摘要:

A field using radioisotopes to estimate consumption of vegetation by insects was evaluated by comparisons with feeding rates measured in the laboratory. The uptake of137Cs was investigated for beetle larvae (Chrysomela knabi Brown) feeding on willows in the White Oak Lake bed, an area contaminated with radioactive waste products. Beetle larvae and adults accumulate137Cs from willow leaves and reach steady—state equilibrium concentrations. Information on biological half—lives (elimination rates) for cesium was used to convert the137Cs concentrations attained by the beetle larvae into estimates of137Cs intake rates. Food intake rates were estimated from radiocesium intake rates, by measuring137Cs concentrations in willow leaves. Food intake rates estimated by this method for field areas were 7 to 16 mg dry wt of plant per larva per day. Laboratory measurements of food consumption rates, by comparison, were about 9 to 10 mg/larva per day for larvae of similar size. Influences of temperature on biological half—lives were also studied, but no correction was applied to the field estimates since mean field temperatures were close to those used in laboratory experiments. The good agreement between laboratory and field measurements supports the validity of previous applications to entire communities of plant—feeding insects. The method would be equally useful with predaceous animals as with herbivores. Measurements of food eaten can be converted to energy units by bomb calorimetry.

ISSN:0012-9658    

DOI:10.2307/1935739

出版商:Ecological Society of America    

年代:1966

数据来源: WILEY

摘要:

Specimens of the sand—dwelling lizard, Uma notata, were collected monthly, primarily in the Algodones Dunes, Imperial County, California, from July 1958 through September 1962. These animals were autopsied to determine the breeding cycle of both sexes. Most individuals reach reproductive maturity during the second summer following hatching. Adult testis volumes change markedly during the year, generally reaching maximum size in May. Males were found as potential breeders from mid—April to mid—September. Females were found with eggs (usually two) in oviducts from mid—May to the late August. Females probably lay more than one clutch per year, based on observations of egg—laying captives. The reproductive period yields slightly from year to year due, at least in part, to the amount of rainfall that occurs the preceding winter. Breeding activity in males and the emergence of juveniles are delayed following dry winters. This is attributed to a series of interactions between organisms. U. notata tests do not become reproductively active if the lizards do not obtain adequate food. Insects that live in low—growing plants (annuals) normally are used for food by these lizards. However, insects that develop on these plants can do so only if sufficient rainfall occurs in winter to produce annuals. On the other hand, the larger plants (perennials) in the dunes acquire sufficient moisture from deep in the sand to flower each year, regardless of winter rains. Consequently, insects that utilize perennials are relatively plentiful every year. Following dry winters, Uma must rely on obtaining sufficient food from these insects, which presumably are more difficult to capture by sand—dwelling lizards. Thus, breeding activity is delayed until the requisite amount of food can be acquired. The reproductive responses of Urosaurus graciosus, a lizard that lives in perennial plants on these dunes, support this explanation.

ISSN:0012-9658    

DOI:10.2307/1935740

出版商:Ecological Society of America    

年代:1966

数据来源: WILEY

摘要:

MSX, a pathogen of oysters (Crassostrea virginica), produced a drastic epizootic in high—salinity areas of Chesapeake Bay from 1959 to 1963. The patterns of infection and mortality were determined by imports from disease—free seed—oyster areas. Winter and spring imports became infected in early summer and began dying in late summer. Late—summer imports apparently became infected promptly but infections remained subclinical until the following May. Death rates were highest during warm months but losses occurred throughout the year. MSX was assigned as the cause of a high percentage of deaths by sampling live and dead oysters. Mortality for the first and second years after import was usually 50 to 60% annually. A fungus disease caused by Dermocystidium marinum was also prevalent in some areas. Prevalence of MSX did not decline as oyster populations were decimated; hence nearly half of Virginia's private beds have been forced out of production.

ISSN:0012-9658    

DOI:10.2307/1935741

出版商:Ecological Society of America    

年代:1966

数据来源: WILEY

摘要:

Shore birds are important trophic components of tundra communities during summer months, preying chiefly on insects. The Red—backed Sandpiper (C. alpina), studied in five seasons near Barrow, Alaska, 71°N, feeds largely on larvae and adults of the families Tipulidae and Chironomidae (Diptera). Sampling for availability and abundance of insect populations shows that the food source readily available and heavily used in early summer and again in late summer consists of tipulid larvae; as summer predation proceeds, important changes in numbers, and availability of different food species result from progression of their life—cycle stages and from changes in environmental conditions. Food supply and diet are most varied in July. Although feeding behavior and diet of redbacks change with prey availability, preferences are shown by adult sandpipers for tipulid larvae in early and late summer and to a lesser extent for chironomid larvae in midseason. Recently hatched young feed entirely on small—sized adult insects, mostly chironomid flies, which are obtained easily on the tundra surface. Differences between adult and young redbacks in habitat and food selection during late summer represent an intrapopulational means of apportioning food supply in a critical part of the season. With arctic insect faunas depauperate in variety of taxa, there is a limited diversity of food species for sandpipers. Adverse weather conditions characteristic of high—latitude climates can cause local food shortages. Interacting with the timing of generation replacement of important insect prey species, adverse weather promotes the widest variations in food conditions in July when young sandpipers are hatching and growing.

ISSN:0012-9658    

DOI:10.2307/1935742

出版商:Ecological Society of America    

年代:1966

数据来源: WILEY

摘要:

The distribution and ecology of the woodland jumping mouse, Napaeozapus insignis, were studied in the light of its behavior in the field, its physiology in the laboratory, and by comparison with other species of small rodents. Data from 36 traplines show that jumping mice have no preference for habitats near water. Shrubby ground cover appears to be the most important factor affecting their local abundance. Napaeozapus has probably been associated so often with streams because these areas favor growth of good ground cover. Woodland jumping mice were found in nonwooded areas where shrubby growth cover was found. In one nonwooded area it replaced the meadow jumping mouse, Zapus hudsonius. Removal of the population of woodland jumping mice in the fall was followed by the establishment of the meadow species the next spring. Woodland jumping mice and redback voles seldom occurred together in abundant numbers. This separation was partly the result of distinct habitat differences, but in some areas of mixed woods having ground cover, the presence of voles was accompanied by an absence of jumping mice. When jumping mice were present, redback voles were few or absent. This pattern of distribution could not be explained by differences in habitat selection or by competition. Some form of interference could be involved. Woodland jumping mice show a tendency to be more active on colder nights. This behavior contrasts with observations on deer mice by other workers who state that these mice are more active on warm, cloudy nights. The high population densities of Napaeozapus found in this study were in an area of New York State having boreal elements. The lower densities reported for western and southern areas of the northeastern United States indicate that its overall distribution is affected by the presence of boreal vegetation. Ad libitum water consumption shows that redback voles drink more than twice as much as their predicted weight—relative value. Woodland jumping mice drank normal weight—relative amounts, but deer mice drank less. The rate of evaporation in Napaeozapus was considerably lower than that found in sympatric Peromyscus maniculatus. Its rate of evaporation was closer to values found for some populations of mice from drier climates. These results suggest that moisture is not a critical limiting factor in the distribution of woodland jumping mice. The low rate of evaporation in Napaeozapus could be an adaptation against desiccation during hibernation. The spreading of saliva by the deer mice is an important cooling device. At 37°C deer mice lost 72% of their heat production through evaporation. At this same ambient temperature, jumping mice lost only 38% of their heat by evaporation. Deer mice were able to withstand 39°C with no ill effects, but few jumping mice survived 37°C. Hyperthermia associated with low metabolism was observed in the deer mice. This could be the result of vasoconstriction in nonvital organs, thereby limiting substrates and O2to the cells of these organs. Such an adjustment would not only limit the rate of metabolism but would also increase the body temperature by limiting transfer of heat by the blood. The decreased metabolic rate and the increased rate of evaporation by spreading saliva would increase the efficiency of cooling at high ambient temperatures. Basal metabolic values of deer mice and jumping mice are near their predicted weight—relative values. The high lower critical temperatures in jumping mice are consistent with the idea that hibernators have high rates of heat loss. Jumping mice appear to have more precise thermoregulation over a wider range of ambient temperatures than do deer mice during the summer period. Metabolic patterns of several small rodents are compared. These patterns show little association with specific climatic conditions among distantly related, sympatric forms. The deer mouse complex, the jumping mice, the voles, and the pocket mice seem to have their own distinctive metabolic and thermoregulatory patterns, which may be associated with phylogenetic patterns, as exemplified by populations of Peromyscus, while some of the more specialized phylogenetic patterns, such as the one which characterizes the genus Perognathus, seem to have evolved in the ancestral populations to suit specific climatic conditions.

ISSN:0012-9658    

DOI:10.2307/1935743

出版商:Ecological Society of America    

年代:1966

数据来源: WILEY

摘要:

A method is described for computing daily values of moisture stress on forest vegetation, or water deficits, based on the differences between Thornthwaite's potential evapo—transpiration and computed soil—moisture depletion. More realistic functions are used for soil—moisture depletion on specific soil types than have been customary. These functions related daily rates of depletion to characteristics of soil—moisture tension. Separate functions account for surface soil wetting and drying processes following rain and during dry periods. Two methods of summarizing the day—to—day distribution of moisture stress are illustrated. One utilizes directly accumulated stress values during such logical growth intervals as periods of leaf flushing or bud setting. In an example of a regression of red pine shoot growth on water deficits, 72% of the variation in annual growth was accounted for by moisture stress during certain periods of both previous and current growing seasons. The second method computes moisture stress and weather variables as functions of time over two growing seasons and utilizes the coefficients of orthogonal polynomials as independent variables in regressions of growth. In an example of western white pine basal area growth utilizing this latter method, moisture stress accounted for a 28% reduction in the variance of growth remaining after the effects of temperature and precipitation per se had been removed. The complete model accounted for 78% of the total variation.

ISSN:0012-9658    

DOI:10.2307/1935744

出版商:Ecological Society of America    

年代:1966

数据来源: WILEY

摘要:

Field notes and plats of the original land survey of Sumter County, Alabama (1832), are used to reconstruct the vegetation of the 278,093 acres of Black Belt in the county. Calculation from map sampling at all the 424 section corners shows that 65,074 acres (23.4%) supported no trees or less than 10 trees per acre and thus can be considered open land. When section corners are located on a modern soil map, a strong correlation exists between the 99 points which had low tree density (10 trees or less per acre) and the 167 points which have alkaline clay soils: 70.7% of these open—land points lay on what is now alkaline clay. By contrast, 72.5% of the dense forest of 1832 represented by 62 points of high tree density–120 trees or more per acre) is associated with the 257 acid—soil points (mostly loams, some clays). The association of open land (prairie)in Sumter County which alkaline clay soils made for a distinctive, and probably natural, Black Belt vegetation. Tree densities in this part of the county unmistakably represented dense forest (120 or more trees 2 inches dbh or greater, per acre) at only 14.5% of the sampling points. The commonest trees were oaks (Quercus) and hickories (Carya); pine (Pinus) made up less than 5% of the trees sampled and red cedars (Juniperus) made up less than 0.3%.

ISSN:0012-9658    

DOI:10.2307/1935745

出版商:Ecological Society of America    

年代:1966

数据来源: WILEY

摘要:

The salt—marsh vegetation of Newport Bay was separated into littoral and maritime zones and was sampled quantitatively for frequency of occurrence and cover. The littoral zone (marsh proper) was divided into a narrow lower belt covered by Spartina foliosa, a broadest middle band dominated by Batis maritima and Salicornia virginica, and a narrowest upper strip influenced by Salicornia virginica and Monanthochloe littoralis. The maritime zone consisted of a bluff community composed of Suaeda californica and Salicornia subterminalis, or a dune associate pioneered by Oenothera cheiranthifolia and Heterotheca grandiflora. Nine species, principally Gramineae and Chenopodiaceae, dominated the marsh. Salicornia virginica accounted for the highest total average frequency and cover. Additional important species were Suaeda californica, Batis maritima, and Spartina foliosa. The plant community was extremely simple in the lowest areas (four species) and graded to a more complex, yet relatively simple plant community in the highest regions of the marsh (15 species). Correspondingly, the lower zones had sparse vegetational cover and the higher zones supported heavier growth, both in size and numbers of individuals. Although the marsh was subjectively divided into zones, individual species could not be readily segregated into zones since the frequency of each species varied along environmental gradients to produce a vegetational continum.

ISSN:0012-9658    

DOI:10.2307/1935746

出版商:Ecological Society of America    

年代:1966

数据来源: WILEY

摘要:

The changes occurring on the J. T. Curtis Prairie, an artificial prairie in the University of Wisconsin Arboretum, were studied by means of four surveys spaced at 5—year intervals. Frequency data from more than 650 meter—square quadrats with known locations were obtained at each survey. Five stands, delimited on the basis of their compositional index (CI) as determined by indicator species, were compared with native prairies having similar CI values by means of species lists and sum frequency of the species. When prairie species only are considered, some artificially established stands are as similar to native stands as native stands is the presence of large numbers of non—prairie species. The artificial stands have much larger species lists and higher sum frequencies than native prairies. The results indicate that the Curtis Prairie is becoming very similar to native prairies in numbers and species of prairie plants, and that the non—prairie species are materially reduced in importance.

ISSN:0012-9658    

DOI:10.2307/1935747

出版商:Ecological Society of America    

年代:1966

数据来源: WILEY

摘要:

Root extension in a 24—year—old longleaf pine plantation in the North Carolina sandhills was studied by the application of 10 mc of I131directly to the soil, on the surface, or at depths of 1 or 3 ft, and surrounding trees monitored with a portable scintillation counter. Within 10 ft of the point of application, all trees above 3.0 inches absorbed I131in sufficient quantities to be detected. Beyond 22 ft for surface applications, and 33 ft for 1— and 3—ft depths, no I131was detected in any trees. Regressions were computed to determine whether root extension could be predicted. When distance from the point of application was used as the dependent variable, an index of competition and the angle from the tree row proved to be the most useful, to the exclusion of the various measures of tree size.

ISSN:0012-9658    

DOI:10.2307/1935748

出版商:Ecological Society of America    

年代:1966

数据来源: WILEY