摘要:

Rapid retreat of the Robson Glacier since 1783 has produced a series of moraines well suited for study of vegetation and soil development. The terminal and five recessional moraines ranging in age from 180 to 50 years were suited in August 1963 in continuation of earlier work by W. S. Cooper. Vegetation development shows early dominance of Hedysarum and Dryas, followed by Salix, Arctostaphylos rubra, and other shrubs. Tress enter the stand early, but are largely confined to one species, Picea engelmanni. The vegetation of the two oldest moraines bears a superficial resemblance to the mature forest of the region, but differs greatly in floristic composition and structure. Soil Formation ranges from virtually none on the youngest moriane to a rudimentary podsolic B horizon on the oldest recessional moriane Accumulation of soil nitrogen appears to be slow, despite the existence of root nodules on Dryas octopetala, D. drummondii, and Hedysarum mackenzii.

ISSN:0012-9658    

DOI:10.2307/1933927

出版商:Ecological Society of America    

年代:1966

数据来源: WILEY

摘要:

Incident and reflected visible radiation under clear skies was measured in summer 1960 over surfaces in central Minnesota. Measurements were made with Weston photometers, model 756, on the ground, from ladders, and from a Bell 47—G2 helicopter. Percent albedo over natural upland surfaces at 60—65° solar altitude decrease from 12.0 for inorganic sand to 6.1 for organic sand, to 5.3 for short grassland, and to 2.2 for forest; lowland surfaces decreased from 4.0 for water to 2.3 for forest. Albedo decreased with an increasing chlorophyll a + b content of vegetation, but the decrease was negligible above a chlorophyll content of around 1.0g/m2. Urban surfaces were more reflective than agricultural surfaces, which had a higher mean albedo than natural vegetation. The mean albedo of an aerial transect from Bethel to St. Paul was 6.5% and was estimated to have increased around 15% the settlement of the area by European man. Percent albedo over a Quercus forest increase from 2.4 at 65—70° solar altitude of 11.6 at 8—10° and the decreased to 3.8 at 0° altitude. A similar albedo pattern was found for a pioneer (short) grassland which increased from 5.2 to 13.2 and then decreased to 4.6%. Changes in albedo with solar were attributed to changing proportions of diffuse and direct radiation and to Fresnel's Law. Light penetration into the Quercus forest decreased most rapidly in the lower tree canopy layer and decreased with increasing solar altitude. Albedo within the Quercus forest increased with increasing forest depth and with increasing solar altitude, reaching a maximum of 12.7% at a forestheight of 0—3 m and a solar altitude of>60°.

ISSN:0012-9658    

DOI:10.2307/1933928

出版商:Ecological Society of America    

年代:1966

数据来源: WILEY

摘要:

The vegetation of 24 oases located in the western Colorado Desert was composed of 78 species from 34 families, with an average of 11 species per oasis. Species distributions within an oasis were determined by available water and could be divided into three contoured belts and hydric zone had 10% of the total species, primarily hydrophytes, and accounted for one—fifth of the total plant cover. The oasis—proper zone contained phreatophytes and halophytes, comprising 17% of the total species and producing two—fifths of the cover. The remaining cover was produced by 73% of the species, mainly xerophytes, present primarily in the desert—oasis ectone. Oases were located on hillside seeps or in canyon washes. Although most dominant species were common to both types, they differed in vegetational composition. Hydric species were more common in wash oases. Species requiring stable sites with sub—surface water were more abundant in seep oases. All oases showed individuality since Washingtonia filifera was the only ubiquitous species. Haplopappus acradenius and Prosopis juliflora occurred in 75% of the oases; 10% of the species were restricted to two or three oases; and 33% were confined to one oasis. Eleven rare species were encountered. Absence of palm reproduction was due to inadequate water, lack of stimulating rains, or alkali soils. Alkali soils appear detrimental to plant growth. Optimum conditions for new growth need occur only once a century to sustain oases. Maximum palm ages appear to be about 200 years. Floods alter wash geomorphology and vegetation, but have a rejuvenating effect on dense, stagnating stands of hydrophytes. Fire determines oasis composition and affects the physiognomy, productivity, reproduction, and maintenance of the fire—tolerant palms.

ISSN:0012-9658    

DOI:10.2307/1933929

出版商:Ecological Society of America    

年代:1966

数据来源: WILEY

摘要:

The occurrence and severity of an annual canker disease among sugar maples, Acer saccharum Marsh., were studies with respect to the soil. topographic, three, and stand c characteristics of maple—growing sites in the nonglaciated plateau and mountain region of Pennsylvania. Symmetric correlation, multiple regression, and factor analytic procedures were used in interpreting approximately 100 variables, or interactions among variables, measured on each of 62 plots. The analyses indicated that occurrence and severity of cankering was most closely associated with those characteristics peculiar to slowly permeable soils. On the heavily cankered plots soils were relatively shallow to an impervious layer, and the A horizons contained a greater clay content and more pore space. A decrease in the percentage of the total root count in the surface 6 inches of these soils indicated that the surface layer was not particularly favorable for the development and survival of roots. The lower vigor of sugar maples growing on such sites was significantly correlated with greater canker incidence.

ISSN:0012-9658    

DOI:10.2307/1933930

出版商:Ecological Society of America    

年代:1966

数据来源: WILEY

摘要:

Of the plant species introduced on the Nevada Test site, Nye County, Nevada, Bromus rubens and B. tectorum are well established in the present vegetation mosaic. B. rubens is frequently the dominant winter species in Colegyne (blackbrush) communities at 4,000—5,000 ft. Relative density (or absence) of populations is a site characteristic, as indicated by quantitative data from 18 study sites in Yucca Flat in the Years 1963—65. Like the native species, it occurs in higher densities on disturbed sites of areas where it is already established in the undisturbed vegetation. Its success is in part due to a growth regime and environmental requirements unlike those of the native winter annuals, and perhaps to higher percentage survival to maturity as in the 1963—64 season. It is not aggressive in the region today. B. tectorum is confined to disturbed sites at the higher elevations (5,000—7,500 ft) where vegetation is Artemisi (sagebrush) or Armenisia—Pinyon—Juniper. It is numerically and really increasing with an increase in disturbed sites at these elevations. Fire is promoted by both species, but the contribution of B. rubens is much greater, either directly or indirectly, because it is identified with Coleoptera vegetation, the shrub type in the region most susceptible to fire.

ISSN:0012-9658    

DOI:10.2307/1933931

出版商:Ecological Society of America    

年代:1966

数据来源: WILEY

摘要:

Spectral distributions of shade light between 400 and 740 mm were measured under corn, sugar maple, oaks, pines, and spruce with a portable recording spectrophotometer. Differences were found between hardwoods and softwoods and between clear cloudy days. An energy maximum at 550 nm, a minimum at 670 to 680 nm, and a very high maximum in the near infrared occurred under all species. Four components of light within a plant canopy can be distinguished: both beam solar radiation and diffused sky radiation are transmitted both directly and indirectly (reflected and scattered). Separate consideration of each of these components leads to great understanding of similarities and differences between light regimes in different stands.

ISSN:0012-9658    

DOI:10.2307/1933932

出版商:Ecological Society of America    

年代:1966

数据来源: WILEY

摘要:

Twenty—five self—regulating populations of Daphnia pulex were exposed to different levels of external60Co gamma radiation for 18.5 hr per day for 55 weeks. Dose rates ranged from 0 to 516 R/day. Although the population at the 3 highest dose rates became extinct, the remaining 22 populations established quasi—equilibrium densities which decreased with increasing dose rate. The maximum tolerable dose rate was 436 R/day. Average turnover rates increased with dose rate. An approximate inverse relationship between mean population size and mean turnover rate suggested that net production might be unaffected by the radiation. Estimates of yield to decomposers indicated that net production was, indeed, unaffected. Radiation stress became a limiting factor for population size and turnover rate at much lower dose rates than those needed to limit net production. Within the entire range of indefinitely tolerable dose rates, the population consequences of radiation stress stem almost entirely from effects on individual fertility and survival, whereas individual metabolism is apparently unaffected. Increased individual growth is an indirect effect, due to reduced fecundity at a given food supply per individual or increased food consumption at a given food supply per population.

ISSN:0012-9658    

DOI:10.2307/1933933

出版商:Ecological Society of America    

年代:1966

数据来源: WILEY

摘要:

Crayfish collected from a central Texas farm pond are hosts for two Branchiobdellidae. Evidence indicates the branchiodbellids are commensals, since they survive for long periods in the absence of crayfish, but are dependent upon them as a site for reproduction. Branchiobdellid cocoons, which have incubation periods of 10 to 12 days, are attaches to the exoskeleton of the host mostly on the ventral abdominal surface. Cocoons are not deposited on very small crayfish, apparently because of selection brought about by the loss of eggs through the frequent molts of young crayfish, since eggs left on exuviae perish. Transfer between hosts is accomplished mostly through body contact of the crayfish. The logarithm of the branchiobdellid populations yields a straight line when plotted against crayfish body lengths. This may be accounted for by the increased surface area and the decreased frequency of molts of larger crayfish. Population densities are minimum during the winter, increase distinctly in early spring, and reach a maximum in June. Adverse environmental conditions during the summer and winter likely cause decreased reproductivity activity or increased mortality. A greater proportion of the total brachiobdellid population inhabits small crayfish during the early summer than at other seasons. This may result from population pressures created by overcrowding on larger crayfish during this period of maximum branchiobdellid population density. The structure of the bronchiobdellid populations varies seasonally, with adults composing about half of the winter population and a smaller proportion in other seasons. This can be accounted for by decreased reproductive rates or selective mortality depleting the numbers of young worms during the winter.

ISSN:0012-9658    

DOI:10.2307/1933934

出版商:Ecological Society of America    

年代:1966

数据来源: WILEY

摘要:

The reaction of three species of web—spinning spiders, Araneus cavaticus, Argiope aurantia, and Argiope avara, in their webs and when removed from the webs, to web agitation and airborne sounds at known frequencies and intensities were studies. The reactions to web agitation and airborne sounds are not the same, and the receptors are probably different. The spiders react to web agitation by attacking the source, as they do with trapped insects; the receptors are probably proprioceptors of the legs. The spider respond to airborne sounds, from 200 to 3,000 cycle/sec at 90 to 110 db, by defensive movements; the webs are not needed for reception. The receptors are long, thin hairs which are agitated by near—field air movements of intense sound fields; they are not specialized phonoreceptors, for they are sensitive to direct bending and to air currents. Earlier discrepancies in results with airborne sounds are easily explained by the fact that intensities and distances to sound sources were not controlled. The defensive reactions to high intensity airborne sounds are probably involved, in nature, with escape from or defense against winged predators.

ISSN:0012-9658    

DOI:10.2307/1933935

出版商:Ecological Society of America    

年代:1966

数据来源: WILEY

摘要:

Water loses of small (1.5 to 4.6 g) representatives of three species of Australian lizards, Amphibolurus ornatus (Agamidae), Gehyra variegata (Gekkonidae), and Sphenomorphus labillardieri (Scincidae), were determined from weight losses incurred by the animals in a dry atmosphere. In one set of experiments conducted at 20°C, the animals were unrestrained in their chambers.The rates of total water loss by A. ornatus, G. variegata, and S. labillardieri averaged 1.9 g (100g day)—1, 3.0 g (100g day)—1, and 6.8 g (100 day)—1, respectively. These rates primarily reflect the evaporative loss of water. The differences among them did not appear to result from differences in activity, for the metabolic rates of S. labillardieri and A. ornatus both approximated 0.07 cc O2(g hr)—1. In a second set of experiments conducted at 20 and 30°C, the water losses of restrained individuals were compartmentalized. The total loss by A. ornatus averaged significantly lower than that by G. variegata and S. labillardieri at both temperatures. This resulted primarily from differences in pulmonary water loss among the three lizards. At 20°C cutaneous loss accounts for 70% of the evaporative loss by A. ornatus and variegata and 41% of that by S. labillardieri. The percentages are somewhat lower at 30°C owing to the greater effect of temperature on pulmonary than on cutaneous loss. The distributions of these three lizards correlate well with these observations on water loss, A. ornatus and G. variegata reaching hotter and drier sections of Australia than S. labillardieri.

ISSN:0012-9658    

DOI:10.2307/1933936

出版商:Ecological Society of America    

年代:1966

数据来源: WILEY