bluuebunny/crossref_metadata_2025 huggingface dataset:
Changes in Internal Atmosphere of Submersed Vascular Hydrophytes in Relation to Photosynthesis
Authors: Hartman Richard T. , Brown Doris L.
Published: May 2006

Gases were extracted from the internal atmosphere of Elodea canadensis and Ceratophyllum demersum in a closed system under reduced pressure. The volume of extractable gases varied throughout the daily period. Gases separated and quantitatively measured by gas chromatography included CO2, O2, N2, and CH4. Results from diurnal studies showed a lag between peak values for dissolved oxygen in the surrounding water and oxygen in the internal atmosphere. Lags were also observed in the CO2 values. As a result photosynthetic activity by these plants is not immediately reflected by changes in dissolved oxygen content of the surrounding water. The lacunal system apparently functions as a reservoir for metabolic gases. Experiments in whcih light intensity was controlled by floating screens indicated that at low intensities evidence of oxygen production in E. canadensis may be obtained only by observing the changes which occur within the internal atmosphere. At these intensities no increase in dissolved oxygen can be detected in the surrounding water although internal oxygen concentrations may increase slightly. Confirmation that carbon was being fixed by the plants under these conditions has been obtained by carbon—14 uptake studies using gas phase counting procedures. The observations cast furthur doubt on the reliability of using changes in dissolved oxygen as a sole measure of photosynthetic activity in aquatic ecosystems where submersed vascular plants are dominant.
Effect of Population Density on the Viability and Fecundity in Nasonia Vitripennis Walker (Hymenoptera, Pteromalidae)
Authors: Walker Ilse
Published: May 2006

Viability and oviposition of the parasitic wasp Nasonia vitripennis on its host Phaenicia sericata at various parasite—host densities were analyzed. As the parasite density becomes excessive, an increasing portion of the progeny is reduced. These density—dependent reduction mechanisms are: retention of eggs if a sufficient number of hosts is not available; death and decomposition of superparasitized host pupae resulting in death of the parasite larvae; food shortage within the host leading to parasite mortality shorty before and during metamorphosis; reduced longevity and fecundity of viable female offspring from superparasitized hosts and a decreasing portion of female progeny as the parasite number on a given host supply increases. This change in sex ratio is relatively independent of the number of eggs laid per parasite female or per host pupa. It is mainly determined by the number of simultaneously ovipositing females: the more dense the ovipositing females, the less fertilized eggs they produce. Two categories of density—dependent regulation mechanisms are distinguished: behavioural and pathological mechanisms. The significance of the two categories for the existence of a theoretical population equilibrium on the one hand and for a real equilibrium on the other hand is discussed.
Mortality Statistics of Young Bats
Authors: Herreid Clyde F.
Published: May 2006

Young free—trailed bats, Tadarida brasiliensis mexicana, fall to the floor of nursey caves where they are eaten by beetles and predators. The number of young falling is correlated with the number of young in the cave and the bat's age. During the first two months of life there is a loss of 1.3% of the population. Ths mortality is lower than for the adults over a comparable period.
Factors Affecting the Distribution of Shrub Live Oak (Quercus Turbinella Greene)
Authors: Saunier R. E. , Wagle R. F.
Published: May 2006

The disjunct distribution, reproduction, and rooting habits of Quercus turbinella in the Arizona chaparral were studied on quartz diorite, sedimentary, and volcanic substrata. The oak was less dense on the sediments and volcanics that on quartz diorite. Lower densities on the bedded sediments resulted from restricted root penetration which prevented access to deep soil moisture; on the volcanic substratum heavy clay soils gave an overall poorer moisture regime than soils developed from the quartz diorite. Shrubs growing on the less favorable sedimentary and volcanic substrata probably were more susceptible to damage by drought and fire, and low mobility and low seedling production tended on eliminate the species from these areas. It is suggested that the Q. turbinella islands within large areas of grassland are relicts rather than evidence of invasion.
Nutrition of Tree Sparrows during Winter in Central Illinois
Authors: West George C.
Published: May 2006

Stomach analyses of 131 tree sparrows (Spizella arborea) were made from birds collected from November through March, 1954—1959, near Urbana in Champaign County, Illinois. Simultaneously, 119 collections of seeds from the ground and 452 collections of seeds falling into seed traps were taken and the dry weight in grams per hectare per winter and the relative proportion of different species of seeds available by weight calculated. Seedfall occurred throughout the winter, but in the majority of species 75% or more of the seedfall occurred from September through November. Once on the ground, only 40% of the seeds of most species remained in a condition usable by birds the following year. Grass seeds, primarily Setaria spp., made up 77.7% of the winter diet. However, grass seeds made up only 38.8% of the seeds available on the ground and 44.6% of the seeds falling to the ground during the winter. Tree sparrows selected seeds of low gross energy content in comparison with those seed species not selected. The heat of combustion per gram dry weight of the average stomach contents did not change significantly during the winter and averaged 4690 cal/g. The average projected existence energy requirements of wild tree sparrows during winter was found to be 27.38 kcal/bird/day or equivalent to approximately 7.88 g of seeds (of the average winter diet) per day. On this basis it is possible for individual species of seeds to support flocks of 10 to 20 tree sparrows per hectare for the winter season in central Illinois.
Dynamics of Popualations. II. Factors Controlling Population Growth and Population Size in Drosophilia Pseudoobscura and in Drosophila Melanogaster
Authors: Ayala Francisco Jose
Published: May 2006

Four populations of Drosophila pseudoobscura and four of D. melanogaster were studied for the influence of certain environmental factors on the productivity and size of the populations. For each species a 2 x 2 factorial design was used, the variables being temperature (25°C and 19°C) and amount of food (2 and 3 food unites per week). A serial transfer technique was used to maintain the populations. In both species the main factor determining the productivity of the populations is the amount of food; the main factor limiting the population size is their living space. At 19°C the productivity and the size of the populations of D. pseudoobscura is considerably larger than at 25°C, which is a suboptimal temperature for this species. The D. melanogaster populations produce at 25°C more but smaller flies than at 19°C with no significant effect on the biomass produced. At 19°C the average size of the populations of D. melanogaster is slightly larger than at 25°C due to an increased average longevity. In both species, the number of food units given to the populations per unit time does not have a significant effect on the productivity per food unit. The populations receiving three food units per week produce, therefore, approximately 50% more flies than those given two food units per week. The average size of the former populations is, however, only moderately larger, space being considered the limiting factor. The chromosomal polymorphism initially present in the populations of D. pseudoobscura was maintained, indicating that heterozygotes had a higher fitness than the corresponding homozygotes. The average productivity and the average size of the populations of D. melanogaster are considerably greater than those of D. pseudoobscura. The complexity of the factors affecting the carrying capacity of a population is pointed out in the discussion.
Seals and Group Selection
Authors: McLaren Ian A.
Published: May 2006

Seals have been shown to restrict recruitment in crowded populations because of gregarious and hierarchical behavior. Some authors have suggested that such behavior has evolved through group selection to prevent overutilization of resources. Published data are reviewed to show that more highly social seals have higher potential rates of increase. This is difficult to reconcile with group selection, but easily explained in ordinary evolutionary terms. Females of social breeders have little choice of breeding sites, exercise little intelligence, and mature rapidly. Solitary breeders benefit from accumulated knowledged of the environment, produce young more successfully when older, and therefore mature slowly. Species with lowest potential rates of increase breed biennially at most, because they give their young extended periods of parental care. Deferred maturity, fatal crushing of newborn young, and other restrictions of recruitment in crowded populations of polygynous species can be explained as excesses of sexual selection. There is no necessity for postulating group selection in the evolution of seals.
Color Stereophotography for the Measurement of Vegetation
Authors: Wimbush D. J. , Barrow M. D. , Costin A. B.
Published: May 2006

The field equipment needed for a stereophographic method of measurement of vegetation consists of a camera mounted on a rectangular frame on four legs, from which a stereo pair of photographs of the ground or vegetation surface can be taekn. For color transparencies the stereo pair of images is projected upwards through two specially mounted projectors and prisms onto tracing paper on a glass table, from which the images are examined stereoscopically. Vegetation boundaries and other features are marked on the tracing paper, and the respective areas subsequently measured visually by superimposing a transparent plastic 100—compartment grid.
Seed Populations in Some Natural Australian Topsoils
Authors: Barbour M. G. , Lange R. T.
Published: May 2006

The numbers and types of seeds in topsoils of several South Australian vegetation types were tabulated by microscopic examination of soil samples. Isolation of organic matter by flotation on a dense solution followed by examination under 8x power gave excellent recovery of all seeds present, even of those as small as 1 mm. Relatively small sample volumes (50 cm3) appear sufficient to yield high frequencies for many seeds. On the other hand, seed frequencies of many of the dominant species were very low, even with much larger sample volumes.
A Pressure‐Infiltration Method for Estimating Stomatal opening in Conifers
Authors: Fry Kenneth E. , Walker Richard B.
Published: May 2006

A method is presented for estimating large and small changes of stomatal aperture in conifer needles by means of partial infiltration of alcoholic fluids under pressure. Needles are placed in a small, widowed chamber and are observed while the pressure is increased. Minute reflections of light which emanate from the stomata indicate the specific pressure at which infiltration begins. In theory this characteristic infiltration pressure is primarily a function of the stomatal pore size. In excised needles of Douglas fir (Pseudotsuga menziesii) infiltration pressures were highly correlated with transpiration rates. A basic formula is given for estimating stomatal widths from the infiltration pressure.
Differences in Insect Abundance and Diversity Between Wetter and Drier Sites During a Tropical Dry Season
Authors: Janzen Daniel H. , Schoener Thomas W.
Published: May 2006

During the dry season in Costa Rica, sweep samples were taken of forest understory insects in three adjacent habitats of increasing moistness (Guanacaste Province: Areas I through III) and in another habitat under a much wetter precipitation regime (Limon Province; Area IV). These samples were then compared with respect to numbers of individuals, numbers of species, size frequencies, weight, developmental stages, species diversity, trophic levels, taxonomic composition and species exclusiveness. The absolute numbers of species increased from Areas I through IV; the numbers of individuals, frequency of small insects, dry weight, individuals per species and percent parasitic species increased from Areas I through III. The several indices of species diversity calculated for the samples only show partial agreement in relative values and trends. The data clearly demonstrate that adjacent tropical communities can have greatly different insect components. The possible effects of the differences between the insect communities of Areas I to III on vertebrate predators and plants are discussed. When compared with temperate data on insect communities there are indications that the four tropical communities examined have a much greater number of species and possibly a greater internal uniqueness than similar temperature communities.
Sizes of Feeding Territories among Birds
Authors: Schoener Thomas W.
Published: May 2006

This analysis deals with size variations in the breeding territories of land birds which obtain most or all of their food on the territory. For the species studied as a whole, territory size shows a strong positive relationship to body weight. Predators tend to have larger territories than omnivores or herbivores of the same weight, presumably due to the relatively denser food of the latter species. The home ranges of raptors inhabiting two areas were found to be significantly correlated with an index of the numerical density of their prey and in one area with raptor weight. Higher clutch size is not significantly associated with larger territories in any category of birds tested. The number of individuals defending the territory and the number feeding the young are probably not correlated with territory size. The exponential relationships between body weight of the consumer and three dependent variables–food biomass consumed per unit time, average prey weight and territory or home range size–are used to derive three predictions: a) Heavier predators take fewer individuals per unit time than lighter species; b) If certain restrictions are satisfied, the collective biomasses in a given large area increase as individual biomasses become larger for omnivorous species and decrease as individual biomasses increase for predators; c) For predators, the density of acceptable and accessible food in biomass per unit area decreases as the weight of the consumer increases. Territory or home range size increases more rapidly with body weight for predators than for omnivores or herbivores. This relationship holds true for both birds and mammals and presumably reflects a rapidly decreasing food density for predators of increasing weight. Since smaller predators do not feed over a wider range of food size than larger species, and since there are less species or individuals feeding on large food than on small, the predators of the areas studied probably consume food whose distribution of biomass with food size is declining. The habit of feeding on exclusive areas is considerably more widespread among predators than among omnivores and herbivores. The smaller spatial needs for omnivorous and herbivorous birds of a given biomass and perhaps the greater patchiness of their food when compared to predators are used to explain the higher occurrence of gregarious nesting in the former group. Implications of this study for the functions of feeding territories maintained during the breeding season are discussed.
Modification of the Wiegert‐Evans Method for Estimation of Net Primary Production
Authors: Lomnicki Adam , Bandola Ewa , Jankowska Krystyna
Published: May 2006

The assumptions on which the Wiegert—Evans (1964) paired plots" estimation method of net primary production are based are discussed. An approach is proposed which does not involve the estimation of the disappearance rate of dead plant material and the standing crop of dead vegetation and which uses only measurements of growth of green plant material and of dead plant materials. The Wiegert—Evans method and the modification were compared on a grassland community in Poland. There were no significant differences in the results, but the modified method proved simpler to use.
The Role of Penitella Penita (Conrad 1837) (Family Pholadidae) as Eroders Along the Pacific Coast of North America
Authors: Evans John W.
Published: May 2006

The rock—boring clam Penitella penita is an important agent of erosion in certain localities on the Pacific coast of North America. Erosive factors are separated on the basis of whether they are physical or biological. In the area studied physical factors alone remove the surface rock at the relatively slow rate of 0.5 mm per year. In rock heavily infested by P. penita the erosion rate was estimate to be in the neighborhood of 12 mm per year.
Summer Bottom Fauna of the Mississippi River, above Dam 19, Keokuk, Iowa
Authors: Carlson Clarence A.
Published: May 2006

Over 1400 benthos collections were made from eight sampling areas near the Illinois shore of the Mississippi River above Dam 19 in the summer's of 1960 and 1961. No significant different was found in numbers of macroscopic organisms collected after sifting Ekman dredge contents through 20— and 40—mesh screens. Sphaerium transversum was the most abundant organism and was the only organism collected at every sampling plot on each collection date. Hexagenia naiads were the most abundant insects at all sampling areas in 1960. Coelotanypus, Tendipes plumosus, Stenochironomus, oligochaetes, Campeloma, and Lioplax subcarinata were also abundant and frequently collected. Somatogyrus depressus and Oecetis sp. b were abundant during certain time intervals. Tendipes plumosus became the most abundant insect in 1961 at the part of the study area nearest Dam 19. Several organisms were more abundant in 1961, when mayfly population densities were low, than in 1960. As the most abundant insects emerged during each summer, other elements of the benthos increased in abundance. An average of 2,924 organisms/m2 was collected in the study area. Major elements of the benthos seem to have changed little in the last 30 years. The study area had a climax community characteristic of mature streams and showed no evidence of serious pollution.
Systems Analysis and Ecology
Authors: Dale M. B.
Published: May 2006

Systems analysis is defined as the use of scientific method with conscious regard for the complexity of the object of study. It has strong relationships with problem solving, in that the same four phases–lexical, parsing, modelling, and analysis–are identifiable in both. Examination of each of these phases reveals some of the problems involved in the use of systems methods in ecology. A model of a precipitation—evaporation system is presented as an example. Problems in experimenting with models of systems and with control, optimization, and comparison of such models are considered.
Microtus Population Biology: Behavioral Changes Associated with the Population Cycle in M. Ochrogaster and M. Pennsylvanicus
Authors: Krebs Charles J.
Published: May 2006

If aggressive behavior regulates population size in small rodents (as claimed by Chitty 1967), periodic fluctuations must be associated with behavioral changes. In an attempt to test this hypothesis, exploratory activity and aggressive behavior were measured in 645 male Microtus ochrogaster and 570 M. pennsylvanicus of 7 populations in southern Indiana from August 1965 to September 1967. Exploratory activity was measured in an open—field test under daylight conditions, and aggressive behavior was measured by fighting voles in pairs in a neutral fighting arena. Exploratory activity could not be related to the individual attributes of home range size or duration of life in males of either Microtus species. On the population level, mean exploratory activity could predict the mean rate of population growth in M. ochrogaster populations, but not in M. pennsylvanicus populations. Aggressive behavior changed significantly over the population cycle in both species, and males from peak populations were most aggressive. Multiple discriminant analysis was used to characterize the behavior patterns of males from increasing, peak, and declining populations. These discriminant scores predicted the mean rate of population growth in M. pennsylvanicus populations but not in M. ochrogaster populations. Aggressive behavior types characteristic of increase, peak, and decline phases showed differential survival rates, but no association was found with body weight or transferrin genotype in either species. Home range size was related to aggressive behavior type in M. ochrogaster but not in M. pennsylvanicus. These data on two species of Microtus do not refute the hypothesis that aggressive behavior may act to regulate population size. However, there is no information on what causes these behavioral changes, and the next step is to see if these changes occur in other populations of these two species and to determine whether they are genotypic or phenotypic.
Eruption of Ungulate Populations, with Emphasis on Himalayan Thar in New Zealand
Authors: Caughley Graeme
Published: May 2006

An eruptive fluctuation is defined operationally as an increase in numbers over at least two generations, followed by a marked decline. Reported eruptions in ungulates suggest that the upswing is initiated by a change in food or habitat and is terminated by overgrazing. An apparent exception–the Kaibab eruption–probably also fits this pattern. The interpretation causally linking reduction of predators on the plateau with increase of deer is an overstatement of evidence. Eruption of established populations is essentially the same process as the buildup of populations initiated by liberation, with the difference that in the second case a zone of high density migrates radially from the point of liberation. Eruption of thar (a goat—like bovid) after liberation in New Zealand was studied by sampling populations at different distances from the point of liberation. The aim was to determine trend of demographic statistics across an eruptive fluctuation that spans 50 years. Although fecundity varied across the eruption, the major influence on rate of increase was traced to variation in death rate. The major component of this variation was the rate of mortality over the first year of life. Trend in death rate, and hence in rate of increase, was associated with trends in other population statistics that are easier to measure. The most useful correlative of rate of increase is probably the level of fat reserves. While we do not know whether trends in population statistics of thar reflect those of other ungulates during an eruptive fluctuation, the generality of the reported trends may usefully serve as a testable hypothesis.
Seed Germination in Iva Annua L.
Authors: Ungar Irwin A. , Hogan William C.
Published: May 2006

Optimum germination of Iva annua seeds occur at 15° C. Temperature and salinity interact in their effect on germination. Increases in osmotic concentration of media cause a gradual decrease in germination percentages at optimal temperatures. Sodium chloride, the most common salt in saline areas occupied by I. annua, has an osmotic rather than a toxic effect on germination.
Regression Models Relating Soil Nutrients and Growth of Eucalyptus Gummifera and Eucalyptus Maculata Seedlings
Authors: McColl J. G.
Published: May 2006

Growth of Eucalyptus gummifera and E. maculata seedlings is statistically correlated with the concentrations of a number of soil nutrients. Step—wise multiple linear regression models of seedling growth are presented with soil nitrogen, phosphorus, calcium, and aluminum as independent variables. Regression models with soil calcium and phosphorus as independent variables give the best estimates of seedling growth.
The Transformation of Energy by a Stream Detritivore, Pteronarcys Scotti (Plecoptera)
Authors: McDiffett Wayne F.
Published: May 2006

The bioenergetics of a detritus—feeding stonefly Pteronarcys scotti, were invetigated. The nymphs were collected from a north Georgia trout stream and held under simulated field conditions of temperature and photoperiod in a laboratory stream. Rates of respiration and egestion were measured at temperatures approximating those in the field at the time of collection. An estimate of the growth rate of nymphs was made from a statistical analysis of monthly field samples. Calorimetric determinations were made of nymphs, molted exoskeletons, and feces. A 17—month energy budget for the average nymph was tabulated on the basis of the data collected. Assimilation and growth efficiencies were found to be low with mean values of 10.6%, 34.2%, and 3.6% for assimilation and net and gross growth efficiencies, respectively. An assessment was made of the rate of leaf breakdown by the nymphs, and a value of approximately 29.1% of the dry body weight per day was calculated. The functional importance of the organism to the stream community is discussed.
Some Developmental Consequences of Handling, Egg‐eating, and Population Density for Flour Beetle Larvae
Authors: Mertz David B. , Robertson J. Roy
Published: May 2006

Unhandled larvae of Tribolium castaneum (genetic strain cIV—a) were reared in a whole—wheat flour medium (Fortified with dried powdered brewer's yeast, 5% by weight) in a climate of 29°C and 70% RH at three levels of crowding: 100, 200, and 400 per 8 g of flour. At all three densities the median time for pupation was about 18.15 days. Mortality of the developing stages was 3—4% at the 2 lowest densities and about 8% for 400 larvae. Larvae which were subjected to daily handling and reared at the same densities developed more slowly, the prolongation of the larval stage being greatest at density 400. Handling also induced increased mortality at this density but not at lower densities. Handled larvae which were fed eggs of their own kind grew more rapidly than those not fed eggs, and, at the highest egg—feeding rates, the effects of handling and density were almost completely compensated. Evidence is presented that egg—eating would also accelerate the development of unhandled larvae. This is one of the most convincing demonstrations of a nutritional gain on the part of Tribolium cannibals as opposed to noncannibals. We suggest that cannibalism, which is capable of regulating Tribolium populations, is a form of social parasitism which may be favored by natural selection.
Slow Accumulation and Transfer and Radiostrontium by Young Loblolly Pines (pinus Taeda L.)
Authors: Dayton Bruce R.
Published: May 2006

Stems of seven young loblolly pines on the Savannah River Plant Reservation, South Carolina, were each inoculated with 3.28 x 103 μCi of radiostrontium. Accumulation of radiostrontium in foliage continued for 13 months after inoculation, when a maximum of 1.27 x 103 μCi/tree was attained. Radiostrontium concentration was consistently higher in lower crown foliage than in upper crown foliage, and higher in second—year needles than new needles. There was little evidence of basipetal translocation of radiostontium to roots. About 2% of the maximum foliage burden of radiostrontium was released by leaching during the 16 months following inoculation. Radioactivity of rainwater falling through crowns was best correlated with needle radioactivity, but was also inversely correlated with intensity of precipitation. Transfer of leached radiostrontium to the ground by rainwater flowing down stems was only 23% of that transferred by rainwater falling through tree crowns. Twenty per cent of the maximum foliar uptake was released by needles falling from the trees. The inoculated pines accumulated three times more radiostrontium in foliage than they released by needle fall and leaching. After 16 months 94% of the radiostrontium released from the inoculated trees was in litter and only 4.6% in mineral soil. Radiostrontium transferred to soil was generally confined to the top 2.5 cm where feeder roots are most abundant, but less than 10% of the radionuclide accumulated in soil was in roots. Accumulation in soil and roots closely approximated input from needle fall and foliar leaching, indicating that there was negligible input of basipetally translocated radiostrontium and negligible output due to leaching to subsoil, runoff, blowing away of litter, or recycling. The radiostrontium burden of a pine forest might be reduced considerably by removal of litter after contaminated needles have fallen.
Resource Partitioning in Species of the Water Mite Genus Eylais
Authors: Lanciani Carmine A.
Published: May 2006

Resource partitioning was studied in 20 species of the water mite genus Eylais, the larvae of which parasitize adult Coleoptera and Hemiptera living in shallow ponds. Co—existence of sympatric species is possible because the mites exploit host resources in different ways. Most commonly they parasitize different species, but when hosts are identical, the mites remain segregated by differences in the precise site of attachment, biotope, or season of parasitism. Mite biology, host dispersal, and competition for attachment sites from other water mite species may restrict further subdivision of host resources.
Soil Microarthropod Abundance Following Old‐Field Litter Manipulation
Authors: Gill Robert W.
Published: May 2006

A field experiment was set up in an old field in Michigan in spring and summer 1964, to test whether or not litter determines the abundance of soil microarthropods. Treatments were established to distinguished the importance of litter as a nutritional substance from its importance as a moderator of the microclimate or as a refuge for prey organisms. Treatments were: 1) no litter; 2) high litter; and 3) natural litter replaced with dacron polyester fiberfill, a nondecomposing insulative substance. The first fall the abundance and distribution of microarthropods in the dacron treatment were most similar to that in the high—litter treatment, whereas with respect to the amount of decomposable litter present, the dacron treatment was identical to that in the no—litter treatment. At this time the physical factors in the environment were more favorable in the high—litter and dacron treatments than in the no—litter treatment. The following spring, differences in physical factors among treatments were minimal, and there were no detectable effects of treatment on abundance of microarthropods. The following summer there were significant effects of treatment on physical factors, and the dacron treatment was again most similar to the high—litter treatment with respect to the abundance and distribution of microarthropods. The results demonstrated that physical factors in the environment were of major importance in determining the vertical distribution and abundance of soil microarthropods. Evidently, these organisms were not limited by the nutritional properties of the litter, at least over the 14—month period of the study.
Fire and Litter Effects in Undisturbed Bluestem Prairie in Kansas
Authors: Hulbert Lloyd C.
Published: May 2006

Two— by two—meter plots of undisturbed, nearly pure Andropogon gerardi prairie were subjected to four treatments: burning, clipping and removal of the litter, burning the clipped litter and returning the ash, and the control (natural litter). Treatments were started in early April before growth began. Differences in results among the denuded plots were small and nonsignificant, but highly significant differences were found between denuded and control plots. Tiller number was increased 1.5 to 2.7 times by removal of litter. Growth began earlier in denuded than control plots. On May 31 yields were twice as great in denuded as in control plots. On September 1 ovendry yields were about 340 g/m2 in denuded and 180 in control plots. Soil temperatures were 1°/5°C higher in denuded than control plots the entire growing season, the differences lessening as the season progressed. Soil moisture was appreciably higher in control plots the entire season. The short—term effects of spring burning in undisturbed bluestem prairie with clay—loam soils are apparently related primarily to litter removal rather than to nutrient changes.
Intra‐ vs. Interspecific Aggression in Pygmy Nuthatch Flocks
Authors: Bock Carl E.
Published: May 2006

Pygmy Nuthatches, White—breasted Nuthatches, and Mountain Chickadees travel in mixed flocks in winter in Colorado. The species exhibited different by overlapping foraging niches. Both intra— and interspecific aggression occurred, supporting the idea of niche overlap. The ratio of intra— to interspecific encounters was higher than expected if encounters were in proportion to flock composition, indicating that niche overlap was not complete. At artificial feeding stations, where found niches were identical for all species, the level of interspecific aggression initially was higher than in nature. However, the dominance of Pygmy Nuthatches at the feeders soon resulted in a "competitive exclusion" of the other birds and a lessening of interspecific contact.
Cycles of Temperature and Carbon Dioxide Evolution From Litter and Soil
Authors: Witkamp Martin
Published: May 2006

Periodic measurement of CO2 evolution from various biotopes reveals a daily cycle in soil respiration with a predawn minimum and an afternoon maximum that parallels the daily temperature cycle. A second maximum occasionally occurs between midnight and dawn when soil temperatures exceed temperature of the surface air. This predawn flush may result from thermal convection of CO2—rich subsurface air to the surface. The time of measurement must be considered for comparisons of rates of CO2 evolution from different sites, and measurements should be made over a 24—hr period for estimates of daily CO2 evolution.
Observations on Deepwater Plants in Lake Tahoe, California and Nevada
Authors: Frantz Ted C. , Cordone Almo J.
Published: May 2006

Deepwater macroscopic hydrophytes in Lake Tahoe were found to a depth of 500 ft. They consist of algae, mosses and liverworts. Most were concentrated at depths from 200 to 350 ft. Only Chara occassionally invaded areas as shallow as 20 ft. Other deepwater hydrophytes were restricted to depths below 50 ft.
Population Growth in Micro‐Organisms Limited by Food Supply
Authors: Caperon John
Published: May 2006

It is suggested that an hyperbolic equation of the form (1/n) (dn/dt) = rb/(b + A) where n is the population density, b the concentration of limiting food supply and A and r are constants, is widely applicable as a density—dependent growth model. An attempt is madse to state explicitly the conditions under which it would apply. A consideration of the kinetics of food uptake leads to the interpretation of the constant A as representing a ratio of two rate constants, k3/k1 where k1 is the rate constant associated with first step in food uptake and k3 is associated with the second step which results in the freeing of the adsorption site. The constant r represents a composite expression, k3co/(qn) where co/n is the number of adsorption sites per individual, and q is the amount of food required to produce a new individual. Density dependent population growth models must always include a second equation which describes the effect of population growth on the environment (in this case food supply). The failure of the logistic equation to provide the necessary generality for this effect is pointed out. The applicability of this model for a number of different bacterial populations using a variety of both energetic and substantive food as the growth—limiting factor has been established for several years. Data are presented to show that it is also applicable to the unicellular alga, Isochrysis galbana, growing under limiting nitrate concentration and to several species of phytoplankton growing under limiting light intensity. The quantitative effects of preconditioning light intensity on chlorophyll per cell (co/n) and on k3 are noted as examples of the usefulness of this more detailed consideration of the growth constants, r and A.
Gradient Analysis: The Use of Species and Synthetic Indices
Authors: Goff F. Glenn , Cottam Grant
Published: May 2006

Gradient analysis by means of species indices and stand synthetic values provides a very fruitful approach to ecological investigation. Bivariate analysis of unweighted and variously weighted stand averages shows that there is little practical difference between the results obtained at the gradient level using tree species frequency, density, basal area, and various combinations of these measures. Although they are highly significantly correlated, there is considerable variation between weighted stand values and the unweighted stand means. Several alternative methods of deriving species sociologic indices are demonstrated to give very similar species indices along the primary sociological dimension in southern Wisconsin upland forests. An iterative technique for maximizing the information content of sociologic dimensions is suggested.
Starling Roost Dispersal and a Hypothetical Mechanism Regulating Rhthmical Animal Movement to and from Dispersal Centers
Authors: Hamilton William J. , Gilbert William M. , Heppner Frank H. , Planck Roy J.
Published: May 2006

A hypothetical mechanism is proposed that may regulate the dispersal pattern of animals aggregating at cores and dispersing from them into the surrounding terrain to forage. This hypothesis is that the number of individuals per unit of area in the space foraged by individuals using the same dispersal center declines with distance from the core, relaxing intraspecific competition for available resources, thereby compensating individuals that have ranged farther afield for the increased energy expenditure and time required to reach these more distant ranges. The compensation is the increased availability of resources due to reduced resource exploitation rates. The balance of advantages and disadvantages may be accomplished by comparison, each individual comparing and modifying alternative courses of action available to it. Since all individuals will be using essentially the same criteria for comparison, the result will be equivalent strategies for all individuals in terms of energy gain and loss. These hypotheses are applied to a California winter starling roost. In winter, California starlings aggregate in large numbers at roosts from which they disperse into the surrounding countryside to forage. Some individuals travel up to 50 miles daily to reach their feeding grounds. Other individuals disperse much shorter distances from the same roost. Strategies represented by 10, 20, 30, 40, 50 and 60 mile dispersal from the roost with respect to intraspecific competition, time available for foraging, and relative amounts of energy expended in various activities are compared. Only intraspecific competition promotes more distant dispersal from the roost. Measurements of starling densities at various ranges from the roost following morning dispersal show that the number of birds per unit of area declines steadily with distance from the roost. From these data it is assumed that competition is reduced at more distant ranges. Time and energy factors become less favorable at greater distances from the roost. Competition, both intraspecific and interspecific, promotes more distant dispersal from the roost. If the relative values for the components evaluated are assumed to be correct and the further assumption is made that the starlings are comparing alternatives and selecting optimum strategies, it follows that those strategies used by dispersing starlings will be equivalent to one another. It is thus possible to determine the relative weighting of the several strategy components and thus to measure variables such as time and competition in terms of calories.
Evidence that Drift of Stream Benthos is Density Related
Authors: Dimond John B.
Published: May 2006

The abundance of bottom fauna and of fauna in drift was studied in streams treated with DDT at various times in the past. Recovery of the bottom fauna was found to be rapid, but that of drift was delayed. The relationship of quantity of drift to the increasing bottom standing crop during recovery from spray effects was found to be curvilinear. This suggested that drift is a density—related process. Possible mechanisms to explain drift are discussed, and the conclusions of earlier reports on recovery of streams following insecticidal treatment are questioned.
Leopard Seal Predation of Adelie Penguins
Authors: Penney R. L. , Lowry George
Published: May 2006

Systematic observations on a beach at the Cape Crozier, Antarctica Adelie Penguin (Pygoscelis adeliae) rookery provided data on the effects and form of Leopard Seal (Hydruga leptonyx) predation on adult and young penguins. Active predation, involving up to four seals, was observed during 56% of the time with average kill rates of 0.61 birds/hr. Predation rates increased with the height of incomingwaves and also when landing penguins were encumbered by floating ice on the behcn. Time of day was not found to influence predation rates. When young penguins began their exodus from the rookery in Jan. seals no longer preyed on adults. Seasonal depredation from Leopard Seals on the Cape Crozier beaches approximates 5% of the breeding population. The predators are thought to be utilizing a temporary, but abundant food resource.
Root Parasitism of Castilleja Coccinea
Authors: Malcolm William M.
Published: May 2006

The showy Indian paint—brush, Castilleja coccinea (L.) Spreng., is photosynthetic, but its roots produce haustoria that penetrate the roots of plants growing near it. It interacts with those plants as a parasite; unless it penetrates them, it does not mature beyond the seedling stage, and once it does it significantly lowers their dry weight. Phosphate, sulfate, and fructose are known to move across the haustoria rapidly, but what the plant actually uses from its hosts is not known. Artificial feeding of common vitamins, phytohormones, and respiratory substrates does not take the place of a host. C. coccinea will attack plants of many vascular species, including several that do not occur in its range.
Decomposition of Leaf Litter in Relation to Environment, Microflora, and Microbial Respiration
Authors: Witkamp Martin
Published: May 2006

Bacterial and fungal counts, mycelial growth, microbial evolution of Co2, and substrate moisture and temperature in bags with litter of either mulberry, redbud, white oak, loblolly pine, or beech were measured biweekly over the period November 1960—November 1961 in oak, pine, and maple stands at Oak Ridge, Tennessee. Serial dilution plate method and closed—box technique were effective for measuring microbial densities and microbial respiration respectively. Microbial densities, microbial respiration, and annual weight losses of species declined in the order mulberry, redbud, white oak, pine, beech, ad were significantly positively correlated. Stand effects were not significant possibly due to partial exclusion of stand effects in the bags. Microbial densities and moisture conditions of the various leaf species converged with time and their short—term fluctuations decreased indicating homogenation of substrate and stabilization of microbial populations. Microbial respiration was controlled in decreasing order by temperature (T), bacterial density (B), moisture (M/D), and the number of weeks (W) since leaf drop. An effective model for prediction of microbial respiration (C) is C = 46.5 + 3.2T + 26.9 M/D + 11.4 log B — 0.6W. Mean CO2 production was 0.17 liters/g substrate decomposed. Production was higher for rapidly decomposing leaf species dominated by relatively inefficient bacterial flora than for slowly decaying litter with predominantly more efficient fungi. Loss of weight and respiration were highly correlated with a microbial population estimate, combining bacterial and fungal counts.
Comparative Drought Resistance of Five Conifers and Foliage Moisture Content as a Viability Index
Authors: Pharis Richard P.
Published: May 2006

Whole plant lethal points of foliage moisture content (FMC) for ponderosa pine, sugar pine, Douglas—fir, grand fir, and incense—cedar were established from foliage tissue of various ages. Exact lethal level depended upon the age of the tissue, but there was a general plateau between the ages 6 and 13 months for sugar pine and Douglas—fir and 3 and 13 months for incense—cedar. Whole plant relative turgidity (RT) lethal points were set for the pines and firs using 13—month—old needles. Dry—weight loss upon soaking the needles was found to increase with the severity of the drought, especially for the firs. Soil moisture content (SMC) lethal points were established for all five species on builders' sand (death began at an SMC probably equivalent to tension above 24 atm) and on pumice soil (death points equivalent to tensions from 15 to 19 atm). Foliage moisture content declined with decreasing soil moisture stress in a straight—line relationship; FMC may be used as an index of soil moisture stress within a rather narrow range of SMC and may also be calibrated with leaf tissue diffusion pressure deficits developing under soil moisture stress to give an index of the water balance of the plant. Based on the SMC at the death point and also upon some species' ability to outlive other under competitive conditions, ponderosa pine, incense—cedar, and Douglas—fir were the most drought resistant, sugar pine the least, and grand fir intermediate. Ways are suggested in which the mixed—conifer forests could become established and retain their mixed composition through maturity. The findings suggest that if planting is used to regenerate clearcuts, ponderosa pine and incense—cedar would be first choice, but that sugar pine would also be a preferred species if seeding is used.
Macroflora, Mycoflora, and Soil Relationships in a Pine Plantation
Authors: Witkamp Martin
Published: May 2006

Species distribution of the ground cover of a Scots pine stand along the slope of a fixed inland dune closely reflected micro—relief and profile of the soil. Depth of a fine sand deck on coarse sand varied from 0 cm at the bottom to 150 cm at the top of the dune. Corresponding water—holding capacity (WHC) to a depth of 150 cm varied from 459 to 284 liters/m2. Tree height was significantly correlated with WHC. Dependance of litter and humus formation on primary production, and of mycelium growth on litter and humus resulted in significant correlation of these factors and moisture. Mycelium length was significantly correlated with fungal plate counts in January. The annual cycle of mycelium length did not show a peak in autumn as was found in broad leaft forest, presumably a result of differences in nutrient release from the litter. Of the organic mass to a depth of 1 m trees contributed 13%—34%, ground cover + litter + humus 49%—66%, soil organic matter 16%—22%, and fungal mycelium in soil 0.6%—0.9%. Reasons for the low fungal mass may be its ephemeral character, low influx of organic matter into the soil, and presence of much mycelium which was not measured on top of the soil.