摘要:

It is shown that Cole's (1949) coefficient of interspecific association (C7) is biased in that it is influenced by the species' frequencies. The formulas given by Cole (1949) for the calculation of C7all can be written in the form: C7= ad — bc / °ad — bc° ° / Obs g2/Max g2° where a, b, c, and d refer to the four cells of a 2 x 2 contingency table. Obs g2is simply the value of g2associated with the observed values of a, b, c, and d. Max g2is the value of g2when a is as large (if ad ° bc) or as small (if ad

ISSN:0012-9658    

DOI:10.2307/1934657

出版商:Ecological Society of America    

年代:1969

数据来源: WILEY

摘要:

The Soil microfungi in 36 northern Wisconsin conifer—hardwood forests have been surveyed by the dilution plate technique. Populations of 180 isolates from six sites in each forest examined, and frequency (sites of occurrence) was used to assess species importance. The 6,461 isolates represented 476 taxonomic entities, but only 87 (18%) of these occurred in three or more forests or had one frequency of at least 50% The principal forms in the conifer—hardwood unit were Mortierella vinacea II, Trichoderma spp., Mortierella isabellina, Penicillium nigricans, Mortierella nana, Pullularia pullulans, and Monocillium humicola var. brunneum. A few of the top—ranking conifer—hardwood microfungi are widely distributed in Wisconsin soils, others have occurred in similar types in northern and southern Wisconsin, and a third assemblage (including Mortierella vinacea II and M. nana) has been isolated only from conifer and conifer—hardwood soils in the State. An ordination, based upon compositional similarity in the microfungal communities, revealed a greatest difference between maple and hemlock soil populations. When tree importance values were superimposed on the three—dimensional microfungal ordination, spheres of occurrence were apparent for all major tree dominants. This finding confirmed the hypothesis that species composition in soil microfungal communities is correlated with vegetation, but litter calcium content, rather than the linear dry—to—mesic vegetational gradient, correlated with the first axis in the microfungal ordination. In a beech—hemlock forest soil, related densities for several dominant taxa varied with season. Both spores and hyphal fragments gave rise to colonies on the dilution plates prepared for six forest soils, and there was a direct correspondence between total colonies and numbers of germinating spores. A comparison of densities for four dominant species indicated a possible antibiotic interaction.

ISSN:0012-9658    

DOI:10.2307/1934658

出版商:Ecological Society of America    

年代:1969

数据来源: WILEY

摘要:

Measurements of phenological development, herbage production, basal area, and density of annual and perennial grasses and of the half—shrub burroweed (Aplopappus tenuisectus (Greene) Blake), over a 4—year period show that production of each class of plant was affected to some extent by each of the others, except that annual grasses had no effect on burroweed crown area. Production of Arizona cottontop (Trichachne californica (Benth.) Chase), the dominant perennial grass, was restricted about 25% on plots with annual grass or burroweed competition and 46% by both together. Annual grass production averaged 18% lower with burroweed competition and 44—54% lower with perennial grass competition. Burroweed crown area increased 220% on plots with no perennial grass, but only 111% on plots with perennial grass competition. Presence of burrowed reduced perennial grass yield only moderately, because the root systems of burroweed and grass do not overlap greatly, and their main growth periods are at different seasons. High evaporation rates during the summer growing season masked most differences in moisture extraction between species. During the winter—spring growing period, on the other hand, burroweed depleted the available soil water rapidly, while water loss on perennial grass plots was little more than from bare soil.

ISSN:0012-9658    

DOI:10.2307/1934659

出版商:Ecological Society of America    

年代:1969

数据来源: WILEY

摘要:

A chemical light meter that uses chlorophyll is described. The quantity of radiant energy that is utilizable for photosynthesis can be estimated through use of crude chlorophyll extracts in conjuction with a thermopile and recorder. Two hundred or more determinations can be made per day at a negligible cost relative to the cost of using a comparable number of thermopiles and recorders. Preliminary tests with this apparatus revealed that about 75% of the forest floor under a dense hardwood stand received enough radiation to compensate for the respiration losses by the plants. The light in a 28—year—old, 6— by 8—ft Pinus virginiana Mill. plantation was considerably brighter than that under a dense hardwood stand. All of the sample points under the pine plantation received sufficient radiation to permit photosynthesis to compensate for respiration. The experimental results and theoretical analysis of several research workers are combined to develop the generalization that radiant energy is transmitted through a canopy of leaves in the same manner as radiant energy is transmitted through a solution–i.e. in accord with Beer's law: Optical density @8 —log (fraction of radiant energy transmitted) ° KF K is a constant of proportionality and F is the concentration of leaves per acre. Because of the exponential relationship between basal area per acre and quantity of leaves, basal area may be substituted for quantity of leaves in the equation.

ISSN:0012-9658    

DOI:10.2307/1934660

出版商:Ecological Society of America    

年代:1969

数据来源: WILEY

摘要:

At four constant thermoperiods (65°, 75°, 85° and 95°F) and three alternating diurnal thermoperiods (65° —75°, 65° —95°F), good germination (above 70%) was obtained with seed of Ammophila breviligulata Fern., Panicum amarulum Hitch. and Chase., and Spartina patens (Ait.) Muhl. without cold treatment under certain temperature conditions. None of the constant temperature treatments yielded good germination. All attempts to obtain good germination with Uniola paniculata L. without cold treatment were unsuccessful. Various periods of cold treatment had no effect upon subsequent germination in the 65° —95°F alternating diurnal thermoperiod in A. brevilligulata and S. patens. In P. amarulum cold treatment for 15 days was sufficient to ensure good germination. Cold treatment for 30 days was adequate for good germination in U. paniculata, but 15 days was not always sufficient. When cold treatment for 30 days at 43°F preceded germination in the seven temperature conditions, germination was increased in all species. Maximum tolerance limits for A. breviligulata and U. paniculata to NaCl lie between 1.0% and 1.5%. The upper limit of NaCl concentration for germination of P. amarulum is between 1.5% and 2.0% and for S. patens about 4.0%. Germination response to salinity was primarily an inverse linear relationship for A. breviligulata, P. amarulum, and U. paniculata, but a curvilinear relationship in S. patens. In this species germination was successful at 2.0% NaCl. Germination inhibition in A. breviligulata, P. amarulum, and S. patens was apparently primarily an osmotic effect. Based on germination response, S. patens is the most salt tolerant, followed by P. amarulum which is more than U. paniculata. A. breviligulata is the most salt sensitive.

ISSN:0012-9658    

DOI:10.2307/1934661

出版商:Ecological Society of America    

年代:1969

数据来源: WILEY

摘要:

Bristlecone pines (Pinus aristata Engelm.) locally attain ages over 4,000 years. In the White Mountains, California, old trees are widely distributed near the lower forest border, but are restricted to exposed, rocky areas at higher altitudes. Comparative aridity seems to be an important feature of the "old—age" habitat. Occurrences of older (1,5000—4,900 years) bristlecone pines in the moister mountain ranges of Nevade and Utah are analogous to those at higher altitudes in the White Mountains, suggesting that local edaphic and physiographic factors can offset the effects of a regional precipitation gradient. Attainment of an age greater that about 1,500 years apparently depends on the adoption of a strip—growth habit, which permits the aging bristlecone pine to maintain a nearly constant ratio of green to non—green tissue. Slow growth rates, wind damage, and soil erosion may be conducive to cambial area reduction. Other features of old—age stands, such as the wide spacing of the trees, the compactness of their crowns, the sparsity of litter, and the low density of the accompanying ground—cover vegetation, would also provide a measure of protection from fire and from competition, permitting the older trees to survive.

ISSN:0012-9658    

DOI:10.2307/1934662

出版商:Ecological Society of America    

年代:1969

数据来源: WILEY

摘要:

The interaction between Asplanchna, predator, and Paramecium, prey, was studied in the laboratory using many experiments of short duration to insure maintenance of a uniform environment over a wide range of population densities. The results of the experiments were used to construct a vector map describing population changes. Regions of uniform vector direction were delineated to produce the isoclines of a graphical model formulated by Rosenzweig and MacArthur (1963). These isoclines were used to predict successfully the instability of this experimental interaction. The effect of time lag in predator response to changed food conditions was incorporated into the model. Time lag increases the instability of this interaction. The relationships between predator and prey and their physiologies determine the shapes of the isoclines. This analysis may be used to help explain other experimental results and naturally occuring situations.

ISSN:0012-9658    

DOI:10.2307/1934663

出版商:Ecological Society of America    

年代:1969

数据来源: WILEY

摘要:

Arcturus Lake is a stratified hypersaline lake occupying a caldera near the center of Genovesa Island. It is about 500 m in diameter and has a maximum depth of 30 m. The lake is frequented by large numbers of seabirds and is an outstanding example of guanotrophy. Organic production in the epilimnion was great, and the hypolimnion was anoxic at the time of these studies. The lake is probably stratified during the entire year. There appear to be no fishes in the lake. The invertebrate fauna is dominated by corixids and tanaid shrimps. Tagus Crater Lake on Isabele Island, occupies a crater about 100 m from Tagus Cove. It is about 400 m in diameter and 10 m deep over most of the basin. The lake is saturated salt brine with a bottom of rock salt. The fauna is dominated by corixids and anostracan shrimps. Of three small ponds at Noah's Coves. Isabele, one has low salinity from top to bottom, whereas the other two are markedly stratified with regard to salinity. The upper "fresher" water in the stratified ponds is poor in phytoplankton compared to the underlying high—salinity water. Several species of fish, Odonata, corixids, water striders, and crustacean larvae were living in the ponds at the time of these observations.

ISSN:0012-9658    

DOI:10.2307/1934664

出版商:Ecological Society of America    

年代:1969

数据来源: WILEY

摘要:

Population growth efficiencies (GE) of 22 laboratory populations of Hydra pseudoligactis fed Artemia sp. nauplii were determined. Maximum growth efficiencies of ca. 37% were observed for ingestion rates greater than 0.5 cal each day per calorie of hydra. The instantaneous growth rate increased continuously with increased ingestion above the minimum of ca. 0.25 cal each day per calorie of hydra. The maximum calculated net efficiency was ca. 55%. Although GE was constant above ingestion rates of 0.5, net efficiency and growth rates continued to increase with increasing rates of ingestion.

ISSN:0012-9658    

DOI:10.2307/1934665

出版商:Ecological Society of America    

年代:1969

数据来源: WILEY

摘要:

Eleven species or functional types of heterotrophic bacteria were isolated during the study of a heterotrophic succession of an aquatic microcosm. Bacterial populations changed rapidly in numbers and in dominant types. The dominant primary producer, Chlorella, was dependent upon thiamin supplied by 5 of the 11 bacterial isolates. Bacteria were functional in four ways: as contributors of thiamin, CO2and possibly sources of nitrogen to primary producers; as primary consumers of algal excretions; as secondary consumers of bacterial excretions and as decomposers. During succession net photosynthesis (Pn) surpassed night respiration (Rni) from day 5 through 45; as maturity approached the Pn/Rniratio fluctuated around 1. Dissolved carbon was present at 240 mg C/liter at zero time and decreased owing to the heterotrophic activity of 1.5 x 109bacterial cells/ml by day 8. Dissolved carbon was maintained at approximately 20.7 mg C/liter from day 8 through maturity. Particulate biomass increased steadily until day 50, after which there was no further increase. A bimodal pattern was apparent in bacterial numbers, Chlorella numbers, community metabolism, C14—U—glyoxylate uptake and bacterial species diversity in which peaks were recorded early and late in succession while a mid—succession decrease in activity occurred. The microcosm exhibited trends expected of larger, more open, developing ecosystems. The microcosm and methods used in the study are useful laboratory tools for examining various ecological principles.

ISSN:0012-9658    

DOI:10.2307/1934666

出版商:Ecological Society of America    

年代:1969

数据来源: WILEY