Absolute Population Density Research Articles

Use of a line intercept snow track index and plot sampling for estimating densities of wild boar (Sus scrofa) in southwestern Poland

In Bory Dolnośląskie Forest (southwestern Poland), in 8 forest districts with a total of 121,783 hectares (ha) of forest area, 16 sampling plots of a total area of 7,100 ha were marked. Using the block count method, the presence of 157 wild boars was found in 12 sampling plots where the population density ranged from 2.2 to 52.9 individuals/1000 ha. By counting snow tracks along 16 line transects situated within the sampling plots (total length – 70.9 km), the presence of 103 wild boars was found. In places where tracks of wild boars were found, the relative population density of this species ranged from 0.10 to 5.6 individuals/km of transect. Using non-linear regression, a mathematical formula was derived where the relative population density index (N/km) was the independent variable, and the absolute population density (N/1000 ha) was the dependent variable. A high correlation was found between these variables (R2=0.85). It is suggested that the population numbers evaluated by snow tracks of wild boars found on line transects, and the regression equation derived in this study be used in the management of this species.

OBSERVATIONS ON THE BIOLOGY OF ORGANIC ORCHARD SOILS

Three studies were used to evaluate the biology of organic orchard soils. The work focused on the three phases of organic systems: development, dynamic equilibrium and senescence. The first study consisted of a comparative analysis of the vertical distribution of nematodes, ciliates, flagellates, amoebae and endomycorrhizae associated with four pairs of mature organic and conventional cherry orchards. The second study investigated the dynamics of nematode community structure associated with transitioning a corn-soybean site into a certified organic apple orchard. In the third study, the soil biology of the new organic apple orchard was compared with the soil biology of an organic vegetable site that had been certified for 20 years, a neighboring conventional corn-soybean field with similar soil physical characteristics, and an old field secondary succession site at the Michigan State University, Kellogg Biological Station, Long Term Ecological Research project. Absolute population densities of bacterial feeding nematodes, ciliates, flagellates, amoebae and endomycorrhizae were significantly higher in the O-horizon in all eight cherry orchards, compared with the population densities at 0-15 or 15-30 cm soil depth. The O-horizon of organic orchards had significantly higher absolute population densities of flagellates and total soil-borne organisms compared with soil from the conventional orchards. In general, soil biological diversity was greater in the organic orchards than in the conventional orchards. During the apple orchard organic transition process, the relative population density of herbivorous nematodes declined. The data indicate that the soil biology of the new organic apple orchard took seven years to reach a state of dynamic equilibrium.

Ecological and Environmental Modelling Workshops

The Centre for Research into Ecological and Environmental Modelling (CREEM) is hosting three linked workshops in the summer of 2012 in our purpose-built facilities at the University of St Andrews, Scotland. The aim of these workshops is to train participants in the latest methods for design and analysis of distance sampling surveys, including line and point transects. The workshops are taught by leading researchers in the field, using industry-standard software. The first workshop (21–24 August) will run at an introductory level, and will focus on “conventional” distance sampling methods, as described in the standard reference book Introduction to Distance Sampling. The workshop will be a blend of theory and practice, and participants will learn how to use the program “Distance.” Participants will gain a solid grounding in both survey design and methods of analysis for distance sampling surveys. Note that we have moved the “automated survey design” topic out of the advanced workshop into the introductory workshop. The advanced distance sampling workshop (27–30 August) will include advanced treatment of: incorporating covariates in detection function modeling, analyses in which detectability on the transect line is not assumed to be perfect (the so-called g(0) problem) and spatial (or density surface) modeling. The aim of this workshop is to bring participants up to date with the latest developments in distance sampling methods and software. It is also an opportunity for those actively engaged in the design, analysis, and execution of distance sampling surveys to discuss common issues and problems, and set future research directions. The workshop will be a combination of lectures and computer sessions, with considerable time for discussion. In addition, this year we are running a one-day introduction to density estimation from passive acoustic data (25 August). Passive acoustic monitoring is often used to obtain indices of relative abundance, such as number of detections per unit time. However, for many applications, the quantity we really want to estimate is absolute population abundance (i.e., the number of animals in the population) or density (number of animals per unit area). This day-long tutorial will give an insight into methods to achieve this. For all workshops, participants are encouraged to bring their own data sets, and can expect to do some preliminary analyses with their data. Computer sessions take place in our modern computer classroom (attached to the seminar room); participants can use our computers or bring their own laptops. Additional details regarding the workshop can be found at our web site 〈http://www.ruwpa.st-and.ac.uk/distance.workshops/distance2012/workshop_overview.html〉

Estimating Brownian motion dispersal rate, longevity and population density from spatially explicit mark–recapture data on tropical butterflies

1. We develop a Bayesian method for analysing mark-recapture data in continuous habitat using a model in which individuals movement paths are Brownian motions, life spans are exponentially distributed and capture events occur at given instants in time if individuals are within a certain attractive distance of the traps. 2. The joint posterior distribution of the dispersal rate, longevity, trap attraction distances and a number of latent variables representing the unobserved movement paths and time of death of all individuals is computed using Gibbs sampling. 3. An estimate of absolute local population density is obtained simply by dividing the Poisson counts of individuals captured at given points in time by the estimated total attraction area of all traps. Our approach for estimating population density in continuous habitat avoids the need to define an arbitrary effective trapping area that characterized previous mark-recapture methods in continuous habitat. 4. We applied our method to estimate spatial demography parameters in nine species of neotropical butterflies. Path analysis of interspecific variation in demographic parameters and mean wing length revealed a simple network of strong causation. Larger wing length increases dispersal rate, which in turn increases trap attraction distance. However, higher dispersal rate also decreases longevity, thus explaining the surprising observation of a negative correlation between wing length and longevity.

Characteristics of the Spread of Apple Proliferation by Its VectorCacopsylla picta

The distribution and natural phytoplasma infection of Cacopsylla picta were investigated during a long-term field survey between 2002 and 2009 in commercial and abandoned apple proliferation-infected orchards throughout Germany, northern Switzerland, and eastern France. Comparable population dynamics were described for the different sites whereas considerable variations in the absolute population densities were observed among the years. Individual polymerase chain reaction (PCR) testing revealed, for each year, a rather stable natural infection rate with ?Candidatus Phytoplasma mali? of ?10% for overwintered adults of C. picta. Both genders were equally highly infected although more females were caught. The overall male/female ratio was 1:1.5. No direct correlation was found between the infection status of the orchard and the infection rate of overwintered C. picta. No influence of agricultural practices was seen. However, a relationship between the incidence of the disease and the vector population density became evident on a regional scale. Successful transmission of ?Ca. P. mali? occurred each year with overwintered individuals as well as with new adults. The transmission efficiency varied among the years within 8 to 45% for overwintered adults and 2 to 20% for individuals of the new generation. The load of single C. picta with ?Ca. P. mali? was determined by quantitative real-time PCR. High phytoplasma titers were measured in overwintered adults already at their first appearance in the orchards after remigration from their overwintering hosts. Thus, the data indicate the transmission of the disease on a regional scale by remigrant adults of C. picta and at a local scale within the same season by emigrant adults which developed on infected plants.

Bird community responses to cattle stocking rates in a Pacific Northwest bunchgrass prairie

In 2006–2010, effects of four different cattle stocking rates (0, 14.4, 28.8, and 43.2 animal unit months) were compared, representing 0%, 20%, 32%, and 46% utilization of vegetation by domestic livestock, on vegetation structure (as indexed by visual obstruction), and songbird population and apparent nest density, community composition, and diversity in a Pacific Northwest bunchgrass prairie in northeastern Oregon, USA. Overall paddock-level visual obstruction decreased and structural heterogeneity increased with increasing stocking rates, and those effects carried over 1 year after grazing had ceased. Most species were able to locate nesting sites regardless of differences in visual obstruction, except western meadowlark and vesper sparrow, for which obstruction was lower in paddocks with higher stocking rates. Apparent nest density for grasshopper sparrows was negatively affected by higher stocking rates. Grazing effects on absolute songbird population density were restricted to negative effects of higher stocking rates on savannah sparrows, but this relationship was not observed until 1 year after grazing had ceased. Songbird community composition differed between control and heavily-grazed paddocks, driven by an increase in the proportion of horned larks and a decrease in the proportion of savannah sparrows in heavily-grazed paddocks from pre-treatment to post-treatment years. Bird diversity indices were unaffected by stocking rate. Negative effects of high stocking rates on densities of two species and the absence of any clear positive effect for the other three species suggest high stocking rates as applied in this experiment may not provide suitable habitat for all grassland songbirds. The absence of negative responses of density to low and moderate stocking rates suggests these grazing regimes generally provided suitable habitat for all species.

Resonantly laser induced plasmas in gases: The role of energy pooling and exothermic collisions in plasma breakdown and heating

The present work is a systematic experimental study of the plasma formation in cesium vapor induced by a continuous laser tuned to the resonance transition 6 S 1/2–6 P 3/2. Taking into account the measured absolute population densities of Cs ground and excited state atoms as well as the electron densities derived from Stark broadening of the Cs lines, complete local thermodynamic equilibrium in the laser-produced plasma was found for laser power densities ≈ 10 Wcm − 2 at cesium ground state number densities of about 10 17 cm − 3 . Direct conversion of the excitation energy or parts of the excitation energy in exothermic collisions of laser-excited atoms is concluded to be the major process for atomic vapor heating and subsequent formation of LTE plasmas.

LIF measurements on an atomic helium beam in the edge of a fusion plasma

A method for the absolute measurement of population densities of selected atomic helium levels, which has been applied on the tokamak TEXTOR at the Forschungszentrum Jülich in Germany, is presented. The method is based on the resonant excitation of selected levels by a high-power, narrow-band, pulsed laser beam saturating the optical pumping process. Observation of the fluorescence response is performed at the laser wavelength and elsewhere in the spectrum: this gives information on collisional population transfer between some excited levels. Data analysis, as required for the derivation of absolute population densities, includes due consideration of the Zeeman splitting of spectral lines in a strong magnetic field. The first results of the measured population densities are compared with those provided by simulation based on the collisional–radiative model for atomic helium in the edge of fusion plasmas. This code has been extended to include the laser interaction with atomic helium, in order to simulate the measured time traces of radiation from the laser-perturbed levels. A combination of this simulation procedure with laser-induced fluorescence measurements is suggested as a possible method for determining the electron density in the edge plasma.

Estimation of abundance and dispersal distance of the sugarcane click beetle Melanotus sakishimensis Ohira (Coleoptera: Elateridae) on Kurima Island, Okinawa, by mark-recapture experiments

The absolute population density and natural mean dispersal distance of the sugarcane click beetle Melanotus sakishimensis Ohira (Coleoptera: Elateridae) were estimated by using mark-recapture experiments in an agricultural area (180 ha) on Kurima Island, Miyakojima, Okinawa in mid-February, from 2002 to 2006. Funnel-vane traps with synthetic sex pheromone were uniformly placed along field roads at 100 points to capture adult males. Estimates of population densities of males that were obtained by the Jolly-Seber and Yamamura methods from 2002 to 2006 were 33,761, 29,727, 14,960, 11,360 and 8,634, respectively. The Yamamura method was adopted in 2004 and 2005 when the survival rates estimated by Jolly-Seber method became larger than 1. The estimate of lifetime natural mean dispersal distance (±SE) that was calculated by eliminating the influence of artificial trap removal was 193.8±11.0 m. The estimate of the male removal rate (and the 95% profile likelihood confidence interval) was 0.131 (0.117–0.147), indicating that the amount of male removal was not sufficient for the population control in this experiment.

An evaluation of single-pass versus multiple-pass backpack electrofishing to estimate trends in species abundance and richness in prairie streams

Backpack electrofishing is a common method used to compare total species richness and relative abundance of stream fishes across space and time. However, as with any sampling method, it is important to evaluate the sampling effort necessary to capture patterns of variation in fish assemblage structure across samples. Thus, we evaluated the efficacy of single-pass versus multiple-pass backpack electrofishing for minnows and darters in intermittent prairie streams. We found that in 14 of 19 three-pass electrofishing samples, we detected all species during the first pass. The samples where we missed species on the first pass were in pools with six to nine species, suggesting a single-pass sample worked best for pools with lower species richness. We also found that both the raw abundance (i.e., catch rates) and rank abundance of four common species based on the first pass is highly concordant with the second and third passes. Nevertheless, differences in capture efficiency varied by species and density. In particular, our ability to deplete a species from a stream pool was highly variable when fish densities were low, and for Phoxinus erythrogaster, it was variable across all densities. Overall, our data suggest single-pass electrofishing can be used to detect spatial and temporal trends in abundance and species richness given standardized effort, but may not be representative of absolute population densities.

Carabid movement and vegetation density: Implications for interpreting pitfall trap data from split-field trials

Abstract This paper presents data from an extensive study of a carabid beetle, commonly dominant in agricultural habitats, within a split-field trial with different vegetation density in each half-field. Pitfall trapping provided data on activity-density and spatial distributions. Mark–release–recapture data estimated absolute population density and quantified individual movements within and between the two half-fields. The results revealed extensive population exchange between half-fields, both within areas of the same crop and between different crops. Activity was strongly influenced by vegetation density such that pitfall trap activity-density data indicated significant differences between treatments when there were none between absolute population density estimates. Field data and simulation models showed that movements of individuals between treatments differing in vegetation density can be substantial and directionally biased.

Determination of absolute population densities of eroded tungsten in hollow cathode lamps and fluorescent lamps by laser-induced fluorescence

The high energy ion bombardment during instant start of a fluorescent lamp (FL) leads to intense sputtering of the electrode material including tungsten and emitter. Thus, a cold started FL often suffers from early failures due to coil fracture. The main goal of this paper is to investigate tungsten erosion. We have employed the ultra-sensitive method of laser-induced fluorescence. This technique is particularly well-suited to determining absolute population densities of neutral and singly ionized atoms of liberated electrode material. In addition to FL, our investigations have been performed also on hollow cathode lamps (HCLs). These are useful because they provide a variable source of sputtered tungsten atoms and can serve as tuning tools for precise adjustment of the laser radiation.We will present absolute atomic tungsten population densities in a commercial FL and in an HCL. Furthermore, the results of a theoretical investigation of the argon plasma and the tungsten density in the HCL are represented.

INDIRECT EFFECTS OF AN INTRODUCED UNGULATE ON POLLINATION AND PLANT REPRODUCTION

Herbivores can affect plants not only directly through browsing and trampling, but also indirectly through other species. For example, herbivores could affect the interaction between plants and their pollinators. Because plant population density may affect plant–pollinator interactions and plant reproductive success, we hypothesized that herbivores could affect pollination and plant reproduction indirectly by modifying plant population density. Unlike previous hypotheses, which concerned individual‐level effects on vegetative and reproductive traits, our hypothesis focuses on population‐level effects and involves a feedback mechanism. To test this hypothesis, we conducted field studies in the temperate forest of the southern Andes, where introduced ungulates are a major source of anthropogenic alteration. For 10 animal‐pollinated understory plants, we compared population density, pollinator visitation, pollen deposition in stigmas, and reproduction in four pairs of grazed and ungrazed sites. We found evidence of indirect effects of ungulates on pollination and reproduction only for the herbAlstroemeria aurea(Alstroemeriaceae). The general lack of evidence for indirect effects on most of the species may result from resistance to cattle browsing and trampling, or low statistical power. ForA. aurea, we present additional evidence from trampling and hand‐pollination experiments, plus path analyses of the effect of density on pollination and reproduction showing that: (1) cattle decrease the absolute and relative population density of this species through trampling; (2) density, particularly relative density, affects pollen deposition on stigmas; and (3) conspecific pollen deposition affects reproduction. Thus, our results indicate that, by directly reducing the population density ofA. aurea, cattle are indirectly affecting its reproduction.

Characterization of a high-pressure microdischarge using diode laser atomic absorption spectroscopy

A high-pressure dc glow discharge based on micro-structured-electrode (MSE) arrays was investigated by diode laser atomic absorption spectroscopy. The microdischarge was studied at constant current in pure Ar for pressures ranging from 50 to 400 mbar. The measurements of the absolute population density of the excited 1s5, 1s4, 1s3, and 1s2 levels of Ar in the discharge revealed a population density of excited atoms in metastable and resonance states in the range 1012–1015 cm−3. The gas temperature and the electron number density were evaluated from the analysis of the absorption line profiles, taking into account significant broadening mechanisms. The gas temperature, derived from the Doppler broadening, was found to increase with pressure from 380 K at 50 mbar to 1100 K at 400 mbar. The electron number density was calculated from the Stark broadening and shift, and it ranges from 9×1014 to 5×1015 cm−3. The MSE-sustained discharges are combining the non-equilibrium character with the advantage of high-pressure, which recommends them for non-thermal plasma processing e.g. surface treatment, plasma chemistry and generation of UV and VUV radiation.

Nonequilibrium excited-state distribution of atoms in dense mercury plasmas

The nonequilibrium excited-state distribution of mercury atoms up to the ionization limit in high-pressure discharges is deduced through comparison of the actual level-population densities with those calculated from the Saha equation at the plasma-electron temperature. Emission data obtained from two ac (50 Hz) mercury discharges at 2 and 5 bar are used to deduce the absolute excited-state population densities and the electron temperature. It is found that at the maximum emission phase (5 ms), the excited states deviate from the Saha equilibrium, the levels are overpopulated, the overpopulation decreases with the level-excitation energy, the deviation is larger for the higher-pressure discharge, and the two discharges are closer to the equilibrium at the minimum emission phase (0.5 ms). Possible causes of the observed deviations from the Saha equilibrium are suggested. The plasma temperature and densities are also found assuming equilibrium conditions and compared with the results obtained initially.

Pre-adult mortality in the blowfly Lucilia sericata.

Populations of the blowfly, Lucilia sericata (Meigen) (Diptera: Calliphoridae), have a considerable potential for rapid increase; the lifetime reproductive output of each adult female has been estimated to be between 130 and 172 eggs. Nevertheless, in the field, absolute population densities of this species are relatively low. To account for this difference, the levels of mortality affecting the eggs, feeding and wandering larvae and pupae of L. sericata were assessed in the field and laboratory. Percentage egg hatch was dependent on relative humidity with no egg eclosion at humidities below 50%; there was no significant effect of temperature on egg hatch. On infested sheep, the mean mortality of feeding larvae was 53%, but this ranged widely from 0% to 96%. There was no effect of atmospheric temperature or humidity on the mortality of feeding larvae in vivo. In the laboratory, only 10% of wandering larvae pupariated at 10 degrees C. At above 20 degrees C pupariation was consistently almost 100%. Percentage emergence increased from 0% at 10 degrees C to about 80% between 20 and 30 degrees C. The upper lethal temperature for pupae was approached at 35 degrees C. Analysis of the predation of pupae in the field revealed a weak, but significant curvilinear relationship between temperature and proportionate mortality and a median mortality of 0.49% per 24 h exposure (interquartile range = 5.2%). There was no evidence of density dependence in pupal predation. Overall, it is estimated that pre-adult mortality accounts for losses of approximately 97% of each generation, but this figure is subject to considerable variation depending on factors such as climate, time of year and host susceptibility.

Evaluation of population densities of the common wolf spider Pardosa agrestis (Araneae: Lycosidae) in Hungarian alfalfa fields using mark-recapture

The absolute population density of adult Pardosa agrestis (Westring, 1862), the dominant epigeic spider species in many arable lands in Central Europe, was quantified in two alfalfa fields using a multiple mark-recapture method. The resulting density estimates are presented together with catch data from simultaneously performed suction sampling and pitfall trapping. Two week long mark-recapture surveys were conducted in August 1995 and 1996 using grids of 11 × 11 live-catching pitfall traps covering a square area of 400 m2 in the first, and 900 m2 in the second survey. The trap checking and marking procedure, using individual codes, was done daily. Over 5,000 spiders were marked in the two surveys. The number of spiders caught varied greatly between days. The recapture rate was also variable, ranging between 5-19%. Recaptured animals moved considerable daily distances, marked animals left the area of the trapping grid within a few days. Population sizes were estimated for 3 day time windows during which period the population could be considered closed. Spider densities were calculated from the estimated abundances and the capture area, which consisted of the grid area plus a boundary strip calculated from the estimated movement ranges of spiders. The resulting densities were close to 2 males and 1 female per m2 in the first, and 4.5 males and 4.5 females per m2 in the second experimental site. Suction sampling caught very few adult individuals and gave unsatisfactory data for statistical comparison. Live catching pitfall trap catches did not correlate with the derived mark-recapture density estimates across the short time windows, but for the entire trapping sessions the catches were consistent with the density estimates.

The pitfalls of pitfalls: a comparison of pitfall trap catches and absolute density estimates of epigeal invertebrate predators in Arable Land

In an agroecosystem, catches of epigeal invertebrate predators obtained by pitfall traps were compared to absolute population densities estimated by ground photoeclectors in two different habitats, a field and an adjacent set-aside land. In general, abundance of Carabidae and Lycosidae were overestimated by pitfalls, while Staphylinidae and Linyphiidae were underestimated, and beetle larvae showed no obvious trend. The overestimation of Carabidae and Lycosidae by pitfalls had its maximum in spring and summer. Numbers collected by pitfalls did represent actual population densities better in the field than in the set-aside. This is probably caused by the higher vegetation diversity and complexity of the set-aside land which additionally influenced the catches. Pitfalls recovered higher numbers of animals and species, and species composition differed significantly between pitfalls and photoeclectors, in the field as well as in the set-aside. Body size seemed to be the main factor in determining the catch, the relatively larger species being more frequently caught by pitfall traps. In sum, the relationship between pitfall trap catches and actual population densities appeared to be either absent, weak or highly variable among taxa, habitat and time of the season. Thus numbers caught in pitfall traps cannot be considered as reliable indices of “real” abundance nor do they reflect the relative abundance within a given predator community correctly. Therefore, in most cases absolute density estimates should be preferred for the study of epigeal invertebrates in arable land. However, I suggest a combination of both pitfall traps and standardised area samples, because the two approaches possibly provide information of different qualities equally important for the evaluation of epigeal predator species, namely searching activity and population density.

Efficiency of Drag Sampling for Estimating Population Sizes of <I>Ixodes pacificus</I> (Acari: Ixodidae) Nymphs in Leaf Litter

Abstract Drag sampling is a commonly used method to obtain relative estimates of the density of questing nymphalIxodes scapularis Say andI. pacificus Cooley & Kohls ticks, which are primary vectors of Lyme disease spirochetes to humans in North America. However, the efficiency of drag sampling in determining absolute population densities of questing nymphs has not been evaluated previously. Therefore, we assessed the efficiency of a single drag-sampling occasion to estimate the total population size of questingI. pacificus nymphs in a leaf-litter habitat in California. Repeated daily removal sampling was carried out in four areas, each covering 300 m2, on 17 occasions over a 23-d period in the spring of 1999. In total, 573I. pacificus nymphs were collected, of which 55 (9.6%) were collected on the initial sampling occasion and 20 (3.5%) on the last occasion. The total population size of questing nymphs, i.e., the intersection with the horizontal axis of a linear regression of daily nymphal catch rates on ...

Efficiency of Drag Sampling for Estimating Population Sizes ofIxodes pacificus(Acari: Ixodidae) Nymphs in Leaf Litter

Drag sampling is a commonly used method to obtain relative estimates of the density of questing nymphal Ixodes scapularis Say and I pacificus Cooley & Kohls ticks, which are primary vectors of Lyme disease spirochetes to humans in North America. However, the efficiency of drag sampling in determining absolute population densities of questing nymphs has not been evaluated previously. Therefore, we assessed the efficiency of a single drag-sampling occasion to estimate the total population size of questing I pacificus nymphs in a leaf-litter habitat in California. Repeated daily removal sampling was carried out in four areas, each covering 300 m2, on 17 occasions over a 23-d period in the spring of 1999. In total, 573 I. pacificus nymphs were collected, of which 55 (9.6%) were collected on the initial sampling occasion and 20 (3.5%) on the last occasion. The total population size of questing nymphs, i.e., the intersection with the horizontal axis of a linear regression of daily nymphal catch rates on the number of nymphs caught previously, was estimated to be 936. Thus, the efficiency of the initial sampling occasion to estimate the total population size was 5.9% (4.8, 5.0, 5.8, and 9.1%, respectively, for the four individual sampling areas). Further, the overall mean efficiencies of the two, five, and 10 first removal sampling occasions to estimate the absolute nymphal density was 5.2, 4.7, and 4.3%, respectively, and 13 sampling occasions were required to collect 50% of the estimated total nymphal population.