bluuebunny/crossref_metadata_2025 huggingface dataset:
Digital Art — A Field of Inquiry for Contemporary Architecture
Authors: Santos Jose dos , Filho Cabral
Published: May 2006

This article investigates the interplay of digital technology, art and architecture and it presents a series of experimental workshops developed at LAGEAR (Graphic Laboratory for the Experience of Architecture, School of Architecture at UFMG, Brazil). The intention of these workshops is to include an artistic approach to the work in a computer lab dedicated to teaching and researching architecture. At first, a discussion on the relationship between art and architecture is presented, followed by an analysis of the enhancement of such relationship with the advent of digital technology. Then a series of works developed by artists and students in collaboration is described. The article concludes with a discussion on the role of digital art for architectural education. It is proposed that it may be one of the most adequate fields for students to freely investigate contemporary issues, such as interactivity and automation, which are now shaping our built environment.
Tribute to Professor Arturo F. Montagu
Authors: Montagu Lilia Chernobilsky
Published: May 2006

Professor Arturo Montagu passed away on 8th April, 2005, after a five-year long courageous battle against cancer. Arturo was one of the world's pioneers in architectural computing whose work and teaching influenced generations of professional and researchers, in Latin-America and beyond. It was through him that SIGraDi was created and that many of today's relationships among people in the rchitectural computing community got started and thrived. Despite his illness, he continued working unabatedly until the very end. In fact, few people ever noticed that he was sick. The sheer force of his intellectural activity for a long period of time in the 20th century – dense and valuable like few in architectural computing – and his invincible spirit hid the marks of his illness for a long time. This article summarizes Professor Montagu's contributions to the field of architectural computing and includes tributes from four people who knew him well but through very different circumstances.
A Wood Frame Grammar: A Generative System for Digital Fabrication
Authors: Sass Larry
Published: May 2006

A novel design system is presented that generates information for house construction exclusively from 3/4“plywood sheets. A shape grammar routine is employed to subdivide an initial solid shape into constructible components for desktop digital fabrication and design evaluation as a physical model. Once approved final construction can happen with components cut on a CNC wood router after the design has been validated by a laser cut model. Shape grammar rule format is used to design functions that build geometry later converted to a scripting language in CAD. Future goals for the grammar are to develop a complete CAD program that translates 3D designs to 2D drawings for flat digital fabrication. The ultimate goal of the program is to automate the translation of solid models to information for digital fabrication. Currently a manual process the translation allows the designer to focus on the visual aspects of evaluation at any scale with little concern for constructability.
iSphere: A Free-Hand 3D Modeling Interface
Authors: Lee Chia-Hsun Jackie , Hu Yuchang , Selker Ted
Published: May 2006

Making 3D models should be an easy and intuitive task like free-hand sketching. This paper presents iSphere, a 24 degree of freedom 3D input device. iSphere is a dodecahedron embedded with 12 capacitive sensors for pulling-out and pressing-in manipulation on 12 control points of 3D geometries. It exhibits a conceptual 3D modeling approach for saving mental loads of low-level commands. Using analog inputs of 3D manipulation, designers are able to have high-level modeling concepts like pushing or pulling 3D surfaces. Our experiment shows that iSphere saved steps in the selection of control points in the review of menus and leading to a clearer focus on what to build instead of how to build it. Novices saved significant time learning 3D manipulation by using iSphere to making conceptual models. However, one tradeoff of the iSphere is its lack of fidelity in its analog input mechanism.
Towards Architect-Aided Computing Design
Authors: Sowa Agnieszka Katarzyna
Published: May 2006

In the design process of some recent, specific architectural projects the part elaborated by computers and machines significantly grows. They could generate, optimize and produce the most complicated and complex solutions, taking over some tasks which before were the domain of architects. This article presents a project carried out by postgraduate students at Eidgenossische Technische Hochschule in Zurich, Switzerland, where such a digital design process was implemented, with all its advantages and disadvantages. The observations and conclusions gained during the work allow the author to formulate the concept of Architect-Aided Computing Design, to define some challenges for architects created by such a working method, and to present an analysis about the potential new software for architectural production.
Coaches' Perceptions of Non-Regulated Training Behaviors in Competitive Swimmers
Authors: Young Bradley W. , Starkes Janet L.
Published: May 2006

Athletes who fail to self-regulate are less disciplined and motivated, show less initiative, and fail to maximize opportunities for acquisition during training. This investigation attempted to identify a short list of behaviors that swim coaches recognized as indicators of non-regulation by their swimmers during training. In Study 1, five coaches described the behavior of swimmers in various contexts during interviews. Qualitative analysis of interviews resulted in two lists of 28 activities that characterized self-regulation and non-regulation, respectively. In Study 2, two different samples of coaches (n=18; n=16) rated the items identified in Study 1 for how well they represented self-regulated and non-regulated training behaviors among swimmers. Based on inclusion criteria, two lists of 28 items were shortened to one list of seven non-regulated training habits, including: poor attendance; off-task in warm-up; incomplete volume in warm-up; incomplete volume for the entire workout; inaccurate recall of pace times; last to arrive on deck; and lack of focus during kick sets. The authors discuss the relevance of an observational checklist for helping coaches identify athletes in need of remedial self-regulatory strategies, as well as how measures for these items may be employed in intervention research.
A Branch-and-Price Approach to the Vehicle Routing Problem with Simultaneous Distribution and Collection
Authors: Dell’Amico Mauro , Righini Giovanni , Salani Matteo
Published: May 2006

The vehicle routing problem with simultaneous distribution and collection (VRPSDC) is the variation of the capacitated vehicle routing problem that arises when the distribution of goods from a depot to a set of customers and the collection of waste from the customers to the depot must be performed by the same vehicles of limited capacity and the customers can be visited in any order. We study how the branch-and-price technique can be applied to the solution of this problem and in particular we compare two different ways of solving the pricing subproblem: exact dynamic programming and state space relaxation. By applying a bidirectional search we experimentally prove its effectiveness in solving the subproblem. We also devise suitable branching strategies for both the exact and the relaxed approach and we report on an extensive set of computational experiments on benchmark instances with both simple and composite demands.
Reflections on the teaching of drawing in the digital age: attitudes of senior academics in the United Kingdom to the place of drawing tuition on the design curriculum in higher education
Authors: Schenk Pamela
Published: May 2006

A new study has recently been completed investigating current attitudes towards drawing and drawing tuition among senior academics in design education in higher education institutions (HEIs) in the United Kingdom. This study examines some of the main aspects of existing educational
practice while also exploring academics' aspirations for ideal drawing tutors and drawing studios. It forms part of an extensive research programme conducted over twenty years on the role of drawing in design practice and its implications for design education, earlier findings being used here
for comparison. Primarily based on interviews with deans and programme leaders from HEIs in England and Scotland, and supplemented by interviews with senior design researchers, views on the forms of drawing ability crucial to today's designers, the impact of computer-based technology on the
role of drawing in design, the curriculum structure and content with regard to drawing studies, and the use of academic resources are discussed.
Immobilization of soil nitrogen as a possible method for the restoration of sandy grassland
Authors: Török K. , Szili‐Kovács T. , Halassy M. , Tóth T. , Hayek Zs. , Paschke M.W. , Wardell L.J.
Published: May 2006

Abstract.Experiments were designed to test the applicability of nitrogen immobilization as a means of accelerating the recovery of an endemic open sandy grassland (Festucetum vaginatae danubiale) on old fields in the Great Hungarian Plain. Effects of various carbon sources (sucrose, starch, cellulose and sawdust) and their combinations in different quantities were studied in laboratory microcosms. Carbon addition decreased nitrogen availability in all cases, the intensity and timing of change being dependent on the type of carbon source applied. The combination of 2 g each of sucrose and polysaccharides (starch, cellulose, sawdust) per kg soil was found to be the most effective, as sucrose decreased available nitrogen content of soil intensively and the polysaccharides maintained the immobilized nitrogen for a longer period. In a follow‐up experiment, sucrose and sawdust were selected for field application to test their effectiveness in immobilizing N and accelerating restoration. The field experiment was established to test the importance of abiotic site differences in the immobilization of soil nitrogen. Selected sites were located along an elevation, moisture and productivity gradient. Soil organic matter, microbial biomass‐C and decomposition rate varied between sites depending on the elevation gradient. At two sites with lower soil moisture and organic matter levels carbon addition increased microbial activity and nitrogen immobilization significantly.
Mapping vegetation in an arid, mountainous region of Western Australia
Authors: van Etten Eddie J. B.
Published: May 2006

Abstract. Predictive mapping of vegetation using models linking vegetation units to mapped environmental variables has been advocated for remote areas. In this study, three different types of model were employed (within a GIS) to produce vegetation maps of the Hamersley Ranges region of Western Australia. The models were: (1) decision trees; (2) statistical models; and (3) heuristic/conceptual models. Maps were produced for three different levels of a floristic classification, i.e. 16 communities in two community groups with eight subgroups. All models satisfactorily established relationships between the vegetation units and available predictor variables, except where the number of sites of a particular unit was small. The different models often made similar predictions, especially for more widespread vegetation units. Map accuracy (as determined by field testing of maps) improved with increasing level of abstraction, with plant community maps ca. 50 % correct, subgroup maps ca. 60 % correct and group maps 90 % correct. Map inaccuracies were due to several factors, including low sample numbers producing unrepresentative models, poor resolution of and errors in available maps of predictor variables, and available predictor variables not being able to differentiate between certain vegetation units, particularly at the plant community level. Of these factors, poor resolution of maps was seen as the most critical. One type of model could not be recommended over another; however the choice of model will be largely dependent on the nature of the data set and the type of map coverage required.
Two vegetation maps of the same island: floristic units versus structural units
Authors: Lux Andrea , Bemmerlein‐Lux Florian A.
Published: May 2006

Abstract. This paper presents a comparison of two alternative methods to describe and map vegetation: on the basis of plant species and growth forms, respectively. A stratified random sampling was taken from spontaneous vegetation in 1989 on the volcanic island of Pantelleria (near Sicily, Italy). Cartographic and other comparisons of the results from classification and ordination analysis suggest that the major differences were associated with differences in the time scale of the underlying processes. Species results (leading to floristic vegetation units) were representative of longer‐term processes, growth‐form results (leading to structural vegetation units) with shorter‐term processes. Further implications of these results are discussed.
An outline and map of the potential natural vegetation of Ireland
Authors: Cross J.R.
Published: May 2006

Abstract. A map of the potential natural vegetation of Ireland with an outline description of the vegetation units is presented. The vegetation of Ireland has a distinctive and highly oceanic character as a result of its location on the northwestern extremity of the Eurasian landmass and its recent geological and vegetation history. Forests would naturally cover the greater part of the island but the long history of forest decline over the last 6000 yr, due to clearance by man and paludification, has led to the present situation where native forest cover is less than 1 % of the land area. Together with intensive land use, drainage, peat cutting and the introduction of alien species, this presents considerable difficulties in the construction of mapping units.

The map, which has been compiled as part of the Vegetation Map of Europe at a scale of 1 : 2.5 million, contains 20 mapping units. They comprise: nine forests, i.e. montane birch forests (one unit), acidophilous oak forests (two units), forests of oak or oak and ash with hazel on mostly base‐rich soils (four units), forests on alluvium and gleyed clays (one unit each); five mire types, i.e. blanket mires (two units), raised bogs (one unit), sedge mires (one unit), degraded raised bogs (one unit); and six minor units viz. heaths (two units), sand dunes (two units), salt marshes (one unit) and polders (one unit). As a result of human activity, the potential natural vegetation, especially the forests, will differ considerably from the former natural climax vegetation.
Succession of secondary forests affected by pine wilt disease in western Japan followed on vegetation maps
Authors: Toyohara Gentaro , Fujihara Michiro
Published: May 2006

Abstract. Succession, changes in the distribution pattern of forest vegetation, and Pinus forest survival following pine wilt disease were clarified based on phytosociological analysis and vegetation maps. Survival of Pinus forests was restricted to the early successional stages, which were located on ridges and the upper part of slopes. Subsequent to pine wilt disease, the succession progressed from early to late substages of Pinus forest, mixed deciduous and evergreen Quercus, to evergreen Quercus forest. Succession occurs in abandoned pine forests which apparently are in a bad state and are vulnerable to attacks by pine wilt disease.
Conservation of bog plant species assemblages: Assessing the role of natural remnants in mined sites
Authors: Poulin Monique , Rochefort Line , Desrochers André
Published: May 2006

Abstract. Bogs, economically valuable wetlands, are subjected to exploitation in southern Canada. We addressed plant conservation within bogs mined for peat, in which small undisturbed remnants are left, mostly at the margins of the mined areas. The main goal of the study was to test whether these remnants act as refuges for plants which could recolonize areas that are planned for restoration after mining is completed.

Mosses, lichens and vascular plants were sampled in remnants of 24 mined bogs in southeastern Canada during the summer of 1997. The vegetation was also sampled at the margins and centres of 24 nearby natural bogs in plots similar in size to these remnants. Using similarity analysis and ordination techniques, we found that plant species assemblages in remnants of mined bogs differ from those near the margins of natural bogs, and that certain species are associated with the centre of natural bogs, due to the presence of pools. We also showed that water conditions of remnants are affected by drainage due to peat mining. Sphagnum moss showed itself to be a key indicator of mining effects on vegetation. Implications for peat resource management and bog conservation are discussed.
Determinants of floristic diversity and vegetation composition on the islands of Lake Burollos, Egypt
Authors: Khedr Abdel‐Hamid , Lovett‐Doust Jon
Published: May 2006

Abstract. A floristic and environmental survey was carried out on 22 uninhabited islands (0.1‐8.4 ha) in Lake Burollos, Egypt. A total of 58 vascular plant species was recorded. The number of habitats on each island was counted. There was a positive correlation between island area and number of habitat types. Island area was significantly positively correlated with various measures of floristic diversity, including the total number of species present, and the numbers of annual, herbaceous, and shrublet species. Perennial and shrub species numbers did not differ significantly with island area. In addition to island area, elevation and soil salinity, as well as distance to the Mediterranean Sea, all contributed significantly to variation in species composition in the terrestrial habitats. Water salinity and transparency accounted for 69% of the variation in aquatic species numbers. There was a weak effect of isolation on similarity of species composition on islands.

Eight vegetation types, represented by 13 indicator species identified after TWINSPAN analysis, were distinguished by soil characteristics. Species richness was inversely correlated with clay, organic carbon and total nitrogen in the soil, but positively correlated with calcium carbonate content.

From a management perspective, long‐term monitoring of threatened habitats in the lake is urgently required as a starting point to preserve biodiversity. Finally, we conclude that the present study supports the hypothesis indicating that larger areas feature higher species richness due to increased numbers of habitats.
Quantitative comparison of the diversity of landscapes with actual vs. potential natural vegetation
Authors: Ricotta Carlo , Carranza Maria Laura , Avena Giancarlo , Blasi Carlo
Published: May 2006

Abstract. In the past 20 years, several metrics have been developed to quantify various aspects of landscape structure and diversity in space and time, and most have been tested on grid‐based thematic maps. Once landscape patterns have been quantified, their effects on ecological functions can be explained if the expected pattern in the absence of specific processes is known. This type of expected pattern has been termed a neutral landscape model. In the landscape‐ecological literature, researchers traditionally adopt random and fractal computer‐generated neutral landscape models to verify the expected relationship between a given ecological process and landscape spatial heterogeneity. Conversely, little attention has been devoted to distribution patterns of potential natural vegetation (PNV) as an ecological baseline for the evaluation of pattern‐process interactions at the landscape scale. As an application for demonstration, we propose a neutral model based on PNV as a possible reference for a quantitative comparison with actual vegetation (AC V) distribution. Within this context, we introduce an evenness‐like index termed ‘actual‐to‐potential entropy ratio’ (HA/P = HACV/HPNV, where H is Shannon's entropy). Results show that, despite the hypothetical character of most PNV maps, the use of PNV distribution as a baseline for a quantitative comparison with ACV distribution may represent a first step towards a general model for the evaluation of the effects of disturbance on vegetation patterns and diversity.
Ecological subregions of the Interior Columbia Basin, USA
Authors: Hessburg P.F. , Salter R.B. , Richmond M.B. , Smith B.G.
Published: May 2006

Abstract. Land evaluations are not always conducted with adequate understanding of the relevant geologic and climatic contexts and their appropriate scales. This understanding is essential for developing representative sampling, monitoring, and conservation designs, and for pooling results of landscape analysis. To provide context for several regions of the interior northwestern United States, we conducted an ecoregion classification of the interior Columbia River Basin and vicinity (‘the Basin’). We grouped land units that are influenced by the same higher order geology and landform features, and share similar areal composition of potential vegetation and climate attributes. We used the TWINSPAN procedure to group 7496 watersheds of the Basin into 53 ecological subregions. We evaluated the contribution of attributes to group separation by discriminant analysis, and evaluated subregion robustness to prediction by cross‐validation. Classification accuracy ranged from 80‐97% across the subregions. All watersheds were classified to a subregion, and there were strong resemblances between members of adjacent subregions. Subregions with strong resemblances shared a similar composition of attributes, but differed in relative abundance and attribute combinations. We evaluated the geologic and climatic context of each subregion considering four levels in a nested land unit hierarchy. Most subregions nested at one of at least four scales, but some overlapped. Our results suggest that observation levels for a given ecological phenomenon need not be nested within their appropriate context levels, and across broad geographic areas context of the same phenomenon occurs at different scales.
Nutrient content of incident rainfall, throughfall and stemflow in a Nigerian secondary lowland rainforest
Authors: Muoghalu Joseph I. , Oakhumen Arthur
Published: May 2006

Abstract. Nutrient content of rainfall, throughfall and stemflow was studied over one year in the open and under the crowns of three tree species in a secondary rain forest at Ile‐Ife, Nigeria. Throughfall and stemflow comprised 78.8 % and 5.2 % respectively; 16.0 % of the incident rainfall was intercepted by the forest canopy. The concentrations of various nutrient elements in throughfall and stemflow were higher than those of incident rainfall. In throughfall and stemflow potassium concentration was highest and that of ammonium nitrogen was the lowest. Only calcium and sodium concentrations showed significant monthly variation in incident rainfall. Ca, Mg, K. Cu and P showed significant monthly variation in throughfall and stemflow. The concentrations of the elements were highest during the heavy‐rain months (May‐September). High concentrations of some of the elements were recorded also in November, the last rain month and the beginning of the dry season.

The concentration of these elements in stemflow and throughfall was affected by tree species. The highest quantity of each element was deposited in the forest via throughfall followed by incident precipitation and the lowest via stemflow. The tree species affected the quantities of these elements by the volume of their stemflow and throughfall and the concentration of the various elements herein. Total nutrient concentration was much higher than available (dissolved) nutrient concentration. This was very pronounced with micronutrients.
Impact of rewetting on the vegetation of a cut‐away peatland
Authors: Tuittila Eeva‐Stiina , Vasander Harri , Laine Jukka
Published: May 2006

Abstract. We tested whether rewetting improved environmental conditions during peatland restoration and promoted colonization and development of mire vegetation. Vegetation change was monitored in a cut‐away peatland one year before, and four years after, rewetting. Colonizers before rewetting were perennials, mostly typical of hummocks or bare peat surfaces. The main variation in vegetation was related to variation in the amounts of major nutrients and water table level. The wettest site with the highest nutrient level had the highest total vegetation cover and diversity, as well as some species typical of wet minerotrophic mires. Raising the water table level above, or close to, the soil surface promoted development of wet minerotrophic vegetation. Diversity initially decreased because of the disappearance of hummock vegetation but started to recover in the third year. Eriophorum vaginatum and Carex rostrata were both favoured, and bryophytes typical of wet habitats colonized the site. Moderate rewetting promoted the development of Eriophorum vaginatum seedlings and an increase in the cover of tussocks. Bryophytes typical of disturbed peat surfaces spread. In the control site development continued slowly towards closed hummock vegetation. The study showed that raising the water level to, or above, soil surface promotes conditions wet enough for a rapid succession towards closed mire vegetation.
A Short‐Term Experimental Investigation of Resource Partitioning in a New Zealand Rocky Intertidal Habitat
Authors: Paine R. T.
Published: May 2006

The effects of single—species removals on community composition and overt appearance were examined in an exposed, rocky, intertidal habitat at Anawhata, New Zealand. Two experiments were performed. A carnivorous starfish, Stichaster australis, was removed manually and kept removed from a stretch of shore for a period of 9 months (September 1968 through May 1969). This manipulation resulted in the mussel Perna canaliculus extending its vertical distribution by 40% of the available range, and a decrease in the species richness of the invaded area from 20 to 14 species. The second manipulation involved the removal of both Stichaster and a large brown alga, Durvillea antarctica, from two areas. Results were striking. Within 15 months 68% of the available space in one area, and 78% in the other, was occupied by Perna, to the almost total exclusion of other fauna or flora. These events not only duplicated the results of the Stichaster removal experiment, but also suggested that space, as the prime limiting requisite for Perna, could be occupied by that species alone throughout the middle and lower intertidal. The relative influences of predation and competition on the allocation of a basic resource are discussed in light of these experiments. Further, factors contributing to the competitive vigor of mussels are discussed,and the enigmatic relationship between Stichaster and another predator of comparable trophic status, Neothais, is probed. Finally, those general features of community structure especially sensitive to the ecological character of the predator, or the intensity of predation, are discussed.
Woodrats and Cholla: Dependence of a Small Mammal Population on the Density of Cacti
Authors: Brown James H. , Lieberman Gerald A. , Dengler William F.
Published: May 2006

In the deserts of Southern California, stands of jumping cholla cactus (Opuntia bigelovii) are usually inhabited by desert woodrats (Neotoma lepida). The density of woodrats is obviously correlated with the density of cacti. On our study area, an alluvia fan in Joshua Tree National Monument, 80% of the variability in the density of woodrats could be attributed to variation in the density of cacti. The turnover of the woodrat population (mortality and replacement) apparently was greatest in areas of low density of cacti. The dependence of woodrat populations on the density of cholla may be attributed to the fact that the cacti provide most resources required by the woodrats; food, water, materials, for den construction, and a means of avoiding predation. Woodrats also are abundant in some habits where there is little or no cactus of any king, so that their dependence on cholla is not obligate.
Escape in Space by Sterculia Apetala Seeds from the Bug Dysdercus Fasciatus in a Costa Rican Deciduous Forest
Authors: Janzen Daniel H.
Published: May 2006

When a seed of the large tree Sterculia apetala falls to the ground beneath the parent tree in a Costa Rican tropical deciduous forest, it is typically found and fed upon within a few minutes by cotton—stainer bugs (Dysdercus fasciatus). The rate of seed discovery by the bugs is highest where the seed fall is most intense and tapers off to zero between 30 and 60 m from the tree trunk. Seeds that fall beneath the parent appear to have no chance of survival under forest conditions. Seeds in open pasture are not found by the bugs, but probably die of desiccation. The bugs are not present under sterile S. apetala trees. Squirrels and monkeys appear to be the primary dispersal agents; after carrying the pods away from the parent, they appear to lose some seeds because of their face and hands being stuck by the hairs on the inner walls of the seed pods. The coevolution of the Dysdercus—Sterculia‐mammal interaction is discussed with respect to the effect of seed predators on the density of adult trees in the habitat.
Growth and Population Dynamics of a Spider Mite (Tetranychus Urticae K., Acarina: Tetranychidae)
Authors: Mitchell Rodger
Published: May 2006

Female T. urticae deposit eggs in a circumscribed area and the young tend to mature in that area. Pheromones released by developing females are effective over very short distances; hence, sib—mating is the rule at low densities. Males grow to about three times the egg biomass; 20%—30% of the eggs are males. Mature females weight eight times as much as males but they disperse at one—half or less of their mature weight and may reduce their weight by even more when resources are poor. This suite of adaptations allows 70%—80% of the eggs to be female and delays almost half the increase in the biomass of a set of young until after the mated females disperse to new resources.
Effects of Size‐Selective Predation and Food Competition on High Altitude Zooplankton Communities
Authors: Sprules W. Gary
Published: May 2006

Two distinct communities exist in a series of small subalpine ponds on Galena Mountain, Colorado, at 3,400 m. In the deep ponds, two predators, the culicid larva Chaoborus and the axolotl Ambystoma tigrinum, coexist with two small herbivores, the copepod Diaptomus coloradensis and the cladoceran Daphnia rosea. In the shallow ponds the predatory salamander (Ambystoma tigirinum) coexists with three large herbivores, Daphnia pulex, Diaptomus shoshone (which may be predatory as an adult), and the fairy shrimp, Branchinecta shantzi, as well as the small Diaptomus coloradensis. Despite the proximity of deep and shallow ponds, each community has remained resistant to invasion from the other for at least 5 years. To determine why, I recorded the survival of organisms placed in cages in foreign ponds alone and in combination with the native species. Results revealed that chemical or physical conditions were limiting only for Daphnia pulex, which did not survive well in deep ponds. The large Diaptomus shoshone and Daphnia pulex could not invade deep ponds probably because they were heavily preyed upon by Chaoborus and the axolotl, respectively. This occurred in the presence of small prey, since laboratory experiments showed that predators selected large food items. Branchinecta shantzi was restricted by axolotl predation as well. Light predation pressures in shallow ponds were unimportant. Results suggest that Daphnia rosea could not invade shallow ponds because the larger native cladoceran D. pulex outcompeted it for food. Diaptomus coloradensis survives in shallow ponds because it avoids competition with its larger congenitor D. shoshone. Only the deep ponds are suitable for the aquatic Chaoborus larvae and axolotl since shallow ponds freeze completely each winter and periodically dry up during the summer.
Coenocline Simulation
Authors: Gauch H. G. , Whittaker R. H.
Published: May 2006

Characteristics of coenoclines, or community gradients, were studied as a basis for simulating the distribution of species populations along environmental gradients. A computer program is described which is inexpensive, realistic in the manner in which species are distributed, and flexible in that levels of alpha and beta diversity, sampling error, and other parameters can be varied. The simulated coenoclines are of interest in connection with dominance and diversity relations, measurement of ecological distance, and ordination of community samples.
Availability of Carbon Dioxide for Photosynthesis at High Altitudes: Theoretical Considerations
Authors: Gale J.
Published: May 2006

Contrary to current opinion, the reduction of the availability of carbon dioxide for phytosynthesis with increasing altitude, due to reduced barometric pressure, is only very small. The increased rate of diffusion of CO2 in air with altitude compensates for the effect of its lower partial pressure. The relation between CO2 availability and barometric pressure depends also on the characteristics of the plant's CO2—uptake mechanism and on the prevailing air temperature.
Effects of a Non‐Selective Arsenical Herbicide on Plant Biomass and Community Structure in a Fescue Meadow
Authors: Malone Charles R.
Published: May 2006

Community structure and standing crop biomass of vegetation were affected similarly in a fescue meadow by single applications of sodium cacodylate and by severe heat stress. Recovery of species diversity and percentage similarly toward control levels was rapid, although not complete in one growing season. Repeated applications of the herbicide were necessary to suppress fescue growth, and this treatment regime caused sustained simplification of community structure and reductions in biomass throughout the growing season. Litter accumulated on heat—stressed areas, but its rapid decomposition on sprayed areas diminished an important nutrient sink and exposed the ecosystem of possible leaks in nutrient pools.
Edaphic Control of Plant Distribution in the White Mountains, Eastern California
Authors: Marchand Denis E.
Published: May 2006

Vegetation in a part of the southern White Mountains is primarily distributed according to geologic substrate, although superimposed trends controlled by climatic, microclimatic, and topographic gradients are also evident. Carbonate—noncarbonate discontinuities are the most striking, but distinct plant assemblages on basalt, adamellite, and sandstone are also recognizable. Certain species, chiefly but not entirely those associated with the more favorable noncarbonate substrates, occur independently according to nutrient, moisture, temperature, or root—stability requirements. Lupinus argenteus, a strict calcifuge, was found to require high available P, and to a lesser extent, high available Fe. Many species occur on carbonate substrates, unstable slopes, and other unfavorable sites because of competitive exclusion imposed by more tenacious species, especially sagebrush. The principle adverse properties of carbonate soils are chemical (low available P. and Fe, low percentage exchangeable K, high pH) and, secondarily thermal (low soil temperature caused by high albedo). A number of other unevaluated factors must be involved in the observed vegetational patterns, however. Factor analysis of edaphic, geographical, and botanical parameters indicates many associative and mutually exclusive relationships which may provide an informational basis for future investigations.
The Utilization of Leaf Litter by Stream Detritivores
Authors: Cummins Kenneth W. , Petersen Robert C. , Howard Frederick O. , Wuycheck John C. , Holt Virgina I.
Published: May 2006

Investigations of large and fine particle feeding detritivores (shredders and collectors) fed on conditioned hickory leaves (Carya glabra) revealed density—dependent intra— and interspecific interactions. Shredder (Tipula and Pycnopsyche) growth rates ranged from 0.47 to 1.53% increase in body wt/day depending upon density, species combinations, and culture temperature. Collector (Stenonema) growth rate ranged from 0.13 to 1.80% body wt/day, being greatest at high densities, particularly in combination with shredders. Food consumption ranged from 15.7 to 33.2% body wt/day for shredders and 4.0 to 23.2% body wt/day for collectors. After non—shredder feeding losses are accounted for, estimated shredder standing crop required to account for processing of report leaf litter inputs compare generally to measured shredder standing crop.
Air Temperature, Heat Sums, and Pollen Shedding Phenology of Longleaf Pine
Authors: Boyer William D.
Published: May 2006

Between 1957 and 1966, pollen shedding by longleaf pine (Pinus palustris Mill.) in southwestern Alabama peaked at dates ranging from February 23 to April 3. January 1 and 50 degrees F was the combination of starting date and threshold air temperature that minimized annual variations in heat sums before the trees flowered. The heat sum required for peak pollen shedding declined as the season advanced. The regression Y= 19009—89.26X, in which Y is the degree—hour heat sum above 50 degrees F and X is days from January 1 through date of peak pollen shedding, accounted for nearly all observed annual variations in peak date. For of peak pollen shed averaged 0.3 day. For eight subsequent observations, including two in North Carolina and one in northern Alabama, the deviation averaged 1.6 days.
Studies of Cation Budgets in the Southern Appalachians on Four Experimental Watersheds with Contrasting Vegetation
Authors: Johnson Philip J. , Swank Wayne T.
Published: May 2006

Nutrient fluxes within and through watershed ecosystems at the Coweeta Hydrologic Laboratory are under study. This paper describes the annual budgets and seasonal fluctuations for selected cations. Concentrations and flux of cations moving through a hardwood forest stand, a weed to forest succession, a hardwood coppice stand and an eastern white pine stand on steep mountain topography are compared. Stream discharge was greater by 6% for the successional weed stand, and 10% for the second hardwood coppice, but 15% less for the young pine stand in contrast to pretreatment levels. Although concentrations for Ca(++), Mg(++), K+ and Na+ combined were usually less than 3.5 ppm, over 98% of the loss of each cation was in dissolved form on all four watersheds. Regression analysis showed that 50 to 60% of the variation in monthly weighted average concentration was accounted for by monthly discharge amounts. Annual losses of the four cations from the mature hardwood stand were in the amounts of approximately 7, 3, 5, and 10 kg/ha respectively for the Ca(++), Mg(++), K+ and Na+. Annual budgets showed net changes to be —0.8, —2.0, and —4.3 kg/ha, respectively, for this mature hardwood ecosystem. In contrast, the weed stand lost significantly greater amounts, and the young pine and hardwood coppice watersheds showed a net gain in Ca(++) and significantly lower losses than the mature ecosystem for the other three ions. These budgets show that major alterations to these forest ecosystems are not now producing a substantial out—flux for these cations.
Predation by Coccinellid Beetles: Experiments on Switching
Authors: Murdoch William W. , Marks J. R.
Published: May 2006

The predatory behavior of a ladybird, Coccinella, was examined as it preyed upon varying ratios of two aphid species, Acrythosiphon pisum and Aphis fabae. Experiments were done in petri dishes and on bean plants. The ladybirds attacked the two prey species in direct proportion to their relative abundance. There was little variability among predators in a given treatment. Training had no effect on the subsequent diets of the predators, and all treatments provided a very good fit to a simple no—switching" model. Predation on each species was density independent. This simple type of predation contrasts markedly with the results of earlier experiments on predatory snails in which variability among predators and a strong training effect produce switching.
Creation of Relatively Stable Shrublands with Herbicides: Arresting "Succession" on Rights‐of‐Way and Pastureland
Authors: Niering William A. , Goodwin Richard H.
Published: May 2006

Two decades of selective—use herbicide management on a demonstration right—of—way within the Connecticut Arboretum has resulted in a mosaic of relatively stable shrub communities and less stable herblands within the central hardwoods forest region. Areas of continuous dense shrub cover have resisted tree invasion for at least 15 yr. On abandoned pastureland shrub clones of Gaylussacia baccata, Smilax rotundifolia, and Vaccinium vacillans, from which associated tree growth was selectively removed, were analyzed for subsequent tree invasion. They have remained essentially stable for 5 yr, with virtually no tree invasion in the closed clones, as compared to pronounced invasion of the graminoid periphery of the clones. This stability can be explained in terms of Egler's "initial floristic composition" hypothesis for vegetation change, as explained in this paper. The ability of shrub communities to resist tree invasion has always belied the so—called classical concepts of succession and climax, as have the findings of other investigators. The substitution of the term "vegetation development" for "succession" and "relative stability" for "climax" would stimulate a more creative interpretation of vegetation dynamics. Creating relatively—stable shrub communities by the selective use of herbicides has practical applications in right—of—way and wildlife habitat management, naturalistic landscaping, and the maintenance of habitat diversity.
A Simple Method for the Dry Combustion of 14C‐Labeled Materials
Authors: Burnison B. Kent , Perez Kenneth T.
Published: May 2006

Current methods for the determination of radioactive carbon in samples of biological material are either expensive, elaborate, dangerous, time consuming, or subject to contamination. A simple and inexpensive method is described here which eliminates these disadvantages and allows for the determination of 14C—activity in simple (14C—glucose) or complex (chloroform extract of ground 14C—labeled wax moth larvae) compounds.
Contrasting Foraging Strategies and Coexistence of Two Bee Species on a Single Resource
Authors: Johnson Leslie K. , Hubbell Stephen P.
Published: May 2006

The foraging patterns of two eusocial stingless bees, Trigona fuscipennis and Trigona fulviventris, were studied on a population of the shrub, Cassia biflora, in a tropical dry forest in Costa Rica. Trigona fuscipennis, which forages in large groups that monopolize plants, restricted its visits to large, dense clumps of Cassia. Visited plants had significantly more flowers than nonvisited plants. Trigona fulviventris, which forages as individuals of in small groups, visited more widely spaced or isolated plants. In the isolated plants visited by T. fulviventris, there was no significant difference in the number of flowers on visited vs. nonvisited plants. In clumps, however, the few plants visited by T. fulviventris had significantly fewer flowers than plants not visited. This observation and observations of interspecific aggression suggests that T. fulviventris is excluded from the better plants in clumps by T. fuscipennis. We believe the observed foraging patterns result from both evolved strategies and displacement due to short—term ecological competition. To explain the results, we hypothesize that two species may stably partition and coexist on a single resource, provided that (1) the resource has a highly variable spatial dispersion pattern, ranging from dense local patches to large regions of thinly spread resource, (2) the thinly spread resource is profitably harvested by only one of the species, (3) the dense patches are controlled by the second species, and (4) the resource is nonmobile such that not mixing of resource occurs between dense and sparse areas. We propose the terms low— and high—density specialists to describe such species.
Migration and Metabolism in a Temperate Stream Ecosystem
Authors: Hall Charles A. S.
Published: May 2006

Fish migration, total stream metabolism, and phosphous were studies in New Hope Creek, North Carolina, from April 1968 to June 1970. Upstream and downstream movement of fish was monitored using weirs with traps. Most of the 27 species had a consistent pattern of larger fish moving upstream and smaller fish moving downstream. Both upstream and downstream movements were greatest in the spring. For example, in the spring of 1969, a daily average of seven fish weighing a total of 1,081 g were caught moving upstream, and 17 fish weighing a total of 472 g were caught moving downstream. Although more moved downstream than up, the larger average size of the fish moving upstream resulted in a large transfer of fish upstream. Diurnal oxygen series were run to measure the metabolism of the aquatic community. Gross photosynthesis at the principal sampling station ranged from 0.21 to almost 9 g O2 m—2 day—1, and community respiration from 0.4 to 13 g O2 m—2 day—1 (mean of 290 and 479 g O2 m—2 yr—1). Both were highest in the spring. Area values of metabolism were often similar for different parts of the stream, but both production per volume and respiration per volume were always much larger near the headwaters than farther downstream. Migration may allow populations to take advantage of such differences in productivity by maintaining young fish in areas of high productivity. Other effects of migration may include: prey control, recolonization of defaunated regions, genetic exchange, and mineral distribution. An energy diagram was drawn comparing energies of insolation, leaf inputs, currents, total community respiration, fish populations, and migrations. About 1% of the total respiration of the stream was from fish populations, and over 1 year about 0.04% of the total energy used by the ecosystem was used for the process of migration. If it is assumed that upstream migration is necessary to maintain stocks, which may be periodically decimated by droughts, each Calorie invested by a fish population in migration returns at least 25 Calories (kilocalories). Even without that assumption returns are 3—fold. Analysis of phosphorus entering and leaving the watershed studied indicated that flows were very small relative to storages and that this generally undisturbed ecosystem is in approximate phosphorus balance. Upstream migrating fish were important in maintaining phosphorus reserves in the headwaters of New Hope Creek.
Thermal Balance and Prey Availability: Bases for a Model Relating Web‐Site Characteristics to Spider Reproductive Success
Authors: Riechert Susan E. , Tracy C. Richard
Published: May 2006

Analyses of the movements and web—site characteristics of the desert spider Agelenopsis apera (Gertsch) demonstrate that web locations offering the following habitat features are actively selected: shrubs, depressions, litter, and flowering herbs. A model of the effects of the thermal environment and prey avalability on the reproductive success of spiders occupying various web—site types is developed. The estimated productivity for an excellent web site (grassland depression with attractants) is 13x that determined for a poor site (larva surface). Model results suggest that more energy is to be obtained from selection of a favorable thermal environment (eight—fold difference) than from a site offering greater numbers of prey (two—fold difference). The presence of flowers at web sites increases the probability of receiving on occasional high prey density, whereas litter and habitat features providing shade (shrubs and depressions) allow increased spider activity through limitation of body temperature.