bluuebunny/crossref_metadata_2025 huggingface dataset:
The Quercus Garryana Forests of the Willamette Valley, Oregon
Authors: Thilenius John F.
Published: May 2006

Quercus garryana forests, prominent at low elevations throughout the Willamette Valley, Oregon, have developed from oak savanna subsequent to settlement of the valley in the mid—nineteenth century. Interruption of the ground fires that were common in the pre—settlement environment probably caused the change. The understory of the oak forest is dominated by shrubs, and well—defined strata are present. Four plant communities occur: (1) Quercus garryana/Corylus cornuta var. californica/Polystichum munitum (most mesic); (2) Quercus garryana/Prunus avium/Symphoricarpos albus; (3) Quercus garryana/Amelanchier alnifolia/Symphoricarpos albus; and (4) Quercus garryana/Rhus diversiloba (most xeric). All are in seral condition because of their relatively recent development and because they have been disturbed throughout their existence by man's activities. The soils supporting the oak forest are generally deep and well drained and have developed profiles with illuvial horizons and acidic reaction. They are derived from sedimentary and basic igneous rocks and old valley—filling alluvium. Seven established soil series are present: Steiwer, Carlton, Peavine, Nekia, Dixonville, Olympic, and Amity. The Steiwer series and its catenary associate, Carlton, are the most common soils.
The Effect of the Choice of Temperature Scale on Simple Linear Regression Equations
Authors: Zar Jerrold H.
Published: May 2006

When a simple linear regression equation has been derived using observations recorded on either the Fahrenheit or Celsius temperature scale, one can determine what equation would have resulted had the observations been made using the other temperature scale. Conversions are described for such transformations.
A Method for Measuring Light Intensity Under Dense Vegetation
Authors: Getz Lowell L.
Published: May 2006

A description of an instrument for obtaining light intensity readings below dense herbaceous vegetation. Readings can be made with almost no disturbance to the manner in which the sunlight is intercepted by the vegetation.
Endoparasite Patterns in Mammals of the Malayan Rain Forest
Authors: Dunn F. L. , Lim B. L. , Yap L. F.
Published: May 2006

Helminth—host and blood parasite—host records for lowland rain forest and commensal mammals of the southern Malay Peninsula are examined in relation to host food preferences and habitat. A distinctive pattern of endoparasite frequencies is demonstrated and described for each major parasite category. Parasite records for mammals of other rain forest formations are not yet available for comparison with the data and patterns of correlation presented here. Some implications of these observations for studies in mammalian population genetics are discussed.
Tagging Native Grassland Vegetation with Carbon‐14
Authors: Dahlman Roger C. , Kucera Clair L.
Published: May 2006

Techniques using a plastic tent to contain C14O2 gas over herbaceous vegetation were effective for applying a tracer to Missouri tallgrass prairie. The grasses incorporated 67 to 41 μCi of C14/m2 from a single exposure to 151 μCi of C14O2/m2 for 6 hr on clipped and unclipped areas, respectively. Regenerated shoots, which had been clipped 6 weeks earlier, possessed 8 times higher specific activity than unclipped shoots (0.134 vs. 0.017 μCi/g of carbon in foliage biomass). The root systems of both areas possessed over 50% and the roots of mature vegetation as much as 85% of the assimilated C14 remaining in the plant biomass 8 weeks after tagging, thus illustrating the tendency for food reserves to accumulate in underground storage organs late in the growing season. Specific activities in the root systems were similar (0.02 vs. 0.016 μCi/b C) for both revegetated and mature areas and were adequate for study of later translocation, transfer to soil, and in situ decomposition of organic material in soil.
Response of Mountain Grassland Vegetation to Clipping in Southwestern Montana
Authors: Mueggler W. F.
Published: May 2006

Native vegetation composed of a mixture of grasses and forbs was clipped at different times during the growing season to determine when major species were most damaged by herbage removal. Production of herbage and flower stalks was compared on treated and contiguous control plots the years following 1, 2, and 3 successive years of clipping. Clipping harmed the forbs much more than the grasses and caused a conspicuous shift toward grasses in total herbage composition. Production of Aster integrifolius and Potentilla gracilis was affected adversely by a single clipping in July just before and during flowering; by the end of 3 years of clipping, herbage production of these species was reduced approximately 50%, and the number of flower stalks was reduced approximately 80%. Festuca idahoensis, Bromus marginatus, and Agropyron trachycaulum generally were most harmed by clipping in late July and August, from flowering to seed ripening. Removal of herbage either during early growth or after the foliage began to dry did not damage either the forbs or grasses appreciably. Both Bromus and Agropyron benefited temporarily from reduced forb competition. Total vegetative production did not decrease significantly until the third year of clipping.
Measurement of Leaf Water Potential by the Dye Method
Authors: Knipling Edward B.
Published: May 2006

The dye method for measuring leaf water potential is simple, inexpensive, and suitable for both laboratory and field work. Leaves are immersed in a graded series of solutions, and the solution which neither gains nor loses water is assumed to have a water potential equal to that of the leaf. Although limited by certain inherent errors, the dye method can be used to measure relative values and changes in potential. Specific procedures are described for the successful use of the method.
Bluegills Dominate Production in a Mixed Population of Fishes
Authors: Cooper Edwin L. , Wagner Charles C. , Krantz George E.
Published: May 2006

The effects of exploitation on growth, condition, and surplus production were measured over an 8—year period for a population of seven species of warm—water fishes in a 4.05—ha lake. The lake was shallow, fertile, and moderately productive. Population estimates of individual species were made each spring concurrently with the annual removal of 34% to 71% of the existing population. The initial stock density of all species was 48.66 g/m2 in the spring of 1962. The optimum yield for this mixed population was calculated to be 14.56 g/m2 per year at a stock density of 18.67 g/m2, with the bluegill producing most of this surplus weight. When species were considered separately, there was poor correlation between exploitation rate and either growth or condition. The response of the entire population to thinning was more predictable, with both growth and condition related to stock density. Best growth occurred at densities near 20 g/m2 or approximately at the level for optimum yield.
A Model for Population Reproducing by Fission
Authors: Sinko James W. , Streifer William
Published: May 2006

A partial differential equation which describes the dynamics of a single species population for animals reproducing by fission is set forth. The equation is then applied to Dugesia tigrina. Whenever possible, experimental results are used to determine pertinent parameters. Tests are performed to determine those parameters upon which the model has a critical dependence. The model gives results which are qualitatively in agreement with empirical populations.
Competition in Tropical Stream Fishes: Support for the Competitive Exclusion Principle
Authors: Zaret Thomas M. , Rand A. Stanley
Published: May 2006

Two collections of fish were made from the same Panama lowland stream, one during the dry season, and a second during the wet season. Food overlaps among nine sympatric fish species were calculated for each collection by examining fish stomach contents. Species habitats and feeding methods were determined from field and laboratory observations. Estimates of food abundance, measured independently from food overlap, were made by direct and indirect methods, and were used to determine relative levels of competition. The results show that food overlaps among the fishes are at a minimum during the dry season. Food abundance is also lowest during the dry season, which suggests increased competition for food at this time. This seasonal coincidence of the most distinct species separations with the time of increased competition are exactly those consequences predicted by the principle of competitive exclusion. It is concluded that this study provides strong support for the validity of this principle.
Marine‐Dependent Terrestrial Biotic Communities on Some Cays in the Coral Sea
Authors: Heatwole Harold
Published: May 2006

Coral cays devoid of vascular vegetation were found to contain terrestrial invertebrates, the number of species being related to island size. Sea birds, through contributing guano and carrion were chiefly responsible for the energy transfer from the marine to the insular community.
A Coefficient of Interspecific Assciation
Authors: Hurlbert Stuart H.
Published: May 2006

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 C7 all 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 g2 is simply the value of g2 associated with the observed values of a, b, c, and d. Max g2 is the value of g2 when a is as large (if ad ° bc) or as small (if ad < bc) as the marginal totals of the 2 x 2 table permit. The bais of C7 is considerably diminished if Min g2 is subtracted from the numerator and the denominator of the fraction under the square root sign. Thus a new coefficient is defined. C8 = ad — bc / ° ad — bc ° ° /Obs g2 — Min g2 / Max g2 — Min g2 ° Min g2 is the value of g2 when the observed value of a differs from a, the expected value of a, by less than 1.00. Except when a — a equals zero or 0.5, the value of Min g2 depends on whether (ad —bc) is positive or negative. It is suggested that C8 is the only coefficient of interspecific association appropriate for use with contingency data. An artificial two—species community was constructed and used to demonstrate the inadequacies of association coefficients which utilize abundance rather than presence—absence data. Such coefficients can be influenced strongly by interspecific competition, the species' frequencies, and variability of within—quadrat heterogeneity and, hence, have little value. However, a correlation coefficient based only on those quadrats containing both species may be useful as an indicator of competition.
Environment in Relation to Age of Bristlecone Pines
Authors: LaMarche Valmore C.
Published: May 2006

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.
Studies of a Simple Laboratory Microecosystem: Bacterial Activities in a Heterotrophic Succession
Authors: Gorden Robert W. , Beyers Robert J. , Odum Eugene P. , Eagon Robert G.
Published: May 2006

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, CO2 and 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/Rni ratio 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 109 bacterial 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.
Behavior and Physical Factors Causing Migration and Aggregation of the Sand Crab Emerita Analoga (Stimpson)
Authors: Cubit John
Published: May 2006

Migration and distribution of Emerita on sand beaches can be explained in terms of water flow and a simple behavioral response. Wash zones of sand beaches are bounded burrow out of fluid sand and so are kept within the boundaries of the wave wash. As the position of a wash zone is shifted with the tide, Emerita are carried in it to new locations on the beach. Lateral flow within the wave wash distributes Emerita into clumps along the shore.
Internal Leaf Surface and Stomatal Abundance in Arctic and Alpine Populations of Oxyria Digyna
Authors: Au Shu-Fun
Published: May 2006

Internal leaf surface is greater in alpine populations of Oxyria digyna than in arctic populations grown under identical conditions. Outlines of lower epidermal cells of leaves vary among 10 arctic and alpine populations. Numbers of stomata, as well as epidermal cells, per unit area in the upper epidermis increase from north to south. Such a trend is not found in the lower epidermis. An alpine population from Mt. Washington has many more stomata per unit area on the lower epidermis than the upper, suggesting a closer affinity to the European alpine populations and to arctic populations than to its western North American and alpine conditions may be due to the development of ecological races which differ in structure and metabolic potential
Territory and Breeding Density in the Great Tit, Parus Major L.
Authors: Krebs John R.
Published: May 2006

This paper describes an investigation into whether or not spring territorial behavior was limiting the breeding density of a population of Great Tits on Wytham Estate, near Oxford. The analysis of distances between neighboring nests showed that nest sites were more spaced out than would be expected from a random distribution; this indicated that interactions between the birds produced at least a local density—limiting effect. In 2 successive years, established territorial pairs were removed from a stable spring population in mixed woodland. The removed birds were rapidly replaced by new pairs. These newcomers were largely first—year birds; they came from territories in the hedgerows that surrounded the wood; the vacated hedgerow territories were not refilled. The hedgerows were found to be suboptimal in terms of reproductive success. Thus territory limited the breeding density in the optimal habitat. Song advertisement is probably important in maintaining territorial boundaries, hedgerow birds being able to detect the presence of individual woodland territory holders by recognizing their songs. The effect of winter food supply on the population was investigated by supplying excess food throughout one winter. This artificial food supplement appeared to have no effect on the number of Great Tits breeding in the wood, but did produce an increase in the case of a related species, the Blue Tit. The results show that territorial behavior influences density; this is not considered to be a function of territory in the evolutionary sense, but rather a consequence of spacing out that has been selected for in some other context. A possible advantage of spacing out in the Great Tit is as a defense against predators. Territory size varies considerably from year to year. These variations are the result of interactions between the birds themselves, rather than direct adjustments of territory size to fluctuations in some environmental resource. Even though territory has an effect on the number of birds breeding in the wood,it is not an important density—dependent factor acting to regulate the population.
The Developmental Response of Predators to Changes in Prey Density
Authors: Murdoch William W.
Published: May 2006

If a predator eats more prey at higher prey densities, grows more as a consequence, and then kills more prey because of its larger size, this produces a developmental response to prey density. In its functional response a predator sea shore snail caused a decreasing percentage mortality as prey (barnacle) density increased (type 2 response). This causes instability in prey numbers. However, when account was taken of the developmental response in a hypothetical pseudosnail, the prey mortality caused over a year by a single—predator as a function of prey density, was different from that expected on the basis of the functional response alone. There is a tendency for the mortality to be a fairly constant percentage of prey density over a rather large range of prey densities. This results in the reduction of the destabilizing effect. Problems of integrating these responses with the numerical response and of generalizing the results are discussed.
The Reproductive Cycle of a Neotropical Lizard
Authors: Sexton Owen J. , Turner Olga
Published: May 2006

The reproductive cycle of a neotropical sphaerodactylid lizard, Gonatodes albogularis, was studied at Ancon, Panama Canal Zone, from September 1968, until October 1969. Counts of eggs oviposited at seven selected sites were made biweekly over this period; adults were collected monthly to provide information about reproductive condition. The maximum number of ovipositioned eggs was made just before the height of the rainy season and the minimal one during mid—dry season. The apparent reproductive condition of the adults did not reflect the decline in number of oviposited eggs during the end of the wet season.
A Technique for Regulating Artifical Populations of Drosophila
Authors: Scudo Francesco M. , Peschiera Giordano
Published: May 2006

A modification of the standard technique of rearing Drosophila in bottles (with paper supports for pupation) allows one to obtain rather stable populations and to control, to some extent, their age distribution. It consists in transferring, at constant time intervals, appropriate fractions of adults, pupae and larvae to new bottles. A number of combinations of such fractions, the number and size of bottles and different quantities of medium have been tried.
Intraspecific Differences in Nitrate Half‐Saturation Constants for Three Species of Marine Phytoplankton
Authors: Carpenter Edward J. , Guillard Robert R. L.
Published: May 2006

Half—saturation constants (K) for NO_3 uptake were measured on eight clones, belonging to three species, of marine phytoplankton. The clones isolated from oceanic, low—nutrient areas had K values of below 0.75 (mu)M NO_3, while clones of the same species taken from estuarine regions had higher K values (over 1.5 (mu)M NO_3). Other isolated from shelf areas had intermediate (1.2 (mu)M NO_3) or low (0.1 (mu)M NO_3) K values. These data suggest that physiological races of marine phytoplankton are adapted to high or low nutrient levels.
A Quantitative Analysis of Wisconsin Forest Vegetation on the Basis of Plant Function and Gross Morphology
Authors: Knight Dennis H. , Loucks Orie L.
Published: May 2006

The structural and functional features of the trees, shrubs, and herbs in the upland forest communities of Wisconsin have been studied for their potential in describing relationships between vegetation and environment. Structure is defined here as the spatial arrangement of the plant biomas, e.g., height, leaf size, and growth form. Functional features include those which are apparent adjustments or response to the environment, e.g., deciduousness, shade tolerance, method of seed dispersal, and fire resistance. Quantitative estimates of the importance of plant features such as these, regardless of species, were obtained for each of 149 forest stands distributed throughout Wisconsin in all types of upland forest vegetation. Using the index of similarity, c = 2w/a + b, each of the 149 stands was compared to every other stand on the basis of 29 tree structural—functional features. The spatial relationships in the resulting ordination demonstrate that the upland forest communities can be distinguished and studied using these features. Although adjacent stands in the ordination are similar on the basis of tree structure and function, they can be different in species composition. The usefulness of grouping species with similar structural—functional features is discussed and related to the concept of ecological equivalence. Finally, the spatial relationships in the ordination are used to derive indices that allow calculation of stand values along structural—functional coordinates. Although the indices are based solely on plant structure, the resulting coordinates can be used to infer some functional features of the vegetation as well as successional status and certain environmental relationships.
Stomatal Number and Size as Related to Soil Moisture in Tree Xerophytes in Israel
Authors: Gindel I.
Published: May 2006

Stomatal density and length were analyzed in 32 species of indigenous and acclimatized tree species grown under different ecological conditions. Mean leaf was calculated in 14 of them. Stomatal density was significantly higher in nonirrigated than in irrigated trees, whereas no significant differences were found in leaf area in 11 species. Stomata are present in the upper and lower epidermis of the leaf in most of the successfully acclimatized species and in some indigenous ones. These species, as compared to others in which stomata are present only in the lower epidermis, are distinguished by xerophytic properties. Many of them are able to grow without irrigation in an arid climate, in semidesert and water—depleted soil, surviving even during years of drought.
Atriplex Species [or Taxa] that Spread by Root Spouts, Stem Layers, and by Seed
Authors: Nord Eamor C. , Christensen Donald R. , Plummer A. Perry
Published: May 2006

Some low—growing Atriplex species can reproduce vegetatively as well as by seed. This characteristic suggests that these plants may be used to reduce fire hazard by replacing highly flammable, high—volume chaparral plants in southern California. They may also be suitable as forage for livestock and game, and as a protective soil cover. Root sprouting of Garner's saltbush (A. gardneri) was abundant and widespread under various site conditions in its native habitat in the eastern Great Basin in Utah, upper Colorado River drainage in Wyoming, and in test plantings in southern California. Nuttall's saltbush (A. nuttallii), which reproduces largely by stem layers, also produces some root sprouts.
A Bioclimatological Comparison of the Summer Day Microenvironments of Two Species of Arid‐Zone Kangaroo
Authors: Dawson Terence J. , Denny M. J. S.
Published: May 2006

Two large kangaroos, the red kangaroo (Megaleia rufa) and the euro (Macropus robustus) live in the arid regions of Australia. On hot summer days they are found in entirely different microenvironments: red kangaroos in the shade of small desert trees in relatively open country and euros around rocky outcrops in caves and under rock ledges. Measurement of the temperature and radiation characteristics of these microhabitats showed that the euro avoided much of the heat load of the desert, particularly the radiation heat load. While the solar radiation influx reaching the red kangaroo resting site was only about 20% of that incident on open ground it still resulted in the radiation temperature of this microenvironment exceeding the animal's body temperature by as much as 30°C when air temperature also exceeded the body temperature. Considerable evaporative water loss would be expected under these circumstances. Radiation heat loss from the red kangaroo microenvironment to the sky, possible in the late afternoon, may be used by the animal to reduce the amount of water required for temperature regulation.
Tree‐Ring Characteristics Along a Vegetation Gradient in Northern Arizona
Authors: Fritts Harold C. , Smith David G. , Cardis John W. , Budelsky Carl A.
Published: May 2006

Tree—ring samples of Pseudotsuga menziesii (Mirb.) Franco, Pinus ponderosa Laws., and Pinus edulis Engelm. for 1860 through 1962 were obtained from sites along a vegetational gradient, ranging from forest interior sites to semiarid lower forest border sites. Samples were analyzed using a stratified nested plot design. Near the lower forest border tree rings are narrowest, the variability in the relative ring—width response from year to year is greatest, and the variance in common or the correlation between radii and between trees is highest. This variability is more highly related to climatic fluctuations than the variability in highest. This variability is more highly related to climatic fluctuations that the variability in forest interior trees and may be attributed to longer and more frequent periods during which water stress is limiting to physiological processes in the trees. Hence, at the arid forest border tree—ring chronologies contain the most consistent, but variable, growth responses and provide the best record of climatic fluctuations. The semiarid lower forest border trees exhibit a high frequency of partial growth layers. Chronologies from the forest interior exhibit very few partial growth layers. Crossdating between both types of sites and among many individuals of different species makes absolute dating not only possible but exceedingly reliable. Such tree—ring analyses may have considerable application to the evaluation of ecological forest gradients.
Growth Patterns of Some Native Annual and Perennial Herbs in Southern Wisconsin
Authors: Struik Gwendolyn J.
Published: May 2006

Temporal growth patterns and adaptive characters were studied in 17 perennial, 16 annual, and 4 biennial native herbs for one to three growing seasons in dry—mesic, mesic, and wet—mesic forest and in open barrens in southern Wisconsin. In annuals almost all dry matter produced was retained in aerial organs following the initial growth period. Below—ground weight increased rapidly in early season and then slowly increased or declined. In perennials there was a predominantly upward weight movement during growth initiation and during flowering and fruiting and a downward movement between growth initiation and flowering and preceding aboveground senescence or death. Between autumn and spring, all perennials, including wintergreens, lost weight. Most winter annuals increased in both above— and below—ground dry weight over winter, demonstrating maintenance above the compensation point. Growth patterns of biennials in their first year were similar to perennials and in their second year were similar to annuals. Forest herbs lost less water before wilting, were more succulent, wilted in a shorter time, and had heavier seeds than herbs of open habitats. The seeds of the forest annuals were heavier and germinated more readily than seeds of forest perennials. Although most annuals are pioneer, drought—resistant plants, fores annuals wilted easily and were very succulent. This suggests that stems and leaves of the annuals apparently are supported more by turgor pressure, while the perennial plants are supported more by cell wall thickening. This special dependence of annuals on water correlates with their greater numbers in wet—mesic and mesic forests compared with drier forests. Growth characteristics are discussed for eight forest annuals: Amphicarpa bracteata, Ellisia nyctelea, Floerkea proserpinacoides, Galium aparine, Impatiens pallida, Parietaria pennsylvanica, and Pilea pumila.
Necessity for Decontamination of Filters in C^{14} Measured Rates of Photosynthesis in Fresh Waters
Authors: Wetzel Robert G.
Published: May 2006

Extracellular deposition of C{14} can lead to large errors in estimates of photosynthesis in many aquatic situations where C{14} techniques are employed. Of the available pre—radioassay techniques for the removal of extracelluar deposition, exposure to fumes of concentrated HC1 for a brief period is superior. Loss of radioactivity upon treatment differs among lakes, seasonally, and between illuminated and dark samples. Exposure of desiccated filters to fumes of concentrated HCl for a 10—min period is suggested as a standard procedure prior to assays of radioactivity.
An Ancient Bristlecone Pine Stand in Eastern Nevada
Authors: Currey Donald R.
Published: May 2006

A 4,900—year—old bristlecone pine (Pinus aristata) in a stand on Nevada's Wheeler Peak, in the eastern Great Basin, is comparable in age to the oldest in California's White Mountains, at the western margin of the Basin. The current hypothesis regarding distribution of age limit in bristlecone pine must therefore be reexamined. Part of the Wheeler Peak bristlecone stand is situated on Little Ice Age features, rendering datable a sequence of Little Ice Age events.
Relative Abundance of Species and MacArthur's Model
Authors: King Charles E.
Published: May 2006

MacAthur's model was derived to predict the relative abundance of species in adequately sampled sympatric associations in which niches are contiguous and nonoverlapping, the species are comparable in size and physiology and are maintained in equilibrium so that relative abundances are constant. The model is applicable only to homogeneously diverse biotopes in which the range of the environmental mosaic is small in relation to the requirements of the inhabitant species. These factors require that the niche arrangement be the outcome of competitive exclusion. Data are presented on the adequacy of the MacArthur model in describing the relative abundance of fish, ophiuroids, gastropods, pagurid crabs, and ciliates. In addition, summaries of previously reported tests are included. By comparing groups which are adequately and inadequately described by the MacArthur model, it is possible to examine the characteristics which may establish the equilibrium. It is hypothesized that characteristics of importance are length of life cycle, duration and frequency of reproduction, and relative (to generation time) constancy of environmental conditions. It is shown that when fish or gastropod species are tested, the goodness—of—fit to the model's predictions is related to the taxonomic affinity of the group being tested. Stable associations of species with high taxonomic affinity must be highly organized. A high degree of organization is required to maintain the random distribution of abundances. Density dependent competition for food is the most likely bases of this organization.
Possible Relationships Between Plankton‐Diatom Species Numbers and Water‐Quality Estimates
Authors: Williams Louis G.
Published: May 2006

Semimonthly samples from 103 scattered stations on the major rivers and Great Lakes of the United States reveal differences in kinds and numbers of dominating planktonic organisms. Diatoms dominate at these stations. A counting of 250 to 300 individuals per sample of diatoms using special hyrax mounts gives an adequate proportional representation of the four most abundant species of the population. Samples with high representation of individuals in the four most abundant species reliably indicate low species diversity, which in most situations is an indication of enrichment or eutrophication. Samples with high standing crops (productivity) usually show low species diversity. A study of the four most abundant species of diatoms and the six most abundant genera of algae demonstrated, with few exceptiosn, that the most frequent dominants have the highest standing crops. Dominating diatom species with highest frequency and composing 50% of the total abundance of diatoms for each of 2 years were calculated for each station, and the results indicate differences among the stations for studies of enrichment. An overall "trophic index" was computed by multiplying the percentage of the total abundance by the density level for each station. There is a correlation between the trophic index value and a range of stations known to be clean to heavily enriched. Eutrophic stations generally were represented by a few species composing a large portion of the diatom population, and the density level was usually high. "Clean" stations, on the other hand, had more species composing a small portion of the total live diatom population, and the overall density level and low. A parallel study of the most frequently occurring dominant algal genera showed the same trend.
Sodium Transport by Skin of Amphibian Species from Different Habitats
Authors: Schmid William D. , Underhill James C.
Published: May 2006

Net sodium transport was measured in isolated skin preparations for five species of anuran amphibians from different habitats. Although previous reports had described differences in the rates of water uptake for anurans from differences habitats, the results of the present study have indicated a lack of significant differences in active sodium flux. The mean rate of sodium flux (all species) was 1.05 microequivalents of sodium per cm2 surface, hour.
Breeding Home Range in the Nighthawk and Other Birds: Its Evolutionary and Ecological Significance
Authors: Armstrong Joseph T.
Published: May 2006

Nighthawks, Chordeiles minor, lay their eggs on flat surfaces–in cities on flat roofs–roost in trees, and feed on flying insects which in turn presumably feed on vegetation. Thirteen neighboring nighthawk breeding home ranges in the center of Detroit, Michigan included on the average 10.4 ha total area, 97 small trees (including large shrubs), 70 large trees, and 38 flat roofs, representing 2.25 ha. More or less centrally in each home range and preferentially over flat roofs, whether being used for nesting or not, resident males performed diving and booming displays. High average and minimum distances between the centers of activity of the residents, together with observations of conflict between neighbors indicated that the home ranges were mostly defended and, since including feeding and breeding activities, constituted type A territories. Home range size which varied more than threefold, showed no significant correlation with the density of any environmental feature, including an index of photosynthesis, except for a negative correlation with number of flat roofs per ha. Six of the 13 home ranges bounded a 42 ha area unoccupied by nighthawks, which was, compared with the home ranges, deficient in trees and especially in flat roofs. These six home ranges tended to be larger than the remaining seven, though not to differ from them in density of trees and roofs, and in neither group was there correlation between size and density of these features. Thus, variation in home range size seems best explained by birds settling thickly where flat roofs are numerous, and through mutual aggressiveness having small home ranges, by birds not settling at all where flat roofs are scarce, and by home ranges next to such unoccupied areas expanding into them and/or at the expense of neighbors who must defend their entire boundaries. Although nighthawks do not always defend combined nesting and feeding areas, the apparently primary importance of aggressive interaction in determining home range size, in the present study, suggests that in nighthawks, as well as in other species having more strictly type A territories, aggressiveness at high population levels may reduce the proportion of individuals breeding and population natality rate below what resources would allow. A variety of evidence is reviewed on this point including the interspecific variation of home range size in relation to body mass which suggests that bird home ranges generally contain more food resources than required by the occupants.
Further Evidence of the Passive Dispersal of Small Aquatic Organisms via the Intestinal Tract of Birds
Authors: Proctor Vernon W. , Malone Charles R.
Published: May 2006

Viable disseminules of freshwater algae and crustaceans were recovered from feces of representatives of three orders of birds in addition to waterfowl. This indicates that dispersal of small aquatic organisms via the avian intestinal tract can occur in diverse groups of birds. Because of difference in effects upon the viability of disseminules, some birds are probably better suited as agents of dispersal than others.
Occurrence of Isoetes Echinospora in Eutrophic Lakes in Wales
Authors: Seddon Brian
Published: May 2006

Isoetes echinospora is reported in two eutrophic lakes. The water chemistry of typical sites is contrasted with one of the eutrophic sites and with Scandinavian occurrences in similar conditions. Competition is held responsible for its more usual restriction to oligotrophic waters.
Decline of Old‐Growth Redwood Forests in Relation to Some Soil Microbiological Processes
Authors: Florence R. G.
Published: May 2006

Observations on a number of old—growth coast redwood Sequoia sempervirens (D. Don) Endl. forests indicated unusual features of stand decline. To test the hypothesis that this decline resulted from some deterioration in the forest—site relationship, a series of studies was made on forest soils under old—growth redwood and at various stages of the hardwood succession following logging. Proliferation of redwood seedling roots was restricted in old—growth redwood soil and some evidence of seedling susceptibility to a root pathogen was found. Soil respiration patterns indicated that the availability of carbonaceous material from the organic matter in a form suitable for microbial digestion may be the primary factor limiting biological activity. The end results may be failure of, or abnormalities in, the process of nitrogen mineralization, and the establishment of an edaphic condition in which pathogens can attack seedling roots. Although nitrogen was found to be strongly immobilized in soils from an age sequence of tan oak developed on former redwood sites, it seems possible that tan oak litter could stimulate a higher level of microbial activity and so accelerate the decomposition of redwood humus. Deterioration in both the soil microbiological processes and the plant—soil relationship in a redwood forest are discussed in terms of the long—term incorporation of redwood litter into the soil.
Home Range and Movements of the Wood Frog in a Northern Bog
Authors: Bellis Edward D.
Published: May 2006

Wood frogs were marked by toe clipping and were recaptured in a northern Minnesota peat bog for three summers. The study area, dominated by tamaracks and calla lilies in the northern half and by spruces and alders in the southern half, measured 120 yards on each side and was divided into 100 equal quadrats. A total of 1,377 individuals was handled; many were recaptured one or more times, 2,101 captures being made altogether. Frogs captured once were transients; they were on the area but not reflushed, or they died. Most recaptured individuals appeared to remain in restricted areas, distances between successive capture sites averaging 12.3 yards with a median of 7.7 yards for adults. Long distances were few and probably represented nomadic individuals. Distances between the first and second capture sites did not differ significantly from first to third distances, nor from first to fourth distances. However, distance between capture sites was significantly correlated with time elapsed, this owing to a few far—ranging individuals. For frogs at least one year old, movement in the calla lilly—tamarack cover did not differ significantly from that in the alder—spruce zone; males did not differ significantly from females in movement; and 28 to 42 mm (body length) frogs did not differ significantly from 43 to 55 mm frogs. The mean home range size was 77.2 yards2, but it was highly variable. Young, recently metamorphosed frogs invaded the study area from upland ponds in July and August. A few showed long distances between capture sites but most appeared to settle down soon after arrival distance between captures was not correlated with time elapsed. Several frogs were recaptured the year following marking, many near the original capture site. These showed significantly greater movement than those captured in one summer only, but 50% showed overwinter distances of only 15 yards or less, and 78% showed 32 yards or less. These either remained in the area to hibernate or returned after migrating to a hibernation site off the area; probably many left the area to breed and then returned. The results are discussed in the light of earlier studies in relation to home range size, general summer movement, overwinter movement, and the effects of humidity on movement.
A Very Sensitive Electric Dendrograph for Recording Radial Changes of a Tree
Authors: Impens I. I. , Schalck J. M.
Published: May 2006

An instrument is described which measures radial changes of tree trunks, roots, or branches with an accuracy of about .0002 mm. The basic component consists of an electro—mechanical displacement transducer. Results of preliminary measurements are discussed.
Micrometeorology and Energy Exchange in Two Desert Arthropods
Authors: Hadley Neil F.
Published: May 2006

Incoming solar, net, and reflected radiation, wind velocity, relative humidity, and temperatures at various levels above and below an open desert surface were recorded simultaneously at 30—minute intervals for a 3—day period. Concurrent measurements were also made of arthropod burrow temperatures and relative humidities, scorpion body temperatures, and body and subelytral temperatures of tenebrionid beetles. The burrowing habit enabled arthropods to escape the hot, desiccating conditions recorded on the desert surface during the day. Temperatures and humidities to which scorpions were subjected while in their subterranean retreats depended upon the burrow's depth and subsequent movements in the burrow. Vertical movements between the surface and maximum burrow depths during a 24—hour period provided arthropods with a wide choice of micro— environments. Tenebrionid beetles on the surface were able to achieve a temperature equilibrium only under low temperature and radiation loads. Subelytral cavity temperatures in black Eleodes armata were generally 2—7°C warmer than body temperatures after exposure to direct sunlight. Temperature differences between subelytral cavities of black beetles and beetles with their elytra painted white were small, but suggested that a white dorsal surface was, at least, paritally effective in reducing absorption of solar radiation. The subelytral cavity, in addition to reducing transpiratory water loss, apparently provides a mechanism for increasing convective cooling, and may serve as a temperature “buffer zone” against heat conduction resulting from high intensity solar radiation. A heat exchange budget was estimated for E. armata on the desrt surface. Major contributing factors were heat gained from incoming radiation versus heat lost from convection and reradiation. Contributions from evaporation and metabolism, as determined by laboratory experiments, were very small in comparison, while the role of conduction in energy exchange was assumed to be negligible. Inherent problems in the estimation of contributing factors to net energy exchange, and comparison of similar budgets for mesic arthropods are discussed.
Chilean Bird Distribution
Authors: Cody Martin L.
Published: May 2006

The results of bird censuses from 13 Chilean habitats are presented. Any one habitat supports a slighly higher bird species diversity than structurally similar habitats in North America and Australia. The bird species turnover between habitats in the same locale, in contrast to other temperate areas, is very low–an island characteristic. Turnover between geographically distinct habitats within Chile is comparable to that between adjacent habitats in North America. Chilean birds exhibit wide habitat tolerance in narrow geographic areas, whcih is attributed to a slow development rate of this bird fauna. Character convergence, where similarities in appearance have evolved to faciliate interspecific aggression and aggregation, is a byproduct of this type of distribution.
A Rapidly Equilibrating Thermocouple Contact Thermometer for Measurement of Leaf‐Surface Temperatures
Authors: Gale J. , Manes A. , Poljakoff-Mayber Alexandra
Published: May 2006

The iron—constantan thermocouple contact thermometer here described is mounted on spring clamp and can be quickly attached to the leaf; a large number of determinations can be made in a short time. The thermocouple junction equilibrates very rapidly (1.5 sec), has a low heat capacity, and is spring loaded. The performance of the contact thermometer compares well with that of a thermocouple inserted within the leaf mesohyll and with measurements made with an infrared radiation thermometer.
A Determination of Live‐Weight Caloric Conversion Factors for Laboratory Mice
Authors: Brisbin I. Lehr
Published: May 2006

Regression equations are described which allow the calculation of the calories of energy consumed by a carnivore fed on whole laboratory mice (Mus musculus) given the individual weights of the mice eaten. The live—weight caloric density of mice weighing 4.8 g or less may be determined by the linear relationship: kcal/g live weight = 0.657 + 0.306 (g live body weight). Mice weighing more than 4.8 g may be considered to have a uniform live—weight caloric density of 2.14 ° 0.08 (SE) kcal/g. These conversion factors may be used for either frozen or freshly killed laboratory mice or laboratory raised Peromyscus polionotus. Fat indices (g fat/g lean dry weight) were not correlated with body weight. However, water indices (g water/g lean dry weight) decreased exponentially with increasing body weight. There was no change in the caloric value of the lean dry weight of the mice with increasing body weight.