bluuebunny/crossref_metadata_2025 huggingface dataset:
On Modeling Density‐Independent Population Change
Authors: Brockelman Warren Y. , Fagen Robert M.
Published: May 2006

Several recent papers have shown that when statistical and graphical tests for regulation are applied to artificially generated "density—independent" populations containing random variables, enigmatic evidence for regulation (density dependence) is obtained. In one instance, density independence is confused with randomness of population size. In the other instances, Morris's method of regressing log Nt+1 on log Nt yields evidence of regulation in density—independent populations. It is shown here that regression analysis is inappropriate in Morris's test, and that the principal error axis rather than the regression line yields the slope tending toward unity in the absence of regulation. However, the sensitivity of the slope of the principal axis to density dependence depends on the amount of initial displacement from equilibrium and on the number of serial samples. Hence, this statistic is of little usefulness. The effect of serial correlation on tests for the presence of density dependence is discussed briefly.
Quantification on the Aspect Parameter in Ecological Site Characterizations
Authors: Fribourg Henry A.
Published: May 2006

A digital computer was developed which uses the Okanoue equation for evaluating the total potential solar radiation striking a point on the surface of the earth daily between 60° N and 60° S latitude, taking into account solar declination, radius vector, latitude, day length, azimuth from N and slope. Output consists of the relative insolation striking a sloping site expressed as a percentage of that striking a flat exposure at the same geographical location, elevation and time. Results may be obtained on a daily basis, a yearly basis, or a seasonal basis. Also, daily or weekly average day lengths can be obtained.
Caloric Content and Available Energy in Plant Matter
Authors: Verduin Jacob
Published: May 2006

Caloric content of plant matter, as indicated by bomb calorimetry, includes energy which is not available to metabolic processes of the plant. Consequently such data have limited nutritional significance.
The Role of Behavioral Thermoregulation in the Growth Energetics of the Toad, Bufo Boreas
Authors: Lillywhite Harvey B. , Licht Paul , Chelgren Pamela
Published: May 2006

Newly metamorphosed Western toads, Bufo boreas, are diurnally active and thermoregulate by the behavioral exploitation of available microenvironments including exposure to solar radiation. In the laboratory, toads thermoregulate by basking beneath incandescent lamps when placed within a photothermal gradient. Basking depends on feeding, and when food is withheld, individuals abandon the available heat source and assume lower body temperatures. The preferred temperature of feeding individuals is around 26—27 degrees C as determined from animals both in the laboratory and in nature; fasting animals remain between 15—20 degrees C. Growth of young toads with ad libitum food supply was measured at a variety of temperatures. Energy ingestion (appetite), linear growth, weight increase, and gross conversion efficiencies were all maximal at 27 degrees C and were nearly identical to that of toads allowed to thermoregulate in a photothermal gradient. Weight—specific energy ingestion, weight—specific growth, and gross conversion efficiency decreased with age. Survivorship of starved toads in a thermal gradient was prolonged over that of toads maintained at a constant 27 degrees C. Metabolism increased with body temperature over the range 10—33 degrees C. We have concluded that this terrestrial ectotherm has evolved a behavioral thermoregulatory mechanism which maximizes growth and economic utilization of energy. The diurnal behavior patterns of small toads (compared with the more strictly nocturnal adults) may have evolved to maximize the growth rates of younger individuals, thus shortening their time to adult size.
Social Facilitation of Egg‐Laying In Experimental Colonies of a Weaverbird
Authors: Victoria J. K. , Collias N. E.
Published: May 2006

Different—sized experimental colonies of African Village Weaverbirds (Ploceus cucullatus cucullatus) were observed in large outdoor aviaries over a period of 4 years. At the height of the breeding season there was little social facilitation of egg—laying, with most females apparently laying clutches at or near a maximum rate regardless of the colony size, as long as there was no shortage of nests. The number of nests available appeared to limit egg—laying more than did number of males present. However, an increase in colony size stimulated the females to visit male territories and the nests included within them at an increased rate and also tended to reduce the females' clutch replacement interval. Social facilitation appears to exert its strongest effect at the onset and the close of the breeding season. At the beginning of the season, the start of egg—laying depended upon the start of male nest—building, but birds in a large colony began breeding sooner than in a small one. Crowding the birds at the end of the season resulted in a definite resurgence of egg—laying activity, the amount of which depended upon how late in the season the birds were crowded.
Net Photosynthesis of Cladonia Mitis (Sand.) From Sun and Shade Sites on the Wisconsin Pine Barrens
Authors: Lechowicz Martin J. , Adams Michael S.
Published: May 2006

The lichen Cladonia mitis (Sand.) from the Wisconsin Pine Barrens showed no significant differences in the light—dependence of net photosynthesis of sun— and shade—grown mats. Maximal net photosynthesis was 1.13 mg CO_2. g(—1) (air dry weight). hr(—1) at 3.88 x 105 ergs. cm(—2). sec(—1), 22.5 plus or minus 1.0 degrees,and near optimal thallus water content; the light compensation point was 0.36 x 105 ergs. cm2. sec(—1). After dormancy was broken by wetting the sun— and shade—grown C. mitis mats had comparable initial dark respiration rates of —0.47 and —0.48 mg CO2. g(—1). hr(—1), respectively, at high thallus relative water content (ca. 90% RWC). After drying to thallus RWC in the range 62—72%, the dark respiratory rates of the sun—and shade—grown C. mitis, respectively —0.33 and —0.25 mg CO_2. g(—1). hr(—1), differ significantly. The decreases in thallus RWC over 196 plus or minus 3.7 minutes of 37% and 29% for the sun— and shade—grown C. mitis, respectively, also differed significantly. The average annual growth rate of 5.2 plus or minus 0.2 mm. yr(—1) was the same for both sun— and shade—grown C. mitis. These characteristics of sun— and shade—grown C. mitis may be an important aspect of the physiological ecology of the plants.
Competition for Food Between the Intertidal Gastropods Acmaea Scabra and Acmaea Digitalis
Authors: Haven Stoner B.
Published: May 2006

The limpets Acmaea scabra and A. digitalis graze on encrusting microalgae in the upper intertidal and splash zones in central California, differing in habitat distribution but with considerable overlap. Controlled field experiments tested for interspecific competition in a habitat where both species were common but where A. scabra was similar than A. digitalis. Removal of A. digitalis from fenced exclosure plots resulted in significant growth increases in A. scraba, correlated with pronounced increases in the algal food supply. A converse effect on A. digitalis occurred in one of three experiments. It is concluded that in the habitat studied, limpet grazing strongly limited algal crop most of the year, and interspecific competition (exploitation type) for food limited growth rates and maximum size in A. scraba.
A Model of Ion Transport During Moisture Flow from a Douglas‐Fir Forest Floor
Authors: McColl J. G.
Published: May 2006

The electrical conductivity and flow—rate of solution in a forest floor were continuously monitored in the field using a tension—lysimeter system coupled with automated recording instruments. Forest floor temperature was also automatically recorded. The field study site was in a uniform second—growth Douglas—fir forest on a glacial outwash soil in western Washington. Total ion amounts released from the forest floor during the movement of individual wetting fronts resulting from natural precipitation were calculated. These field data, together with data obtained in the laboratory, were used to develop a model of the transport process. Over the temperature range experience in the field, I, which is the total ion amount transport by a given total flow of solution, can be described by the algebraic model: I=M/1 + A exp(— BT), (0 degrees C < T < 20 degrees C) where M is the maximum ion amount transported by the given flow, T is the mean temperature of the dry period preceding flow, and A and B are constants. Values of M, A and B are also given for total flows up to 26 mm, so that I can be calculated for any combination of flow and temperature.
Estimation of Energy Flow in Bird Communities: A Population Bioenergetics Model
Authors: Wiens John A. , Innis George S.
Published: May 2006

We describe a simulation model that estimates population density flux, biomass changes, and bioenergetic demands of bird populations, especially with reference to the breeding season. changes in the population density of adults of each species considered were calculated from breeding census values and information on migratory movements. Using field or literature values for clutch size, mortality rates, and reproductive phenology, we computed the population densities of the nestling, fledgling, and juvenile age classes of each species. Given information on adult body weights, weight changes of young were obtained from a logistic function, and the age class distributions within a population were used to estimate biomass changes in each age class through time. Coupled with an ambient temperature function, the bioenergetic formulations of Kendeigh, and considerations of the energy costs of digestion, activity, molt, egg production, and growth, this allowed an area—based estimation of the daily energy requirements of each age class of a population. When a community of several populations was considered, estimates for the total community as well as for each population were made. A sensitivity test of model constants and input variables suggests that output estimates may be most sensitive to variations in digestive efficiency, adult population density, the timing of arrival and departure, and ambient temperature. In general, however, the model appears to be fairly robust. We discuss examples of model output and uses of the model in theoretical and management investigations.
Genetic and Social Structure of Feral House Mouse Populations on Grizzly Island, California
Authors: Myers Judith H.
Published: May 2006

Two populations of house mice living in open grassland in northern California were tested for demic structure, which has been reported for populations living in farm buildings. Mice captured in each of two 0.8—ha trapping areas were typed for two blood proteins (hemoglobin and an esterase). Nonrandom distributions of genotypes within the populations occasionally occurred, but were not temporally stable. During part of the study, allele frequencies at the hemoglobin locus were significantly different in the two populations. An analysis of selection showed that differential survival and reproduction favored different genotypes in each population. Numbers of mice fluctuated dramatically on the two areas, reflecting the variability of conditions to which feral mice are exposed. A period of colonization occurred in one of the trapping areas, and young females that became sexually mature just before or immediately after their movement to this area were prevalent among the colonizing mice. Dispersal, caused by fluctuating environmental conditions, appears to be an important aspect of feral house mouse population structure, and feral populations are not divided into temporally stable, closed genetic units as are populations living in farm buildings.
Habitat Selection of Breeding Birds in an East Tennessee Deciduous Forest
Authors: Anderson Stanley H. , Shugart Herman H.
Published: May 2006

Bird populations were sampled between May 30 and July 20, 1972, on twenty—four 0.08—ha plots on Walker Branch Watershed, a primarily deciduous forest located in Anderson County, Tennessee. Univariate analysis of variance was used to test for differences in abundance categories of each bird species with respect to 28 habitat variables. Differences in habitat preferences within major bird families (Picidae, Parulidae, Paridae, and Thraupidae) were apparent from this analysis. Discriminant function analysis was therefore used to order the variables according to their strength in separating abundance categories for 13 of the more abundant bird species. This analysis indicated that some bird species were distributed according to specific habitat variables. For example, Downy Woodpecker abundance was highly correlated with the number of saplings on a plot. Distributions of other species (e.g., the Scarlet Tanager) were not strongly related to any single variable but were related weakly to a large number of variables. The results form a basis for predicting avifaunal composition changes resulting from alteration of habitat structure.
A Solid State pH Control System for Algal Culturing and Uptake Studies
Authors: Sperling Jon A. , Grunewald Ralph , Dovala Donald
Published: May 2006

An inexpensive solid state pH control circuit was built for external use with existing pH meters that can use either a gas or a liquid solution for pH control of culture media. Mastigocladus laminosus showed a 49% reduction in the rate of radiophosphate (P—32) uptake between gas—controlled (30% CO2 in air) pH intervals of 8.7 (optimal uptake) and 5.7. Isotope uptake rates at higher pH values (achieved by manual additions of 0.1 N NaOH) decreased slightly between pH 8.7 and 9.7 and declined 36% between 9.7 and 10.7, where trichome motility and the ability to colonize new substratum were inhibited. Suppression of growth based on short—term (96 hr) dry weights, of which only 24 hr were at the selected pH values, was not evident throughout the experimental pH range.
Growth Rates of Young Passerines and the Flexibility of Clutch Size
Authors: Fretwell Stephen D. , Bowen Daniel E. , Hespenheide Henry A.
Published: May 2006

This note clarifies and amplifies Ricklefs' (1968) demonstration that the growth period for passerines laying a small clutch has a wider range than for those laying larger clutches. We show that his argument does not distinguish between food— and predator—limited clutch size theories, and that the theoretical variances predicted by Ricklefs do not follow from his assumptions. We extend the theory to include nest mortality and maintenance costs.
Bottom Fauna‐Substrate Relationships in a Northern Colorado Trout Stream: 1945 and 1974
Authors: Ward James V.
Published: May 2006

A study of bottom fauna—substrate relationship conducted on North St. Vrain Creek, Colorado, USA in 1945 was repeated in 1974 to determine changes in the stream environment and in the community structure and standing crop of macroinvertebrates. The stream remains a clear, unpolluted trout stream with soft water of neutral pH. Despite differences in flow, temperature, and riparian vegetation, macroinvertebrate composition was similar to that of 1945; most differences can be attributed to normal year—to—year fluctuations and slight shifts in emergence periods. Total density was less on all substrate in 1974, which is attributed to the higher discharge. Total biomass was comparable except for lower values on bedrock in 1974.
Sceloporus Undulatus: A Study of the Intraspecific Comparative Demography of a Lizard
Authors: Tinkle Donald W. , Ballinger Royce E.
Published: May 2006

Population studies were conducted on the eastern fence lizard in South Carolina, Texas, Ohio, and Colorado. Hatching occurs in early to middle summer and well into the fall in southern populations, but is restricted to late summer and early fall in Colorado and Ohio. The hatchlings in Texas reach a mature size in 3 months and these lizards, as well as those in South Carolina, reproduce before they are a year old. In Colorado and Ohio the lizards do not mature until almost 2 years of age, but at a larger size than those in Texas or South Carolina. Lizards in the four populations differ significantly in average clutch size (7.4—11.8) and in clutch frequency (1—3) and in egg size (.23—.42 g per egg). In all populations there is a significant positive correlation between clutch size and body and the regression lines for these variables differ in slope between populations. Survivorships of eggs, hatchlings, yearlings, and adults differ among the populations and these differences have been related indirectly to increased predation in the southern and western populations. The adult mortality rates are inversely related to population density. Life tables for the populations show large differences among the populations in the contributions made by each age class to the total population replacement rate. The life table characteristics of each population show that the measured parameters are consistent with maintenance of stable population numbers even though the life history strategies are clearly different. Evolutionary explanations are provided for these differences and the relevance of the data to the concept of r— and K—selection is discussed.
Microdistribution and Density as Factors Affecting the Downstream Drift of Mayfiles
Authors: Lehmkuhl D. M. , Anderson N. H.
Published: May 2006

During high volume of flow in a stream that has considerable seasonal fluctuation, the microdistribution of five species of mayflies was determined by displacement of individuals by drift from rapid current areas to those with gentle or no current. The major effect of drift was dispersal, not depletion, of the mayfly population. Occurrence in drift is determined by a species—specific complex of interdependent factors including life cycle, microdistribution (both before and after the effect of spates), and the behavioral characteristic of individual species.
Water‐Stress Patterns in Honey Mesquite
Authors: Haas R. H. , Dodd J. D.
Published: May 2006

Water stress (LWP) was measured in honey mesquite, Prosopis glandulosa var. glandulosa [Torr.], trees by using pressure—chamber method to detect negative hydrostatic pressure in the xylem of leaf petioles. The method was sufficiently sensitive to measure short—term changes of ± 1 bar LWP throughout the diurnal priod. Mean differenes between sun—exposed and shaded leaves averaged 4.7 bars LWP on a clear day in May. Although the mean LWP for five trees ranged from 15.8 to 18.1 bars LWP, the interaction of exposure and tree was relatively minor in comparison with the large diurnal differences in LWP. Diurnal changes in LWP, often greater than 20 bars, were associated with changes in the evaporative potential of the atmosphere. Total daily water stress (ΣL) and net daily water stress (ΣL ‐ ΣL0) were calculated by integrating the area under a curve formed by the periodic measurements of LWP during the diurnal period. Net daily water stress was more sensitive to changes in environmental variables than other daily summaries. Throughout the range of available soil moisture there was a close relationship between net daily water stress and the integrated evaporative potential on a daily basis.
Density Dependence and Population Regulation in Laboratory Cultures of Paramecium
Authors: Gill Doublas E.
Published: May 2006

Two experiments with laboratory cultures of Paramecium were performed to test the hypothesis that (1) density is limited by food, and (2) dissolved oxygen in culture tubes of narrow shape is the primary limiting resource. The procedure for estimating saturation density was not repeatable over years and probably abnormally inflated the estimate of sampling error in the experiments. Differences observed between treatments were therefore of dubious biological significance. On the other hand, the estimates of intrinsic growth rates were reliable and repeatable. Contrary to expectation, all the species grew slower in food—enriched medium than in unenriched medium, and no effect of oxygen limitation could be demonstrated. It is concluded that population density regulation of Paramecium is principally determined by accumulation of metabolic wastes of bacteria and the ciliates themselves.
The Second Derivative and Population Modeling: Another View
Authors: Innis George
Published: May 2006

In a paper with a similar title (see Ecology: 606—613), John Clark argues for the use of second—order differential equations in population modeling. To refute his arguments, this paper (1) demonstrates the similarity of sets of higher order ordinary differential equations to sets of first—order ordinary differential equations, (2) discusses both practical and philosophical aspects of the inclusion of "historical" effects in a biological model, and (3) argues that intrinsically second—order biological or physical processes have not been observed.
Relation of Topography and Vegetation to the Occurrence of Douglas‐Fir Dwarf Mistletoe at Its Northern Limits in British Columbia
Authors: Smith R. B.
Published: May 2006

The northernmost occurrence of Douglas—fir dwarf mistletoe (Arceuthobium douglasii Engelm.) is near Sicamous, British Columbia. Its presence in the Interior Western Hemlock Zone, characterized by a higher summer precipitation than the parasite's usual habitat is partially explained by an ecological survey of infected and neighboring uninfected stands. The parasite is concentrated on a steep, southwest—facing slope which possesses many of the same floristic features as the drier Interior Douglas—fir Zone, including the tendency for perpetuation of almost pure Douglas—fir stands. In contrast, the adjacent northwest—facing slope, which supports vegetation characteristic of the Western Hemlock Zone, is free of A. douglassi. Because of the restriction of A. douglassi to a single host in this area, and its relatively slow rate of spread, the extension of the parasite into areas within the Western Hemlock Zone would undoubtedly be checked except in edaphically dry situations or where continuous disturbances such as logging favor the host tree, Douglas—fir.
Nitrogen Loss from Flooded Soil
Authors: Patrick W. H. , Tusneem M. E.
Published: May 2006

An appreciable loss of labeled nitrogen occurred in flooded soils exposed to atmospheric oxygen. Nitrogen added as ammonium was apparently nitrified in the aerobic surface layer of soil and then diffused downward into the underlying anaerobic zone where it was denitrified and lost from the system.
Monitoring Activity of Small Mammals by Temperature‐Telemetry
Authors: Osgodd David W. , Weigl Peter D.
Published: May 2006

A temperature—sensitive radio transmitter for small mammals is described. Its range was 200 meters, and it provided valuable information about movements of small mammals in and out nests. The only limitation is that the nest or burrow temperature must differ from that of ambient air by at least 3°C.
Spatial Interactions and Microhabitat Selections of Two Locally Sympatric Voles, Microtus Montanus and Microtus Pennsylvanicus
Authors: Douglass Richard James
Published: May 2006

Microtus pennsylvanicus and Microtus montanus are sympatric in south central Montana, and the two occur in intermixed populations. This study attempted to assess the relative importance of interspecific interactions and habitat preference on movements and habitat selection of the two species. Radioisotope telemetry in 20—m x 20—m field enclosures showed that M. montanus had larger home ranges in the presence of M. pennsylvanicus than in single species treatment. Spacing between individuals was closer for M. montanus when alone as compared to mixed treatments. There was more overlap in M. montanus home ranges in single species treatments than in mixed treatments. Microtus montanus selected different vegetation when alone than in the presence of M. pennsylvanicus. The vegetation selected by each species was different from that selected by the other in all treatments. Enclosure experiments indicated only slight differences in emigration rates, survival rates, or weight changes for either species between single and mixed species treatments. Trap lines in natural areas outside of the enclosures showed that the two species are sympatric throughout the year but have different habitat preferences. Both interspecific interactions and divergent habitat preferences are important in maintaining separation between M. pennsylvanicus and M. montanus but the importance of each changes along habitat gradients. As habitats become uniformly optimal for M. pennsylvanicus, they are able to exclude M. montanus from an area.
Water Relations of Selected Plant Species in the Alpine Tundra, Colorado
Authors: Ehleringer James R. , Miller Philip C.
Published: May 2006

The purpose of this study was to measure some aspects of the water relations of selected plant species in the alpine tundra, Colarado, in order to assess the possible role of water limitation on primary production. Leaf water potentials were measured in Kobresia myosuroides, Geum rossii, Bistorta bistortoides, Deschampsia caespitosa, and Caltha leptosepela. Leaf resistances to water loss were measured in Bistorta and Caltha. Measurements were made at dawn and midday throughout the season and several times through selected days in plants along a moisture gradient. Leaf resistance was related to leaf water potential, light, and temperature. Leaf water potentials decreased throughout the season and were higher on the wetter site. Minimum water potentials of the species in the order listed above were —40, —23, —17, —31, and —17 bars. Minimum leaf resistances of Bistorta and Caltha were 0.8 and 1.6 s.cm—1, respectively, and were lower on the wetter site. Both Bistorta and Caltha on the wet meadow showed partial midday stomatal closure, but Bistorta on the dry meadow did not At —16 bars leaf resistance increased abruptly in Caltha, but was still low in Bistorta. Leaf resistances were low at incident solar radiation levels of 0.2 ly ° min—1 and at temperatures near 20°C. Leaf resistances increased with temperatures below 15°C. Root resistances for Bistorta were 0.9 x 104 s ° cm—1 ° bar—1 at the dry site and 0.8 x 104 at the wet site, and for Caltha were 0.6 x 104 s ° cm—1 ° bar—1 at the wet site. The changing daily pattern of leaf water potential and leaf resistance is shown to be related to the diurnal environmental pattern, to root resistances, and to the relationships between leaf resistance and leaf water potential and between leaf water potential and leaf relative saturation deficit.
Lizard Reproductive Effort: Caloric Estimates and Comments on Its Evolution
Authors: Tinkle Donald W. , Hadley Neil F.
Published: May 2006

The energy content of eggs of 10 lizard species was determined and used as a measure of reproductive effort (ratio of clutch calories to body calories). Values for eggs ranged from 5.87 to 7.20 cal/mg ash—free dry weight (°=6.37). Species differences in calories going into reproduction during a breeding season, however, were primarily due to differences in clutch size and clutch frequency between species. Correlation analysis between three measures of reproductive effort, including the preceding, and a suite of demographic variables revealed only one significant correlation (negative) between clutch calories to body calories ratio and mean annual adult survivorship. The energy allocated to eggs in comparison to total annual energy expenditure was estimated for three of the species investigated. Sceloporus graciosus had the highest reproductive effort, with proportional values for first and older breeders about the same. The proportion of total energy expended on reproduction was slightly lower for UTA stansburiana, with first and older breeders exhibiting the same effort. Sceloporus jarrovi had the lowest reproductive effort, but showed an increasing effort with increasing age. These data suggest that the demographic environment may not be the primary selective pressure determining reproductive effort, and that reproductive effort may not be positively correlated with age in all species.
Photosynthesis of Cladophora in Relation to Light and CO2 Limitation CaCO3 Precipitation
Authors: Wood Kenneth G.
Published: May 2006

In productivity studies of Cladophora by the light—and—dark—bottle method, errors may arise from CaCo3 precipitation, self—shading, pH/Co2 limitation, or variations in the condidtion of the alga. Precipitation of CaCo3 and MgCo3 by Cladophora may equal one—third of production at pH 9.3 to 10.4, resulting in overestimation of photosynthesis by either the 14C or pH method. The calcification is readily removed by acid rinse without loss of fixed carbon. Consideration of such errors in relation to a recent study leads to the refutation of the conclusion the Cladophora shows an unusual ability to utilize low light intensities.
Behavior of Pycnopsche (Trichoptera: Limnephilidae) on Mineral Substrates in Laboratory Streams
Authors: MacKay Rosemary J.
Published: May 2006

Three species of Pycnopsyche larvae were given a choice of mineral substrates ranging from medium sand to small pebbles in laboratory streams. Pycnopsyche luculenta avoided depositing substrates and remained on or near firm, smooth surfaces. Pycnopsyche gentilis also avoided depositing substrates except during a short period in the fifth (final) instar when leaf—disc cases were transformed to sand—grain cases of particles 1—2 mm in diameter. Mature larvae of P. scabripennis burrowed into gravel particles 4—16 mm in diameter for a 3—mo aestivation period. Apart from the short—term selective behavior of P. gentilis and P. scabripennis, all species responded positively only to organic substrates and showed no mineral substrate selection that was concordant with larval distribution in a woodland stream. Only those species which use mineral particles for cases or burrows demonstrated a size preference. The very precise size of particles selected by aestivating P. scabripennis larvae may be an important limiting factor for this species.
The Distribution of Asphodelus Microcarpus and Associated Species on the Western Mediterranean Coast of Egypt
Authors: Ayyad M. A. , Hilmy S. H.
Published: May 2006

This study is a quantitative analysis of the distributional behavior of Asphodelus microcarpus in relation to the main environmental factors. Its abundance was estimated in 40 stands covering most of the apparent physiographic and edaphic variations in an area extending about 500 km along the western Mediterranean coast of Egypt. In each stand, the number of shoots of A. microcarpus was counted in fifty 1—m2 quadrats, and its density and frequency were calculated. Variations in these two phytosociological characters were then evaluated in different types of habitat. Associated perennials were recorded in each quadrat and their relative frequencies estimated. These frequencies were used in ordering stands along there different axes according to the degrees of dissimilarity between them. This three—dimensional ordination was used to illustrate the phytosociological behavior of A. microcarpus and its relationship with other species. Quantitative estimations of conductivity and percentages of CaCO3, organic carbon total nitrogen, sand, silt, and clay were made for the soil in each stand. Also, the nature of surface, depth of soil, and physiographic position of each stand was rated. Variations in each of these environmental parameters, or their combinations, were then correlated with the distributional behavior of A. microcarpus. Variations in the abundence of A. microcarpus within each of the major types of habitat were found to be at least as significant as those between them. This indicated that local environmental variations had a substantial role in determining the distributional pattern of that species. The position of A. microcarpus in the ordination, which represented the phytosociological structure of the vegetation, was intermediate. The conclusion is that abundance of A. microcarpus is controlled mainly by the moisture availability and the total nitrogen and CaCO3 percentage in the soil. The moisture availability correlated significantly with more than 85% of the variation in its abundance. Its ecological amplitude in relation to local variations in this factor conformed roughly to that based on an geographical scale. Along the gradient of total nitrogen, the abundance of A. microcarpus exhibited a significant abrupt increase at the category of the highest value. In relation to the CaCO3 gradient A. microcarpus increased in abundance at medium categories and decreased toward low, as well as high ones. However, significant variation with either nitrogen or CaCo3 percentage was less than one—third of that with moisture availability, implying that moisture is ore important in controlling A. microcarpus distribution.
Niche Measurements of Frog Larvae from a Seasonal Tropical Location in Thailand
Authors: Heyer W. Ronald
Published: May 2006

Niche parameters of breadth and overlap were calculated on a collection of frog larvae made in 1969 in a seasonal tropical location in Thailand to determine what adaptive strategy characterizes seasonal tropical anurans. Calculation of values of niche breadth and overlap show that space is much more important than food in niche partitioning.
Niche Relationships Among Parasitic Insects Occurring in a Temporary Habitat
Authors: Miller Jeffrey C.
Published: May 2006

Pattern in the parasitism of a lepidopteran host, Spodoptera praefica, were assessed through an analysis of niche relationships among the parasitic species. No parasitized hosts were recovered from nondisrupted habitats. However, three species, Chelonus insularis, Apanteles marginiventris, and Hyposoter exiguae, commonly parasitized S. praefica in a disrupted habitat (mowed alfalfa field). Overall, H. exiguae was numerically dominant as well as the most rapid exploiter of hosts following habitat disruption. Species diversity within the parasitoid guild significantly increased with time following each habitat disruption. Significant trends were also observed in species evenness. The niche breadth of C. insularis and H. exiguae varied with time of year and time following habitat disruption while the niche breadth of A. marginiventris remained relatively constant. Niche overlap was generally high between the two larval parasitoids, A. marginiventris and H. exiguae, and low between these species and C. insularis, an egg—larval parasitoid. The values determined for species diversity, niche breadth, and niche overlap suggest that a low degree of temporal stability rather than interspecific competition strongly influenced species composition within the parasitoid guild of S. praefica.
Sceloporus Undulatus: Comparative Life History and Regulation of a Kansas Population
Authors: Ferguson Gary W. , Bohlen Charles H. , Woolley H. Patrick
Published: May 2006

The demography of a small, isolated population of the lizard, Sceloporus undulatus garmani from eastern Kansas, USA was studied for 5 yr. Growth rates were relatively rapid; age of maturity, relatively low; clutch size was small and decreased in successive clutches of the same females; juvenile survival, while low, was high for the species; adult survival was relatively low. The population size was the most variable yet studied. Winter—spring mortality rates, probably due to predation, were constant regardless of density, but density—dependent mortality operated in at least 1 yr during this period. Summer—fall recruitment was density dependent, probably due to predation on egg—laying females, but flooding and possible temperature—dependent predator susceptibility resulted in instability of the population size. The population is probably below its resource limits most of the time. The comparative demography of this and eight other populations of S. undulatus reported in the literature was summarized. There are three ecological regions to which this species has adapted: eastern woodland, grasslands, and canyonlands. There are both regional and latitudinal differences in suites of correlated traits, but comparative data on ecological pressures are not sufficient to support any single current theory of how these different populations are adapted.
Water Relations: Soil Fertility, and Plant Nutrient Composition of a Pygmy Oak Ecosystem
Authors: Reich Peter B. , Hinckley Thomas M.
Published: May 2006

The water and nutrient relations of Buzzard's Roost, an unusual pygmy oak ecosystem in southwest Missouri, USA, were studied in 1976 and 1977 in an attempt both to characterize the ecophysiology of the individuals's and find the causative agents for the existence of the pygmy forest. The stunted trees were mostly blackjack oak (Quercus marilandica) with some northern red oak (Q. rubra) and a few black oak (Q. velutina.?). In addition to being stunted, the trees were gnarled and twisted and had miniature leaves and acorns. Results of soil analysis showed the pygmy forest soil to be very acidic (pHw = 4.6), with very low levels of Ca and Mg (0.25 and 0.12 meq/100g, respectively) and very high levels of Al (600 ppm). Adjacent non—pygmy forest soils did not display these characteristics. Foliar analysis of blackjack, northern red, and black oak showed Ca and Mg to be much lower in pygmy foliage than in non—pygmy foliage, at three times during the growing season. Diurnal and seasonal pattern of xylen pressure potential, leaf conductance, and soil moisture content illustrated the development of very severe tree water deficits at Buzzard's Roost. Predawn and midday xylem pressure potentials declined to as low as —3610 and —4200kPa, respectively, accompanied by complete daytime stomatal closure. However, water stresses in nearby non—pygmy oaks sites, implying that water stress was not the major factor or causative agent in the stunting process. The evidence suggests that the very low nutrient levels in the soil, especially of Ca and Mg, plus the very high levels of Al, may be deficient (and/or toxic) for normal tree growth and development, and possibly responsible for the existence of the pygmy oak forest. Also, the xeric site characteristics add another severe stress to this ecosystem.
Utilization of Space by Peromyscus Leucopus and Other Small Mammals
Authors: Myton Becky
Published: May 2006

Mark—recapture studies were made on a grid over an extended period of time to investigate home range utilization by small mammals, especially Peromyscus leucopus, the most numerous small mammal on the study area. Since captures were largely concentrated around a home range center, Calhoun's (1963) bivariate normal density, which predicts a more diffuse capture pattern, did not adequately describe space utilization in Peromyscus. Mark—recapture results showed a similar pattern as a continual removal regimen: 50% of the total Peromyscus contrary to Calhoun's (1963) predictions that as dominant species are removed (here Peromyscus), subordinate" species (here Blarina and Pitymys) enlarge their home ranges and are caught more often. My results can better be explained by invoking behavior—mediated differences in trappability between species and/or ecological differences in the use of the habitat (fossorial vs. runaways in undergrowth, etc.). Finally, my evidence suggests that Peromyscus are arranged in family groups consisting of one adult female, several adult males (one dominant, several subordinate), and a number of juveniles.
Niche Structure in Freshwater Zooplankton: A Principal Components Approach
Authors: Miracle Maria R.
Published: May 2006

The niche structure of a zooplankton community is demonstrated by factor and principal components analyses performed on 895 samples collected at different depths during a 1—yr cycle in Banyolas Lake in Spain. Data on 17 species have been used. The first three principal components, equivalent to the first three factors, account for 58% of the variance in the data. These three components are associated respectively with (1) upwelling and diversity, (2) temperature, and (3) trophic factors (phytoplankton species composition) and nitrate concentration. The zooplankton species separate in the principal components space; they occupy different niches in the ecological space. The trophic basis of niche differention is for practically not considered, since only factors of niche separation that influence the distribution of species in space and time are detected. Congeneric species are far apart in ecological space, whereas predator and prey are closely associated. At any one time and depth coexistence of species is limited to one small particle feeder, one or two predators with different selected prey, and a few intermediate forms ranging from filtering to raptorial feeders.
Vegetation Studies and Modern Pollen Spectra from the Red Lake Peatland, Northern Minnesota
Authors: Griffen Kerstin O.
Published: May 2006

Vegetation studies in the Red Lake peatland, a patterned fen studded with forested islands, resulted in the recognition and description of plant communities typical of the following environments: Menyanthes pools, furrows, sedge—strings, forested tussocks, and forest hollows. Pollen analyses of 15 surface samples taken along a transect in the same area separated two distinct local pollen assemblages. The Larix forest assemblage corresponds to the forest tussock and forest hollow communities, and the sedge fen pollen assemblage corresponds to the Menyanthes pool, the furrow, and the sedge—string communities.
Use of Life Tables in Analysing the Dynamics of Copepod Populations
Authors: Gehrs Carl W. , Robertson Andrew
Published: May 2006

The population parameters have been characterized for the generations that developed during a complete reproduction year of a population of the calanoid copepod Diaptomus calvipes Schacht. A model is presented to calculate the numbers of each of the various instars of a copepod produced during any previous interval of time. Life tables were constructed from laboratory data and for the five generations of the 1971 field population as an aid in studying the population dynamics. Successful reproduction in the field population occurred from mid—March until mid—October. Development time increased for successive instars of the same generation. All generations had similarly shaped survivorship curves and there was a progressively lower rate of survival in successive generations. This lower survival rate was related to decreasing survival during the early naupliar stages. Survivorship of adults was characterized by a rectangular curve. Greatest mortality rates occurred during the egg to fourth naupliar interval (N—IV) and in the sixth naupliar stage (N—VI). Critical controlling factors in this population appear to be those which affect either survivorship in the interval between egg and N—IV or reproductive activity of adults.
A Search for Emergent Competitive Phenomena: The Dynamics of Multispecies Drosophila Systems
Authors: Richmond Rollin C. , Gilpin Michael E. , Salas Santiago Perez , Ayala Francisco J.
Published: May 2006

Theoretical analyses of multispecies competition suggest that the stable coexistence of three competition species may occur even when all the pairwise combinations of the same species do not result in stable equilibria. In an attempt to discover such an emergent property of multispecies competition, we constructed laboratory populations consisting of one, two, and three species of Drosophila in all possible combinations. Two series of experiments at 19° and 22°C were conducted. We found no evidence of emergent behavior; the outcome of competition in three—species populations could be adequately predicted from a knowledge of the pairwise interactions among the species.
Altitudinal Variation of Chlorophyll Concentration and Reflectance of the Bark of Populus tremuloides
Authors: Covington W. Wallace
Published: May 2006

Although quaking aspen (Populus tremuloides Michx.) bark appears greener at higher elevations in the Sangre de Cristo mountain range of New Mexico, chlorophyll concentrations are inversely correlated (p = .001) with altitude. The higher concentration of chlorophyll at lower elevations is effectively masked by a white bloom of dead periderm cells which is also characteristic of exposed site trees. At higher elevations the bloom is yellow—brown and more translucent, thus allowing the chlorophyll layers beneath to show through. Therefore, trees at higher elevations appear greener even though they have lower cortical chlorophyll concentrations. The altitudinal gradient in bark reflectance characteristics may be of adaptive value. If cortical photosynthesis is more important at higher elevations, the translucent bloom would be advantageous in making more light available for photosynthesis. Increased light absorption might also be important in raising bark temperatures for physiological activity during the winter months. At lower elevations where air temperatures are higher, the highly reflective bloom may protected the trees from high bark temperatures and sunscald.
Comparative Photosynthetic Production of Mojave Desert Shrubs
Authors: Bamberg S. A. , Kleinkopf G. E. , Wallace A. , Vollmer A.
Published: May 2006

Transpirational and net photosynthetic rates of several species of desert shrubs were measured as a function of season and environmental variables at the Nevada Test Site in the northern Mojave Desert. Drought—deciduous species, Ambrosia dumosa (Grey) Payne, Lycium andersonii Grey, and Lycium pallidum Miers, had higher maximum rates and greater water loss than the evergreen, Larrea tridentata Munz, and summer green, Krameria parvifolia Benth., species. Moisture status was the most critical factor determining gas exchange rates and affected temperatre optima and acclimation as the season progressed. Because of a dry spring season, the drought—deciduous species became dormant in late May—early June: the other two species exhibited by mid—June a small positive CO2 uptake during the morning period. Desert plant species, with few exceptions, are extremely labile and exhibit large variability and different adaptive strategies.
Analysis of Insect Consumption in a Forest Conopy
Authors: Reichle D. E. , Goldstein R. A. , Van Hook R. I. , Dodson G. J.
Published: May 2006

A mathematical model has been developed for estimating the consumption of canopy vegetation by insects. The model divides canopy leaves into age classes according to time of leaf emergence. Periodic measurements were made of gross leaf area and hole area initiated by insect consumption for each generation. Gross area distributions were used to determine empirical growth functions for the canopy vegetation. The rate of change in hole area is a function of both insect consumption and subsequent hole expansion due to leaf growth. The hole expansion rate was determined empirically by punching holes in known area in growing leaves and correlating hole expansion with leaf growth. From these relationships, a linear differential equation was derived to describe the dynamics of insect grazing in the canopy. This model was used to interpret the effect of insect herbivory on the dry matter and nutrient cycles in a Liriodendron tulipifera forest. Average herbivorous insect consumption over 3 years was equivalent to 2.6% of the net primary production of foliage biomass but represented an annual loss of 7.7% in photosynthetic surface area.