bluuebunny/crossref_metadata_2025 huggingface dataset:
History and Fire Rocord of a Timberland Brush Field in the Sierra Nevada of California
Authors: Wilken Gene C.
Published: May 2006

Evidence from surveyor's notes, news articles, and fire records indicates that a timberland brush field site in the California mountains is well suited to timber but has been occupied by brush for at least a hundred years. The high fire factor in the area favors brush at the expense of tree growth. With a combination of highly inflammable brush and frequent fire starts it seems unlikely that this brush field will remain free of fire for sufficient time to permit natural forest regeneration.
Differential Predation on Cocoons of Hyalophora Cecropia (Lepidoptera: Saturniidae) Spun on Shrubs and Trees
Authors: Waldbauer G. P. , Sternburg J. G.
Published: May 2006

The cocoons of Hyalophora cecropia (L.) were found at various heights on the branches of trees or close to the ground on the stems of shurbs in urban environments in Champaign and Urbana, Illinois. Over 81% of the pupae in cocoons on shrubs survived the winter to emerge as adults. Less than 4% of the pupae in cocoons on trees survived, over 86% having been killed by birds, almost certainly woodpeckers. Cocoons on trees are exposed while those on shrubs are usually well hidden. We suggest that the differential destruction of pupae on trees may be a recent phenomenon caused by characteristics of the urban environment, and that it would be reasonable to look for a rapid selection against spinning on trees.
Tropical Savanna Vegetation of the Llanos of Colombia
Authors: Blydenstein John
Published: May 2006

The Llanos Orientales of Colombia are between 3° and 7° lat N, extending as a level plain between 600 and 200 m above sea level, east of the Andes Mountains. The hot tropical climate shows a seasonal pattern of rainfall, divided between one rainy season and one dry season. In the survey of a 45,000—square—mile study area within this llanos region, 10 savanna types were recognized and classified on a floristic basis. Three of these types were floristically distinct, but with the homologous factor of all having relict forests. The other seven savanna types intergraded along a gradient of increasing humidity, and for convenience were divided into dry, humid, and inundable savannas. A great number of species were shared by these last seven types, their distinction being based on the relative dominance of species in the different types. The various theories on the origins of tropical savanna are discussed in the light of this new information on vegetation and that found in a concurrent soil survey. No single factor is believed responsible for savanna formation, but deflection from forest development is considered the result of several adverse factors, with savanna formation accelerated once the process has started.
Fire, Vegetation Structure, and the Ant X Acacia Interaction in Central America
Authors: Janzen Daniel H.
Published: May 2006

The effect of fire on swollen—thorn acacias and their tenant obligate acacia—ants in the Central American dry lowlands is discussed. Fires may either consume the entire acacia shoot and ant colony, scorch and kill the acacia but not the ants, or kill neither acacia nor ant colony. Which alternative occurs depends on the structure of the immediately surrounding vegetation which in turn depends on how much of it has been killed by the ant colony and how fast the acacia has grown. The survival of the acacia population in frequently burned areas is almost entirely dependent upon some ant colonies surviving the fire to occupy the new sucker shoots from acacia stumps. The effect of these fires on the evolution of the interaction between the ant and the acacia is discussed.
Foraging Relationships of Brown‐Headed Nuthatches and Pine Warblers
Authors: Morse Douglass H.
Published: May 2006

Foraging behavior and interactions between Brown—headed Nuthatches (Sitta pusilla) and Pine Warblers (Dendroica pinus) were studied in longleaf pine lands of Louisiana during the fall and winter of 1963—64 and 1964—65. Both species frequently were members of flocks that formed around Carolina Chickadees (Parus carolinensis) and Tufted Titmice (P. bicolor). Most contact between the former two species occurred in these flocks. While in flocks, Brown—headed Nuthatches foraged most heavily on the distal parts of limbs and on twigs, Pine Warblers on proximal parts of limbs. When alone, Brown—headed Nuthatches foraged more heavily on trunks and proximal parts of limbs than they did when Pine Warblers. When pine seeds were abundant, Brown—headed Nuthatches fed upon them heavily and regularly ventured to large limbs and trunks to crack seeds, causing increased hostilities with Pine Warblers. Attempts to crack seeds where bark was not sufficiently rough to permit adequate anchoring met with little success. Pine Warblers fed upon pine seeds much less frequently than did Brown—headed Nuthatches. During the height of seed abundance, Brown—headed Nuthatches lingered behind mixed flocks and often became separated from them. More competition for food apparently exists between Brown—headed Nuthatches and Pine Warblers than between either of these species and others. The noticeably different foraging distribution of the two species when together and apart is probably largely the result of the presence or absence of the other. Dividing the habitat in each other's presence avoids fighting over a similar foraging station. Abundant food sources may cause this system to break down.
The Loss of Elements from Decomposing Litter
Authors: Attiwill P. M.
Published: May 2006

The rates of loss of dry matter, phosphorus, magnesium, calcium, potassium, and sodium during decomposition of plant materials were studied in mature Eucalyptus obliqua (L'Herit.) forests in southeastern Australia. The loss of elements follows the order Na > K > Ca > Mg > P, and can be largely explained by the behavior of these elements in terms of both mobility within the living biomass and of leaching from the forest canopy. The difference with respect to phosphorus between the mobility series for E. obliqua litter and that for the litter of some Russian hardwoods suggests that the two plant systems differ also with respect to the cycling and mobility of phosphorus within the living biomass.
Thermal Energy Exchange of a Birch Tree and a Spruce Tree at Night
Authors: Moen Aaron N.
Published: May 2006

Measurements of thermal radiation from a birch tree (Betula papyrifera) and a spruce tree (Picea glauca) were made on four clear summer nights at five distances from the base of each tree. Slightly higher net radiation values were observed under the spruce crown. A rapid reduction in net radiation was observed on the periphery of the crowns. Ecological relationships dependent on the distribution of infrared radiation are discussed.
The Influence of Weight and Temperature on the Metabolic Rate of Sunfish
Authors: O'Hara James
Published: May 2006

Oxygen consumption was determined for sunfish between 1.4 and 116.0 g at 25° and 30°C. Metabolic rates of smaller fish are less affected by temperature change than those of large fish. Interspecific comparison indicates that bluegills (Lepomis macrochirus) are better adapted to higher temperatures than pumpkinseeds (L. gibbosus).
Natural Variations in Nitrogen Excretion of Amphibians from Different Habitats
Authors: Schmid William D.
Published: May 2006

Analyses of ammonia and urea concentrations of anuran amphibians from different habitats showed that aquatic species had significantly lower levels of plasma urea than more terrestrial species. There was also a greater tendency for urea to be partitioned into the urine of aquatic species. Ammonia content of urine was higher in the more aquatic forms, but varied greatly within species depending upon the state of hydration of the specimen. High levels of urinary ammonia were used as a basis of critical evaluation of the ecology of B. hemiophrys. The adaptive values of natural variations in patterns of nitrogen are discussed relative to interspecific differences in ecology and water balance.
The Full‐Glacial Vegetation of Northwestern Georgia
Authors: Watts W. A.
Published: May 2006

Two small ponds in Bartow County, Georgia, northwest of Atlanta, originated by subsidence of unconsolidated surface deposits into solution hollows in the underlying lower Paleozoic Knox Dolomite. The pond sediments consist of copropelic clays 250—400 cm thick with well—preserved plant remains, covered by as much as 150 cm of colluvial deposits with moderately to poorly preserved plant fossils. The clays yield radiocarbon dates of 20,100 and 22,900 BP near their base, contemporaneous with the main Wisconsin glaciation. The full—glacial sediments are rich in pollen and plant macrofossils. The pollen assemblage is dominated by Pinus (pine), with small amounts of Picea (spruce), Quercus (oak), Ostrya type (hophornbeam), and herbaceous types. It closely resembles published full—glacial pollen assemblages from southeastern North Carolina. Pinus banksiana (jack—pine) and Picea sp. are represented by fossil needles at many levels, and the rich macroflora of aquatics shows a marked phytogeographical relationship with the modern flora of northern New England. A floristic displacement of about 1,100 km would be needed to account for the presence of this flora in Georgia. Deciduous trees, primarily Quercus and Ostrya type, may have had a minor role in the full—glacial vegetation. In the postglacial an early Quercus—dominated phase is followed by a Pinus—dominated phase, which lasts to the present. Familiar southern tree genera such as Liquidambar (sweet gum) and Nyssa (black gum) appear to have migrated into the region in postglacial time. Species that occur primarily on the Coastal Plain but have disjunct occurrences at the two ponds and farther into the central United States, such as Itea virginica (Virginia willow) and Psilocarya nitens (sedge), first appear in the fossil record in the postglacial. It is supposed that they and perhaps other "Coastal Plain disjuncts" migrated into their present localities during the postglacial.
Dynamics of Carbon Dioxide and Productivity in an Arctic Biosphere
Authors: Johnson P. L. , Kelley J. J.
Published: May 2006

Concentrations of atmospheric CO2 were measured continuously throughout the 1966 thaw season at two stations on the Arctic coastal plain of Alaska. A seasonal decrease in CO2 of 15 ppm was demonstrated, as well as changes in concentration associated with storm frequencies and diurnal gradients. Correlation between rate of plant growth and declining CO2 concentration in the atmosphere was high (r = .98). Tundra growth was initiated by mid—June and was 90% completed in mid—July. Standing crop above ground and below ground was estimated to be 82 and 100 g/m2, respectively. A 23% turnover of 273 g/m2 of litter was confirmed. Gross primary production was estimated at 344 g/m2. An annual budget for CO2 in an Arctic biosphere is postulated and efficiencies for both energy and carbon storage calculated. Based on seasonal net radiation a photosynthetic efficiency of 0.7% was determined, whereas atmospheric CO2 was apparently used at the rate of nearly 12%. Estimates of CO2 turnover due to biological activity are similar to the 10—year residence time of a molecule before absorption in the sea.
Interspecific Plant Association as Influenced by Three Variables
Authors: Byer Michael D.
Published: May 2006

Changes in interspecific association related to variation in quadrat size, position on a gradient, and abundance measure used in calculating indices yielded information about the nature and causes of this association, and results often corroborated one another mutually. Distribution of species along the gradient and interspecific association within gradient segments appeared to be continua, with varying steepness of transition. Strong association of some rare species suggested that they are highly specific ecologically and/or controlled by few factors. Association changes related to quadrat size suggested general grouping of species on two scales. Possibly, Pteridium and litter generate this grouping between patches where they inhibit plants generally. Weaker positive correlation of cover than of presence suggests unequal competitive restriction of plastic response within the patches of high cover formed by grouping. Large and abundant species in particular seem to inhibit others. Strong positive and negative association characterized heterogeneous habitats and vegetation, extreme habitats in which small environmental differences may be critical, species whose restricted distributions along the gradient may reflect narrow tolerances and consequent microsite specificity, and extremes of species' ranges along the gradient. At these extremes, species perhaps require specific uncommon microsites, and these requirements seem to be similar for species having similar distributions along the gradient. Weak species—environment correlation may reflect low variability of environmental parameters, strong correlation between the latter suggesting that few stochastic processes and complex interactions affect them. In a bog, the major patterning element seems to be hummock—hollow microtopography.
The Population Structure of Erebia Epipsodea (Lepidoptera: Satyrinae)
Authors: Brussard Peter F. , Ehrlich Paul R.
Published: May 2006

The satyrine butterfly Erebia epipsodea shows a population structure unlike that of any other butterfly studied in detail. Rather than being divided into numerous small populations which only rarely exchange individuals, E. epipsodea occurs in vast, effectively panmictic populations which may cover hundreds of square kilometers. There is a great deal of individual movement, and the butterflies are able to recognize and leave ecologically unsuitable areas. Such areas do not, however, seem to pose substantial barriers to their movement.
Nitrogen in the Growth of Araucaria Cunninghamii Ait. Underplanted in Pinus Stands
Authors: Bevege D. I. , Richards B. N.
Published: May 2006

Hoop pine (Araucaria cunninghamii Ait.), a nitrogen—sensitive rain—forest species can be grown without fertilizers as an underplanting to established stands of Pinus, on soils which will not support open plantings of pure hoop pine without fertilizing with nitrogen at the rate of 112 kg/ha per year. Stem volume growth rates of 6.6 m3/ha per year representing 28% of total stand increment have been obtained in 15—year—old underplantings. Removal of the Pinuscomponent from mixed stands of Pinus and Araucaria led to chlorosis of the remaining hoop pine but no significant decline in foliar nitrogen levels nor loss in growth over the ensuing 3 years. In contrast, 2—year—old transplants of Araucaria established on a site from which mature Pinus had been clear felled exhibited extremely slow growth and chlorosis, which could be overcome either by shading or applying nitrogen fertilizers. Underplants responded only slightly to added nitrogen compared to open plantings. Nitrogen requirements of fertilized open plants and unfertilized underplants were similar, however, being approximately 0.005 g nitrogen/g dry matter produced. The rate of immobilization of nitrogen by 8—year—old underplants established at 1,160 trees/ha was only 3.4 kg/ha per year. The source of nitrogen for underplantings is discussed, and nitrogen requirements of hoop pine are considered in relation to light intensity. It is concluded that the success of underplanting is due to a multiplicity of factors,including (1) the role of nitrogen fixation in conjunction with Pinus and Araucaria; (2) the increased availability of nitrogen as a consequence of changes in the soil—nitrogen cycle; and (3) the effect of reduced light intensity on improving the carbohydrate/nitrogen balance in Araucaria under conditions of low soil—nitrogen availability.
Environmental Fluctuations on South‐Facing Slopes in the Santa Catalina Mountains of Arizona
Authors: Haase Edward F.
Published: May 2006

Solar radiation, evaporation, air— and soil—temperature extremes, soil moisture, and precipitation were measured on four aspects (SSE, S, SSW, SW) of constant slope in the desert foothills of the Santa Catalina Mountains over a 1—year period. The sequence of warmest and driest aspects based upon annual means was S, SSW, SW, SSE. The warmest and driest aspect may change with the environmental factor considered or the time of year. Drought extremes reached a high peak on the SW aspect during the arid spring, although during all other seasons the SW aspect had the mildest drought conditions. The warmest and driest aspect during the summer rainy season was SSE, during the winter rainy season it was S, and during the fall arid season S and SSE were nearly equal. Few significant differences were found throughout the year between S and SSW aspects. When vegetation and environment are considered, the warmest and driest aspect may also change with the species because plants may utilize different microenvironments at different seasons and vary in their response to similar environmental changes.
The Behavior and Distribution of the Intertidal Sand Beetle, Thinopinus Pictus (Coleoptera: Staphylinidae)
Authors: Craig Peter C.
Published: May 2006

Both larvae and adults of Thinopinus pictus are nocturnal predators, feeding primarily on beach hoppers (Orchestoidea). When the nighttime tide is low, the beetles emerge onto the sand surface and are characteristically inactive, waiting for passing prey. Mark—recapture studies showed that dispersal is low. Some beetles emerge at almost identical times on successive nights, remaining out for only a few hours. The observable density at any one time may be only one per several square meters, while the actual density is several times greater (e.g., 5 p/m2) because some individuals are always buried. Pitfall traps revealed at 15— to 30—m—wide band of beetles which moves seaward with neap tides and landward with approaching spring tides. Laboratory gradients of sand permeability and moisture indicate that preference for soft wet sand could account for the movements.
Plant and Mannal Changes on a Clearcut In West‐Central Oregon
Authors: Gashwiler Jay S.
Published: May 2006

Plant composition and coverage and small mammal populations were compared in virgin forest (control) and clearcut (experimental) areas from April 1954 to October 1965. Changes in ground cover vegetation were modest on the control area but marked on the experimental area. A late fall burn on the experimental area may have retarded herbaceous plant establishment. Nearly half of the herbaceous species were invaders not found in the virgin Douglas—fir (Pseudotsuga menziesii) forest. Ground plant coverage was less than 23% in the virgin forest; 1 year after the clearcut area was burned, the cover was 2%; and by 10 years it was above 53%. Woody plant coverage (mostly sprouts) was slightly more abundant the first 2 years after burning. Herbaceous species then became dominant for a 3—year period, after which woody plants gradually gained dominance. Deer mice (Peromyscus maniculatus) increased on the experimental area soon after the burn. The populations varied from an estimated 0.9 to 12.8 animals per acre and fluctuated widely and irregularly. Townsend's chipmunk (Eutamias townsendii), Oregon vole (Microtus oregoni), and snowshoe hare (Lepus americanus) populations also increased on the area at different periods after the burn. Trownbridge's shrews (Sorex trowbridgii), vagrant shrews (Sorex vagrans), and ermine (Mustela erminea) were present on both areas in relatively low numbers. Redback voles (Clethrionomys occidentalis), Douglas' squirrels (Tamiasciurus douglasii), and northern flying squirrels (Glaucomys sabrinus) were not found on the clearcut. California ground squirrels (Spermophilus beecheyi) migrated to the clearcut and established a modest population. Richardson's voles (Microtus richardsoni), jumping mice (Zapus trinotatus), bushy—tailed woodrats (Neotoma cinerea), and a pika (Ochotona princeps) were visitors.
Soil Microorganisms at Paradise Harbor, Antarctica
Authors: Boyd William L. , Rothenbg Irwin , Boyd Josephine W.
Published: May 2006

Bacterial counts were generally higher and molds were much more extensive and widely distributed at Paradise Harbor on the Antarctic Peninsula, well above the Antarctic Circle, than in areas to the south. Thermophilic bacteria were found only in soils that had been disturbed or contaminated by man and other animals. Mesophilic counts on media made with deionized or sea water, with few exceptions, were in the same range as psychrophiles. Spore—forming bacteria were present in regions where contamination had taken place or where birds nested. During the short summer, significant growth response of the soil microflora to organic additives (peptone and glucose) was observed. However, no correlations could be made with physiological and metabolic activity, which showed no measurable increase.
Post‐Fire Response of Four Plant Communities in South‐Central New York State
Authors: Swan Frederick R.
Published: May 2006

Four plant communities–northern hardwoods, oak woods, goldenrod (Solidago sp.)—poverty grass (Danthonia spicata) fields, and little bluestem (Andropogon scoparius) fields–were studied in seventeen areas on west to southeast slopes which had been burned by wildfires in 1962, 1963, or 1964. Stability of oak woods after fire was greater than that of northern hardwoods as shown by the lower percentage of dead and dying trees (16% vs. 35%), higher percentage of saplings sprouting (87% vs. 43%), higher average number of sprouts per sapling 4.4 vs. 2.5), and higher percentage of ground—layer species remaining unchanged or increasing in frequency (87% vs. 67%). In goldenrod—poverty grass fields, fire caused goldenrods to increase and poverty grass to decrease. Average weight of dicots was 24% more and that of monocots was 50% less in burns than in unburned portions. These fields appeared to revert to poverty grass dominance after several years without fire. In little bluestem fields, red top (Agrostis alba) and little bluestem increased after fire. Average weight of monocots was 32% more than that of dicots was 35% less in burns than in unburned portions. Wildfires top—killed 63—93% of saplings invading fields; 77—90% of saplings in burns produced sprouts.
Effects of Long‐Term Deer Exclusion on a Pinus Resinosa Forest in North‐Central Minnesota
Authors: Ross Bruce A. , Bray J. Roger , Marshall William H.
Published: May 2006

Trees, shrubs, and herbs were sampled inside and outside an exclosure in a 230—year—old Pinus resinosa forest in north—central Minnesota from 1946 to 1969. Prior to the building of the exclosure in 1937, white—tailed deer had existed at or above starvation population densities for 10 or more years. Overbrowsing continued outside the exclosure until 1945 when the deer were virtually eliminated by hunting. Since then deer numbers have gradually increased. Before 1937, severe browsing had apparently removed all tree reproduction greater than 1—2 years old. Since 1937, inside the exclosure the occurrence of seedlings and samplings has increased greatly and has followed a normal successional sequence dominated by Pinus strobus with lesser amounts of Betula papyrifera, Acer rubrum, Quercus borealis, and Abies balsamea. Outside, tree reproduction was scarce until after 1945; then Pinus resinosa, P. strobus, and Betula papyrifera saplings increased substantially. Only P. resinosa and B. papyrifera have grown above the sapling class in appreciable numbers, probably because B. papyrifera is of low preference as deer browse compared with the other intermediate species, Pinus strobus, Acer rubrum, and Quercus borealis. Thus, moderate—to—high browsing has continued to inhibit successional development.
Relation of Canopy Area and Volume to Production of Three Woody Species
Authors: Peek James M.
Published: May 2006

Shrub canopy area, which more closely resembled an ellipse than a circle, shrub volume, and numbers of twigs per plant were highly correlated with weight of current leaves and twigs in aspen (Populus tremuloides), beaked hazel (Corylus cornuta), and pussy willow (Salix discolor). Lower correlations were obtained for shrub height with weight of current leaves and twigs. No appreciable change in correlations was obtained by using logarithmic regressions instead of linear regressions, except for weight versus height. Canopy area of shrub volume—weight relationships may be most applicable where floristics and production studies are combined.
Effects of Disturbance on Seed Germination in Some Annual Plants
Authors: Smith Theodore A.
Published: May 2006

Herbage removal, fire, and soil disturbance significantly reduced the numbers of germinating seedlings of Bromus mollis, B. tectorum, and Trifolium microcephalum the first season following alteration. Burining and soil disturbance caused the largest reduction in numbers of grass seedlings; clipping reduced the numbers to half that found on the undisturbed plots. Soil disturbance caused the greatest reduction in numbers of germinating clover seedlings. Burning and clipping reduced the clovers significantly below the undisturbed plots, but the reduction was much less than that caused by soil disturbance. Differences between the test conditions were not significant in subsequent years.
Ecological Isolation and Competitive Exclusion in Two Crayfish (Orconectes Virilis and Orconectes Immunis)
Authors: Bovbjerg Richard V.
Published: May 2006

The two crayfish, Orconectes virlis and O. immunis, have similar ranges but are ecologically isolated within these ranges; the former species inhabits streams and lake margins, the latter inhabits ponds and sloughs. Field and experimental data suggest that the stream species, O. virilis, is excluded from ponds by summer drying and periodic low oxygen periods of those ponds. It is not as competent a burrower as O. immunis nor is its as tolerant of low oxygen levels. Neither current nor substratum excludes the pond species, O. immunis, from the stream. But both field and laboratory observations strongly indicate a competitive exclusion of O. immunis by O. virilis. The latter was demonstrated to be intrinsically more aggressive in interspecific contacts, and in other experiments, evicted O. immunis from crevices in the substratum.
Density Estimation of Corn Rootworm Egg Populations Based upon Frequency of Occurrence
Authors: Gerrard Douglas J. , Chaing H. C.
Published: May 2006

A new approach is developed for the estimation of insect population densities which eliminates the necessity of counting every individual per sample. Although the method was developed for populations of corn rootworm eggs, it seems as applicable to other organisms featuring contagious distributions. Estimation by the proposed method is based upon the proportion (p) of samples containing at least t insects each, where t, termed threshold density, can be any positive integer specified. For example, if t is 1, counting is entirely unnecessary since the only information required is the proportion of samples in which the organism is present. The prediction equation which links mean density to the variables ° and t must be estimated beforehand from a series of samples extending over a wide range of population densities. Expressing the model in terms of logarithms premits the estimation of its parameters by linear least squares. The study indicates that there is an optimal threshold level associated with every population density and specified allowable error. Estimation near these optima is apparently more efficient than conventional estimation involving complete sample enumeration. By enlisting a two—stage sampling scheme, one should consistently be able to approach the optimum threshold and thereby produce estimates comparable in efficiency to direct counts but free from much of the labor.
The Seasonal Food Regime of Arctic Beavers
Authors: Aleksiuk Michael
Published: May 2006

Seasonal variation in food of the beaver (Caster canadensis Kuhl) was examined on the Mackenzie Delta, Northwest Territories, Canada. Leaves and, to a lesser extent, growing tips of willow (Salix spp.) were the main food items during July and August; during the remaining 10 months food consisted of the bark of willow (76%), poplar (Populus balsamifera) (14%) and alder (Alnus crispa) (10%). Protein: calorie ratios in the diet were approximately 40 and 8 mg/cal during those two periods respectively. The northern beaver has adapted to low energy availability characteristic of winter by storing food in the autumn and again in the spring, and by intrinsically lowering food intake during the winter. It has adapted to seasonal variation in protein availability by utilizing high—protein willow leaves almost exclusively when they are available. The heavy dependence upon willow, and its resultant removal from the community, can impart a high degree of instability to northern beaver populations.
Some Ecological Factors Influencing a Community of Adult Odonata
Authors: Lutz Paul E. , Pittman Annette R.
Published: May 2006

A community of adult Odonata, composed of 18 species, was studied during June and July of 1968 at a small pond in piedmont North Carolina. Studies were made on the influences of time of day, ambient temperature, and light intensity on flight activity, and on the frequencies of intra— and inter—specific interactions. Most species initiated their flying periods by mid—day and terminated them by 1930 hr with considerable variations among the species. Maximum reproductive behavior occurred near the mid—point of the patrolling period. Minimal temperature thresholds for activity ranged from 20—28°C, whereas maximal thermal thresholds were from 30—40°C. Adult activity decreased proportionally to a decrease in light intensity during cloudy periods or thunderstorms. Activity of individuals to some species was controlled chiefly by one environmental factor, but in others activity presumably was related to a combination of several factors. Intraspecific interactions, usually between males, were much more common than interspecific interactions. Threat behavior was far more prevalent than actual physical contact.
Some Factors Affecting Drift and Upstream Movements of Gammarus Pulex
Authors: Hughes D. A.
Published: May 2006

Laboratory experiments, conducted within a current chamber, suggest that upstream movements of the amphipod Gammarus pulex, especially in regions of slower current flow, are sufficient to compensate for the downstream displacements of animals by drift. They indicate also that drift was greater in slow—flowing than in faster waters.
A Quantitative Study of the Foraging Ecology of Downy Woodpeckers
Authors: Jackson Jerome A.
Published: May 2006

Studies of the foraging ecology of Downy Woodpeckers (Dendrocopos pubescens) at the University of Kansas Natural History Reservation indicate that there is intersexual partitioning of the foraging niche, seasonal variation in the relative frequency of the modes of foraging, variation in the mode of foraging on live versus dead trees, and seasonal variation in the use of live and dead trees. Partitioning of the foraging niches by the sexes is accomplished behaviorally by a differential use of the available substratum according to limb height and diameter. The degree to which these unisexual subniches are expressed varies on live versus dead trees. Males tend to forage on small branches, generally 5 cm in diameter or less; females tend to forage on the trunk and larger limbs. The mean foraging height of males in live trees (6.0 m) is significantly different from that of males in dead trees (8.9 m); the mean foraging height of females in dead trees (8.4 m) is not significantly different from that of females in live trees (8.1 m) or of males in dead trees. The mean foraging height of males in live trees is significantly different from that of females in live trees. A similar relationship exists among the heights of the trees in which Downy Woodpeckers forage. Both male and female Downy Woodpeckers use sub—surface foraging techniques to a greater extent during the winter and superficial techniques during the warmer months. Greater use of dead trees during winter is also indicated. Dead American elms (Ulmus americana) are used as foraging sites by both sexes to a greater extent than expected by chance. Some other tree species seem to be favored and some avoided by one or both sexes.
Occurrence of Athiorhodaceae in Woodland, Swamp, and Pond Soils
Authors: Pratt Douglas C. , Gorham Eville
Published: May 2006

Tests (by enrichment culture) for nonsulfur purple photosynthetic bacteria in surface soils showed them in all of three sediment cores sampled in a shallow pond and in all of six peats from nearby swamp hollows beneath cedar and tamarack. They also occurred in two of three peats from swamp flats and three of five peats from swamp hummocks. For woodland and grassland surface soils, proportions were three out of seven and five out of nine sites respectively. For the total number of tubes inoculated at varying dilutions from each of these sites, the following proportions of positives were recorded: uppermost lake sediments 92%, swamp hollows 67%, swamp flats 38%, swamp hummocks 20%, woodlands 14%, grasslands 8%.
Epizootiology of Trypanosomes in Red Squirrels and Eastern Chipmunks
Authors: Dorney Robert S.
Published: May 2006

To determine the natural fluctuations of lewisi—like trypanosome populations in red squirrels (Tamiasciurus hudsonicus), I examined 151 stained blood slides over a 3—year period and found that parasitemias were almost absent (4% positive) in 1961, had significantly increased in 1962 (37% positive), and then decreased in 1963 (15% positive). This sharp rise in 1962 presumably may have been related to the original absence of immunity among members of the population, and the decline in 1963 related to an increase in the general level of immunity in the population in combination with a reduction in the recruitment of susceptible juveniles during the 1963 reproductive season. Fluctuations of trypanosome populations in eastern chipmunks (Tamias striatus) based on examination of 283 stained blood slides followed a pattern different from that in red squirrels. In 1961 animals with parasitements were common (42%), but then the declined in both 1962 (26%) and 1962 (12%). Consecutive blood histories on marked animals and analysis of population age structure suggested this 3—year decline was caused primarily by a decrease each year in the proportion of susceptible juveniles recruited into the population. Although parasitemias in both hosts tended to last only a few months, suggesting that immunity develops rapidly, occasional retained parasitemias through the winter into the next spring. Pathogenicity of these trypanosomes must be minimal since animals with parasitemias had similar rates to those of parasites. The pattern of annual fluctuation of trypanosomiasis observed in these two hosts suggested that the study area may have been a primary focus for the lewisi—like trypanosome in chipmunks and a secondary focus for that in the red squirrel. That the squirrels on the study area moved from winter nest sites under the snow to tree nests in summer also may account for the irruptive occurrence of trypanosomiasis in this host. Whatever the explanation, the occurrence of trypanosomes at Trout Lake exhibited extreme variability from year to year and from host to host. This points up the necessity, in epizootiological studies of blood protozoa in sciurids, to examine the host—parasite system over a period spanning many years.
Critical Factors During the First Years of Life of the Saguaro (Cereus Giganteus) at Saguaro National Monument, Arizona
Authors: Steenbergh Warren F. , Lowe Charles H.
Published: May 2006

Germination and establishment of the saguaro giant cactus were studied by periodic observations on natural seedling populations, seedling distribution within rocky, rolling hill, and flat terrain habitats, and field—germination experiments in the Sonoran Desert. As a result of bird, mammal, and insect activity, a very small percentage of seeds (<1 x 10—3 of the seed crop) remains on the ground until suitable conditions for germination occur during the summer monsoon. Germination begins after the start of summer rains in July and continues in August and September. The principal apical stem growth of seedlings takes place during these months, with a few plants exhibiting slight growth during favorable late winter and early spring months. Establishment of seedlings is limited primarily by frost, drought, rodents, and insects, which affect the differential survival associated with seedling size, microhabitat, and season. Initial high rates of seedling mortality drop sharply after the first year and are lowest for plants associated with microenvironments among rock outcrops. The large number of seeds germinated in the alluvial soils of the flat terrain habitats is offset by a higher seedling mortality there. In the rocky habitats more seedlings survive from fewer germinations. The significant difference is attributed primarily to the effect of the microhabitat upon the operation of the critical controlling factors listed above.
Overlap in Foods and Foraging of Four Species of Blackbirds in the Potholes of Central Washington
Authors: Orians Gordon H. , Horn Henry S.
Published: May 2006

Overlap in foods and foraging of four species of breeding blackbirds in the Potholes of central Washington was estimated from samples of food delivered to the nestings obtained by the pipe—cleaner technique. Prey distribution and availability were sampled with emergence traps for aquatic species and by sweeping with a standard insect net for upland species. Overlap was estimated by the probability than an item of food drawn randomly from the diet of one species would be of the same prey category taken from the same habitat as an item drawn at random from the diet of another species. Because of the diurnal cycle of emergence of aquatic insects, overlaps were calculated for three periods of the day (preemergence, emergence and postemergence) and averaged for the final overlap value. The overall food overlap for three of the species is high for all periods of the day and there is little evidence for differential specialization within habitats. Habitat overlaps, however, are varied, being highest during the emergence period for Redwings and Yellowheads but highest during the afternoon between Redwings and Brewers. The total overlap values are very similar to the theoretical maximum values derived from competition theory by MacArthur and Levins.
Growth Inhibition in Crowded Tadpoles: Intraspecific and Interspecific Effects
Authors: Light Lawrence E.
Published: May 2006

Tadpoles are inhibited in growth when raised in water previously crowded by other larger tadpoles. The ‘alga—like’ cells described in earlier crowding studies were found in the fecal material and intestinal tracts of inhibited tadpoles. Results of 38 crowding experiments using 17 species of tadpoles show that the effects of the inhibitory cell are nonspecific. Water (with cell—laden fecal matter) from crowded tadpoles of one suborder can inhibit the growth of assay tadpoles of a different suborder. There is no decreasing level of inhibition with phylogenetic distance. Bufo woodhouse is the only one of 17 anuran species tested that seems immune to these inhibitory effects. Tests with Bufo woodhouse indicated the existence of a possible intraspecific growth—promoting substance. The substance may also inhibit some species, and not affect others. Metamorphosing tadpoles may release a nonspecific growth—stimulating substance (thyroxine?) into the water, which may alleviate the effect of inhibitory substances.
Growing Seasons of Cottonwood and Sycamore as Related to Geographic and Environmental Factors
Authors: Kaszkurewicz Anatol , Fogg Peter J.
Published: May 2006

The hypothesis that variation in dates of the beginning and end of growing seasons of eastern cottonwood (Populus deltoides Bartr.) and American sycamore (Platanus occidentalis L.) can be attributed to variation in air temperature andphotoperiod was tested by using data collected during a single year (1963) from trees widely distributed throughout their natural ranges. Dates of bud breaking and winter—bud formation were used as the criteria for the beginning and end of growing seasons. Correlation and regression analyses were used to elicit the relationships of these dates with latitude, altitude, air temperature, photoperiod, and with the dates of frost occurrence at the locations of the sampled trees. The growing season in these two species was not confined to the period between killing frost in spring and fall. The lengths of growing seasons were inversely related to the latitude. With increasing latitude, growth began later and stopped earlier. Both air temperature and photoperiod at the time of growth initiation and cessation varied with latitude. At a given latitude between 30°N and 50°N cessation of growth occurred at higher temperature than that at initiation of growth, and growth cessation between 33°N and 50°N was associated with shorter photoperiods than those at growth initiation. Temperature and photoperiod, acting in combination, appeared to be important, although not exclusive, factors in controlling the initiation and cessation of growth of these species. The regression line of monthly mean temperature on photoperiod on the day of growth initiation appeared to delineate a boundary between the period of dormancy and the active growing season. The cessation of growth could not be as clearly defined.
Phenological Variation within Seven Transplanted Grassland Community Fractions from Texas and New Mexico
Authors: McMillan Calvin
Published: May 2006

Community fractions, consisting of population samples of Andropogon scoparius Michx., A. gerardii Vitman, Panicum virgatum L., and Sorghastrum nutans (L.) Nash, were transplanted to Austin, Texas, from six sites in Texas and one site in New Mexico. A behavioral gradient among the transplanted community fractions was correlated with the length of the growing period (over 300 to less than 200 days) and altitude (sea level to near 2,800 m) of origin. Late maturity characterized the populations from shorter growing periods and higher altitude. The population samples of 10 clones were compared in time of initial flowering with earlier samples of three clones taken from the same geographic area. Despite variations in site and year the gradient of mean flowering time was similar. The uniformity of flowering time and morphology within certain population samples of A. gerardii and P. virgatum suggested vegetative replication. Local differentiation was show in P. virgatum, caespitose (tetraploid) plants from a river bottom being later flowering than rhizomatous (octoploid) plants from an adjacent sandhill area. During an extended summer drought, the community fraction originating in central Texas showed selective superiority in the central Texas transplant habitat.
Parameters for Seasonally Breeding Populations
Authors: Caughley Graeme
Published: May 2006

Lotka's equations relating the parameters of populations with no seasonal trend in birth rates and Fisher's formula for "reproductive value" are modified to describe populations with restricted annual seasons of birth. The parameters "net reproductive rate" and "mean generation length" provide statistics and dubious utility for populations with overlapping generations. New definitions of birth rate and death rate are proposed whereby the relationships between the crude, finite and exponential rates are simplified. The use of these parameters is illustrated by statistics calculated for a population of sheep.
A Field Study of the Lava Lizard (Tropidurus Albemarlensis) in the Galapagos Islands
Authors: Stebbins Robert C. , Lowenstein Jerold M. , Cohen Nathan W.
Published: May 2006

The effect of removal of the parietal eye (parietalectomy) was studied in free—living lava lizards at the Charles Darwin Research Station in the Galapagos Islands, and the results were compared with those obtained with parietalectomized temperate zone iguanids. Behavior, activity, body temperature, and Iodine—131 uptake by the thyroid gland were studied from Jan. 23 to Feb. 27, 1964. Parietalectomy had no detectable effect on any of the parameters investigated. Home ranges of adult male and female lizards were measured, and defensive and antagonistic behavior was noted. The home ranbges of males often encompassed those of several females. Most adults arose and retired with the sun, and sharply reduced exposure to sunlight at midday. At night, lizards buried themselves in soil and leaf—litter, and the same bed sites were often regularly used. Individuals injected with Iodine—131 were located at night with a scintillation counter. Active lizards had body temperatures averaging 34 to 35°C (range 22.6 to 39.0°C), which showed a bi—modal distribution. Cloud cover was a significant factor in body temperature fluctuations. Sexual dimorphism, both in color and in size of adults, was marked. Females had red "cheek" patches and were smaller than males.Most males had sperm in their sperm ducts and some females contained large—shelled oviducal eggs. Mating males seized females with their jaws, and sometimes carried them some distance before attempting copulation. Posturing and perhaps the odor of refractory females discouraged males. The lizards were found to be insectivorous, but some plant material was also eaten. One small gecko (Phyllodactylus galapagoensis) was recovered from stomach contents.
Seasonal Variations in the Availability of Food for Benthos in a Coastal Environment
Authors: Stephens K. , Sheldon R. W. , Parsons T. R.
Published: May 2006

The quantity of suspended and deposited particulate material was measured over a period of 1 year in a coastal environment. Maximum deposition of sediment occurred during periods May to July, and October to December. The first maximum occurred approximately 2 months after the spring phytoplankton bloom and consisted largely of phytogenous material. The total quantity of this material deposited represented approximately half of the annual primary production. The second sediment maximum was due to terrigenous material from the immediate vicinity of the coast.
A Tropical Hammock on the Miami (Florida) Limestone‐‐A Twenty‐Five‐Year Study
Authors: Alexander Taylor R.
Published: May 2006

Data from two studies 25 years apart support the idea that the hammock, composed of West Indian tropical flora, is the climatic climax in southern Florida. In the absence of fire during the 25—year period, the pineland surrounding the hammock was invaded by the tropical species. Lysiloma bahamensis acted as the invader tree. The succession occurred well within the 25—year period.
Interrelationships of Two Scale Insects on Citrus
Authors: Gerson Uri
Published: May 2006

The interrelationships of 2 diaspidid scale insects of the geunus Parlatoria, infesting citrus, were investigated during several years in the field. It was found that P. pergandii Comstock was more numerous in the summer, P. cinerea Hadden in the winter. With reference to the respective geographical distribution of these species, it is postulated that climatic conditions annually modify the common habitat and thus determine the outcome.