bluuebunny/crossref_metadata_2025 huggingface dataset:
Contributions to the Biology of Larrea Species
Authors: Barbour M. G. , Diaz D. V. , Breidenbach R. W.
Published: May 2006

Seeds were collected from three taxa: L. divaricata from Arizona in the Sonoran desert of North America (LDNA); and L. divaricata and L. cuneifolia from northwestern Argentina, in the monte of South America (LDSA and LC). These three desert shrubs are generally not sympatric, and LDSA appears to occupy the most mesic sites. Seedlings were grown to the age of 3—7 mo in a greenhouse and compared as to root— and shoot—growth rate, photosynthesis and transpiration under high and low water stress, pathway of photosynthesis employed, leaf stomatal density, and leaf anatomy. Herbarium specimens collected from 55 sites along moisture gradients were also analyzed for path of photosynthesis, leaf stomatal density, and leaf anatomy. Under mesic conditions, LDSA had a higher growth rate, yet maintained the lowest biomass fraction in leaves and the highest in roots. There were no differences among taxa in net photosynthesis, though LDSA had a significantly higher transpiration rate. Under xeric conditions (plant pressure potential about —45 atm), the photosynthetic rates of LDSA were depressed the most, but variability within taxa prevented conclusions on differences in rates of photosynthesis and transpiration. Stomatal density was greatest for LDSA and least for LC, and these differences were maintained in the greenhouse. Reduction in stomate number seems to be a major mechanism for transpiration reduction between Larrea taxa, but within a taxon there was no relationship between site precipitation and stomatal density. The path of photosynthesis (from 13C/12C and enzyme—activity ratios) was consistently C3. Leaf cross—sections appeared to reveal mesophyll differences between LC and the two LD taxa. Two ecotone sites, where LDSA and LC share dominance, were sampled for community structure and the presence of putative hybrids. One site, with a one—to—one ratio of Larrea taxa, showed no evidence of biotic interaction between the taxa or between them and associated species, and hybrids accounted for less than 1% of all shrubs. Analysis of mass—collected random leaf samples also showed little evidence of hybridization in leaf shape or stomatal density. A second ecotone site, 600 km to the south, differed in some respects from the above, but, again, hybridization was a rare event. The basis of the mesophytic nature of LDSA might lie with its shrub architecture as well as with its physiological properties.
Biomass, Annual Net Primary Production, and Dynamics of Six Mineral Elements in a Post Oak‐Blackjack Oak Forest
Authors: Johnson Forrest L. , Risser Paul G.
Published: May 2006

Dimension analysis was used to estimate biomass and annual net primary production for a post oak—blackjack oak (Quercus stellata—Q. marilandica) forest in central Oklahoma. Concentrations of six mineral elements in various plant tissues were determined and used with biomass and production estimates to calculate the annual cycle of N, P, K, Ca, Mg, and Mn in the forest. Total organic material in the forest is 245,000 kg/ha, of which 1.6% is leaves, 26.4% live branches, 5.9% dead branches, 44.8% trunks, 15.9% roots, 9.6% understory, and 4.4% litter. Annual net primary production is 14,900 kg/ha, distributed as follows: 32.0% leaves, 28.0% twigs and branches, 24.9% trunks, 15.1% roots, and 2.0% understory. Maximum leaf area index was 4.8. Yearly mean litterfall is 5,400 kg/ha and is distinctly biomodal, with peaks in November and March. The biomass contains 1,157 kg/ha N, 101 kg/ha P, 1,258 kg/ha K, 4,549 kg/ha Ca, 311 kg/ha Mg, and 124 kg/ha Mn. Yearly mineral budgets were determined for the six elements. Unusually high values for Ca in the biomass and in the mineral cycle were due to high concentrations of Ca in post oak bark (90,200 mg/g). High annual values for increment of biomass and for retention of mineral elements indicate that the stand has not reached a steady state, a conclusion that is confirmed by observations of stand structure.
Turbulence and the Visualization of Wind Flow
Authors: Moen Aaron N.
Published: May 2006

Air flow in the natural environment affects the distribution of organisms, mechanical stresses, heat losses by convection, and moisture distribution. Air flow was visualized by bubble tracers in a wind tunnel, and the flow patterns over solid barriers 5 and 15 cm high and 0%, 25%, and 47% porosity barriers, each 10 cm high, were photographed. The leeward circulation pattern is very similar regardless of the barrier height. The leeward effect of the barrier extends a greater distance for the 47% porosity than for the 25% and 0% porosities. The three—dimensional characteristics of visualized turbulent flow clearly indicate the limitations of cup anemometers for measuring field velocities since these instruments do not respond to angles of attack from 70° to 90°.
The Role of Grass Shrimp, Palaemonetes pugio, in a Tidal Marsh Ecosystem
Authors: Welsh Barbara L.
Published: May 2006

The grass shrimp, Palaemonetes pugio, is a dominant species uniquely adapted to a highly stressed tidal marsh embayment. Monthly sampling of length and dry weight revealed that its life cycle was a single year, with spawning in May, June, and July and most rapid growth in late summer and fall. Mark and recapture estimates conducted quarterly and quadrat net estimates calculated monthly indicated that shrimp were present throughout the year and that densities peaked in the fall (over 1.2 million in 0.01 km2 in October). Production of biomass (growth) equated loss to predation (including decomposition) over the annual cycle, averaging 0.2 kcal°m—2°day—1. Respiration averaged 1.1 kcal 1.1 kcal°m—2°day—1. Average daily production per square meter of total consumables (fecal pellets = 0.8 kcal, dissolved organic matter [DOM] = 0.7 kcal, biomass = 0.2 kcal) was 60% of total ingestion (2.9 kcal); production of feces and DOM thus outweighed biomass production 15:2. Microcosm studies and observations by scanning electron microscope revealed that shrimp macerated detritus into a heterogeneous assortment of uneaten particles by plucking away the cellular matrix from surfaces of large detrital fragments. This action provided cavities that became heavily invaded by pennate diatoms, and particles that became suspended in the water column and populated by bacteria. Nutrient analyses indicated the shrimp excreted large quantities of ammonia and phosphate which together with DOM release was presumably responsible for heavy growth of microflora and increased protein fraction in both feces and large and small uneaten detrital fragments. Palaemonetes pugio, while supporting its own trophic requirements, accelerated breakdown of detritus, preventing blockages or accumulations that might have occurred from pulses of emergent grass and macroalgal detritus in the embayment. This repackaging into feces, heterogeneous fragments, DOM, and shrimp biomass made detrital energy available at a variety of trophic levels, smoothing out organic pulses over time and space, and raising the efficiency of transfer to the food web. The special adaptation of P. pugio to the low—oxygen environment of the decomposer system appeared to limit predation and competition, allowing the shrimp to develop large populations necessary to carry out its role effectively.
Model Estimation of Energy Flow in Northwestern Coniferous Forest Bird Communities
Authors: Wiens John A. , Nussbaum Ronald A.
Published: May 2006

A simulation model developed in the Grassland Biome Program of the US/IBP is applied to data gathered in the Coniferous Forest Biome Program to estimate the magnitudes and patterns of energy flow in breeding bird populations in Northwestern coniferous forests. Six stands along a moisture—temperature gradient in the central Oregon Cascades supported breeding avifaunus of 7—15 species, with standing crops of 223—526 g/ha. Total energy flow through these avifaunas during the April—October breeding season was estimated at roughly 10 kcal m—2 season—1 in the low—elevation, moderately xeric stands; 12 kcal m—2 season—1 in the high—elevation stands; 17 kcal m—2 season—2 in a mesic floodplain stand; and 21 kcal m—2 season—1 in a midelevation transitional stand. About 1% of the seasonal energy flow was channeled into production, while reproduction—related processes accounted for 15%—16% of the total energy intake. Thermoregulation required 13%—19% of the seasonal total, with the higher relative costs associated with the cooler, higher elevation stands. Foiliage—gleaning bird species accounted for the greatest proportion of the energy intake at most stands, but within this guild the importance of granivorous opportunistic species generally increased through the stand sequence as the growing season became shorter and environmental conditions more severe.
Localized Ecotypes of Thuja occidentalis L. in Wisconsin
Authors: Musselman Robert C. , Lester Donald T. , Adams Michael S.
Published: May 2006

Northern white cedar (Thuja occidentalis L.) sometimes occurs in wet lowlands, and adjacent, relatively dry upland sites suggesting potential localized ecotypic differentiation as a response to selection for moisture stress tolerance. This study examined morphological and physiological responses to root—zone water potential (RWP) of adjacent upland and lowland northern white cedar populations, and related the responses to soil moisture of the habitats as a basis for ecotypic differentiation. In common environment experiments, seedlings from one pair of upland and lowland populations separated by less than 0.7 km illustrated separate ecotypes presumably resulting from natural selection for response to moisture stress. Variation between two study areas in degree of ecotypic differentiation suggested a polytopic origin of the upland and lowland ecotypes. Lowland soils had higher moisture—holding capacity than did upland soils. A study of seedling growth in different soil media showed that as moisture—holding capacity increased in the soil, seedling tops increased in size and root form changed from a long taproot with few laterals to shorter, thicker roots with many laterals. In test of photosynthetic response to temperature, irradiance, and RWP, 6—mo—old northern white cedar seedlings maintained high rates of net phytosynthesis under a wide range of environmental conditions.
Pattern and Seral Composition in an Old‐growth Beech‐Maple Forest
Authors: Williamson G. B.
Published: May 2006

A nested quadrat pattern analysis suggests that the adult members of early seral tree species exhibit maximal clumping at a quadrat size corresponding to the sizes of natural lightgaps created by treefalls. However, the dominant species show a pattern of randomness at nearly all quadrat sizes. Some seral characteristics of forest trees support the idea that the beech—maple forest is a mosaic of species of different seral stages.
Food‐Habitat Relationship of Sea Ducks on the New Hampshire Coastline
Authors: Stott Richard S. , Olson David P.
Published: May 2006

Use of habitat, food preferences, and food availability were studied for seven species of waterfowl (white—winged scoter (Melanitta deglandi), surf scoter (M. perspicillata), common scoter (Oidemia nigra), oldsquaw (Clangula hyemalis), common goldeneye (Bucephala clangula), bufflehead (B. albeola), and red—breasted merganser (Mergus serrator)) on a 34—km section of the New England coastline during 1968—70. The three scoters selectively used areas of sandy substrate and had very similar food habits. The principal foods were the Atlantic razor clam (Siliqua costata) and Arctic wedge clam (Mesodesma arctatum), which were characteristic of, and abundant in, sandy substrate. In contrast to scoters, goldeneye preferred areas of rocky substrate associated with rocky headlands. They fed primarily on amphipods, isopods, crabs, and gastropods, which were commonly found in the Irish moss (Chondrus crispus) covering of the rocky sublittoral areas. Red—breasted mergansers, like goldeneye, also used the rocky areas. They fed primarily on several small fish species that were observed among the Irish moss and crevices of the rocky substrate. Bufflehead had the most restrictive distribution, being confined mostly to estuaries. Bufflehead fed primarily on sand shrimp, which were found only in harbors with soft ooze bottoms. Oldsquaw had the most generalized diet of all the sea ducks. The major food items consisted of bivalves, gastropods, sand shrimp, and isopods, which were found throughout the study area and accounted for the generalized distribution of oldsquaw along the coastline and in the harbors. Sea ducks were concentrated near the mouths of the estuaries, where more abundant food resources particularly bivalves, were found. Although the species vary, the types of foods eaten by sea ducks were similar to those described in other studies. Thus, food availability, coupled with the physical structure of the substratum in the different coastal habitats, is apparently a major determinant in the way that coastal waterfowl selectively use habitat types. The described patterns of habitat usage appear to have implications for other wide geographical areas.
A Study of the Ozark Hellbender Cryptobranchus Alleganiensis Bishopi
Authors: Nickerson Max A. , Mays Charles E.
Published: May 2006

A tag—recapture study of the Ozark Hellbender salamander, Cryptobranchus a. bishopi, was made on the North Fork of the White River, Ozark Co., Missouri. During the summers of 1969 and 1970, animals were tagged along a 2.67—km stretch of stream bed. Population estimates were 428 with 95% C.L. of 341—573 hellbenders/km of stream bed. Biomass estimates were 156 kg/km with 95% C.L. of 124.5—210 kg/km of stream bed. Density estimate in prime habitat was one/8—10 m2 with 95% C.L. of one/6—7 m2—one/13—16 m2. Recaptures indicated little movement. Ozark Hellbenders are one of the dominant organisms in this stream system.
Adaptive Strategies and Energetics of Tail Autonomy in Lizards
Authors: Vitt Laurie J. , Congdon Justin D. , Dickson Nancy A.
Published: May 2006

Various methods were used to study and qualify components of tail autotomy adaptation in four species of lizards; Coleonyx var eiegatus (Gekoniadae), Eumeces skiltonianus and Eumeces gilberti (Scincidae), and Gerrhomotus multicar inatus (Aguidae). High frequency of tail breaks in natural population of these species (65%, 62%, 52%, and 74% respectively) suggests the effectiveness of autotomy for predator escape. In species where tail autotomy is most important for escape, regenerated tails are as large or larger than the original tails. Regenerated tails were higher in lipids and energy than original tails, which were, in turn, higher than bodies. The species with alternate uses for the tail (other than predator escape via autotomy) exhibited lower rates of energy allocation to regeneration and the regenerated tails were lower in energy content (both per unit weight and total, proportionately) than tails of other species studied. Total growth energy allocated to tail regeneration varied from 24.7% in G. multicarinatus (the species least adapted for autotomy) to 56.5% in E. gilberti (a species highly adapted for autotomy). Regeneration was most rapid in short—lived early—maturing species, those with several breeding opportunities in a given season. Species with high probabilities of future reproductions (long—lived, late—maturing) and short, seasonally restricted breeding seasons, regenerated tails at low rates. Energy allocations to tail regeneration were varied within and among species. Generally, immatures of all species except G. multicarinatus allocated proportionately less to tail regeneration and more to body growth than adults. Energy allocations to tail regeneration in G. multicarnatus were relatively consistent across age groups. A summary of pathways by which autotomy adaptations may be selected for, or by which retention adaptations may evolve, is presented.
A Complex Community in a Simple Habitat: An Experimental Study with Bacteria and Phage
Authors: Chao Lin , Levin Bruce R. , Stewart Frank M.
Published: May 2006

Continuous culture populations of the bacterium especially coli and its virulent virus T7 have been studied as a model of a predator—prey in a simple habitat. These organisms maintain apparently stable states of coexistence in: (1) a phage—limited situation where all of the bacteria are sensitive to the coexisting virus and the sole, and potentially limiting carbon source, glucose, is present in excess; and (2) a resource—limited situation where the majority of the bacteria are resistant to these phage and in which there is little free glucose. The composition of these interacting populations is examined in detail and evidence indicating that this simple experimental culture system can support relatively complex communities is presented. In the predator—limited situation, two populations at each of two trophic levels can be maintained; the wild—type bacterial and phage strains, denoted B0 and T70, a mutant bacterial clone which is resistant to T70, denote B1 and a host range mutant phage, T71 which is capable of growth on both B0 and B1. In the resource—limited situation, three populations of bacteria and two populations of phage can coexist. The include the above described clones and a third bacterial strain, B2, which is resistant to both T70 and T71. In phage—free competition, the wild—type B0 bacterial clone has a marked advantage relative to both B1 and B2 while no difference is detected between B1 and B2. When competing for a B0 host, the wild—type T70 phage clone has a marked advantage over T71. The fit of these observations to some previously developed theory of resource—limited growth, competition and predation is discussed and a mechanism to account for the persistence of these communities is presented. The latter assumes that their stability can be attributed solely to intrinsic factors, i.e., the population growth and interaction properties of the organisms in this continuous culture habitat.
Density Dependent and Density Independent Regulation of Reproduction in the Gila Topminnow, Poeciliopsis Occidentalis (Baird and Girard)
Authors: Schoenherr Allan A.
Published: May 2006

Studies of the Gila topminnow, Poeciliopsis occidentalis, indicate that onset of reproduction, proportion of reproducing ♀ ♀, and numbers of embryos carried by ♀ ♀ are influenced by H2) temperature, photoperiod, food, and predation. Water temperature and photoperiod act upon the fishes regardless of population density, whereas, nutrition influences and predation are proportionate to population density. Therefore, density dependent and density independent factors operate to regulate reproduction and neither is mutually exclusive.
Optimization of Diets through Food Preferences by Heteromyid Rodents
Authors: Reichman O. J.
Published: May 2006

The number of seeds requiring per day by four species of Sonoran Desert rodents (Dipodomys merriami, Perognathus amplus, Perognathus baileyi, and Perognathus intermedius), and the average energy content/seeds of the species the rodents ingested, were determined from information on the rodent daily energy requirement, proportions of seeds in the diets and cheek pouches of the rodents and the soil near their capture sites, and the energy content per seed of the important seed species. All rodent species except P. amplus gather seeds which are energetically superior to those randomly available in the soil, and all species choose to ingest, from the seeds they have gathered, those seeds which are richest in energy. The data indicate that the rodents primarily base their dietary preferences on energy considerations. The rodents do not, however, maximize energy intake, but rather optimize their diets by also ingesting a number of seed species which are relatively low in energy content, but which apparently provide some undefined value (e.g . nutrition, moisture).
Trophic Diversity Measurement in Sympatric Predatory Species
Authors: Hurtubia Jaime
Published: May 2006

It is suggested that Pielou's method (1966a) of estimating the diversity of a plant community from a series of randomly placed quadrats, can be applied to measuring dietary diversity of predatory populations. Treating each stomach as a sampling unit, an equivalent of a quadrat, it is possible to calculate for the whole predatory population the trophic diversity and the average of the trophic diversity with its standard error, and obtain a satisfactory representation of the prey species. The method proposed here may serve to produce important descriptive parameters in comparative ecological studies among sympatric species.
A Gray‐Scale For Measuring Reflectance and Color in the Insect and Human Visual Spectra
Authors: Kevan P. G. , Grainger N. D. , Mulligan G. A. , Robertson A. R.
Published: May 2006

A simple gray—scale, for measuring reflectance and color in the insect and human visual spectra, was produced by painting mixtures of magnesium oxide and carbon black powders in Collodion on filter paper.
Influence of Environmental Variability on Land Snail Population Properties
Authors: Randolph Polley Ann
Published: May 2006

Population characteristics of two species of land snails (Mesodon roemeri, Bulimulus dealbatus) were investigated in field and laboratory experiments. Field experiments consisted of transplantations of populations and artificial manipulations of temperature, moisture, and light levels in the two environments in which these species occurred. Results showed that the species which was part of an ecosystem with a more variable physical environment (and lower species diversity) exhibited a wider tolerance—niche, higher "r" value, shorter lifespan, smaller litter size, shorter developmental time, more general behavior relative to its habitat, more general food requirements, and smaller maintained biomass than did the species which occurred in a less fluctuating environment. Laboratory experiments confirmed field results on size of the tolerance niches and provided detailed description of the size—specific influences of the physical environment on the growth of Mesodon roemeri. The results are in agreement with a developing theory that relates environmental variability to ecosystem diversity and stability through these population properties.
Analysis of Insect Trophic Diversity in Two Salt Marsh Communities
Authors: Cameron Guy N.
Published: May 2006

This study analyzes tropic relationships of the insect components of two intertidal salt march communities dominated by Salicornia pacifica and Spartina foliosa, respectively. Seasonality of that component is determined and influence of physical microenvironmental factors on trophic diversity is assessed. Adult insect populations were monitored weekly, trophic diversity was computed, and relationships with primary production and litter accumulation were quantified. Temporal diversity trends were similar in both communities although the amplitude was slightly greater in Salicornia. In both communities, herbivore diversity was highest during the spring months while saprovore diversity was highest during midwinter. Predator diversity responded to both herbivore and saprovore diversity, although it was more closely tied to herbivore fluctuations in Salicornia. Standing crop biomass was maximum during October and litter accumulation was highest during Janurary. Two classes of adult insects occurred: peristent species, representing a low percentage of the total species compliment, were present as adults throuhout the year in both marsh communities; seasonal species, on the other hand, were present as adults only during the growing season. Seasonal succession in species of herbivores and saprovores reflected productional and transformational changes in plant matter; predators responded likewise, but more impressive was the numerical response to prey populations by particular predators. Correlations were high between each trophic group and its respective resource. Physical microenvironmental factors, especially temperature and vapor pressure deficit, seemed to be important in cuing larval development, but did not exert a dramtic effect on adult diversity trends. Several strategies of habitat utilization are considered. It is hypothesized that the persistent and seasonal species have evolved as specialists to avoid competitive interactions and maximize resource utilization. During annual expansion of resource states, the salt marsh insect component undergoes speices packing wherein additional species enter the system temporarily to utilize the expanded resource base.
Environment of a Costa Rican Forest
Authors: Allen L. H. , Lemon Edgar , Müller Ludwig
Published: May 2006

Wind speed and turbulence were measured at five heights simultaneously in a Costa Rican forest with non—stalling, heated—thermocouple anemometers. A persistent daytime stable thermal stratification of the air beneath the top canopy decreased small—scale turbulence, which may increase boundary—layer resistance of leaf—to—air transport of water vapor and CO2. Three CO2 source layers (ground level, trunk space, and above the top canopy) and two CO2 sink layers (top canopy and bottom canopy) were found in this forest. Low nocturnal wind speed allowed CO2 from respiration to accumulate at night.
Ecological Characteristics of Aristida Longiseta and Agropyron Spicatum in West‐Central Idaho
Authors: Evans G. R. , Tisdale E. W.
Published: May 2006

Germination requirements, root development, phenology, and the effects of moisture—saturated soils were studied in Aristida longiseta and Agropyron spicatum. Agropyron germinated well at temperatures of 20°—22°C, but Aristida showed little response until temperatures were increased to 40°C. Prior stratification at 0°C had no appreciable effect on germination of either species. Rapid primary root elongation enabled Aristida to establish itself in droughty habitats, but saturated soils strongly inhibited its growth. In the field A. longiseta starts growth late in the spring, develops at a rapid rate, and flowers 10 days later than A. spicatum. The seed of Aristida matures slowly and is shed in September. Fall regrowth, which occurs normally in A. spicatum, is rare in A. longiseta. The hypothesis is developed that excessive grazing has so reduced the abundance of A. spicatum that A. longiseta has been able to replace it and form long—lived communities.
Lake Mussel Distribution as Determined with Scuba
Authors: Cvancara Alan M.
Published: May 2006

Mussels were surveyed by SCUBA in Long Lake (47° 16½ N, 95° 17½ W), northwestern Minnesota, in 1969 along belt transects paralleling depth contours. Three species (in order of decreasing abundance)–Lampsilis radiata luteola (Lamarck, 1819), Anodontoides ferussacianus (Lea, 1834), and Anodonta grandis Say, 1829–were found at maximum depths of 9, 2, and 8 m, respectively. Mussel density descreased with depth from a maximum of 54 mussels/m2 at 1 m to 0.6 mussels/m2 at 9 m. A significant (P=0.05) decrease in shell height with depth was exhibited by Lampsilis radiata luteola and Anodontoides ferussacianus. Mussels occurred in lesser concentrations and at lesser depth (1 m vs. 9 m) on the northeast side of the lake where aquatic plant cover was greater. One species, Lampsilis radiata luteola, was significantly (P = 0.05) larger on the northeast side at 1—m depth.
On the Covariance of the Community Matrix
Authors: Vandermeer John H.
Published: May 2006

A clarification of the meaning of the covariance of the community matrix is presented along with calculating equations for both the mean species covariance and the covariance of the row and column means. A brief discussion of α selection and its determination of the covariance is given, followed by table for determining the expected number of species in a community from a knowledge of mean α and cov α.
Inhibition of Reproductive Development in Laboratory Populations of Prairie Deermice (Peromyscus Maniculatus Bairdii): Influence of Tactile Cues
Authors: Terman C. Richard
Published: May 2006

Eight populations were founded by releasing 4 ♂ ♂ and 4 pregnant ♀ ♀ into circular enclosures containing 18 546 cm2 of floor area and 8 nest boxes. Food and water were maintained in surplus. Half of the young born into the populations were reared as bisexual pairs in No—Contact Cages within the enclosures where they received visual, auditory and olfactory stimuli from the populations. Their sibs remained freely ranging in the enclosures and based upon previous studies, would be expected not to mature reproductively. The data indicate that rearing young in the wire No—Contact Cages within the population enclosures resulted in their development of significantly larger reproductive organs compared to freely ranging animals. The reproductive rate of the caged animals was also higher but not significantly so. Tactile cues thus appear of primary importance to the reproductive inhibition observed in the populations.
The Effects of Insect Parasitism on Plant Competition: Greenbugs and Barley
Authors: Windle Phyllis N. , Franz Eldon H.
Published: May 2006

Two cultivars of barley (Hordeum vulgare L.) with an isogenic difference in greenbug resistance were grown with and without greenbugs (Schizaphis graminum Rond., Biotype C: Aphididae). Two pots were grown per treatment for a total of 10 pots without aphids at each 2—wk harvest. Two weeks after infestation, total aboveground biomass was greater for both the resistant and susceptible plants with aphids. Four weeks later, biomass was significantly lower for aphid—infested plants compared to plants without aphids. Belowground biomass also declined after 6 wk of infestation. Root—shoot ratios remained statistically the same between harvests and between the control and experimental treatments with aphids. There was 1 exception. Two weeks after infestation, the root—shoot ratio for plants with aphids was significantly < for those without. Analysis of the de Wit replacement series for aboveground biomass showed that plants with aphids differed from control plants in competitive relationships. With aphids, there was a larger disparity in growth of the resistant and susceptible plants and the resistant plants were generally better competitors.
Emergent Seedlings from Coniferous Litter and Soil in Eastern Oregon
Authors: Strickler Gerald S. , Edgerton Paul J.
Published: May 2006

Seedlings emerging from litter and soil samples from three mixed conifer forests were observed for 1 yr in the greenhouse. A total of 536 seedlings emerged from litter, 0— to 2—cm and 2— to 4—cm soil depth samples subjected to 28 degrees C, 60 degrees C, 80 degrees C, and 100 degrees C heat treatments, and from 28 degrees C treated samples under 80% and 92% shade treatments. Identification included 29 pieces of forbs, four grasses, one sedge, and four shrubs; no conifer seedlings emerged. A significant majority of seedlings emerged from litter, and most were species which produce abundant windborne seed. Only Epilobium watsonii Barbey seedlings showed a significant reduction in their emergence under shade. Applicability of the results to postlogging management is suggested.
Intra‐ and Interhabitat Variations in Guazuma ulmifolia (Sterculiaceae) Seed Predation by Amblycerus Cistelinus (Bruchidae) in Costa Rica
Authors: Janzen Daniel H.
Published: May 2006

The severity of seed predation of Guazuma ulmifolia (Sterculiaceae) by the beetle Amblycerus cistelinus (Bruchidae) ranges from 12% to 42% (averages of 13—31 seed crops at each site) in a series of progressively drier habitats ranging from extremely dry deciduous to semievergreen riparian moist forest in Guanacaste Province, Costa Rica. Within a site, the range of seed predation per individual's tree's crop is from 2%—22% at he driest site, to 7%—75% at the wettest site. These extreme ranges emphasize that seed predation records on single seed crops must be evaluated with care and that seed predation by one species of host—specific predator may vary strongly among habitats. No parasitoids of A. cistelinus were found in a total of 23,285 fruits of g. ulmifolia.
A Model of Calcium‐Cycling in An East Tennessee Liriodendron Forest: Model Structure, Parameters and Frequency Response Analysis
Authors: Shugart H. H. , Reichle D. E. , Edwards N. T. , Kercher J. R.
Published: May 2006

A 29—compartment model of the kinetics of calcium in an east Tennessee Liriodendron forest is developed. The model structure is based on the functional components of the Liriodendron forest determined after more than a decade of intensive studies on the structure and function of the forest. Parameters for the model and initial conditions for the state variables were determined from coordinated ecological studies in the Liriodendron forest. These studies included characterization of chemical pools, quantification of ecosystem processes and analyses of mineral transport dynamics using radioactive tracers. The calcium model was analyzed for stability and controlability using frequency response analysis, a classic control theory technique. The model was stable for each of the 29 possible feedback loops connecting an ecosystem monitoring point (e.g., Ca content of soil H2O) to an input source (e.g., atmospheric deposition). Certain monitoring points in the system, although they resulted in stable responses, caused natural variations in the system input to be amplified. The results proscribe arbitrary assignment of components as ecosystem monitoring points, and identify this potential problem in ecosystem management.
Selection of High Temperatures for Hibernation by the Pocket Mouse, Perognathus Longimembris: Ecological Advantages and Energetic Consequences
Authors: French Alan R.
Published: May 2006

Daily metabolism was calculated from food consumption in pocket mice, Perognathus longimembris, at 8 degrees C, 18 degrees C, and 31 degrees C. At temperatures below thermal neutrality for this species, daily metabolism was related to the amount of time the mice spent in torpor. Ambient temperature has no net effect on the minimum energy expenditure during a typical 5—mo hibernation season. Once an animal has accumulated a food store of 130 g of millet seeds, it has the minimum energy necessary to hibernate at any environmental temperature. Such temperature compensation results from the complex effects of temperature on (1) the ratio of time of euthermy to time of torpor, (2) the energetic cost per hour of torpor, (3) the energetic cost per hour of euthermy, and (4) the energetic cost of arousal from torpor. The amount of time spent in torpor was inversely dependent on the food supply, indicating that euthermia is preferred even during the hibernation season. Mice also maximize the time of euthermia by selecting high environmental temperatures at all times of the year. Torpor probably occurs naturally only during the winter when the highest temperatures available to the mice are below thermal neutrality. The maximization of the time of euthermia reduces the chances of freezing during hibernation and enhances the animal's ability to escape from predators.
Population Dynamics of the Burrowing Mayfly Hexagenia Limbata
Authors: Horst Thomas J.
Published: May 2006

Population regulation of burrowing mayflies was investigated by modeling the population dynamics of Hexagenia limbata at Tuttle Creek Reservoir, Kansas, USA. Census data were obtained for the egg, nymph, and adult life stages to construct the basic statistics for life tables. Estimates were derived for survivorship of nymphs during 4 yr and for egg and adult survivorship in four areas in 1 yr. Fecundity was estimated from a random sample of adult ♀ ♀. Density dependence between segments of the life history was tested by key factor analysis and also by discrete time simulation. Population growth rate, calculated using the exponential model, had a negative linear relationship with population density, suggesting regulation at some life stage within the cycle. Population growth rates calculated for Leslie matrices with different nymphal survivorships but constant egg and adult survivorship also had a negative linear relationship with population density. Therefore, it is concluded that the population is regulated in the aquatic environment in the nymphal portion of the life cycle.
Ecological Factors in the Development of Intensive‐Management Ecosystems in Midwestern United States
Authors: Auclair Allan N.
Published: May 2006

This paper quantifies changes in the importance of ecological parameters associated with the development of intensive agriculture in midwestern USA. Changes in the important of 20 edaphic and 31 cover—type parameters were measured for three stages of development: (1) conversion of natural vegetation to pre—intensive agriculture (1833—1934), (2) agricultural intensification associated with chemical subsidies and mechanization (1934—1948), and (3) recent shifts in crop diversity and production (1934—1972). Between 1833 and 1934 all the natural upland vegetation, and two—thirds of the original marshlands were transformed. Of the original prairie surface, 92% was converted to a cropland—temporary pasture system by 1934. Much less of the original savanna was converted to cropland. By 1934 the alteration of savanna to cropland, permanent pasture, and oak forest was in the ratio of 4:3:2. A principal components analysis of the factors significant in the alternation of the natural vegetation indicated strong interactions with soil attributes of the first component. Prairie and cropland were bimodally distributed on the catenal gradient. The distribution of savanna and forest vegetation was related primarily to steep, shallow soil types. Intensification of agricultural production was accompanied by a reduction in the total cropland acreage, and forest cover increased by 10.6% in the 1934—1961 period. With agricultural intensification there was an increase in crop specialization. In fact, crop diversity declined by 35% between 1950 and 1965; since 1965 the tendency toward monoculture increased only slightly. Furthermore, the trend toward monoculture coincided with a shift toward large—stature plant forms. The models of canonical correlation indicated that with agricultural intensification the moisture—related variables became more important while those related to fertility and catena did not. The dependence of intensive agriculture on favorable sites and large energy inputs is discussed from the viewpoint of growing problems of energy supply and population.
Habitat and Prey Selection of Sceloporus Occidentalis and Sceloporus Graciosus
Authors: Rose Barbara R.
Published: May 2006

Sympatric populations of the western fence lizard, Sceloporus occidentalis and the sagebrush lizard, Sceloporus graciosus were compared with respect to morphological measurements, and habitat and resource utilization. An allopatric population of S. occidentalis was studied to determine whether any differences among sympatric populations result from species—specific differences or from a shift in characteristics of S. occidentalis because of the presence of a congener. The presence of sympatric S. graciosus does not alter the size of prey selected by S. occidentalis. Sceloporus graciosus selects a significantly smaller mean length of prey (4.6 mm) than S. occidentalis (5.4 mm). Two factors theoretically contribute to the variation in size of prey taken by a population: each individual shows variation in length of prey, and morphological variation in size of adult lizards results in differences among individuals in average length of prey. The first factor explains the variation in size of prey taken by these populations, because there is no correlation between mean prey length and adult body length for either species. Although there is a significant difference between the two species in mean size of prey taken, extensive overlap in prey utilization is revealed directly by the high overlap values between species (66%) and indirectly from the low value of niche separation to niche width ratio. The significantly larger mean prey size of adults to immatures reduces the intraspecific competition between age classes. Adult S. graciosus, with a smaller mean prey length than S. occidentalis, overlaps the most with immatures, particularly S. occidentalis immatures. The significantly larger head size of sympatric compared with allopatric S. occidentalis is not explained by character displacement in trophic apparatus to decrease overlap between species in prey utilization because the same size prey is selected in both areas and by both sexes. The larger head size of S. occidentalis males in sympatry may increase species identification between species in push—up displays. Sympatric S. occidentalis and S. graciosus segregate themselves significantly between habitats, and within a habitat between structural microhabitats. This minimal spatial overlap between sympatric species allows their coexistence despite extensive overlap in prey utilization.
Fecundity and Seed Dispersal of a Tropical Tree
Authors: Howe Henry F. , Vande Kerckhove Gayle A.
Published: May 2006

We observed feeding assemblages of birds at a Costa Rican dry—forest population of Casearia corymbosa (Flacourtiaceae) in order to distinguish effective dispersers from a incidental visitors and to examine the relationship between fruit production and depletion by birds at individual plants. On the basis of 1956 recorded visits by birds, the Yellow—green Vireo (Vireo flavoviridis) was the most reliable disperser throughout the season, accounting for 65% of the arillate seeds removed. Other common visitors were the Streaked Flycatcher (Myiodynastes maculatus) 12%, Golden—fronted Woodpecker (Melanerpes aurifrons) 9%, Pale—throated Flycatcher (Myiarchus nuttingi) 8%. All stripped off the oily arils in the crop and regurgitated viable seeds from perches in surrounding forest. Sporadic visitation by 10 other trogons and passerines accounted for the remainder of fruit utilized by birds. Capsules opened early in the morning, and fruit accessible to birds was depleted by early afternoon. At 17 closely monitored plants, birds removed 91% of the accessible arillate seeds. Crop sizes ranged from 1—2700, with dispersal success highest among plants of intermediate fecundity. Variance was attributable to individuals with low fecundity, often missed by birds on all but the most productive days, and to an exceptionally fecund tree that satiated its visitors. The dispersal ecology of the small dry—forest tree offers a unique comparison to that of a more fecund overstory ecotype in wet forest. In secondary dry forest, a protocooperative relationship exists between several bird species and this plant, with an abundant and efficient vireo responsible for most dispersal.In the wet forest, dispersal occurs through a mutualistic relationship with a cotinga (Tityra semifasciata), while most common visitors are "fruit thieves" of little benefit to the plant. These differences are considered in light of comparative ecology of the 2 forms.
The Adaptiveness of Wing‐Dimorphism in the Salt Marsh‐Inhabiting Planthopper, Prokelisia Marginata (Homoptera: Delphacidae),
Authors: Denno Robert F. , Grissell E. E.
Published: May 2006

Populations of the multivoltine planthopper, Prokelisia marginata (Delphacidae), contain two wing—forms, flightless short—winged brachypters and macropters with fully developed wings capable of flight. P. marginata feeds selectively on the grass, Spartina alterniflora, which dominates the vegetation of Atlantic and Gulf Coast tidal salt marshes. We demonstrate that along most of the Atlantic seaboard S. alterniflora occurs as a harlequin environment composed of stable patches that provide life history requisites year—round and unstable ones that disappear altogether during winter. The proportion of macropters in planthopper population is significantly correlated with the proportion of unstable patches in the local environment. A dimorphism is maintained along most of the Atlantic Coast because brachypters remain and effectively exploit stable patches and macropters colonize and subsequently escape unstable habitats. Along the Gulf Coast S. alterniflora occurs as one rather stable habitat, and here planthopper populations are composed mostly of brachypters. The percentage of macropters in populations is positively correlated with levels of crowding incurred during the nymphal stage, suggesting that wing—form is determined by a developmental switching mechanism triggered by various environmental cues that predict habitat deterioration. The relationship between crowding and macroptery is linear at Atlantic and Gulf Coast localities, but greater proportions of macropters are produced on Atlantic marshes under similarly crowded conditions. As a mechanism to explain differences in the wing—morph composition of populations, we propose that selection has altered the threshold at which a developmental switch responds to environmental cues such as crowding.
Forest Vegetation of the Lower Alabama Piedmont
Authors: Golden Michael S.
Published: May 2006

Forest community types were distinguished for the lower Alabama Piedmont using a combination of two agglomerative clustering algorithms with a similarity sorting technique. All stands classified in 8 of the resulting 10 community types has within—type similarity values of at least 45%. Ordination by reciprocal averaging using the tree basal areas indicated that community types can be segregated into three topographically defined groups: streambottom communities (Sweetgum—Water Oak—Red Maple and Small Steambottoms), mesic upland communities (White Oak, Chestnut Oak, Pine—Hardwoods, Mixed Oak—Hickory, and Loblolly Pine), and xeric upland communities (Oak—Pine, Blackjack Oak—Pine, and Longleaf Pine). A reciprocal averaging ordination using understory plants successfully separated most of the same community types. The combined clustering—similarity sorting procedure identified "core " stands that provide a clearer representation of definable forest community types than would have resulted from inclusion of atypical or transitional stands. The combination of classification for description of vegetation and ordination for definition of vegetation—site relationships proved complementary and useful. The highest tree species diversities were in mesic upland hardwood and pine—hardwood communities; the lowest were in pine communities. Diameter size class distributions revealed general underrepresentation in the seedling/sapling size classes for all important canopy species, even the climax Quercus and Carya. Underrepresentation was most severe in wet—to—mesic stands. Natural succession from pine toward hardwood dominance is more rapid on bottomlands, stream terraces, and other moist sites than on drier, more fire—prone uplands. Forest cutting practices of many nonindustrial owners accelerate the trend toward dominance of hardwoods, even on uplands.
Density Dependence and Homing Behavior in Adult Red‐Spotted Newts Notophthalmus Viridescens (Rafinesque)
Authors: Gill Douglas E.
Published: May 2006

Natural populations of adult red—spotted newts were experimentally manipulated to test for density dependence and homing behavior in breeding adults. Transplantation of adults from one pond to another effectively depleted the density of one population and overloaded the density of the other; four other ponds were unmanipulated controls. Populations sizes in both experimental ponds recovered to near pre—experimental levels within 1 yr. The majority of the surviving transplanted individuals were recaptured in their pond of origin. Body weights of both sexes were significantly depressed in the overloaded pond relative to controls. Annual survival of adult females were negatively correlated with breeding population density.