bluuebunny/crossref_metadata_2025 huggingface dataset:
Desertification, no‐change or alternative states: Can we trust simple models on livestock impact in dry rangelands?
Authors: Skarpe C.
Published: May 2006

Abstract. It is remarkable that after many thousands of years of pastoralism in arid and semi‐arid savannas, there is still no clear answer to the basic question: Does livestock grazing have more than a marginal effect on the dynamics of arid and semi‐arid land vegetation? A small study of semi‐arid savanna vegetation along a spatial gradient in grazing pressure, repeated three times over 19 years is used as a basis for discussing the behaviour of dry land vegetation under heavy grazing. Three basic theories are compared: (1) the theory that heavy grazing causes desertification; (2) the theory that heavy grazing causes no directed change in the vegetation of arid and semi‐arid rangelands; and (3) the theory that heavy grazing leads to a switch between alternative states of vegetation. On the basis of the current data the first two theories are rejected, but the conclusion is that there is much evidence for a more complex behaviour of dry rangelands under grazing than what is accommodated in any of the three theories. Probably, site‐specific properties including interactive and indirect effects of herbivory in the system are important for vegetation development under grazing in arid and semi‐arid rangelands.
Association of a Rainforest Palm and Seed‐Eating Beetles in Puerto Rico
Authors: Janzen Daniel H.
Published: May 2006

The scolytid beetle Cocotrypes carpophagus may attack as many as 100% of the seeds of the common Puerto Rican rainforest palm Euterpe globosa by the end of the fruiting season when the population densities of the beetle are their maximum. At the beginning of fruit fall, the percentage attack is extremely small. It is hypothesized that the build—up of this seed predator on the crop each year is the selective force producing the strong inter—tree fruiting synchrony displayed by E. globosa. Further, this synchrony appears to prevent the beetle from depressing the palm population density to the low level characteristic of most tropical trees. It is also hypothesized that such a beetle—palm interaction could not occur on the mainland of Central America owing to the difficulty of satiating the large mainland community of vertebrates and insects that prey on palm seeds.
Oxygen Requirements for Root Growth in Three Species of Desert Shrubs
Authors: Lunt O. R. , Letey J. , Clark S. B.
Published: May 2006

Shrubs of Artemisia tridentata and Larrea tridentata have unusually high oxygen requirements for root growth. Roots of Franseria dumosa, like many economic plants, need lesser amounts of oxygen. An oxygen diffusion rate of about 0.30 mg cm(—2)min(—1) is required by Franseria to achieve a root growth rate that is 50% of maximum at the experimental temperatures. The corresponding figures for Artemisia and Larrea are about 0.50 and 0.43, respectively. It is concluded that the general exclusion of Larrea and Artemisia from fine—textured and poorly drained soils in the desert is a reflection of their relatively high oxygen requirements for root growth.
Some Ecological Implications of Forest Fire Control in Yellowstone National Park, Wyoming
Authors: Taylor Dale L.
Published: May 2006

Seven areas that were burned in Yellowstone National Park in 1966, 1960, 1954, 1942, 1910, 1856, and about 1665 were studied from 1965 through 1967 in order to document the trends of biotic succession in the development of lodgepole pine communities. Results indicate that there was an increase in the numbers of plant, bird, and mammal species during the first 25 years followed by a decrease in the older communities. The data indicate that elimination of forest fires will limit ecological diversity within the Park by reducing or eliminating certain plants and animals that are present only in the successional communities present before closure of the forest canopy.
Site Fixity in the Caribbean Green Turtle
Authors: Carr Archie , Carr Marjorie H.
Published: May 2006

Although tagged green turtles that return to Tortuguero Beach to nest show definite site fixity, their site discrimination is not absolute. The modal distance between successive returns, whether after the 2—week internesting period of a given season or after the 2— or 3—year remigration interval between nesting seasons, is .2 km; average separation of return points is 1.2 km. In view of the steady reworking of the Tortuguero foreshore by wind, waves, and longshore currents,it seems unlikely that olfaction could be an important cue in landfall and nest—site discrimination, and new delimitation of the homing goal reinforces that belief. The straying of nesting females as far as 7 km from previous nesting sites suggests how colony proliferation may occur. No Tortuguero turtle has ever been found nesting on any other shore.
Relationships between Cell‐Wall Fractions, Nitrogen, and Standing Crop in Aquatic Macrophytes
Authors: Polisini J. M. , Boyd Claude E.
Published: May 2006

Shoot samples of 21 species of aquatic macrophytes were separated into cell—wall and noncell—wall fractions by digestion in a neutral—detergent solution. This method is useful for estimating the digestibility of plant production by native herbivores. Nitrogen content was also used as an indication of nutritive quality. Amounts of noncell—wall material and nitrogen in the dry matter decreased as shoot standing crops of the different species increased.
Predation on Scheelea Palm Seeds by Bruchid Beetles: Seed Density and Distance from the Parent Palm
Authors: Wilson Don E. , Janzen Daniel H.
Published: May 2006

In a test of the following hypotheses, the first was rejected and the second accepted. Rejected: (1) The farther a freshly cleaned [pile of] palm nut[s] (endocarp) is placed from a fruiting parent, the lower will be the probability of the nut[s'] being found by a bruchid. Accepted: (2) The larger the pile of freshly cleaned nuts at a site where there is no parent the more likely that it will be found by bruchids. The study was carried out in a palm forest in Guanacaste Province, Costa Rica, from March until July 1971. In addition to testing the above hypotheses, the study generated natural history data on bruchid oviposition behavior, oviposition intensity, survivorship of the larvae, and developmental rate.
Behavioral Ecology and Fitness Theory in a Tropical Hermit Crab
Authors: Childress John R.
Published: May 2006

Certain aspects of the behavioral ecology of the tropical hermit crab, Calibanarius abidigitus, can be analyzed more fully with the use of fitness set theory. Building on the premise that an optimum shell weight/body weight ratio (termed "weight index") confers maximum fitness to individual crabs, two independent estimates of fitness, clutch size and percentage aggressive dominance, were plotted against a wide range of weight indexes. These measures were made for individuals of C. albidigitus inhabiting two environments (represented as two species of gastropod shells) and behavioral and reproductive fitness sets were constructed. The dissimilarities of the predicted optimum weight indexes for the two fitness sets, combined with the fact that suitable gastropod shell present a limiting resource, indicate a behavioral strategy by which larger shells than necessary for maximum reproductive fitness are utilized. This strategy, termed the optimal ratios strategy, has definite advantages to individual hermit crabs and has probably evolved in response to severe competition for shells.
Vertical Migration and Feeding in Sagitta Elegans Verrill
Authors: Pearre Sifford
Published: May 2006

Field studies established diel vertical migration of Sagitta elegans Verrill. Light reactions of this species were investigated in the laboratory, where positive phototaxis and light—controlled geotaxis were found. Based on these, a model for depth control in diel migration is proposed. The field studies disclosed that light inhibits feeding and suggested that the state of satiation of the animal influences its depth control mechanism. The usual method of assessing vertical migration from stratified samples is criticized, and an explanation of “midnight sinking,” involving rapid turnover of feeding animals in surface waters, is offered. The diet of Sagitta was examined in summer and winter and related to the availability of different copepods. The relationship of diel migration to feeding activity led to a preponderance of surface—living copepods in Sagitta's diet. This effect can distort calculations of food selection. Theories of adaptive value are briefly discussed and it is concluded that Sagitta left the surface waters during the day primarily in order to avoid visually directed predation.
Radiotelemetry for Studying Thermoregulation in Free‐Ranging Snakes
Authors: Kroll James C. , Clark Donald R. , Albert James W.
Published: May 2006

A design for a treatment capable of relaying core temperatures from free—ranging snakes is presented. The transmitter consists of a pulse generator, switch, RF oscillator, and antenna. The completed system is compacted, encapsulated in paraffin and latex, and force—fed to the snake. The transmitter weighs approximately 15 gm, and our models have operated for as long as two months on two 1.35—v cells. Maximum transmission distance observed was 210 m (taken as the point where the signal was first detected across open terrain) from within a snake's body.
Competition in Spatially Heterogeneous Systems: An Analysis of Simple Cave Communities
Authors: Culver David C.
Published: May 2006

A model of competition for aquatic cave invertebrates in the southern Appalachians in which competition affects washout rate in the cave stream is presented. The model accounts for two major generalizations about microdistribution of cave isopods and amphipods in the Applachians: species distribution is uncertain and only one species is found in a habitat patch. The model also predicts the amount of habitat overlap various species pair have. Experiments to verify the model were conducted in an artificial stream.
Life History of an Ordovican Trilobite Triarthrus Eatoni
Authors: Cisne John L.
Published: May 2006

Triarthrus eatoni (Hall) was a trilobite common in Late Ordovician marine environments of the Appalachian region. New aspects of its growth, development, and population dynamics are surmised from a rare census fossil assemblage. Its development from protaspis larva (three stages separated by molts) through meraspis juvenile (at least 14 stages) to adult halospis (many stages) was very gradual. Size—frequency distributions reveal that reproduction was seasonal, probably having occurred in a single burst per year. This provides a means of measuring time in the life cycle. The growth curve for overall length is approximately linear. The protaspid period lasted on the order of a week or so, the meraspid period through most of the rest of the first year, and the holaspid period to a maximum longevity of at least 4 years. The survivorship curve is essentially an exponential decay curve; the probability of an individual's survival was between 0.3 and 0.4 per year. Through its earlier juvenile stages, very roughly through the first month of life, the trilobite was a planktonic suspension—feeder. This was probably a dispersal phase in the life cycle, and its long duration helps explain the cosmopolitan distribution of the genus. Afterward, the trilobite settled to live on or near the bottom as an epifaunal deposit—feeder.
Xylem Sap Tension in Three Woodland Oaks of Central California
Authors: Griffin James R.
Published: May 2006

In mid—August bottomland Quercus agrifolia and Q. lobata trees had low xylem sap tensions, as estimated by a pressure chamber. After a very dry winter, pre—drawn minimum tensions were less than 6 atm, suggesting that these rates were rooted to a water table. Widely spaced Q. lobata trees in upland savannas also had low pre—dawn tensions, presumably due to the lack of woody plant competition. In contrast, all strands of Q. douglasii had high pre—dawn tensions even after a very wet winter. They seem well adapted to dry slopes where the water table is usually unavailable. Quercus douglasii trees appear to drop their leaves when the water supply becomes critical. Trees in some north aspect stands had higher tensions in mid—August than trees in south aspect stands due to soil moisture supply and tree density interactions. During the dry season a size—class effect appeared with tension inversely correlated with crown size and probably root depth.
The Concepts of "Interaction" and "Operational Environment" in Environmental Analyses
Authors: Spomer G. G.
Published: May 2006

It is suggested that interactions between an organism and its general environment represent exchanges of energy or material and that such exchangeable entities, or "operational factors" should be the initial focus of an environmental analysis. It is only through such exchanges that an organism is "aware" of its environment and, hence, the operational portion of its environment is the sum of the sources of and sinks for operational factors. Implications of these concepts in environmental analysis and ecological interpretation are discussed.
Reconstructing Forest History from Live and Dead Plant Material‐‐An Approach to the Study of Forest Succession in Southwest New Hampshire
Authors: Henry J. D. , Swan J. M. A.
Published: May 2006

The purpose of this study is to see if it is possible to determine the course of forest succession over several hundred years by the dissection and close scrutiny of live and dead plant material. The study area was a one—tenth—acre (0.04—ha) square plot in a forest that had never been cut, located near Ashuelot in southwestern New Hampshire. Within it stem—location and growth—rate data were collected from three different classes of stems: 1) living trees, 2), dead unburied stems and stem fragments, and 3), woody remnants buried in the forest floor. The vegetational history of the plot was reconstructed from before 1665 to 1967. During this time, autogenic succession did not contribute significantly to compositional changes, whereas disturbance was an important mediator of such changes. Furthermore, changes in forest structure were often manifestations of species behavior: each tree species had a distinctive stem—distribution pattern in relation to microtopography, mode of germination, and growth. The approach seemed to provide a useful means to obtain evidence about forest change through time that may help prediction and illuminate ecological theory. Limits and modifications of the procedure are discussed.
Energy Requirements of a Population of Pinfish Lagodon Rhomboides (Linnaeus)
Authors: Hoss Donald E.
Published: May 2006

Biomass and rates of metabolism were estimated for a population of pinfish in the Newport River estuary, North Carolina. This information was used to estimate the routine energy requirements of the pinfish population and to relate these energy requirements to primary productivity in the estuary. Population estimations of larval, juvenile, and adult pinfish were made over a 2—yr period. Peak biomass occurred during March—April when both larval fish and juvenile—adult fish were at maximum numbers. Routine metabolism was measured at 10° and 15° C for larval fish and at 5°, 10°, 15°, 20°, and 33° C for juvenile—adult fish. Metabolism—weight coefficients calculated from the data for juvenile—adult fish were lower than values for pinfish reported by other investigators. The yearly routine energy requirement of the pinfish population was estimated to be 1.1 x 109 calories. This annual requirement was compared to total esturaine primary productivity with the assumption of 10% and 20% net growth efficiency for the estuarine system. At 10% efficiency the pinfish would require 0.9% and at 20% they would require 0.4% of the total energy available to secondary consumers.
Developmental Control of Net Productivity in Typha Latifolia Ecotypes
Authors: McNaughton S. J.
Published: May 2006

Population samples of broad—leaved cattail (Typha latifolia L.) from a variety of climates were studied to determine the extent to which net productivity, as dry matter production rate, was determined by (a) net assimilation rate per unit left tissue and (b) rate of production of leaf tissue. Assimilation rates of the eight populations studied were identical. Similarly, acclimation responses stabilized the net carbon balance of the same genotype under different environmental conditions. In contrast, rates of biomass production varied widely in different genotypes in the same environment, and in the same genotype in different environments. Variations in net productivity were regulated primarily by the rate of production of leaf tissue. This relationship held for different genotypes in the same environment, and the same genotype in different environments. Therefore, I conclude that the efficiency of net production in cattails is determined primarily by the rate at which leaf tissue is produced, rather than by inherent differences in the assimilation efficiency of that tissue.
Genetic, Photic and Temperature Effects on the Fecundity of Tribolium
Authors: Hawk James A. , Colaianne J. J. , Bell A. E.
Published: May 2006

Fecundity of two unrelated populations of Tribolium castaneum as measured by eggs laid and hatchability was studied in a factorial design involving two levels of temperature (28°C vs. 33°C) and of lighting (light vs. dark). Significant differences between genotype, temperatures, and lighting regimes were observed for egg numbers, whereas temperature represented the only significant influence on hatchability. Egg numbers were increased considerably by the higher temperature but hatchability declined. In addition, more eggs were laid in continuous dark than in continuous light. Genotypes interacted with levels of temperature in the dark. The photonegative response of Tribolium was the probable mechanism for the observed photic influence. The response of these two genotypes indicated that Tribolium can adapt to continuous light with a resulting decrease in the photonegative sensitivity. There is a possibility of genotype by environment interactions in population studies with Tribolium.
The Divergence of Adjacent Populations
Authors: Kerfoot W. Charles
Published: May 2006

In Union Bay, a temperate embayment in Seattle, Washington, USA two different kinds of predators maintain a polymorphism of the cladoceran Bosmina longirostris. The boundary separating these two Bosmina populations is unusual because it is maintained in a freely mixing body of water, and important because its distinctness is a consequence of trophic dynamics, a result of the interactions of visual predators (fish) and grasping predators (copepods). Not only do the fish directly affect the morph composition by differentially removing the more conspicuous morphs, they also indirectly control the magnitude of counter—selection forces by regulating the abundance of predatory copepods. The joint action of both predators sets up a spatial situation in which adjacent populations of Bosmina actually diverge phenotypically and genetically during the summer.
A Field‐Tested Thermoregulation Model for Two Diurnal Namib Desert Tenebrionid Beetles
Authors: Henwood Kenneth
Published: May 2006

The thermoregulatory strategies of two Namib Desert tenebrionid beetles were studied to determine the methods used to attain relatively high and constant body temperatures for several hours each day. In the field thermoregulatory behavior observations were made simultaneously with microclimate data collection and measurement of body temperatures in free—ranging beetles. A thermal model was developed using beetle heat exchange parameters and combined with microclimate data to predict the range of body temperatures available to the insects in their different environments. The accuracy of the model was validated against measurements of body temperature in the population of free—ranging beetles. Observations of thermoregulatory behavior, when coupled with the effect of such behavior on modeled body temperatures, make it possible to evaluate quantitatively the efficacy of various thermal strategies and the degree of habitat selection practiced by the insects to maintain preferred temperatures. Thermoregulation methods include squatting, stilting, exposure of lighter—colored body surfaces, climbing and burrowing. These methods, when combined with the ability to seek out and move to unique microenvironments, enable the beetles to maximize thermoregulatory control and achieve greater independence from thermal variations in their habitat. Both beetle species were living maxithermal strategies in which body temperatures were maintained at high levels for a maximum time each day.
The Effect of the European Wild Boar, Sus scrofa, on Gray Beech Forest in the Great Smoky Mountains
Authors: Bratton Susan Power
Published: May 2006

The European wild boar Sus scrofa L., an exotic species, entered the Great Smoky Mountains National Park during the 1940s. Because of their high reproductive potential and their adverse impact on the native flora and fauna, the wild hogs have become a major management problem within the park. During the summer of 1973, quadrat sampling of the canopy and understory of Gray Beech Forest was conducted in both the hog—free and hog—occupied sectors of the park. Removal of the herbaceous understory and other types of hog rooting damage showed no direct relationship to the importance of any individual canopy species, including beech Fagus grandifolia. Cover reduction was related, however, to the importance of mesic herbs in a plot. Polynomial and Gaussian regressions of cover against indirect ordination axes indicate that hog rooting within Gray Beech Forest is most intense in the mesic portion of the moisture gradient and decreases both on xeric, south—facing slopes and on more mesic, north—facing slopes. Understory cover in the most severely damaged plots was between 2% and 15%, while understory cover in hog—free plots in the same position on the moisture gradient was usually between 80% and 110%. Hog rooting significantly reduced the number of species in the most disturbed plots but had no effect on the H' values of the largest plot sizes sampled. High H' values for the damaged plots are related to the lack of succession after disturbance of the understory without removal of the canopy.
On Estimating the Aboveground Weights of Tree Stands
Authors: Madgwick H. A. I. , Satoo T.
Published: May 2006

Simulated sampling of nine tree stands was used to compare estimated stand component weights with known weights based on complete harvest. On average, estimates based on regressions of logarithm weight on either logarithm tree diameter or on logarithm (diameter)2 x height overestimated weights of stems, branches, and leaves by ° 3% when the inherent bias of such regressions was accounted for. Ninety—five percent confidence intervals based on random sampling encompassed the measured stand weights 79%—100% of the time. Similar confidence intervals using stratified random sampling based on tree diameter encompassed the measured stand weights only 44%—98% of the time. The small average bias in estimates of stand weight using logarithmic regressions is of minor importance compared with the variation in estimates among replicated samples.
Effects of Aeration, Water Supply, and Nitrogen Source on Growth and Development of Tupelo Gum and Bald Cypress
Authors: Dickson Richard E. , Broyer T. C.
Published: May 2006

Seedlings of tupelo gum (Nyssa aquatica L.) and bald cypress (Taxodium distichum L. Rich.) were cultured in saturated—aerated, saturated, and unsaturated soil. Experiments were designed to (1) measure and evaluate the relative reaction of tupelo and cypress to various soil—moisture conditions (2) determine the effects of aeration and water availability on plant moisture stress and growth; and (3) compare effects of two forms of nitrogen fertilizer (urea and nitrate) on growth. On the basis of height and dry weight, both tupelo and cypress grew best in saturated—aerated soil. Growth was better in saturated soil than in unsaturated soil, but only when water in the unsaturated soil decreased substantially below field capacity before rewatering. Plant moisture stress was determined by a pressure—bomb technique. For tupelo, average daily maximum tensions were 7.2 and 7.0 atm (atm = 1.013 bar) with saturated and unsaturated soil, respectively; for cypress, comparative tensions were 10.9 and 8. 5 atm. When soil moisture decreased from field capacity to the wilting point, the daily maximum tension in plants increased from 7.0 to 12.8 and from 8.5 to 17.6 atm in tupelo and cypress, respectively. Growth of plants was related to the cumulative effect of their internal moisture stress. When tupelo plants were subjected to 595 atm—days (daily maximum tension X number of days with that tension), height growth was 37% and dry weight 40% less than plants subjected to 490 atm—days. Fertilization with urea produced more growth than fertilization with nitrate.
Experimental Manipulation of Population Density in Three Sympatric Rodents
Authors: Joule James , Jameson David L.
Published: May 2006

Three abundant rodents, the cotton rat (Sigmodon hispidus), the harvest mouse (Reithrodontomys fulvescens), and the rice rat (Oryzomys palustris) are sympatric in southeast Texas. From January 1970 to May 1970, six presumably homogeneous areas, three control, were live—trapped. Mark—release—recapture and selective removal techniques were used to monitor species composition within the areas. Estimates of the number of individuals per species, body weights, and sex ratios were obtained at 2—week intervals. When cotton rats were experimentally removed, no change in the mean weights of harvest mice or rice rats were revealed by linear regression analysis. When harvest mice and rice rats were removed, cotton rat females exhibited a significant increase in mean weight. A significant change in sex ratio of cotton rats, from a greater proportion of males to a greater proportion of females, was recorded in the areas where harvest mice and rice rats were removed. Although the number of captures per species declined, comparisons of the different experimental manipulations could be made throughout the study.
Ecological Energetics of Three Species of Ectothermic Vertebrates
Authors: Smith Gary C.
Published: May 2006

Comparisons were made of the energy budgets of three ectothermic vertebrates found in the Southeastern United States. The three species studied were Elaphe guttata (corn snakes), Heterodon platyrhinos (eastern hognose snakes), and Bufo terrestris (southern toads). Values for assimilation efficiency, ingestion, excretion, growth, shedding, metabolism, and reproduction were converted to caloric units and integrated into energy flow models for each species.
Interactions among the Predatory Rotifer Asplanchna and Two Prey, Paramecium and Euglena
Authors: Maly Edward J.
Published: May 2006

Interactions among the predatory rotifer Asplanchna and alternative prey Paramecium and Euglena are examined in a laboratory environment to determine whether the addition of an alternative, less desirable prey stabilizes a simple predator—prey interaction. Rates of increase, carrying capacities, and dynamics of predator resting egg production are determined by both short—term and long—term experiments with partial medium renewal. Isoclines and isoplanes are constructed; relative stability of the Asplanchna—Paramecium and the Asplanchna—Paramecium—Euglena interactions is determined. According to a mathematical analysis of deviations from equilibrium, stability properties change only slightly with addition of Euglena. Although Asplanchna rate of increase is reduced by addition of Euglena, feeding rate on Paramecium remains high, and Asplanchna cannot survive on Euglena alone. The biology of the organisms used in this study affect stability properties of the system more than any other factor.
Species Richness on the Nondisturbed Northwestern Hawaiian Islands
Authors: Amerson A. Binion
Published: May 2006

An examination of selected ecological variables on the 18 low, sandy, non—disturbed islands of the northwestern Hawaiian Islands, and the vascular plants and birds, primarily seabirds, occurring there shows that species richness on low, sandy, oceanic islands is influenced by ecological diversity and is affected by variables similar to those on high, rocky islands. Species richness of vascular plants on these islands can be predicted by means of stepwise regression on the basis of area of vegetation, and to a lesser extent, elevation. In turn, variation in numbers of breeding species of seabirds, total species of seabirds, and total species of birds on these same islands can be predicted on the basis of number of species of vascular plants, and to a lesser extent, area of the island. Ecological diversity, although poor in quality, is of prime importance in regulating use of low, sandy, oceanic islands by any seabird. Although terrestrial bird use islands for obtaining food and for nesting whereas seabird use islands only as a nesting and roosting place, species of terrestrial birds and seabirds on islands are associated with similar ecological variables.
Species Packing and Predation Pressure
Authors: Roughgarden Jonathan , Feldman Marcus
Published: May 2006

The hypothesis that predation presure permits increased niche overlap among prey species is sustained by analysis of a model in which a predator poplulation has been added to the three species "limiting similarity" model of MacArthur and Levins (1967). Also, it is predicted that there is a relation between the niche separation distances among prey and properties of the predators, and that if predation pressure is strong enough there is no limiting similarity among prey; i.e., complete niche overlap should be possible.
Fire and Nutrient Cycling in a Douglas‐Fir/Larch Forest
Authors: Stark Nellie M.
Published: May 2006

Twenty control burns performed with a wide range of fuel loadings and moisture conditions were used to study the effectiveness of old fuel reduction under standing Douglas—fir/larch forest. This paper reports the influence of burning on nutrient retention and loss from the soil. Sixty % of the fires were successful in reducing residual fuels with no accelerated loss of nutrients below the root zone. Net less of Ca+2 and Mg+2 occurred below the root zone when soil surface temperatures exceeded 300°C, but were insignificant when soil surface temperatures remained below 200—300°C. No other elements were loss (net) from the soil as a result of burning. Precipitation on control soils delivers as much Ca+2 as is normally lost below the root zone in the absence of fire. Iron concentration in the soil water is a good indicator of the intensity of burn. The hotter the fire, the less iron in the soil water as a result of the alkaline pH. Ash shows a definite pattern of nutrient release under the influence of precipitation. Homogeneous subsamples of litter showed predictable nutrients losses when ignited at different temperatures. Overland flow and surface erosion are of little significance on this soil type. Decomposition of Douglas—fir litter was only slightly more rapid on hot burned substrates than on control (unburned) substrates. When the biological life concept was applied to this soil, it showed that this soil is young and capable of withstanding many years of cyclic intensive burns.
Patterns of Niche Overlap Among Broadly Sympatric Versus Narrowly Sympatric Kalahari Lizards (Scincidae: Mabuya)
Authors: Huey Raymond B. , Pianka Eric R.
Published: May 2006

Two semiarboreal skinks (Mabuya) are narrowly sympatric in the Kalahari desert, whereas two terrestrial species are broadly sympatric both with one another and with the semiarboreal species. We attempt to discern reasons for these differing distributional patterns. The narrow zone of sympatry of the semiarboreal species is partially congruent with zones of habitat change (rainfall and vegetation), suggesting that the narrow zone probably reflects adaptations of these species of geographic discontinuities of the physical environment. However, the near identity of niches (position on sandridges, microhabitats, body temperatures, times of activity, as well as types and sizes of prey) of the semiarboreal species relative to other species pairs also suggest that intense competition could restrict the zone of sympatry.
Germination Response in Emmenanthe Penduliflora (Hydrophyllaceae)
Authors: Wicklow Donald T.
Published: May 2006

Emmananthe penduliflora Benth., postfire chaparral annual, has been shown in laboratory experiments to incorporate a unique mechanism allowing for the germination of its seeds. Only a few of the hundreds of E. penduliflora seeds tested would germinate following a period of incubation on either moist filter paper or soil. However, when burned stem segments of the chaparral dominant Adenostoma fasiculatum H & H. were placed on or immediately adjacent to E. penduliflora seeds, and incubated on moist soil at 10°C, germination occurred within 4 wk. Chaparral fires are generally believed to stimulate the development of a postburn flora through mechanisms involving sed coat scarification and/or the removal of allelopathic inhibitors to germination. The evidence presented herein suggests that for at least one postfire species the charred remains of chaparral vegetation serve as a germination trigger. Field experiments involving the effects of controlled burning and other manipulations of chaparral vegetation support the results. Relationships between these and other findings to the natural occurrence of Emmenanthe in California are discussed.
Periodic, Pseudoperiodic, and Chaotic Population Fluctuations
Authors: Poole Roberty W.
Published: May 2006

Relatively simple deductive models of fluctuations in population abundance are commonly used to suggest hypotheses about the behavior of populations given certain assumed patterns of interactions. However, if it is not possible to distinguish between different types of behavior in real populations, then the predictions of the models are not testable and the value of deductive models in population ecology limited. This paper discusses periodic, pseudoperiodic, and chaotic population fluctuations and demonstrates that, in practice, it is impossible to distinguish between these three important types of population behavior. It is concluded that much more attention should be given to the problems of characterizing population fluctuations and the testing and validating of the hypotheses generated by deductive representational models.
Predation and Prey Community Structure: An Experimental Study of the Effect of Mosquito Larvae on the Protozoan Communities of Pitcher Plants
Authors: Addicott John F.
Published: May 2006

This work was designed to test the hypothesis: in the presence of predation more species will coexist in the prey community than in the absence of predation. The hypothesis may also be stated in terms of the evenness with which individuals are distributed among species. This hypothesis was tested using the communities that occur within the water—filled pitchers of the northern pitcher plant, Sarracenia purpurea L. The predator in this system is the larval stage of the mosquito, Wyeomyia smithii (Coq.). The prey community consisted of ciliated and flagellated protozoans as well as rotifers. Four approaches were used to gain information about this predator—prey system: (1) observations on the densities of the predator in the field, (2) observations on the correlation between predator density and protozoan community structure in the field, (3) field experiments in which both the predator density and initial protozoan community structure were controlled, and (4) observations on the development of protozoan community structure in the long—term absence of predation. The results show that there is considerable variability of predator densities in both time and space and that the protozoan community responses to these differences. The field experiments show that for the pitcher plant system the hypothesis must be rejected: species numbers tend to drop monotonically as predator densities increase. On the other hand, evenness (H/Hmax) does increase as predator densities increase. These patterns hold except during diapause of the mosquito larvae in the fall. These results are discussed within a general framework of factors which appear to be important for determining how predators affect prey community structure; the four possible mechanisms by which species numbers could increase predation are outlined, and the pitcher plant system is related to each possible mechanism. The Pitcher plant system has very few characteristics that would cause the system to respond to predation with enhanced species numbers. The most important characteristic leading to decreased species numbers appears to be a low level of interaction among the protozoan species. The increase in evenness in response to predation can best be explained by a shift in the factors that control species numbers from species interactions to rates of reproduction.
The Population Ecology of Two Species of Costa Rican Heteromyid Rodents
Authors: Fleming Theodore H.
Published: May 2006

This study compares the demographic characteristics of two tropical heteromyid rodents: Liomys salvini, which inhabits deciduous (seasonal) tropical forests, and Heteromys desmarestianus, which inhabits wet (relatively nonseasonal) tropical forests. The hypothesis is examined that, because of the stronger seasonality of its environment, L. salvini is more r—selected than H. desmarestianus. Mark—and—release techniques were used to document population events occurring between August 1970 and August 1971 and again in June and July 1972 at two localities in lowland Costa Rica. Density fluctuated annually in both species, with the mean density of H. desmarestianus being much higher than that of L. salvini, probably because of the greater productivity of its habitat. Reproduction is more strongly seasonal in L. salvini, and females mature faster and produce larger litters than those of H. desmarestianus. Survivorship appears to be higher in the latter species. Adults of L. salivini increase markedly in weight during the breeding season. Individuals of both species occupied home ranges that were relatively stable in size aNd location for extended periods (1 yr or more). There were seasonal differences in the distances moved between successive capture sites in males of both species. Owing to earlier maturity and greater productivity per month of breeding, L. salvini appears to be more r—selected than H. desmarestianus. Many of the demographic characteristics of these tropical forest—dwelling heteromyids are similar to those of their temperate zone desert—dwelling relatives.
A Simulation Model for Testing the Dynamics of a Grasshopper Population
Authors: Gyllenberg Goran
Published: May 2006

Energy flow of a Chorthippus parallelus (Zett.) (Orthoptera) population was studied for 6 yr (1966—71) on a meadow at Tvarminne, Finland. A difference—equation model, based on biomass and energy, was constructed. The transfer coefficients were functions mainly of two environmental factors, temperature and rainfall. The model, constructed from 1969 data, was tested with values from 1967, 1970, and 1971. Heavy infection with the fungus Entomophthora grylli in 1967 and drought in 1971 resulted in poor fit to the model. The drought caused a sparse food supply and forced the grasshoppers to forage extensively for food. An activity box was therefore introduced to the model, converting animal behavior quantitatively into energy.
Preadult Competition between Drosophila Pavani and Drosophila Melanogaster, Drosophila Simulans, and Drosophila Willistoni
Authors: Budnik Myriam , Brncic Danko
Published: May 2006

When the Chilean endemic species Drosophila pavani compete during the pre—adult stage on a limited amount of food with D. melanogaster, D. simulans, and D. willistoni, developmental periods were significantly retarded, but egg—to—adult viability decreased only in the presence of D. melanogaster. In the same experiments, two of the other three species suffered no modifications in survival and developmental time, but in D. willistoni viability was reduced in the presence of D. pavani larvae. The lengthening of the developmental period of D. pavani may result in utilization of different resources, thus avoiding the direct effects of exploitation competition. The decrease in egg—to—adult viability of D. willistoni in the presence of D. pavani does not seem to be exclusively dependent on food competition. In experiments in which the culture medium was previously "conditioned" by D. pavani larvae, but with an excess of food, the viability of D. willistoni also decreased, indicating that the metabolic waste products of the first species probably interferes with the development of the second.
Studies on Intra‐ and Inter‐Specific Competition in Drosophila
Authors: Wallace Bruce
Published: May 2006

Of eight species of Drosophila (ananassae, funebris, melanogaster, nebulosa, pseudobscura, simulans, virilis, and willistoni), the number of progeny produced per culture vial increases with the number of female parents for D. melanogaster, D. simulans, D. willistoni, D. ananassae, and D. nebulosa; in contrast, the progeny yield is a constant that is independent of the number of parental females per vial for D. funebris, D. pseudoobscura, and D. virilis. Forall species, however, the per capita yield decreases more or less exponentially with the square—root of the number of parental females per vial. The outcome of mixed—species competition depends largely upon the two species concerned. Drosophila simulans seemingly benefits by increases in number of its own females; four or five D. simulans females yield more progeny in the presence of D. funebris, for example, than produces D. simulans. Drosophila simulans alsoproduces greater number of progeny per vial as the number of competing D. funebris females is increased. Drosophila melanogaster and D. simulans females competing in individual culturesyield mixed progeny; the two species share the resources of each vial. In contrast, the progeny of D. pseudoobscura and D. virilis females in individual mixed—culture vials tend to be of one species or the other many cultures containing these two types of females yield few or no flies of either species. For most species—pairs the logarithm of the ratio of the two species among offspring varies directly with that among parents (slope of the regression = 1.00). For three species—pairs, however, the slope of this regression is significantly less than 1.00. If the same relationship were to hold among freelybreeding populations of the two species, the species should establish stable equilibrium proportions. Analyses of the competing species by means of replacement series reveals that the members of individual pairs may enhance or interfere with each other's development, or do neither. Similarly, the competitive abilities of the species differ considerably. The ease with which each species uses different resources within the culture vials differs. Thus, intra— and interspecific competition differentially affect the per capita progeny production of conspecific and heterospecific females. Because the competition between conspecific females differs demonstrably from that between heterospecific ones, it appears that inter—specific frequency—dependent selection may reflect the relative proportions of resources that are used with contrasting ease by the competing species. If so, frequency—dependent selection is precisely the sort of evidence needed to demonstrate that two species are not competing identically for identical resources, the type of competition that is expected to lead to competitive exclusion.
Seasonal Changes in Standing Crop and Primary Production in a Sedge Wetland and an Adjacent Dry Old‐Field in Central Minnesota
Authors: Bernard John M.
Published: May 2006

Seasonal changes in above— and below—ground standing crop and primary production in a Carex rostrata wetland and an adjacent dry Poa pratensis old field were determined. Above ground, the Carex rostrata standing crop of green material varied from a minimum of 114 g/m2 frozen in the winter ice to a high of 852 g/m2 in late August. Maximum daily production averaged about 11 g/m2° day from mid—June to mid—July. Below—ground standing crop was highest in winter at 328 g/m2 in late July. Below—ground standing crop then increased at a rate averaging about 1 g/m2#?day. Poa pratensis growth was rapid in early spring, the green above—ground standing crop peaked at 114 g/m2 in late May—early June. A definite midsummer cessation of growth then occurred, the average summer standing crop averaging jut 87 g/m2during July and August. A second greater peak of production then occurred with a maximum standing crop of 149 g/m2 reached in late September. The daily production rate at this maximum was 3.3 g/m2°day. Below ground the standing crop in the 0—20 cm level was at the season's high of 1667 g/m2 in winter and then declined to an average summer low of 1194 g/m2 after which it rose to 1458g/m2 in late October.
Avian Species Diversity in Desert Scrub
Authors: Tomoff Carl S.
Published: May 2006

Along a gradient of habitat complexity in desert scrub communities of the Sonoran Desert in southern Arizona, nest sites and food niches become more diverse, and breeding bird population density and species diversity increase. Birds are highly specific in their selection of plants for nest placement; densities of nest plants. The MacArthur foliage—height diversity model does not yield consistently accurate predictions of breeding bird species diversities in desert scrub communities. A significant relationship is found between physiognomic coverage diversity and breeding bird species diversity. This index, based on a system of plant life forms, quantifies critical environmental features used by birds in habitat selection. A model that combines aspects of foliage—height diversity and physiognomic coverage diversity may provide greater accuracy and wider applicability for predicting breeding bird species diversity.
Predation by Terrestrial Isopods
Authors: Edney E. B. , Allen Warren , McFarlane Joan
Published: May 2006

Fifty of each sex of two species of terrestrial isopods, Armadillidium vulgare and Porcellio laevis, were each offered 16 live pupae, four each of Drosophilia hydei, D. immigrans, D. pseudoobscura and D. melanogaster, for 24 hr. Both sexes of both predator species fed on all prey species, each predator species taking numbers of prey species in the reverse order of prey size, namely, D. melanogaster > D. pseudoobscura > D. immigrans > D. hydei. The results, however,do not indicate preference by predators. In terms of total weights consumed, Porcellio ♂ ♂ and ♀ ♀ ate 8.91 and 8.04, and Armadillidium ♂ ♂ and ♀ ♀ 11.69 and 11.86 mg/isopod°day respectively. The difference between sexes is insignificant, but between predators it is highly significant (P < 0.001). Ratesof consumption of Drosophila pupae and of Hippelates pupae decreased by about two—thirds or more over a week in the absence of other food. Laboratory experiments using known numbers of 32P—labelled Drosophila pupae fed to Armadillidium proved the feasibility of using the technique for field studies. Such work subsequently showed that A. vulgare ate D. melanogaster pupaein natural conditions in a citrus grove where alternative food was abundant. If predation by isopods in nature proves to be wide—spread, their significance in several ecosystems would deserve reconsideration.
An Analysis of the Pattern of Dispersion of the Hermatypic Coral Pocillopora Meandrina Var. Nobilis Verril
Authors: Stimson John
Published: May 2006

Spatial distribution of the hermatypic coral Pocillopora meandrina is analysed by quadrat—count and nearest neighbor techniques; the nearest technique consistently indicates uniform dispersion of the coral heads. The significant correlation between the sum of the diameters of each pair of nearest neighbors and the distance between the centers of those nearest neighbors suggests that the uniform dispersion is the product of competition between colonies and settling larvae. Several mechanisms are proposed to account for the uniform dispersion.