Analysis Of Competitive Interactions Research Articles

Taxonomy and diversity of coelobite bryozoans from drift coral cobbles on Co To Island, northern Vietnam.

There has been no previous report detailing the taxonomy of marine bryozoans along the coasts of Vietnam. Here we report on the taxonomy and diversity of bryozoans collected among drift coral cobbles from a beach in the tropical Co To archipelago, Gulf of Tonkin, northern Vietnam. We detected 27 bryozoan species (23 cheilostomes, four cyclostomes) in a coelobite assemblage inhabiting crevices in the cobbles, and holes made by boring molluscs. The degree of bryozoan preservation varied greatly, suggesting that the cobbles had accumulated on the beach over a period of months to years, or even decades. Coral reefs in the Co To archipelago underwent a catastrophic decline in 2003-2008, and it is unclear whether the bryozoan assemblage reflects past diversity, present diversity remaining in the coral rubble, or both. We describe six new species: Parasmittina acondylata n. sp., Metroperiella cotoensis n. sp., Microporella tonkinensis n. sp., Rhynchozoon setiavicularium n. sp., R. latiavicularium n. sp., and Disporella phaohoa n. sp. All but two of the previously described species were already known from the Central Indo-Pacific coastal biogeographical realm of Spalding et al. (2007), which includes Vietnam. We report the third Recent record of the thalamoporellid Dibunostoma reversum (Harmer, 1926), which is quite similar to and might be conspecific with the lower Miocene species Thalamoporella transversa Guha Krishna, 2004; while it is premature to synonymize the two, we transfer T. transversa to Dibunostoma, as D. transversum. The calcareous, sheet-like, encrusting foraminiferan Planorbulina larvata was prominent in the coelobite assemblage and was often observed in substrate competition with bryozoans. A limited analysis of competitive interactions indicated that the encrusting bryozoans in the coelobite assemblage encountered P. larvata more often than they encountered other bryozoans, and that P. larvata out-competed bryozoans for substrate, reinforcing a growing sense of the importance of encrusting foraminifera in tropical and subtropical hard-substrate communities.

Analysis of competitive interactions between the limpets Patella depressa Pennant and Patella vulgata L. on the northern coast of Portugal

Inter- and intraspecific competitive interactions among the species Patella depressa Pennant and P. vulgata L. were analysed on the northern coast of Portugal, where both species co-occur in similar proportions. Increased (×2, ×4), normal and decreased (×1/2 intraspecific only) densities of limpets were used to test the effects of competition on the growth and mortality of the limpets, and competitive interactions between the different species. Fenced plots of 25×25 cm enclosing marked limpets at various densities were set up at a mid tidal level on the shore. Twelve treatments with three replicates of different combinations of densities and species were established. Mortality was recorded every 15 days and length was measured monthly during the 5 months of the experiment. At the end of the experiment, limpets were collected for biometry, sex determination and gonad staging. Both species of grazing molluscs showed increased mortality and reduced size and weight in increased density treatments. Limpets in decreased density treatments showed lower mortality and higher size. There were no significant differences between the effect of P. vulgata on P. depressa and the effect of P. depressa on P. vulgata on mortality and length. There were, however, decreases in weight due to intraspecific effects for both species. For P. vulgata, interspecific effects were much less than intraspecific effects and for P. depressa, the interspecific effects depended on density. The analysis of the gonad stage at the end of the experiment showed that the lower stages of development were most prevalent at increased densities and the occurrence of neuter individuals only in increased densities single species plots corroborated the evidence of a stronger intraspecific interaction. The availability of food was indirectly assessed by determination of chlorophyll concentration with spectrophotometric analysis of rock chips. Microalgal food assessment in this experiment, however, did not show any clear trends. The results were compared with previous studies of competition in grazing molluscs and discussed in relation to the limits of distribution of P. vulgata on the Portuguese coast.

Facilitated transport of methotrexate polyglutamates into lysosomes derived from S180 cells. Further characterization and evidence for a simple mobile carrier system with broad specificity for homo- or heteropeptides bearing a C-terminal glutamyl moiety.

Studies are presented further characterizing a facilitative system transporting methotrexate (MTX) polyglutamates into lysosomes derived from S180 cells. Initial influx of [3H]MTX + G1 (MTX with 1 additional glutamyl residue) exhibited a slightly alkaline pH optimum (pH 7.7) and was moderately temperature-dependent (Q10 27-37 degrees C = 3.1 +/- 0.1). An analysis of the kinetics of intralysosomal accumulation of [3H]MTX + G1 showed saturation kinetics for initial influx, but linear kinetics for the steady-state level of exchangeable [3H]MTX + G1 at different external concentrations of [3H]MTX + G1. In addition, the system exhibited substantial directional asymmetry with respect to the interaction with MTX + G1 during influx and efflux. Accelerated homo- and heteroexchange diffusion was demonstrated for influx of [3H]MTX + G1, while decelerated homoexchange diffusion was demonstrated for efflux of [3H]MTX + G1 following trans-positioning of MTX + G1 or glutamyl-gamma-glutamate in the opposite compartment. These observations were consistent with a single mobile carrier system mediating influx and efflux of this polyglutamate. Based upon an analysis of competitive interactions with [3H] MTX + G1, this system displayed specificity for MTX-gamma-glutamates, folyl-gamma-polyglutamates, alpha- or gamma-glutamyl peptides and heteropeptides bearing a C-terminal gamma-glutamate but not for MTX or glutamate, themselves. Among polyglutamates, gamma-glutamyl chain length was not a significant factor for transport except in the case of MTX polyglutamates. Overall, our results appear to delineate in the lysosomal membrane a simple mobile carrier system with broad specificity for folyl- or non-folyl-bearing peptides responsible for the transport of MTX polyglutamates.

Analysis of competitive interactions in triocultures of Drosophila melanogaster

Competitive interactions in complex mixtures of genotypes have rarely been studied despite their obvious importance in both natural and commercial populations. Here, we describe a procedure for the analysis of competition in tripartite mixtures of Drosophila melanogaster genotypes. We have utilised a substitution design coupled with a yield-density regression analysis which describes intra- and inter-genotypic competitive effects in terms of simple linear parameters. The experimental design allows any of the competitors to be considered as the primary or indicator genotype and also incorporates variation in the relative proportions of the two associate competitors. The regression parameters are used to derive estimates of the competitive pressure exerted by each associate on the indicator genotype and also the response or sensitivity of the indicator to the competitive pressure which it faces in mixed culture. The results indicate that the joint pressure exerted by the paired associate genotypes in trioculture is equal to the sum of the individual pressures of those associates. This additive relationship holds for a variety of indicator genotypes isolated from the Texas population and appears to be a general property of Drosophila competition. We identified one indicator genotype which consistently departed from this relationship although additivity of joint pressures could be restored in combination with particular associate genotypes. The possible role of larval interference in the determination of these interactions is discussed.

The use of genetic markers in the analysis of competitive interactions in Drosophila melanogaster.

A range of long established inbred lines derived from the TEXAS population of Drosophila melanogaster have been used to elucidate the nature of the competitive interactions which occur in genetically heterogeneous mixtures. A prerequisite for this type of investigation is the ability to distinguish the genotypes which compete in mixed culture. Specific marker alleles are generally used to achieve this distinction although in the past little attention has been given to the possibility of competitive bias introduced by the marker alleles themselves. For the experiments reported in this paper two specific marker alleles (y2 and wa) have been introduced independently into the TEXAS inbred lines. In this way the original wild type inbred lines could be compared with similar series of genotypes marked with either y2 or wa and the effects of the marker alleles determined. The results indicated that the body colour mutation (y2) was neutral in its effect on the competitive interaction of recipient strains. The introduction of the white apricot eye colour mutation (wa) however, had a pronounced and deleterious effect on competitive ability. This effect was to render genotypes less able to compete effectively in mixed culture by depressing inter-genotypic competitive ability. These effects were found to be consistent over a range of genotypes and for each of two characters measuring competitive success.

An analysis of competitive interactions between 3 hermit crab species.

Competition for empty gastropod shells in a group of three sympatric hermit crabs (Pagurus hirsutiusculus, Pagurus granosimanus, and Pagurus beringanus) was studied in the San Juan Archipelago, Washington State. Estimates of the competitive effects of each species on the others' shell supplies were derived using field data on shell utilization and the results of laboratory experiments to determine rates of acquisition and exchange of shells and preferences for different shell species. Each species experienced approximately an order of magnitude more intraspecific competition than interspecific competition for empty shells. This resulted from differences in preference for shell shapes, shell size use, and habitat use between P. hirsutiusculus and P. granosimanus, and largely from differences in habitat use between P. beringanus and the other two species. Experiments involving the release and recensusing of marked empty shells were used to estimate competitive effects more directly for the interaction between P. hirsutiusculus and P. granosimanus. Results were consistent with the estimates derived from data on resource partitioning. Possible causes of the low levels of interspecific competition are discussed, and results are compared with studies of other organisms that estimated both inter- and intra-specific competition.

Perturbation and change in coral reef communities

Ninety-six percent of surveyed shallow-water Dry Tortugas reef corals died during the severe winter of 1976-1977. Data from skeletal stains indicate that death occurred during the mid-January intrusion of 14 degrees C water onto the reef. In deeper water, community parameters such as percent cover, species number, and relative abundance showed no significant change. However, an analysis of competitive interactions at the growing edges of adjacent colonies reveals a 70% reduction in space competition during this environmental disturbance. These results can explain high variability in the growth rate of Floridian reefs and demonstrate the importance of obtaining long-term spatial information to interpret successional dynamics of complex communities.

An Analysis of Competitive Interactions in a Patch Back‐Reef Environment

Manipulative field experiments were used to test for the existence of competitive interactions between three abundant herbivore species in a shallow back—reef zone. Densities of the territorial threespot damselfish, Eupomacentrus planifrons, and two sea urchins, Diadema antillarum and Echinometra viridis, were altered through addition and removal experiments conducted within patches of staghorn coral, Acropora cervicornis. Removals of each urchin species resulted in population increases of the other urchin. Additions of each urchin species tended to inhibit increases of the other species. Removals of damselfish resulted in increases of the other species. Removals of damselfish resulted in increases in Diadema density within 24 h, while Echinometra density increased during the 3rd d following the perturbation. Dry biomass of algae on ceramic tiles in the lower strata of damselfish removal patches was reduced by 62% as compared with algal biomass in these strata in the presence of damselfish. Wire mesh cages were utilized over a 2—mo period to test the effect of predation on competition at the herbivore level. No significant alteration of species numbers was observed in the absence of predation. Therefore, predation did not appear to affect significantly the distributions and abundances of the adult members of the community. Low predation levels on adults within this system do not appear to alter the competitive interactions between these herbivores. Interference competition by the threespot damselfish appears to mediate competition between the two echinoids, allowing coexistence of all species. The presence of damselfish may reduce destructive echinoid grazing pressure on the coral substrate.