Relative Density Estimates Research Articles

11C]Tropanyl Benzilate—Binding to Muscarinic Cholinergic Receptors: Methodology and Kinetic Modeling Alternatives

Quantitative estimation of cerebral muscarinic receptors was investigated with the use of the antagonist [11C]tropanyl benzilate ([11C]TRB) and positron emission tomography (PET). Kinetic modeling alternatives were examined with the goal of identifying an analysis method providing stable receptor measures, yet avoiding biases from inappropriate reductions in model complexity. Dynamic PET scans were performed on six young normal volunteers. Several modeling approaches yielding relative receptor density measures were evaluated: (a) a single "late" scan using relative tracer concentration values; (b) a slope estimate from graphic analysis (Patlak plot); (c) a two-compartment, two-parameter model (transport and total ligand distribution volume); (d) a three-compartment, two-parameter model using the free+nonspecific distribution volume, DV', fixed to the cerebellar value; (e) an early scan for transport, a fixed value for DV', and a single late scan for the binding rate constant; and (f) a three-compartment, three-parameter model. Both computer simulations and PET scan results indicate all methods provide receptor density index measures with the same rank order as in vitro measures. Oversimplified approaches (methods 1 and 2) yield a more highly nonlinear relation between the estimated receptor density index and the known receptor density than do methods retaining greater model complexity (methods 3-6). However, noise propagation into the receptor measure is greater for the more complex methods. Reliable receptor density information can be obtained from kinetic [11C]TRB PET studies, with methods 3-5 providing the most appropriate levels of model complexity for estimates of relative muscarinic receptor density.

Relative Importance of Bird Species as Hosts for Immature Ixodes dammini (Acari: Ixodidae) in a Suburban Residential Landscape of Southern New York State

Abundance of birds and their tick parasites were estimated in a residential community located in Westchester County, NY, where Lyme disease is endemic. In total, 36 bird species (416 captures) were collected, of which 25 species (69%) were parasitized by ticks. Ixodes dammini Spielman, Clifford, Piesman & Corwin composed 96.4% of the 1,067 ticks found on birds. The bird species most heavily parasitized was house wren, Troglodytes aedon Vieillot (11.1 Ixodes dammini per bird). Relative density estimates of birds, using fixed circle radius counts, revealed dominance by the American robin, Turdus migratorius L. (29.3%), followed by the common grackle, Quiscalus quiscula (L.) (9.3%). Bird density estimates were combined with tick abundance data to calculate an importance value for each bird species as a host for immature I. dammini. The American robin was most important, accounting for 72.7% of all larval I dammini found on birds, followed by the common grackle (8.2%) and the house wren (5.9%). Both the American robin and house wren are reservoir competent for the Lyme disease spirochete Borrelia burgdorferi Johnson, Schmid, Hyde, Steigerwalt & Brenner and therefore may contribute to the risk of Lyme disease for humans. During August when larvae were most prevalent, 39% of the American robins and 70% of the common grackles were observed on lawns. These species are probable contributors to nymphal I. dammini populations found on lawns.

Comparison of Sampling Techniques for Grasshoppers (Orthoptera: Acrididae) in Soybean

A 2-yr study was conducted for evaluating sampling techniques for the grasshoppers Melanoplus femurrubrum (De Geer) and M. differentialis (Thomas) in soybean. Objectives were to establish a technique for obtaining absolute estimates of density and to evaluate the potential for calibrating the sweep net (relative density estimates) for absolute density estimates. Assessments of absolute density were made at night by using a cage-bag method. Sweep samples were collected during both day and night. Night sweeping was more effective than day sweeping for capturing grasshoppers. Regression results of relative on absolute estimates for nymphs indicated that both day and night sweeps adequately reflected population change. In contrast, similar analyses for adults indicated sufficient fidelity for night sweeps only. Day or night, fidelity of sweeps was better for M. femurrubrum than for M. differentialis . Regression coefficients were significantly different between nymphs and adults, but not between species. Therefore, combined-species regression models were formulated for nymphs (day and night) and for adults (night). Satisfactory fidelity of species-specific and combined-species day (nymphs) and night (nymphs and adults) models warrants the use of these models for calibration. Despite both day and night sweeps being biased in estimating age-class structure for nymphs, nymphal models are useful for management.

Seasonal Distributions and Abundances of Loggerhead and Leatherback Sea Turtles in Waters of the Northeastern United States

Seasonal distributions and abundances of loggerhead (Caretta caretta) and leath- erback (Dermochelys coriacea) sea turtles in continental shelf waters off the coast of the northeastern United States were derived from more than three years of aerial and shipboard surveys. There were 3460 sea turtle sightings, including 2841 loggerheads, 128 leatherbacks, and 491 unidentified. Relative abundance patterns, corrected for uneven distribution of survey effort, demonstrated an extensive area of loggerhead distribution from near Long Island, New York, along the mid-shelf to near Cape Hatteras, North Carolina. Areas of high relative abundance of leatherbacks were more scattered, with clusters south of Long Island and in the central and eastern Gulf of Maine. Loggerheads occurred significantly farther south (x = 38?20' N) than leatherbacks (x = 40005' N), and in significantly warmer waters (mean surface temperatures of 22.2 C and 20.4 C, respectively). The two species did not differ significantly in water depth or bottom slope at sighting; the modal depth interval for both was 21-40 m. Patterns of distribution and concentration of sea turtles differed greatly from nearly all species of marine mammals, suggesting little overlap in resource utilization. Both relative and absolute density estimates were much higher for loggerheads. Overall mean relative densities were 21.6 loggerheads per 1000 km of survey track, and 6.85 leatherbacks per 1000 km. Absolute density estimates, derived from 454 special aerial surveys, ranged from 1.64 x 10-3 to 5.10 x 10-1 loggerheads km-2 and 2.09 x 10-3 to 2.16 x 10-2 leatherbacks km-2. The maximum densities for both species were higher than values reported for the Gulf of Mexico and off the eastern Florida shore. Total study area populations during the summer were estimated at 2200-11,000 loggerheads and 100-900 leatherbacks. These estimates are minimal because they are based on observations of turtles at the surface, and may represent much greater abundances. The patterns of relative abundance derived from this analysis could be used as a basis for the designation of critical sea turtle habitat off the northeastern U.S.

Sampling of Heliothis zea (Lepidoptera: Noctuidae) and Orius insidiosus (Hemiptera: Anthocoridae) in Grain Sorghum Panicles by a Modification of the Beat-Bucket Method

A modification of the beat-bucket sample method was evaluated for Helioth18 Zea (Boddie) and Orius insidiosus (Say) in grain sorghum panicles. Grain sorghum panicles were cut and twirled inside a 19-liter plastic bucket rather than beating the panicles against the bucket wall. Based on absolute density estimates, the modified beat-bucket method recovered > 50.0% of the H. zea larvae and O. insidiosus adults and 35.0% of the O. insidiosus nymphs in the grain sorghum panicles. The method provided reliable estimates of population trends of H. zea larvae and O. insidiosus nymphs and adults. The method was calibrated for H. zea larvae. Relative density estimates (y) may be converted to absolute density estimates (x) by the formula x = y/b (b , slope of regression line).

Foraging Behavior and Switching by the Grasshopper Sparrow Ammodramus savannarum Searching for Multiple Prey in a Heterogeneous Environment

Switching among four alternative grasshopper species by the grasshopper sparrow (Ammodramus savannarum) through frequency-dependent predation was examined. Grasshoppers were presented against a heterogeneous natural background in an outdoor aviary where total density was held constant but relative density of each grasshopper species varied. Switching among prey, primarily between two of the four species, and inter-bird variability in switching was observed. Species-specific preferences and interactions among the alternative grasshopper species affected the final diet choice as one grasshopper species was always preferentially selected and another disregarded independent of changes in relative density. Attributes of avian foraging behavior, including: (a) proportion of total time spent handling prey, searching for prey or engaging in nonforaging activity; (b) capture success; (c) time required to catch prey (relative to either total or search time), and (d) attack distance did not vary according to the relative abundance treatments. Results of this study are related to quantitative estimates of predation and relative densities of grasshopper species in a natural grassland setting. INTRODUCTION Generalist predators have been shown to switch among alternative prey as the relative densities vary (Hassell, 1978; Murdoch, 1969; Murdoch and Oaten, 1975). Switching involves a frequency-dependent functional response where predators change from selecting the predominant prey type to another as its relative density increases. The dynamics of switching are contained in the functional response of the individual predator. Functional responses relate the predator attack rate to prey density (Hassell, 1978). Mechanisms proposed to explain switching behavior include: foraging for alternative prey in different patches, the formation of search images by the predator, decreases in handling time with experience, or increases in searching efficiency within patches (reviewed in Murdoch and Oaten, 1975). The first two mechanisms have been studied in most detail. When predators forage for alternative prey living in different patches and transit time among the patches is not negligible, increased foraging activity in the patch with higher prey availability will lead to the sigmoidal switching response described by Oaten and Murdoch (1975). Predators may form search images where the psychological processes involved with locating and recognizing prey against the background are altered depending on the relative abundances of the various prey types (Dawkins, 1971; Gendron and Staddon, 1983; Pietrewicz and Kamil, 1979, 1981). It is likely that all of these mechanisms operate in natural foraging situations. Switching by predators has important implications for many other ecological and evolutionary processes. Frequency-dependent predation within a population is affected by the degree of morphological (or behavioral) polymorphism among individuals in a population and is expected when foraging on alternative prey species as well (Clarke, 1962). Visually orienting predators may select for morphological divergence of coexist-

Frequency Sampling in Microhistological Studies: An Alternative Model

Frequency sampling in microhistological studies is discussed in terms of sampliig procedures, statistical properties, and biological inferences. Two sampling approaches are described and contrasted, and some standard methods for improving the stability of density estimators are discussed. Possible sources of difficulty are highlighted in terms of sampling design and statistical analysis. An alternative model is proposed that accounts for 2-stage sampling, and yields reasonable, well-behaved estimates of relative densities. Frequency sampling is often used for density estimation in biological studies. A typical application involves the determination of presence or absence of some character within quadrats, followed by a transformation of frequency counts to produce an estimate of density or relative density. Density estimates are based on an application of the frequency-density relationship F=l -exp(d),

Sweep-net Sampling for Western Spotted Cucumber Beetle (Coleoptera: Chrysomelidae) in Snap Beans: Daily Fluctuations in Beetle Counts and Correlation Between Relative and Absolute Density Estimates

Sweep-net sampling was evaluated as a method of sampling populations of adult western spotted cucumber beetles (WSCB), Dtabrotica undecimpunctata undecimpunctata Mannerheim, in snap beans, Phaseolus vulgaris L. Each of 18 fields was sampled initially between 0800 and 1000 hours; 1–6 subsequent sets of samples were collected later on the same date. Field means of beetle counts in sweep-net samples collected after the initial sampling episode (subsequent means) were significantly lower than the field mean of initial samples collected in the same field (initial mean) in 16 of 42 comparisons. Subsequent mean/initial mean ratios were negatively correlated ( R 2 = 0.72) with the amount of increase in solar radiation intensity between initial and subsequent sampling episodes. When fluctuations in beetle counts in sweep samples were described in relation to an average daily radiation curve, estimated counts were lowest for sampling conducted at 1300 hours. Time based correction factors used as multipliers to stabilize relative density estimates according to a standard (0900 hours) sampling time ranged from 0.9 for 1800 hours to 2.5 for 1300 hours. The linear relationship between corrected counts of WSCB in sweep-net samples and measures of WSCB absolute density (beetles per meter of row) was described by the equation: y = 0.44 + 2.55 x ( R 2 = 0.69), where x = number of WSCB per meter of row and y = corrected number of WSCB per 10 sweeps.

Density-Dependent Growth of Silver Hakes

Abstract The growth rate of the silver hake Merluccius bilinearis in the northern Georges Bank-Gulf of Maine stock appears to be highly density-dependent after fish reach the size at which they become piscivorous. The correlation between mean weight of age-2 through -5 fish and three estimates of relative stock density (catch per unit effort CPUE from commercial vessels, and virtual population analysis VPA of biomass and abundance) for the period 1962–1979 was analyzed by regression and Spearman rank correlation analyses. Mean weight at age was significantly and inversely correlated with estimates of stock density for all ages, although correlation coefficients were markedly lower for age-2 fish than for older age-groups. The lower correlation for age-2 fish may be due to reduced feeding competition with the adult stock, because silver hakes feed almost entirely upon invertebrates until becoming piscivorous after reaching 20–30-cm fork lengths between ages 1 and 2. Mean weight of age-2 fish was not correl...

Two acoustic surveys of pelagic fish in Hawke Bay, New Zealand, 1980

Abstract The design and execution of two acoustic surveys of Hawke Bay in February and September/October 1980 are described. Though the resulting acoustic data were, for technical reasons, of limited value, they illustrate the information which may be drawn from acoustic surveys. Fish distributions may be rapidly mapped, not only by area, but throughout most of the water column and over time. Qualitative observations on fish distribution may be quantified. The estimation of variance in acoustic surveys is discussed in detail with particular emphasis on the problems of systematic surveys. The role of replicate observations is stressed. Coefficients of variation for relative fish density estimates from the two surveys probably lie between 5 and 30%.

Neurotransmitters of the hypothalamic suprachiasmatic nucleus: Immunocytochemical analysis of 25 neuronal antigens

An immunocytochemical analysis with 33 antisera was undertaken to investigate the localization of 25 different neurotransmitter-related antigens in the hypothalamic suprachiasmatic nucleus in the rat. To obtain estimates of relative densities of immunoreactive axons a stereological approach was used involving counting of intersections of immunoreactive axons with a superimposed semi-circle test grid. All neurotransmitter-related antigens found in perikarya within the suprachiasmatic nucleus, including those stained with antisera against bombesin, gastrin-releasing peptide, neurophysin, vasopressin, somatostatin, γ-aminobutyrate, glutamate decarboxylase and vasoactive intestinal polypeptide were also found in axons within the nucleus. A greater number of these immunoreactive axons was found within the nucleus than in the adjacent anterior hypothalamus. The size of all immunoreactive axons in the suprachiasmatic nucleus was consistently small; immunoreactive axons were found ramifying widely in the nucleus, often ending with terminal boutons near perikarya immunoreactive for the same antigen. All neurotransmitter-related substances found in perikarya of the suprachiasmatic nucleus were also found in axons crossing over the midline to innervate the contralateral nucleus, providing an anatomical substrate for a high degree of communication between the paired nuclei. Axons immunoreactive for other putative transmitters including serotonin arising outside the nucleus were also found in high densities within the nucleus and crossing over the midline between the nuclei. Immunoreactivity for some transmitters was found in axons of similar densities within and outside the nucleus, including antisera against tyrosine hydroxylase; a small number of dopamine β-hydroxylase and a few phenylethanolamine N-methyltransferase-immunoreactive axons were found in the SCN, suggesting that dopamine, norepinephrine and epinephrine may occur in a limited number of axons in the nucleus. Small numbers of axons immunoreactive with antisera raised against cholecystokinin, prolactin, substance P, thyrotropin-releasing hormone and choline acetyltransferase were found within the suprachiasmatic nucleus. Axons immunoreactive for luteinizing hormone-releasing hormone, adrenocorticotropic hormone, α-melanocyte-stimulating hormone and neurotensin were rarely found within the suprachiasmatic nucleus; axons immunoreactive for luteinizing hormone-releasing hormone, adreno-corticotropic hormone, cholecystokinin and tyrosine hydroxylase were found in both horizontal and coronal sections in the area between the left and right suprachiasmatic nuclei. Tyrosine hydroxylase-immunoreactive cell bodies were situated in the same midline area, as well as at the lateral and dorsal borders of the suprachiasmatic nuclei. Although axons immunoreactive for any one substance were not found exclusively in any one area of the nucleus, regional differences in axon density were found; bombesin- and gastrin-releasing peptide-immunoreactive axons, for instance, were more frequent in the ventral suprachiasmatic nucleus near immunoreactive perikarya, while vasopressin-neurophysin immunoreactivity appeared greater in the dorsomedial part of the nucleus. Efferent projections from the nucleus to hypothalamic and extrahypothalamic areas are discussed and the probable cross-reaction of different antisera with a single antigen is considered. The finding of many different putative neurotransmitters within the suprachiasmatic nucleus serves to underscore the complex axonal organization of the nucleus.

CO<sub>2</sub> from fossil fuel burning: global distribution of emissions

The atmospheric concentration of carbon dioxide is increasing. An important source of this excess carbon dioxide is the burning of fossil fuels for energy uses. This paper describes an estimate of the areal distribution of CO2 emissions from energy sources. CO2 from fuel burned in international bunkers is not included nor is CO2 from gas flaring or cement manufacture. Emissions are calculated on a 5° x 5° grid of latitude and longitude, based primarily on United Nations fuel use data. Fuel consumption data by country, by state within the US, and by province in Canada are used to calculate CO2 emissions. Distribution of CO2 emissions within these political entities is based on population distribution, using both discrete population data for subcountry units and population density maps. Aside from errors inherent in the UN fuel data and in our estimates for fuel composition and combustion efficiency, the major sources of error are (a) within-country regional variations in energy use per capita, (b) within-country regional variations in energy sources (e.g., hydroelectric versus coal electric), and (c) errors in our estimates of relative population density within political entities. While we believe regional patterns are accurately represented and that no CO2 parcel is allocated very far from its correct source grid space, individual emission numbers by grid space are subject to large uncertainty. The final tabulation shows that 90% of total emissions are from the latitude band 20°-60° N, with the highest individual numbers from the grid spaces containing Frankfurt, London, and Tokyo.

Statistical estimation of relative density. Technical note : Haldar, A; Miller, F J J Geotech Engng Div ASCEV110, NGT4, April 1984, P525–530

Statistical estimation of relative density. Technical note : Haldar, A; Miller, F J J Geotech Engng Div ASCEV110, NGT4, April 1984, P525–530

Analysis of Sampling Procedures for Corn Earworm and Fall Armyworm (Lepidoptera: Noctuidae) in Peanuts

Relative-density estimates from two insect-sampling devices (sweep-net and shake cloth) were compared with absolute-density estimates for three size classes of the corn earworm, Heliothis zea (Boddie) (Lepidoptera: Noctuidae), and the fall armyworm, Spodaptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae), in peanuts. Linear regression analysis indicated that medium and large larvae of corn earworm and all size classes of fall armyworm were consistently recovered by both devices (r2 ≥ 0.80). Small corn earworm estimates were poor for both devices (r2 ≤ 0.38).

Estimation of relative DNA density in heterochromatin from C-band karyotypes (Critical remarks)

The paper deals with problem of estimating the ratio of DNA densities in heterochromatin and euchromatin from C-band karyotypes of related species, when the observations are subject to errors of measurement. Using a set of data published for Lolium it is shown that under realistic assumptions about the error variances no significant difference of the densities in the two types of chromatin can be detected.

Intracellular transport and storage of secretory proteins in relation to cytodifferentiation in neoplastic pancreatic acinar cells.

The pancreatic acinar carcinoma established in rat by Reddy and Rao (1977, Science 198:78-80) demonstrates heterogeneity of cytodifferentiation ranging from cells containing abundant well-developed secretory granules to those with virtually none. We examined the synthesis intracellular transport and storage of secretory proteins in secretory granule-enriched (GEF) and secretory granule-deficient (GDF) subpopulations of neoplastic acinar cells separable by Percoll gradient centrifugation, to determine the secretory process in cells with distinctly different cytodifferentiation. The cells pulse-labeled with [3H]leucine for 3 min and chase incubated for up to 4 h were analyzed by quantitative electron microscope autoradiography. In GEF neoplastic cells, the results of grain counts and relative grain density estimates establish that the label moves successively from rough endoplasmic reticulum (RER) leads to the Golgi apparatus leads to post-Golgi vesicles (vacuoles or immature granules) leads to mature secretory granules, in a manner reminiscent of the secretory process in normal pancreatic acinar cells. The presence of approximately 40% of the label in association with secretory granules at 4 h postpulse indicates that GEF neoplastic cells retain (acquire) the essential regulatory controls of the secretory process. In GDF neoplastic acinar cells the drainage of label from RER is slower, but the peak label of approximately 20% in the Golgi apparatus is reached relatively rapidly (10 min postpulse). The movement of label from the Golgi to the post-Golgi vesicles is evident; further delineation of the secretory process in GDF neoplastic cells, however, was not possible due to lack of secretory granule differentiation. The movement of label from RER leads to the Golgi apparatus leads to the post-Golgi vesicles suggests that GDF neoplastic cells also synthesize secretory proteins, but to a lesser extent than the GEF cells. The reason(s) for the inability of GDF cells to concentrate and store exportable proteins remain to be elucidated.

The effect of rabies on different fox populations in the south-west of the Federal Republic of Germany

Changes in fox densities during a rabies epidemic were followed in four study areas of different habitats around Saarbrücken in the south-west of the Federal Republic of Germany. Relative density estimates were carried out by snow tracking, search of dens, bait acceptance, and using hunting figures. The direct mortal effect of rabies was highly habitat dependent; in the two forest habitats only a few rabies cases were reported and initially no population decline was observed, while rabies cases were numerous and population decline drastic in the two mainly cultivated study areas. After the front wave had moved through, the rural forest population slowly decreased, while at the same time a partial recovery was observed in the cultivated study areas. Dispersal of foxes from the forest to more open habitats is believed to be the reason. The results are discussed in respect to rabies reservoirs and habitat related fox and rabies control.

Effects of Insecticides on Potato Leafhopper and Nablds in Alfalfa, 1981

Abstract A randomized block design with 50 ft x 50 ft plots replicated 3 times was used to evaluate insecticide effects on potato leafhopper and nabids in an established alfalfa stand near Christiansburg, VA. Insecticides were applied to 9 inch tall 3rd cutting alfalfa Aug 3 using a hand-carried, CO2-powered boom sprayer at 18 psi and 25 gal water/A. A sample unit consisted of 10 pendular sweeps of a 15 inch dia sweep net with the insects counted in the field as they emerged from the net after each sample. Three samples were taken in each replicate, for a total of 9 samples/treatment. Pre-spray relative density estimates of 18 potato leafhopper adults and 1.7 nabids per 10 sweeps were obtained. Pre-treatment counts of potato leafhopper nymphs were not taken.

A quantitative description of the forest vegetation on an altitudinal gradient in the Mount Field National Park, Tasmania, and a discussion of its history and dynamics

The aim of this study was to describe the forest vegetation along an altitudinal transect running from 158 m to 1220 m (treeline) in the Mount Field National Park, Tasmania. Eighteen 1 ha plots were sampled along this transect, using a modified point-centred quarter method for species composition and density. Size frequency distributions were used to calculate basal areas. Estimates of relative density, frequency and basal area for each species were combined in to an importance value. The altitudinal ranges of all woody species were determined. The altitudinal temperature lapse rate was measured, and data on soil pH obtained. The initial ‘direct gradient’ analysis revealed relatively well marked discontinuities in the vegetation which were further examined by ordination and classification techniques. The latter provided a simple threefold classification into altitudinal zones. The lower zone reaches from the Park entrance (158 m) to between 600 and 670 m, and comprises tall open forest dominated by Eucalyptus regnans and/or E. obliqua and with a ‘wet sclerophyll’ understorey characterized by Olearia argophylla. The middle zone stretches from c. 670 to 940 m and comprises closed rainforest or ‘mixed’ forest (i.e. with senescent emergent eucalypts) dominated by Nothofagus cunning hamii and Atherosperma moschatum. This zone is characterized by the absence of O. argophylla and the presence of Phyllocladus aspleniifolius. The upper part of this zone constitutes an interdigitating transition to the subalpine forests, usually dominated by E. coccifera and occurring on suitable sites between c. 880 m and the timberline. The transition to subalpine forests is associated with a marked decline in basal area. Species richness (of woody plants) increases with altitude to reach a peak in the sub-alpine zone. This trend is the reverse of that normally encountered elsewhere in the world, and is mainly due to relatively high α and β diversities in the shrub stratum of this zone. The significance of fires, aspect and substrate is discussed in relation to the variations in composition within each zone. The low diversity of Nothofagus-dominated rainforest is thought to be due, in part, to the intense competitive thinning in the eucalypt re-growth phase following burning, and the subsequent ‘capture’ of the Eucalyptus niche by Nothofagus. It is speculated that, in Tasmania, the downhill migrations during the cooling phases of the Pleistocene were associated with extinctions of lowland forest taxa, while uphill migrations during warming phases were associated with speciation on the plateaux of the present subalpine zone. This hypothesis implies that the relative proportions of land area available at different altitudes, now and in the past, have determined the relative rates of speciation and extinction, and hence the altitudinal gradients of species richness.