bluuebunny/crossref_metadata_2025 huggingface dataset:
Experimental Manipulation of Soil Invertebrate Populations for Trophic Studies
Authors: Edwards C. A. , Reichle D. E. , Crossley D. A.
Published: May 2006

The experimental application of pesticides is developed for manipulation of populations of soil microarthropods, earthworms, and flora to provide controlled populations of soil invertebrates for studies of their role in litter and soil turnover. The technique employs a soil fumigrant (dichloropropene,D—D), an insecticide (aldrin), and an earthworm extractant (formalin) for elimination of various biotic groups. D—D fumigation effectively eliminated earthworms, and reduced microarthropod populations by 98.3%. With periodic application of aldrin to fumigated soil, recolonization by microarthropods was held to 6.5% of control densities after 8 months. Formalin extraction of earthworms remained 80% efficient 6 months after presents the methods of treatment, subsequent population changes, and rates of recolonization of soil by specific invertebrate groups.
Seasonal Adaptations in Photosynthesis and Respiration in Four Desert Shrubs Growing in Situ
Authors: Strain B. R.
Published: May 2006

Field measurements of carbon dioxide exchange and carbohydrate resources show that physiological adaptations occur in the shrubs Larrea divaricata, Encelia farinosa, Hymenoclea salsola, and Acacia greggii growing in situ in the Colorado Desert of California. L. divaricata, the most widely distributed shrub of the North American deserts, exhibited the greatest seasonal adaptation in the field. This study supports the hypothesis that adaptive temperature acclimations occur in plants.
Rapid Estimation of Heat Accumulation from Maximum and Minimum Temperatures
Authors: Baskerville G. L. , Emin P.
Published: May 2006

A method is presented for estimating heat accumulation by using daily maximum and minimum temperatures and assuming the sine curve as an approximation of the diurnal temperature curve. A table is given for estimating heat accumulation for a given day, and a computer program is described for accumulating heat units over a 1—year period. The technique permits the use of an upper as well as a lower threshold and has a precision in the order of ± 5%.
Vegetation of Califonia Fan Palm Oases on the San Andreas Fault
Authors: Vogl Richard J. , McHargue Lawrence T .
Published: May 2006

The vegetation of 24 oases located in the western Colorado Desert was composed of 78 species from 34 families, with an average of 11 species per oasis. Species distributions within an oasis were determined by available water and could be divided into three contoured belts and hydric zone had 10% of the total species, primarily hydrophytes, and accounted for one—fifth of the total plant cover. The oasis—proper zone contained phreatophytes and halophytes, comprising 17% of the total species and producing two—fifths of the cover. The remaining cover was produced by 73% of the species, mainly xerophytes, present primarily in the desert—oasis ectone. Oases were located on hillside seeps or in canyon washes. Although most dominant species were common to both types, they differed in vegetational composition. Hydric species were more common in wash oases. Species requiring stable sites with sub—surface water were more abundant in seep oases. All oases showed individuality since Washingtonia filifera was the only ubiquitous species. Haplopappus acradenius and Prosopis juliflora occurred in 75% of the oases; 10% of the species were restricted to two or three oases; and 33% were confined to one oasis. Eleven rare species were encountered. Absence of palm reproduction was due to inadequate water, lack of stimulating rains, or alkali soils. Alkali soils appear detrimental to plant growth. Optimum conditions for new growth need occur only once a century to sustain oases. Maximum palm ages appear to be about 200 years. Floods alter wash geomorphology and vegetation, but have a rejuvenating effect on dense, stagnating stands of hydrophytes. Fire determines oasis composition and affects the physiognomy, productivity, reproduction, and maintenance of the fire—tolerant palms.
Ecological Studies of the Branchiobdellidae (Oligochaeta)
Authors: Young Willard
Published: May 2006

Crayfish collected from a central Texas farm pond are hosts for two Branchiobdellidae. Evidence indicates the branchiodbellids are commensals, since they survive for long periods in the absence of crayfish, but are dependent upon them as a site for reproduction. Branchiobdellid cocoons, which have incubation periods of 10 to 12 days, are attaches to the exoskeleton of the host mostly on the ventral abdominal surface. Cocoons are not deposited on very small crayfish, apparently because of selection brought about by the loss of eggs through the frequent molts of young crayfish, since eggs left on exuviae perish. Transfer between hosts is accomplished mostly through body contact of the crayfish. The logarithm of the branchiobdellid populations yields a straight line when plotted against crayfish body lengths. This may be accounted for by the increased surface area and the decreased frequency of molts of larger crayfish. Population densities are minimum during the winter, increase distinctly in early spring, and reach a maximum in June. Adverse environmental conditions during the summer and winter likely cause decreased reproductivity activity or increased mortality. A greater proportion of the total brachiobdellid population inhabits small crayfish during the early summer than at other seasons. This may result from population pressures created by overcrowding on larger crayfish during this period of maximum branchiobdellid population density. The structure of the bronchiobdellid populations varies seasonally, with adults composing about half of the winter population and a smaller proportion in other seasons. This can be accounted for by decreased reproductive rates or selective mortality depleting the numbers of young worms during the winter.
Reactions of Orb‐Weaving Spiders (Argiopidae) to Airborne Sounds
Authors: Frings Hubert , Frings Mable
Published: May 2006

The reaction of three species of web—spinning spiders, Araneus cavaticus, Argiope aurantia, and Argiope avara, in their webs and when removed from the webs, to web agitation and airborne sounds at known frequencies and intensities were studies. The reactions to web agitation and airborne sounds are not the same, and the receptors are probably different. The spiders react to web agitation by attacking the source, as they do with trapped insects; the receptors are probably proprioceptors of the legs. The spider respond to airborne sounds, from 200 to 3,000 cycle/sec at 90 to 110 db, by defensive movements; the webs are not needed for reception. The receptors are long, thin hairs which are agitated by near—field air movements of intense sound fields; they are not specialized phonoreceptors, for they are sensitive to direct bending and to air currents. Earlier discrepancies in results with airborne sounds are easily explained by the fact that intensities and distances to sound sources were not controlled. The defensive reactions to high intensity airborne sounds are probably involved, in nature, with escape from or defense against winged predators.
Production Rate, Population Density, and Drift of a Stream Invertebrate
Authors: Waters Thomas F.
Published: May 2006

Production rates of the stream mayfly, Baetis vagans McDunnough (Ephemeroptera: Baetidae), were estimated by two different methods, compared, and related to population density and drift rate. In the year of study, this mayfly had two summer generations and one winter generation. The two production rate methods yielded estimates of 9.1 and 12.6 g/m2 year as the sum of the three generations, although both estimates were minimal. Production rates for the summer generations were higher than for the winter generation, although winter production was still at a significant level. The summer generations drifted in large quantities, up to about 22 g/day, but the winter generation appeared to drift little, if any, until near the end of the generation in early spring. The relation between annual production rate and mean population density, or turnover ratio, was 9.7, or 3.2 times the number of generations.
Season of Birth in Man. Contemporary Situation with Special Reference to Europe and the Southern Hemisphere
Authors: Cowgill Ursula M.
Published: May 2006

The season of birth in man appears to be meteorologically controlled thought minor minima of cultural origin are also apparent. The change of conception may be temperature dependent. The periodicity in the Southern Hemisphere is the reverse of that of the northern one. The Moslem Mediterranean region exhibits patters similar to southern Europe, as does Central America. The United States, Canada and Puerto Rico have a pattern that appears to be anomalous compared to the rest of the world. The seasonality of birth is a sensitive indicator of certain cultural and biological phenomena. The amplitude is increased by illegitimacy, death, belonging to a race other than Caucasian, war, depression, lack of industrialization, poverty of rural living. There is some indication, over time, that the mere process of urbanization and industrialization can cause the amplitude to behave in an erratic fashion. An hypothesis has been suggested to explain changes that have occurred during the past century. It is thought that the effect of urbanization is responsible for the change and in part the improvement of the standard of living has also be an influence. Spain and Sweden have shown no major variation in their season of birth for the period of time for which there are data.
Ionic Composition of Sagehen Creek, California, Following an Adjacent Fire
Authors: Johnson C. M. , Needham P. R.
Published: May 2006

Samples of water from Sagehen Creek, California, were collected at 2—week intervals for 2 years following the Donner Ridge forest fire which burned over the lower part of Sagehen Basin in 1960. Sampling sites included a spring which feeds the stream above the burned area and two sites in the stream, one above the burned area below the spring, the other within the burned area. Analyses included pH, bicarbonate, calcium, magnesium, sodium, and potassium. Seasonal variation in ionic composition was observed at both stream sampling sites. In contrast to the constant composition of the spring water for the 2—year period, the summer, streamflow was low and stream ionic concentrations equalled or exceeded those of the spring water. During periods of runoff snow, March to June streamflow increased greatly and ionic concentrations decreased. There was no specific effect of the fire on the ionic composition of the stream. It is postulated that ash constituents were dissolved by light rainfall and leached into the permeable forest soil before the first snow. Because of the acidic nature of the soil the dissolved cations were absorbed on the exchange complex rather than washed directly into the stream.
An Ecological Study of Hardwood Swamps in North‐Central Florida
Authors: Monk Carl D.
Published: May 2006

The hardwood swamps of north—central Florida may be divided into two groups: (1) mixed swamps and (2) bayheads. The former is characterized by deciduous species and the latter by evergreen species. Mixed swamps occupy sites which are usually higher in calcium, magnesium, calcium/magnesium ratios, calcium/potassium ratios, pH, and depth of maximum flooding. Sabal palmetto, Fraxinum caroliniana, Ulmus floridana, and Taxodium distichum are more restricted to the mixed swamp habitat, while Gordonia lasianthus, Persea palustris, and Magnolia virginiana are more confined to bayhead. Quercus nigra, Acer rubrum, Liquidambar styraciflua, and Nyssa sylvatica occupy both habitats. Though several species link the two communities, the two habitats can be effectively separated by certain edaphic variables.
Dynamics and Regulation of Red Squirrel (Tamiasciurus Hudsonicus) Populations
Authors: Kemp Gerald A. , Keith Lloyd B.
Published: May 2006

This paper describes red squirrel population dynamics on two intensive study areas (Camp and Main) in mixed—forest types near Rochester, Alberta. It also examines local and regional population fluctuations, and their relationship to cone crops and weather factors. Adult red squirrel numbers on our study areas varied little from 1967 to 1968. Yearly differences in reproductive output were caused principally by changing ovulation and pregnancy rates. Mean litter size increased significantly from 3.4 in 1967 to 4.3 in 1968; while the per cent adult females breeding increased significantly from 67 to 88. A life—table analysis of age—ratio data estimated mean annual mortality among juveniles (postweaning) at 67%; and an adult mortality rate of 34% for yearlings and 61% for older cohorts. A time—specific estimate of adult mortality on the Camp study area during the year starting summer 1967 was 21%. Red squirrel territories appeared to be of two distinct types: (1) defended winter food caches which were subsequently abandoned during the summer, and (2) "prime" territories in which a specific area was defended year round. During the summers of 1967 and 1968, 31% and 26% of study—area adult populations occupied prime territories. The distribution of prime territories chiefly reflected the presence of mature seed—producing conifers, and hence a potential year—round food supply. Deciduous areas were particularly important in overwintering the juvenile cohort. Fur returns were used as population indices in determining synchrony and periodicity of red squirrel fluctuations. Fluctuations tend to occur synchronously over much of the Prairie Provinces. Furthermore, mean intervals between peak years in Alberta (2.6) and Saskatchewan (2.8) were significantly shorter than in random series of comparable length, while the 2.9—year mean interval in Manitoba approached significance. A statistically significant correlation was found between white spruce cone crops and red squirrel populations in Alberta as indexed by annual fur harvests. The negative correlation between cone crops in late summer and rainfall during summer of the preceding year was almost significant. This supported the widely held view that weather factors influence bud differentiation and hence determine the size of the following year's cone crop. Our contention that cone production may in this way provide a vehicle through which weather affects squirrel populations was supported by a number of statistically significant negative correlations between Alberta and Saskatchewan fur returns and the preceding year's summer rainfall. Such a mechanism would explain the observed widespread synchrony of population fluctuations, since extensive regional weather patterns could be involved.
The Regression of Log N(n+1) On Log N(n) as a Test of Density Dependence: An Exercise with Computer‐Constructed Density‐Independent Populations
Authors: Maelzer D. A.
Published: May 2006

Four density—independent "populations" were constructed on a computer, and the simple regression of the log density in one generation (log Nn+1) on the log density in the previous generation (log Nn) was calculated for each of a number of replicates for each population. From the resultant sampling distribution of the regression coefficient for each population, it was found that (i) the mean slope was significantly less than the expected value of 1.0 for a density—independent population, and that (ii) the mean slope was influenced by sample size and the serial correlation between successive values of the rate of increase, ϒ. Despite its demonstrated bias the regression coefficient could still be useful if it were capable of distinguishing between populations with density—dependent processes and populations with no density—dependent processes. So data for a number of natural populations were analyzed by simple regression and each of the slopes so obtained was compared with the mean slopes (for simple regression) for the theoretical populations. These comparisons suggested that the simple regression coefficient was not a good criterion of density dependence.
The Effect of Predation on Population Densities of Some Desert Snails
Authors: Yom-Tov Yoram
Published: May 2006

In preliminary investigations it was found that there is a great difference in the population density of two desert snails on southern and northern slopes of a wadi. The density of Sphincterochila boissieri was equal on both slopes, while the density of Trochoidea seetzeni is much lower on the southern slope. It is shown that this difference is due to predation by some rodents, mainly dormice and gerbils, which are more common on the southern slope due to its geomorphologic character. The rodents prefer to eat T. seetzeni because they have thinner shells, while S. boissieri, which have much thicker shells, are seldom eaten. The effect of predation on community stability on the slopes is discussed. It seems that the conclusions of MacArthur and Wynne—Edwards on community stability in extreme regions are valid also in this case.
Diapause in the Nymphs of Canadian Winter Stoneflies
Authors: Harper P. P. , Hynes H. B. N.
Published: May 2006

The nymphs of several winter stoneflies, Taeniopteryx burksi, T. nivalis, Brachyptera fasciata, Capnia manitoba, Allocapnia granulata, A. pygmaea, and A. vivipara, undergo a diapause during the summer. The diapause determines external morphological changes, which are described. This adaptation enables the species to inhabit streams that reach high temperatures or dry up during the summer; its advantages over the more common embryonic diapause are that it permits the nymphs to grow in both spring and fall and to seek a convenient site in which to aestivate.
Experimental Zoogeography of Islands. A Two‐Year Record of Colonization
Authors: Simberloff Daniel S. , Wilson Edward O.
Published: May 2006

In 1966—1967 the entire arthropod faunas of six small mangrove islands in the Florida Keys were removed by methyl bromide fumigation. In earlier articles we described the process of recolonization through the first year, during which the numbers of species in five of the six faunas rose to what appear to be noninteractive equilibria and then slumped slightly to interactive equilibria. The sixth, that of island E1, we believe to be climbing more slowly because of its greater distance from the source area. It had not reached the predefaunation (interactive) equilibrium by 1 year. Here we give the results of censuses taken at the end of the second year on the four islands in the group located in the lower Keys (E1, E2, E3, ST2). The numbers of species were found to have changed little from the previous year, providing further evidence that they are in equilibrium. Species immigrations and extinctions have continued at a high rate, and the species compositions on three of the four islands appear to be moving slowly in the direction of the original, predefaunation states.
Digger Pine Seedling Response to Serpentinite and Non‐Serpentinite Soil
Authors: Griffin James R.
Published: May 2006

Seedlings were grown from 17 seed samples collected throughout the natural range of Pinus sabiniana in California. Five collections came from soils derived from ultra—basic serpentinized rock. The seedlings were grown in a greenhouse in cans filled with two different soils. One series of 36 seedlings per sample grew in a fertile, loamy sand forest soil. This planting was replicated in a sterile, highly serpentinized soil gathered at one seed collection site. Significant differences in shoot and root growth were found between populations within each soil treatment. But the relative ranking of populations was similar in both cases. On both soils populations of non—serpentinite origin made the most vigorous growth. Seedlings from the serpentinite soil collection locality made relatively poor growth in the serpentinite soil. No adaptation to the serpentinite soil conditions by populations which came from serpentinite areas was suggested. All seedlings populations appeared to have a high tolerance for extreme serpentinite conditions. The correlation between mean seed size and mean seedling size was low (r = 0.24) in the fertile soil, but much higher (r = 0.68) in the serpentine soil.
Distribution of Aquatic Vegetation as Measured by Line Intercept with Scuba
Authors: Schmid William D.
Published: May 2006

The aquatic vegetation of Long Lake (T 144 N, R 36, 37 W) in northwestern Minnesota was surveyed by means of line transects run underwater with SCUBA apparatus. Eight stations were established about the lake and 12 transects were run from each station. The transects were run along depth contours at ½—m depth and 1—m intervals from 1 through 11 m depth. No vegetation was observed deeper than 11 m. Each transect was 20 m long, and the presence of plant species was recorded at intervals of ⅓ m. The data were recorded underwater by writing on a sheet of aluminum foil held in a mental clipboard. The aquatic vegetation was more abundant on the southwest—facing slope than on the northeast—facing slope of the lake bottom. This difference has been attributed to a difference in solar insolation. Some of the significant interspecies correlations which were observed appeared to be related to water depth and the texture of the substrate.
Vertical Zonation of Inshore Fishes in the Upper Water Layers of the Hawaiian Islands
Authors: Gosline William A.
Published: May 2006

The Hawaiian Islands are in the trade wind belt; they have about a 1—m tide. Along open coasts the effect of the tide on the zonation of inshore fishes is minor compared to that of the surge. Above sea level, pools depend primarily on wave splash for replenishment. The higher splash pools have few species of fishes, and those that occur there are ecologically well differentiated. On the exposed rocky benches just above sea level, there is usually abundant seaweed, but one herbivorous blenny is the only fish that lives there. For some 6 m or more just below sea level on open coasts horizontal water movement frequently scours the bottom, often with the abrasive action of sand added. The bottom here is of rock or sand. Most of the species of the area are herbivores which graze on such short algal stubble as exists on the rocks. Indeed, in both species and individuals, the maximum number of herbivorous fishes would seem to occur in this zone. In the quiet water offshore from, and just below the surge zone the best live coral formations in the Hawaiian waters grow. Here there is also a fishes below this point are scarce. Preliminary information suggests that the differentiation of the fish fauna at deeper levels is far more gradual, and that there is still a considerable number of species to at least half a mile in depth. Around the high Hawaiian Islands the waters protected by fringing reefs appear to have a mixed zonal fauna containing partly surge zone fishes, partly fishes that come in from quiet, deeper water, and partly forms restricted, so far as known, to such areas.
Estimation of Dry Weight of Tree Components and Total Standing Crop in Conifer Stands
Authors: Baskerville G. L.
Published: May 2006

The distribution of dry weight among six tree components is shown for balsam fir from 1 to 10 inches in diameter at breast height. Component dry weight and total standing crop are estimated and compared for a 0.2—acre plot using methods based on every—tree summation, stand tables, and several short—cut techniques based on “average” trees. It is concluded that the average tree approach is useful only where a rough estimate of total biomass is desired.
Phenological Observations of Spring Geophytes in Quebec
Authors: Vezina Paul E. , Grandtner Miroslav M.
Published: May 2006

Observations were made in a sugar maple (Acer saccharum Marsh.) stand on the phenological response of three geophytes, Claytonia caroliniana, Erythronium americanum, and Trillium erectum, to solar radiation and temperature. The three species started development when the ground was partly covered with snow. The peak of the leafing and flowering stages occurred prior to the lead development of the maple canopy. Two of the geophytes, Claytonia and Erythronium, completed their life cycle prior to leaf development in the canopy. The life cycles appear to be strongly influenced by temperature and solar radiation.
A Study of Population Growth and Control Exhibited in the Laboratory by Prairie Deermice
Authors: Terman C. Richard
Published: May 2006

Freely growing laboratory populations of prairie deermice were founded by releasing four adult males and four adult females into enclosures containing food and water in excess of utilization. Growth ceased in each population at markedly variable numerical levels though under similar conditions of the physical environment. Control of population growth was achieved by one of two means: cessation of reproduction or failure of young to survive. Reproduction by females founding the populations was significantly more frequent than that of females born into the populations. The evidence suggests that factors controlling the growth of laboratory populations of prairie deermice are basically behavioral, are a result of intrinsic differences in each population and are not directly related to the number of animals in each population per se.
The Caloric Content of Migrating Birds
Authors: Odum Eugene P. , Marshall Shirley G. , Marples Timothy G.
Published: May 2006

Determinations of kilocalories per ash—free gram dry weight of 32 individuals of 20 species ranging from exceedingly fat migrants to lean nonmigrant birds revealed the following: 1) Long—range migrants at peak of fat decomposition in the fall had a caloric content of 7.9 to 8.3 (mean 8.1) kcal/g ash—free dry weight. 2) Spring arrivals were between 5.7 and 7.4 (mean 7.0). 3) Lean nonmigrants were between 6.0 and 6.9 (mean 6.3). 4) The caloric value of the ash—free nonfat body component was the same for all three groups, averaging about 5.5, indicating that decomposition and utilization of fat during migration does not affect the caloric content of the nonfat portion of the bird's body.
A Method to Determine Heat‐Caused Mortality in Bunchgrasses
Authors: Wright Henry A.
Published: May 2006

This paper describes a method for separating plant morality due to heat from mortality caused by herbage removal; squirreltail (Sitanion hystrix (Nutt.) J. G. Smith) and needle—and—thread (Stipa comata Trin. and Ruper.) are used as examples. After plants are burned in the field under controlled conditions, ratios are calculated between field—measured durations of temperatures in plants and laboratory—measured thermal death times for plant tissue. If the sum of the ratios for the various temperatures is 1.0 (designated 1 necrotherm) or greater, mortality is attributed to heat; if the sum is less than 1.0, to herbage removal. Further testing of the "predictor" on more species, sites, years, etc., is needed, but the method appears very promising. For the two bunchgrasses tested, heat alone accounted for all mortality by fire, except during July. The time required for a specific temperature to kill plants varied with season. To predict thermal death times for bunchgrasses and thus simplify the laboratory determinations, an empirical equation was developed.
The Role of Food in the Regulation of the Pond Snail, Lymnaea Elodes
Authors: Eisenberg Robert M.
Published: May 2006

Inverse relationships between snail density and mean snail size, mean number of eggs per egg mass, as well as total eggs were found to disappear with food additions. Food additions also appear to have enhanced the survivorship of snails. Evidence is presented with indicates that the food limitation in the snail is one which probably involves accessory growth factors. The sensitivity to and magnitude of regulatory responses during the life history of the snail are discussed.
Correlation of CO2 Exchange with Moisture Regime and Light in Some Wyoming Subalpine Meadow Species
Authors: Scott D. , Hillier R. D. , Billings W. D.
Published: May 2006

Multiple regression analysis showed that CO2 exchange of shoots subalpine meadow plants, as determined by field measurements, was correlated with light and some aspect of moisture regime (either leaf relative turgidity or soil moisture), but not with temperature.
Terrestrial Activity in Aquatic Turtles
Authors: Bennett David H. , Gibbons J. Whitfield , Franson J. Christian
Published: May 2006

Individuals of three species of aquatic turtles (Kinosternon subrubrum, Pseudemys scripta and Deirochelys reticularia) were captured in drift fences after emigrating from a Carolina bay in South Carolina. Each turtle was tagged with Tantalum—182 pins and relocated with a portable beta—gamma survey meter. Turtles were found burrowed at various depths (2—11 cm) below the surface and up to 600 m from the aquatic environment. The number of days an individual was followed the land distance moved were significantly correlated. Temporary emigration and shallow burrowing by K. subrubrum are possibly mechanisms for predator avoidance in that individuals which concentrate in a drying—up aquatic area are selected against.
The Influence of Chronic Gamma Irradiation on Production and Decay of Litter and Humus in an Oak‐Pine Forest
Authors: Woodwell G. M. , Marples T. G.
Published: May 2006

The irradiated forest at Brookhaven National Laboratory was used to examine the flux of organic matter through the organic horizon of soil. Production of litter along the gradient of intensity of radiation proved an excellent criterion of radiosensitivity. The standing crop of organic matter in soil was about 6,300 g (dry weight)/m2. Of this about 4,700 g was humus and 1,600 g litter. Annual input of litter averaged 342 g; of roots, about 311 g. The rate of decay of all organic matter in the surface soil was 10—12%/year. The litter layer decayed more rapidly at about 16%/year, the humus more slowly at about 8.4%/year. Decay of litter of white oak in the first year on the ground was 58%, that of scarlet oak, 67%. Irradiation at 600—700 R/day consistently increased the rate of decay of litter. Studies of the radiosensitivity of the principal species of trees and shrubs showed: (1) a lag of 1 year in the initial effects of irradiation behind the exposure causing them; (2) a regular increase after the first year in total cumulative exposure causing 50% reduction in the production of foliage; and (3) shifts in the relative sensitivities of species with time: the scarlet oak, initially more sensitive than the white oak, recovered in 3 years to be more resistant than white oak, and the sensitivities of white oak and pitch pine appear to converge at about 30 years.
Late‐Pleistocene Boreal Forest in the Western Ozark Highlands?
Authors: Mehringer Peter J. , Schweger Charles E. , Wood W. Raymond
Published: May 2006

The recovery of a spruce—dominated pollen spectrum and associated spruce and larch macrofossils offers evidence for late—Pleistocene boreal forest elements in the Ozark Highlands of southwestern Missouri.
Decomposition of Loblolly Pine Needles With and Without Addition of Dogwood Leaves
Authors: Thomas William A.
Published: May 2006

Weight losses of decomposing loblolly pine (Pinus taeda) needles were measured in two series of litter bags: (1) without deciduous leaves and (b) with addition of dogwood (Cornus florida) leaves. First—year decomposition rates of needles in the two types of litter did not differ significantly. Loss of needle weight averaged 44% after 1 year in litter. Total number of animals extracted during the year from the 26 litter bags containing mixed litter (11,211) surpassed that from the 26 samples of needles alone (6,458). Collembola (springtails), Acarina (mites), Diptera (flies), and Hymenoptera (ants) apparently made the greatest faunal contribution to litter breakdown. Populations in mixed litter in excess of those in needles alone evidently were confined to dogwood leaves and did not aid in needle decomposition.
The Effects of Two Acute Stresses on the Arthropod Component of an Experimental Grassland Ecosystem
Authors: Bulan Carol A. , Barrett Gary W.
Published: May 2006

The effects of two acute stresses, mowing and burning, on the arthropod component of an experimental grassland ecosystem were investigated. Oats (Avena sativa L.) were planted in two comparable and adjacent 1—acre areas. Midway in the growing season (July), one area was mowed and the other areas was both mowed and burned. Density and biomass were used to measure the effects of both stresses on the total arthropod community, while species diversity and equitability were used to analyze the species composition and apportionment of the Coleoptera. Effects of mowing on arthropod density and biomass appeared to be relatively brief (2 weeks) as compared with those of burning (3 months). This difference was attributed to a shift from live primary producer energy to detritus in the mowed area, as compared to the almost complete destruction of the energy source in the burned area. Coleoptera species/area diversity was significantly lower (P < 0.01) in the burned area. This was attributed to a greater energy supply and a larger number of ecological niches in the unburned grid. Margalef's species diversity, D = (S—1)/1nN, for the total Coleoptera community was significantly reduced (P < 0.05) in response to the fire. When analyzed by trophic levels on a long—term basis, herbivorous Coleoptera species diversity was significantly reduced (P < 0.01), whereas that of the carnivorous Coleoptera was not measurably affected. Herbivorous Coleoptera equitability values, in response to mowing, exhibited a brief increase before returning to the premow level. In response to burning, however, herbivorous Coleoptera equitability values remained higher than those in the unburned area, indicating a longterm limitation of resources. Carnivore equitability values did not exhibit a long—term increase in response to the fire stress. Coleoptera responses to fire revealed that biomass, species/area diversity, and primary consumer species diversity and equitability were the most sensitive indicators for evaluating the effects of an acute environmental stress such as fire. Coleoptera responses appeared to be representative of the total arthropod community.
Recurrent Groups of Diatom Species in the North Pacific
Authors: Venrick E. L.
Published: May 2006

Associations of planktonic diatom species in four epipelagic environments of the North Pacific have been defined using a recurrent group analysis. The distribution of the groups was related to the physical habitats. Within conservative environments the species associations appear relatively permanent, undergoing minor fluctuations in composition and distribution, which may be related to the annual hydrographic cycle. Within the non—conservative environments, species associations appear to redevelop each year, and their composition must depend upon the introduction of seed cells from adjacent environments. Multiple regression analysis was used to examine the relation of the biomass of each recurrent group to selected environmental parameters. The regressions were dominated by hydrographic parameters, emphasizing the importance of surface circulation patterns in the ocean for the creation and maintenance of species associations. The increased importance of the depths parameters during the summer suggests that differential responses to vertical gradients in the environmental may result in the segregation of species groups within any one habitat.
Physiological Responses to Temperature in the Alligator Lizard, Gerrhonotus Multicarinatus
Authors: Dawson William R. , Templeton James R.
Published: May 2006

The effects of temperature upon oxygen consumption, heart rate, breathing rate, and evaporative water loss of resting alligator lizards. (Gerrhonotus multicarinatus) were analyzed. The Q10 for oxygen consumption remains constant at 3.1 between approximately 4°C and the upper level of thermal tolerance for this species, 39°—40°C. That for heart rate remains 2.3 between 10° and 39°—40°C, increasing to 7 between 10° and 5°C. The disparity in temperature coefficients for the two functions in the former range means that animals must meet the increased requirements for oxygen that develop with heating by increasing not only heart rate, but also stroke volume and/or the amount of oxygen withdrawn in the tissues from each volume of blood. Breathing rate bears a complex relation to temperature, showing rapid increases (Q10°10) with temperature below 15° and above approximately 33°C. Within this thermal range it changes relatively little (Q10=1.4). At temperatures exceeding 38°C the lizards opened their mouths as if to pant, but the breathing rates and movements accompanying this activity were lower and more limited, respectively, than those found in panting iguanid lizards. Evaporative water loss by alligator lizards increases slowly with temperature between 25° and 30°C (Q10=1.5). Between 30° and 35°C a marked upswing in the evaporation—temperature curve commences. However, even at 38°C, evaporative water loss dissipates only 66% of metabolic heat production. Loss by this route exceeds metabolic production of water at all temperatures studied.
Germination and Growth of Some Semidesert Grassland Species Treated with Aqueous Extract from Creosotebush
Authors: Knipe Duane , Herbel Carlton H.
Published: May 2006

The effects of aqueous extracts from creosotebush (Larrea tridentata) material on germination and initial growth of black grama (Boutelous eriopoda), bush muhly (Muhlenbergia porteri), and creosotebush were studied. There was no apparent difference among extracts obtained from the various creosotebush plant parts. An aqueous extract from leaves and twigs significantly reduced germination of black grama caryopses, but the germination of bush muhly caryopses and of creosotebush seeds (removed from the carpels) was not affected. Less concentrated extracts did not significantly reduce germination of test species. However, radicle and plumule growth of black grama and bush muhly were significantly reduced by all extracts. Apparently the relatively low osmotic concentrations or the moderate pH's were not responsible for these reductions in growth. Comparison among creosotebush seeds (removed from the carpel) watered with a carpel extract and a water—mannitol solution of the same osmotic concentration, and carpels treated with water indicated that there is a structural characteristic or a non—water—soluble chemical compound in the carpel which inhibits germination of creosotebush. Germination of creosotebush seeds treated with water—mannitol solutions of 1.50, 3.50, 5.00, and 7.00 atm osmotic concentration was significantly reduced as compared to those treated with low concentrations simulating field capacity. Nutrient solution recycled for 37 days around the roots of creosotebush plants growing in a gravel—sand substratum was not inhibitory to germination or initial growth. In a pot test, creosotebush extracts created a crust on the soil surface which reduced the infiltration rate of water. Some of the preceding factors may possibly contribute to the degeneration of grassland areas where creosotebush is present.
The Mineral Content of Myriophyllum Spicatum L. in Relation to Its Aquatic Environment
Authors: Anderson Richard R. , Brown Russell G. , Rappleye Robert D.
Published: May 2006

The mineral composition of Myriophyllums spicatum L. (Eurasian water—milfoil) and its aquatic environment were investigated to determine the relationship between ionic contents in the plant and in the water. Systematic samplings were made in several areas. The species was growing in a wide range of environmental situations. Normal—appearing specimens were collected at water temperatures ranging from 0.2 to 30°C. Salinities varied from 0.05 to 16.4 ppt. Each of the estimate collecting sited fluctuated about 7 ppt during the experimental period. The fresh—water pond varied between 0.05 and 0.20ppt. The pH values ranged from 5.8 to 9.5 with alkaline waters predominating at four of the five collecting stations. M. spicatum was capable of regulating salt intake independent of concentrations in the aquatic environment.
Adaptive Significance of Large Size and Long Life of the Chaetognath Sagitta Elegans in the Arctic
Authors: McLaren Ian A.
Published: May 2006

Zooplankton of high latitudes generally develop more slowly, reach a large size, and live longer than related forms in warmer seas. Existing explanations are reviewed and a new one offered. Where generation length is set by marked seasonality of food supply, as in the arctic, high fecundity and associated large size and slow development may be selected for. It is shown from analysis of generation length, fecundity, and natural mortality of the chaetognath Sagitta elegans than its biennial life cycle in the eastern Canacian Arctic is of optimal length.
The Photorefractory Period of the House Finch
Authors: Hamner William M.
Published: May 2006

The timing mechanisms of testicular regression and photorefgractoriness were investigated with the Houswe Finch. Testicular regression is completed by August and is followed by a month and a half photorefractory period. Resumption of complete photosensitivity is an indicidual, gradual precess of several months. Stainable neurosecretion in the median eminence of the hypothalamus appears unrelated to photorefractoriness. Lipids concentrate in regressing testes, disappear by mid—September and then the interstitium stains for fats. Changes in gametogenesis do not occur during photorefractoriness. Testicular regression can be induced at will, and photofractoriness is not a necessary concomitant thereof. Regression of intermediate sixed testes appears related to a lack of gonadotropic hormone release; growth of intermediate sized testes is probably additive on a daily basis. Regression of fully developed testes can occur spontaneously; then regression is followed by photorefractoriness Spontaneous regression can occur under continuous illumination and LD 18:6 regiments; photorefractoriness is porlonged by these regimens. testosterone injections do not induce regression, but enhance testiculargrowth. Prolactin does not affect either growth or regression of the testes, but causes bodily fattening. PMS and testosterone do not hasten refractory termination. Although both promote precocious growth, the testes regress upon hormone withdrawal. Short days (LD 6:18) and long days (LD 10:14, LD 12:12, LD 14:10) all terminate photorefractoriness equally. A circadian rhythm may contribute to termination of photorefgractoriness. Previous photorefractory control hypothesis are enumerated, types of possible timing machanisms are considered, and a new hypothesis proposed, tested, and discussed. A model of breeding control for the entire annual cycle is developed, consistent with all field and laboratory observations.
Temperature Dependent Behavior of the Cactus Wren
Authors: Ricklefs Robert E. , Hainsworth F. Reed
Published: May 2006

Field and experimental observations show that, as temperature become progressively hotter, Cactus Wrens select relatively cooler micorhabitats, and that after the minimum temperature reaches a critical level of stress, activity decreases. These results lead us to conclude that insectivorous desert birds such as the Cactus Wren are true xerophiles, since they show behavioral adaptations for existence in the desert in the face of limited water intake.
Variation in Seed Weight and Germination in Populations of Amaranthus Retroflexus L.
Authors: McWilliams E. L. , Landers R. Q. , Mahlstede J. P.
Published: May 2006

Amaranthus retroflexus L. seeds were harvested from plants grown under uniform conditions in Ames, Iowa, from seeds collected in North America and eastern Europe. Germination of seeds from northern populations was significantly higher at 20°C than that from southern populations at the same temperature. Germination percentages were highest in all cases at 35oC. No correlation was found between percentage germination at 35°C and latitude, but there was wide variation between populations in germination response. Populations from the drier parts of the United States tended to show greater dormancy. This weed species does not appear to have a characteristic dormancy and germination, requirement over its range. Variations in germination percentage between populations at either temperature were concluded to be a result of ecological differentiation. Seed weight decreased significantly from northern to southern sources. Larger seeds and the ability to germinate at lower temperatures may be of selective advantage in northern populations where this annual species must mature in a short growing season.
The Effect of Time of Food Deprivation on the Routine Oxygen Consumption of Largemouth Black Bass (Micropterus Salmoides)
Authors: Glass Norman R.
Published: May 2006

One component of a predatory fish energetics model which is currently being structured and studied in our laboratories is described by the experimental components analysis approach. The purpose of the predictive model is to permit the incorporation of routine metabolic requirements of predatory fish into a much larger mathematical model of the energy needs of largemouth black bass and other predators which behave in similar fashion. The submodel presented here is intended to describe and predict only one of the several components which interact and contribute to the food requirments of largemouth black bass in particular and certain other predators in general.
Life Histories and Community Stability
Authors: Frank Peter W.
Published: May 2006

In stable communities a major fraction of species are longevous; perennial plants in terrestrial, and largely benthic invertebrates in marine situations. The question is raised whether the relationship is fortuitous or depends on positive feedback. Available evidence often seems insufficient to rule out a third alternative, that it is tautological.
Studies on Selective Feeding in the Pacific Starfish Pisaster in Southern California
Authors: Landenberger Donald E.
Published: May 2006

The asteriid starfish Pisaster giganteus and Pisaster ochraceus are important predators of mollusks. Experiments were designed to determine the extent to which predation by starfish on different kinds of prey is selective, and to learn whether selectivity varies according to 1) number and relative density of various alternative prey and 2) past history of feeding of the predators. Seven species of intertidal mollusks were used as prey. When alternatives were presented in equal abundance and in pairs, both species of starfish showed a significant preference for one alternative in all but one pairing. The hierarchy of preferences was well—defined and consistent among replicates. When seven species of prey were presented together in equal abundance, the preferences were of the same patter but were, in general, weaker than those exhibited when prey were presented in pairs. In all experiments, mussels were preferred over other mollusks; the strongest preferences were for Mytilus edulis and Mytilus califonianus over other alternatives. Where mussels (M. californianus) and snails (Tegula funebralis) were presented as alternative prey, changes in their relative densities had little effect on the preference for mussels. When the relative densities of two species of snails (T. funebralis and Acanthina spirata, neither preferred when in equal densities) was varied, a slight preference was shown for the more abundant form at one extreme density only. In this experiment individual starfish exposed to the same relative densities of alternative prey differed in the proportions of alternatives they chose. Starfish fed only on snails (T. funebralis) for 3 months showed an increased preference for these snails over chitons (Nuttalina californica) as well as a reduced preference for mussels; the latter preference reappeared strongly after only 1 week of exposure to both prey. The hypothesis that predators induce stability in prey populations is discussed. The experimental results indicate the importance of preferential feeding to this question. Models of selective feeding based on short—term changes in hunger and situation may be inappropriate when applied to cold—blooded predators. An alternative interpretation, based on learning and hunting behavior, is given for the changes in selectivity observed in these experiments.