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1

Digitale Medien

Colonization of wheat seedling (Triticum aestivum) roots by Pseudomonas fluorescens and Bacillus subtilis (1987)

Dijkstra, A. F. ; Scholten, G. H. N. ; Veen, J. A.

Springer

Biology and fertility of soils 4 (1987), S. 41-46

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ISSN: 1432-0789

Schlagwort(e): Competition ; Migration ; Colonization potential ; Replica printing ; Triticum aestivum ; Pseudomonas fluorescens ; Bacillus subtilis

Quelle: Springer Online Journal Archives 1860-2000

Thema: Biologie , Geologie und Paläontologie , Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft

Notizen: Summary Colonization patterns of Pseudomonas fluorescens and Bacillus subtilis on roots of wheat seedlings growing on water agar were studied qualitatively by replica printing and quantitatively by the plate count method. The results indicated a stronger colonization potential for P. fluorescens (up to 107 cfu/cm root) than for B. subtilis (up to 105 cfu/cm root). Although the numbers of both species were lower when inoculated together, the observed colonization patterns on the roots were comparable to those found with single inoculations. For none of these bacteria was active migration along the root surface in any direction observed, indicating that distal positions are reached mainly by a passive displacement on the root tip and elongating cells. Ecological implications of the observed phenomena are discussed.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/BF00280349

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2

Digitale Medien

Desiccation, predation, and mussel-barnacle interactions in the northern Gulf of California (1987)

Lively, C. M. ; Raimondi, P. T.

Springer

Oecologia 74 (1987), S. 304-309

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ISSN: 1432-1939

Schlagwort(e): Barnacles ; Competition ; Desiccation ; Mussels ; Predation

Quelle: Springer Online Journal Archives 1860-2000

Thema: Biologie

Notizen: Summary Field experiments were conducted in order to determine the potential for desiccation and predation to mediate the effect of mussels (Brachidontes semilaevis) on barnacles (Chthamalus anisopoma) in the highly seasonal northern Gulf of California. We did this by removing both mussels and a common mussel predator (Morula ferruginosa: Gastropoda) and by spraying selected sites with sea water during summertime spring low tides. We also determined the effect of crowding on resistance to desiccation in barnacles, and the effect of barnacles on colonization by mussels. The mussel-barnacle community was not affected by keeping experimental quadrats damp during daytime low tides throughout the summer. Exposure to summertime low tides, however, did affect the survivorship of isolated, but not crowded, barnacles; and barnacle clumps enhanced the recruitment of mussels. Hence crowding in barnacles had a positive effect on both barnacle survivorship and mussel recruitment. Morula had a negative effect on mussel density, and mussels had a negative effect on barnacle density. The effect of Morula on barnacle density was positive, presumably due to its selective removal of mussels. These results suggest an indirect mutualism between barnacles and the gastropod predator, because barnacles attract settlement or enhance the survival of mussels, and the predator reduces the competitive effect of mussels on barnacles.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/BF00379374

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3

Digitale Medien

Effect of competition on the demography of planktonic cladocerans — Daphnia and Diaphanosoma (1987)

Matveev, V. F.

Springer

Oecologia 74 (1987), S. 468-477

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ISSN: 1432-1939

Schlagwort(e): Cladocera ; Competition ; Time lags ; Oscillations ; Plankton

Quelle: Springer Online Journal Archives 1860-2000

Thema: Biologie

Notizen: Summary Isolated and mixed continuous cultures of Daphnia hyalina and Diaphanosoma brachyurum in lake water were maintained under laboratory conditions to elucidate demographic effects of competition. Population dynamics curves were obtained. Interspecific competition was revealed by the decrease in the average density of animals in the mixed versus isolated cultures and by the extinction of one species in the presence of the other. Within the first 50 days either Diaphanosoma (4 cases) or Daphnia (1 case) was the superior competitor, depending on the initial conditions. Further cultivation resulted in the extinction of Diaphanosoma in the mixed cultures. There were no statistically significant differences between the maximum rates of population increase (r m ) in Daphnia and Diaphanosoma at the concentration of edible algae about 2·105 μm3ml-1(0.293 and 0.286 days-1, respectively). Time lags for density-dependent parameters of the populations were evaluated by means of rank cross-correlations. Regardless of the species identity the time lags of fecundity, birth rate, and the rate of population growth were significantly higher in the superior competitor. The initial conditions of culturing affected the time lags which in their turn influenced the outcome of the interaction. Enhanced competitive ability due to the maximized time lags in Daphnia was not associated with the loss of population stability. Conversely, it brought about destabilization of Diaphanosoma populations which seemed to be the ultimate cause of its extinction observed in the end of the experiment. Time lag of the population growth rate was well predicted based on the half-sum of time lags in birth and death rates (r2=0.80, P〈0.001). Daphnia responded to competition with a sharp shortening of the time lags of fecundity, birth rate, and the population growth rate. It increased clutch size and showed inverse relationship between the fecundity time lag and average fecundity even though it was strongly suppressed by Diaphanosoma. The competitive ability was not related to the percentage of adults in the populations. In contrast to the current belief the major result of interspecific competition in the experiment was not a decrease in the rate of population growth but was a reduction in population time lags.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/BF00378946

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4

Digitale Medien

Experimental evidence for interactive habitat segregation between roach (Rutilus rutilus) and rudd (Scardinius erythrophthalmus) in a shallow eutrophic lake (1987)

Johansson, L.

Springer

Oecologia 73 (1987), S. 21-27

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ISSN: 1432-1939

Schlagwort(e): Competition ; Habitat segregation ; Foraging efficiency

Quelle: Springer Online Journal Archives 1860-2000

Thema: Biologie

Notizen: Summary The competitive interactions between roach (Rutilus rutilus) and rudd (Scardinius erythrophthalmus) were investigated in two habitats, the open water and the waterlily zone. The growth rates of both species in enclosures were lower when confined together than when alone, demonstrating interspecific competition. Allopatric roach had the highest growth rate in both habitats although the open water was preferred. The diets of both species were dominated by zooplankton in both the open water and waterlily zones. In laboratory experiments, roach had significantly higher feeding rates than rudd when fed D. magna and Cyclops sp. The impact of roach on the mean sizes and densities of zooplankton in the enclosures, together with the results from the laboratory study, indicate that roach were competitively superior in the open water. Because of high mortality in the sympatric waterlily enclosure, no conclusions about interspecific competition in this habitat could be drawn. The observed habitat segregation between roach and rudd was at least partly interactive.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/BF00376972

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5

Digitale Medien

Experimental studies of exploitative competition in a grazing stream insect (1987)

Hart, D. D.

Springer

Oecologia 73 (1987), S. 41-47

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ISSN: 1432-1939

Schlagwort(e): Algal-grazer interactions ; Competition ; Food depletion ; Food limitation ; Streams

Quelle: Springer Online Journal Archives 1860-2000

Thema: Biologie

Notizen: Summary Field and laboratory experiments were conducted to determine whether intraspecific competition for food occurs during the larval stage of the periphyton-grazing caddisfly Glossosoma nigrior (Trichoptera: Glossosomatidae). Larvae were placed in field enclosures at densities less than, equal to, or greater than their natural densities. Most of these individuals began to pupate after ∼3 weeks, whereupon the mass of each individual was determined. Final mass declined significantly as larval densities increased, whereas neither developmental rate nor mortality/emigration rate was significantly affected by density manipulations. a supplemental experiment comparing the final mass of individuals grown at reduced densities in a laboratory stream with individuals from a natural stream bottom confirmed the results of the more extensive field experiment: reductions in density resulted in significant increases in final mass. Periphyton availability in field enclosures declined according to a negative exponential function as larval densities increased. Over the ∼25-fold range of larval densities used in these experiments, the final mass of individuals increased linearly with periphyton standing crops. This result suggests that Glossosoma larvae may compete for food even at densities below those employed in this study. Path analysis was used to explore the importance of indirect (i.e., exploitative) and direct (i.e, interference) mechanisms for the observed competitive effects. The analysis indicates that a model based solely on exploitation explains nearly as much of the variance in mass as a model incorporating both interference and exploitation.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/BF00376975

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6

Digitale Medien

Herbivory and intraspecific competition in a stream caddisfly population (1987)

Lamberti, G. A. ; Feminella, J. W. ; Resh, V. H.

Springer

Oecologia 73 (1987), S. 75-81

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ISSN: 1432-1939

Schlagwort(e): Herbivory ; Competition ; Periphyton ; Helicopsyche ; Stream

Quelle: Springer Online Journal Archives 1860-2000

Thema: Biologie

Notizen: Summary Field experiments were conducted to assess the effects of different population densities of the herbivorous caddisfly Helicopsyche borealis on periphyton biomass and on its own growth rate in Big Sulphur Creek, a third-order stream in northern California, USA. Stream enclosures were used to vary grazer density from one-eighth to twice natural density (1/8X–2X) in two experiments (35 d and 60 d), which spanned the period of most rapid larval growth. Periphyton biomass and chlorophyll a were inversely related to grazer density. Grazer densities of 1/8X–1/2X moderately reduced periphyton when compared to an ungrazed control, whereas densities of 1X–2X greatly depleted periphyton. The growth rate of H. borealis larvae declined with increasing larval density. Growth rate was highest at densities of 1/8X–1/2X; larvae grew more slowly at 1X and showed no growth at 2X. Weekly supplementation of periphyton to 1/4X, 1X, and 2X densities significantly increased the final body mass of larvae at 1X and 2X (by 26% and 50%, respectively, compared to unsupplemented larvae) but did not change the body mass of larvae at 1/4X. These results suggest that periphyton is a limiting resource in Big Sulphur Creek and that H. borealis larvae compete exploitatively for that resource. Intraspecific competition may be an important, but often overlooked, feature of many herbivore populations in streams.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/BF00376980

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7

Digitale Medien

A comparative study on nutrient cycling in wet heathland ecosystems (1987)

Berendse, F. ; Oudhof, H. ; Bol, J.

Springer

Oecologia 74 (1987), S. 174-184

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ISSN: 1432-1939

Schlagwort(e): Nutrient cycling ; Litter production ; Competition ; Relative nutrient requirement

Quelle: Springer Online Journal Archives 1860-2000

Thema: Biologie

Notizen: Summary The term relative nutrient requirement is introduced in order to measure and to compare the nutrient losses from different perennial plant populations and the amount of nutrient that they need to absorb to compensate these losses. The relative nutrient requirement (L) is defined as the amount of the growth-limiting nutrient that must be taken up to maintain or replace each unit of biomass during a given time interval (e.g., mgN g-1 biomass year-1). It is derived that in a plant community with two competing perennial plant populations, species1 will become dominant if the relative competition coefficient k 12 (sensu De Wit 1960) exceeds the ratio between the relative nutrient requirements of the two species (L 1/L 2), whereas species 2 will become dominant, if k 12 is below this critical ratio. The above-ground litter production was measured inwet heathland communities dominated by Erica tetralix or by Molinia caeruleain order to estimate N and P losses from theaboveground biomass and to calculate the relative N and P requirements of these species. Molinia lost during one year 63% and 34%, respectively, of the amount of N and P present in the above-ground biomass at the end of the growing season. These losses were in Erica 27% and 31%, respectively. The relative N requirements of the two species show the same difference: 7.5 and 2.6 mg N g-1 yr-1, respectively, in Molinia and in Erica. Also the relative P requirement of Molinia is higher as well as that of Erica (0.18 versus 0.08 mg P g-1 yr-1). The relative competition coefficient of Molinia with respect to Erica (k me ) is equal to unity under unfertilized conditions but increases with increasing nutrient supply. Under nutrient-poor conditions k me is below the critical ratio of the relative nutrient requirements of the two species (L m /L e =2.9 or 2.3), so that Erica will be the dominant species. After an increase in nutrient availability k me increases and exceeds this critical limit which results in Molinia replacing Erica. During the last 20 years this replacement of Erica-dominant communities by monocultures of Molinia has been observed in almost all wet heathlands in The Netherlands along with a strong increase in nitrogen availability.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/BF00379357

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8

Digitale Medien

Photosynthetic kinetics determine the outcome of competition for dissolved inorganic carbon by freshwater microalgae: implications for acidified lakes (1987)

Williams, T. G. ; Turpin, D. H.

Springer

Oecologia 73 (1987), S. 307-311

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ISSN: 1432-1939

Schlagwort(e): Algae ; Photosynthesis ; Competition ; pH ; Acidification ; Dissolved inorganic carbon

Quelle: Springer Online Journal Archives 1860-2000

Thema: Biologie

Notizen: Summary Photosynthetic kinetics with respect to dissolved inorganic carbon were used to predict the outcome of competition for DIC between the green alga Selenastrum minutum and the cyanobacterium Synechococcus leopoliensis at pH 6.2, 7.5, and 10. Based on measured values of the maximum rate of photosynthesis, the half-saturation value of photosynthesis with respect to DIC (K 1 2/DIC ), and the DIC compensation point, it was predicted that S. leopoliensis would lower the steady-state DIC concentration below the DIC compensation point of S. minutum. This should result in competitive displacement of the green alga at a rate equivalent to the chemostat dilution rate. This prediction was validated by carrying out competition experiments over the range of pH. These results suggest that the low levels of DIC in air-equilibrated acidified lakes may be an important rate-limiting resource and hence affect phytoplankton community structure. Furthermore, the low levels of DIC in these systems may be below the DIC compensation point for some species, thereby precluding their growth at acid pH solely as a function of DIC limitation. The potential importance of DIC in shaping phytoplankton community structure in acidified systems is discussed.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/BF00377523

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9

Digitale Medien

On the use of response models in mixture experiments (1987)

Connolly, J.

Springer

Oecologia 72 (1987), S. 95-103

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ISSN: 1432-1939

Schlagwort(e): Models ; Bromass ; Competition ; Density ; Resource use

Quelle: Springer Online Journal Archives 1860-2000

Thema: Biologie

Notizen: Summary Methods for assessing mixtures and their dynamic interaction over time are proposed, based on response functions relating biomass yield of each species to the densities of the component species. This approach allows a number of different facets of mixtures to be studied in a common framework. Two examples are given. Substitution rates between species and perceived densities for individuals in mixture are defined. These measure the impact of their environment on individuals. The relative resource total (RRT), is suggested as an index of whether species are capturing the same resource amount in mixture as in pure stand. Two indices of the comparative performance of species over time are proposed. The two examples, one with cattle and sheep and the other a plant mixture diallel with 6 genotypes illustrate the use of the methods. In the animal example the maximum yield mixture was calculated, the species perceptions of each other assessed and it is shown that mixing increased the resource capture by up to 17%. In general, the smaller species performed relatively better in mixture over the experimental period. In the plant example, individual plant size varied considerably over genotypes and this was reflected in their perceptions of each other, but not in their pure stand or mixed crop yield potential. Most genotype pairs showed antagonistic behaviour, whether measured by crop yield potential or by the index of resource capture. These conclusions are contrasted with those from an analysis of the data using substitutive methods.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/BF00385051

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10

Digitale Medien

Resource partitioning and competition for shells between intertidal hermit crabs on the outer coast of Washington (1987)

Abrams, P. A.

Springer

Oecologia 72 (1987), S. 248-258

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ISSN: 1432-1939

Schlagwort(e): Pagurus ; Competition ; Resource partitioning

Quelle: Springer Online Journal Archives 1860-2000

Thema: Biologie

Notizen: Summary Resource partitioning was quantified for 6 species of intertidal hermit crabs in the genus Pagurus, that occur on the outer coast of Washington. This, together with field evidence of shell shortage and with laboratory experiments to quantify the mechanism of interactions for shells, allowed estimation of the relative intensities of inter-and intraspecific competition between these species. The findings were that: (1) the magnitude of intraspecific competition was greater than any single interspecific competitive effect for all of the species; and (2) the relative proportion of intraspecific competition was greater for the middle and upper intertidal species than for the lower intertidal species. Studies at several outer coast sites supported these generalizations. Both of these findings are consistent with the hypothesis that competitive divergence has occurred in the past. The structure of the outer coast hermit crab assemblage is compared with that of the San Juan Archipelago hermit crab assemblage. Differences between the two do not seem to be the result of adaptive responses to the presence of more competing species in the former group.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/BF00379275

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