initial weight. The methodological investigations which allow these sources of bias to be removed are described. The effect of differences in initial weight is corrected with the aid of the environmentally generated coefficient of regression of weight gain on initial weight in a communal pond. This regression requires empirical estimation in each test, by the multiple nursing technique, specifically constructed for this purpose. Relative growth rankings of paris of test progenies were identical when each group was stocked separately into a series of replicated ponds and when both were stocked together into communal ponds. Thus growth estimates from communal testing are reliable predictors of expected genetic differences in separate ponds. Communal testing allows any pond or other growth vessel to be used as a testing facility, irrespective of its area or aquacultural management. Alternatively, it enables breeding studies to be integrated with other unrelated investigations. This results in a more rational utilization of facilities and the possibility of isolating and estimating interactions between experimental variables.

MECHANISMS OF SPATIAL COMPETITION OFDISCINISCA STRIGATA(INARTICULATA: BRACHIOPODA) IN THE INTERTIDAL OF PANAMA

The inarticulate brachiopod Discinisca strigata uniformly wins competitive interactions for space with other sessile epifauna in the intertidal of the Pacific Panamanian coast. This result is achieved through D. strigata's abilities to (1) metamorphose directly on the surface of bryozoan colonies, (2) maintain a pool of particle-depleted water around most of the shell, (3) abrade underlying calcareous epifauna with the shell, eroding them to the level of the substrate, and (4) abrade the tissues of adjacent sponges and bryozoan zooid buds with modified lateral setae. (1) and (2) are allowed by a reversal of the described flow patterns in brachiopods and the possession of a functional siphon formed from modified setae; (3) is possible because the inorganic component of the brachiopod's shell, calcium phosphate, is much harder than calcium carbonate. Three of these mechanisms are not available to articulate brachiopods and the fourth is apparently not exploited, which may explain differences in competitive abilities between the two classes.

The composition of algal vegetation in and outside damselfish territories on a Florida reef

Algal species composition and relative abundance inside and outside territories of Eupomacentrus planifrons (Cuvier and Valenciennes) and E. partitus (Poey) were investigated in a reef formation at 6-m depth at Molasses Reef, John Pennekamp Coral Reef State Park, Key Largo, Florida Keys. In total, 43 species of eukaryotic fleshy and filamentous algae were found inside 9 investigated E. planifrons territories, 35 inside 10 E. partitus territories, and 22 in 6 samples from undefended areas. Cover of fleshy and filamentous algae, as well as mean number of species per unit of surface area, were significantly higher inside E. planifrons territories than inside territories of E. partitus ( P<0.01) or outside territories of both fish species ( P<0.05). Filamentous blue-green algae were conspicuous both inside and outside damselfish territories. Relative cover of crustose corallines did not differ significantly between the three categories. Territories of E. planifrons were characterised by red algae belonging to the family Gelidiaceae and small branched corallines. Herposiphonia secunda (C. Ag.) Ambr. was characteristic of E. partitus territories, while no particular algal species was characteristic of undefended reef areas. The absence of some algal species outside defended areas is an indication that these species escape grazing inside territories. It is suggested that the species composition inside territories of E. planifrons and E. partitus depends mainly on the recruitment of spores which settle inside these territories and on differences in competitive ability between the algal species. Although the damselfishes have a pronounced effect on the density of the vegetation, there is no indication that they influence the species composition by weeding activities or by selective grazing.

The importance of form: Differences in competitive ability, resistance to consumers and environmental stress in an assemblage of coralline algae

Competitors, consumers, and environmental stresses are everpresent factors that most organisms face during their lifetime. On the Pacific northwest coast of North America there are three forms of coralline algae (Rhodophyta, fam. Corallinaceae) differentially distributed within and around large tide pools in the mid and low intertidal region. Observations and experiments were conducted to test whether species of three different forms (finely branched, coarsely branched, and encrusting forms) were differentially susceptible to consumers, competitors and environmental stress. The results indicate that the distributions of these three forms are distinctly different. Although no single factor appears to be controlling this zonation during the time scale of this study, the three forms are differentially susceptible to these potential selective agents. The finely branched coralline ( Corallina vancouveriensis Yendo), found immediately outside of the pools on emergent substrata, is the most resistant to desiccation. This is apparently because its bushy structure holds more water than the other forms preventing drying during times of emersion. The coarsely branched coralline, Calliarthron tuberculosum (Post. & Rupr.), is the most resistant to consumers; it was not eaten by any of four moliuscan herbivores tested. Again it appears to be the structure of the plant that provides this protection. When this species is ground and placed in agar, it is readily eaten by all four herbivores. The encrusting corallines (approximately six species) appear to be the best spatial competitors, occupying the majority of the space within the pools, and were the winners of all overgrowth encounters with articulated coralline species.

The effects of pollen composition on fitness components in a neotropical herb.

Experimental pollinations of Costus allenii (Zingiberaceae) were conducted to assess the effects of pollen composition on fitness. Plants were selfed, outcrossed with the first nearest neighbor, and outcrossed with pollen mixtures obtained from the nearest 2, 3, and 5 plants. Cross type had a significant effect on seed production, seed weight and total-plant dry weight. Progeny from crosses with 3, and 5 parents grew significantly larger than selfed progeny, or those from 1-parent crosses. Competition experiments indicated the superiority of progeny from 3-, and 5-parent crosses over progeny from 1-parent crosses, but no differences in competitive ability were observed between progeny from 3-, and 5-parent crosses. Relative fitness, based on 1) seed production, 2) percent germination, and 3) dry weight, varied significantly among crosses, and was greatest for crosses with 3 parents and lowest for selfs. The relative fitness of progeny from 5-parent crosses was lower than that of all other outcrossed classes. We suggest that the significant effect of pollen composition on fitness results from variation in the genetic similarity of seed and pollen parents, which is a function of spatial distribution and population structure.

Competitive resource sharing: An experimental test of a learning rule for ESSs

Six sticklebacks ( Gasterosteus aculeatus) distributed themselves between two simulated drift food patches in the ratio of patch profitabilities (Milinski 1979). The present study investigated the rule with which each fish decides to stay in one or the other patch, and whether the fish have more difficulties in reaching a decision when the prey is supplied irregularly as is the case under natural conditions. With frame by frame analysis of filmed experiments the hunting success and sampling effort of each individual fish could be determined continuously. The results support the hypothesis that the fish used the relative payoff sum (RPS) learning rule (Harley 1981; Regelmann 1984). There was a close correlation between all decisions of individual fish during a trial, whether to stay or leave a patch, and decisions predicted by the RPS learning rule using the actual experience of the fish. Differences in competitive ability between the fish influenced the dynamics of the distribution in the predicted way, the more successful competitors deciding earlier where to stay than the less successful ones. This had the effect that the good competitors as well as the poor ones were distributed between the patches in the ratio of patch profitabilities. It is also compatible with the RPS learning rule that the fish reached their decision as quickly whether they were supplied with prey regularly or irregularly.

ECTOTYPIC DIFFERENTIATION IN POA ANNUA: WITHIN POPULATION VARIATION IN RESPONSE TO COMPETITION AND CUTTING

SummaryDry weight production of seed‐derived material of eight genotypes from each of two populations of Poa annua, one from an open and the other from a closed habitat, was compared as pure stands and in mixture with Lolium perenne cv. S23. Comparisons were made in a glasshouse experiment after 13 weeks growth, when uncut, and when cut to a height of 1.5 cm at 5, 7, 9, II and 13 weeks from planting‐ Significant differences were found between genotypes within both populations when cut in pure stands and in mixture with Lolium, and also in uncut stands in mixture with Lolium. When uncut and in pure stands inter‐genotypic differences were found only in the open population. Between population differences in within population variation were significant only when the populations were cut and in mixed stands, the open population being more variable. The closed population was significantly more variable when uncut and in mixed stands than in any other treatment combination, whilst the open population did not vary significantly with treatment. The occurrence of genetically‐based inter‐population differences in competitive ability in P. annua is confirmed.

A behavioural polymorphism in the marine snail Nassarius pauperatus: Geographic variation correlated with food availability, and differences in competitive ability between morphs.

The snail Nassarius pauperatus (Lamarck) is common on intertidal sandflats in southern Australia. A behaviour described and defined as being a "Twister" was observed in some individuals. Upon contacting a member of their own species, Twisters gave a very specific response, rotating their shell from side to side in a way similar to the escape responses displayed by many gastropods to predators. However, some individuals, defined as "Non Twisters", never gave this response after contacting another N. pauperatus. Breeding experiments suggested that being a Twister was heritable. The frequency of Twisters varied between populations of N. pauperatus, and was negatively correlated with food availability (as estimated by measuring hunger) and positively correlated with the population density of juvenile N. pauperatus.It was found in the laboratory that Twisters were better than Non Twisters at competing for space to feed, when food was in short supply and distributed as discrete patches. There was also evidence that competition for space to feed occurred when food was in short supply in the field and it was postulated that Twisters thus had a selective advantage compared to Non Twisters in such situations.These results are discussed in terms of whether the behavioural differences between populations can be attributed to either selection or stochastic factors.

COMPETITIVE RELATIONSHIPS BETWEEN ATRAZINE RESISTANT AND SUSCEPTIBLE POPULATIONS OF AMARANTHUS RETROFLEXUS AND A. POWELLII FROM SOUTHERN ONTARIO

SUMMARYThe relative competitive abilities of atrazine resistant and susceptible populations of Amaranthus retroflexus and Amaranthus powellii were compared in a greenhouse experiment using a de Wit replacement series. Both inter and intraspecific differences in competitive ability were apparent when the populations were grown in two‐way combinations of varying proportions but constant overall density. Within both species, the susceptible population had a greater competitive ability with respect to biomass and seed production than the resistant population. The susceptible population of Amaranthus powellii was more competitive than either the susceptible or resistant populations of Amaranthus retroflexus. The resistant population of Amaranthus powellii was more competitive than the resistant population of Amaranthus retroflexus but appeared to have a competitive ability equal to that of the susceptible population of Amaranthus retroflexus.

The effects of prior residence, competitive ability and food availability on the outcome of interactions between shrews (Sorex araneus L.)

Interactions between pairs of shrews on a foraging grid were analysed to test for the effects of prior residence, food density and differences in competitive ability between individuals on the outcome.

Overgrowth in a marine epifaumal community: Competitive hierarchies and competitive networks.

The frequencies with which organisms of a species overgrew or were overgrown by organisms of other species in a marine epifaunal community were estimated. The ranking of the ability of the major taxonomic groups to overgrow others was basically hierarchical:ascidians≧sponges>bryozoans>barnacles, polychaetes, tubicolous amphipods, hydroids. In contrast, the ranking of the competitive ability of species in the community did not form a simple linear hierarchy and there was no single competitively dominant species (measured in terms of overgrowth). There were often no significant differences in the ability of species to overgrow each other within the three major taxonomic groups of sponges, ascidians and bryozoans. Such results were common also between the species of large sponges and ascidiams which dominated substrata immersed for periods longer than two years.A lack of a significant difference in the competitive ability of species was usually the result of (a) frequent formation of delay/ties or "standoffs" and (b) changes in the outcome of interactions due to change in the relative size of interacting colonies. In many two-species interactions the species which had the larger colony in a given encounter had a greater probability of winning.When the range of colony sizes of two species was similar there was often no significant difference between the competitive ability of each species. Such cases without a clearcut winner often represented a backloop in an otherwise hierarchical sequence of competitive ability, i.e. Species A beats Species B, Species B beats Species C, no significant differences in competitive ability between Species C and A. No examples of competitive networks of the form Species A beats Species B, Species B beats Species C, Species C beats Species A were found. Backloops in otherwise hierarchical sequences (no significant differences in competitive ability) occurred most frequently between species within the same major taxonomic groups and were the result of a very even balance in the generalised competitive mechanism of overgrowth.It seems probable that backloops in hierarchical sequences are more commonly due to the absence of clear competitive dominance in interactions between species (reversals in the outcome of overgrowth interactions and "standoffs"), rather than to direct backloops formed by a specialised or to a generalised competitive mechanism. Network-like arrangements of competitive ability formed by the type of processes described here are likely to contribute significantly to the high levels of species diversity observed in many marine epifaunal communities subject to low levels of physical disturbance.

Evaluation of Alfalfa and Rhizobium meliloti for Compatibility in Nodulation and Nodule Effectiveness1

The purpose of this investigation was to develop a procedure for testing strains of Rhizobium meliloti and cultivars of alfalfa (Medicago sativa L.) for symbiotic compatibility. Antiblotic‐resistant mutants were developed from four strains of R. meliloti that differed for plant dry matter yield, days to initial nodulation and nodule numbers when inoculated onto one cultivar of alfalfa. The mutant strains were not significantly different from their corresponding parental strains in either days to initial nodulation or host dry matter production on N‐free medium. The preference of alfalfa for different strains of Rhizobium was not altered by 0 to 300 ppm N and 33 to 300 ppm potassium phosphate.The competitive ability for nodulation of effective and ineffective strains of R. meliloti was investigated using ‘Saranac’ and MnNC 4, an experimental population of alfalfa. Antibiotic‐resistant mutants were used to verify the relative proportions of effective and ineffective nodules on each plant. A significant positive correlation was observed between the percentage of nodules produced by the effective strains and the dry matter production of plants grown at zero N. Acetylene reduction assays indicated that differences in competitive ability of the effective strains against the ineffective strains measured by the antibiotic‐resistant mutant technique and seedling growth were associated with nitrogenase activity.A procedure of inoculating alfalfa plants with a mixture of effective and ineffective strains at zero N and measuring shoot dry weight might be used to identify strains of Rhizobium of high competitive ability and plants with increased preference for effective strains of Rhizobium. This approach should expedite attempts to select Rhizobium‐alfalfa combinations with enhanced N2‐fixation capacity.

The relative competitiveness of atrazine susceptible and resistant populations of Chenopodium album and C. strictum

The total aboveground biomass and reproductive dry weight of one atrazine resistant and one susceptible population from southern Ontario of each of two species of Chenopodium, C. album and C. strictum, were compared. The comparison was made between plants grown under both noncompetitive and competitive conditions. Results from a spaced noncompetitive trial provided evidence for: (1) greater total and reproductive biomass production and earlier flowering of resistant and susceptible populations of C. album as compared with both populations of C. strictum, (2) greater aboveground total and reproductive biomass production of the susceptible population of C. album as compared with the resistant population, and (3) greater total aboveground biomass production (but similar reproductive biomass) of the susceptible population of C. strictum as compared with the resistant population. Results from the competition trials (i.e., plants grown in a de Wit replacement series), provided evidence for inter- and intra-specific differences in competitive ability: (1) the susceptible population of C. album was found to be more competitive than the susceptible population of C. strictum, (2) the susceptible population of C. album was a superior competitor to the resistant population, and (3) the resistant and susceptible populations of C. strictum appeared to be equally competitive.