Needles in haystacks: Estimating detection probability and occupancy of rare and cryptic snakes

The species most in need of conservation or management are often also the most difficult to monitor, because of their rarity, secretive habits, or both. To combat these challenges, presence/absence (site occupancy) models can be used to track species occupancy at landscape scales. However, quantitative knowledge of detection probability (which is almost always <1) is required to reliably estimate site occupancy. Here, we present a case study that combines detection probabilities and site occupancy modeling to monitor a notoriously secretive guild of animals, North American aquatic snakes. Specifically, we use program PRESENCE to estimate detection probability (p) and probability of site occupancy (ψ) for seven snake species in relationship to site covariates, to understand the proximate and ultimate factors that influence habitat suitability. We were able to estimate p (3–46%) and ψ (12–96%) for each species and calculate the amount of unsuccessful effort necessary to declare absence of each species with statistical confidence (5–63 visits; 150–1890 trap-nights). We documented considerable interspecific variation in p and ψ; one species (Nerodia fasciata) was widespread and highly detectable, while another (Agkistrodon piscivorus) had low detectability despite its wide distribution. Five other species were secretive, or restricted to specific habitat types, or both, illustrating that complex and sometimes counterintuitive relationships exist between capture rate and occupancy. Incorporating p and ψ is essential to the success of large-scale monitoring programs for elusive species.     

The status of common seals in Shetland

A search was made for Common Seals (Phoca vitulina) around Shetland in September 1971. The coast was arbitrarily divided into eight areas and the count of Common Seals in each was adjusted to give an estimated total. 1,219 Common Seals were counted and a grand total of 1,800 estimated for the whole of Shetland. The question of whether or not the Shetland Common Seal stock is declining is discussed. It is concluded, on the basis of quantitative evidence and from discussions with local boatmen and seal hunters, that the stock is declining, although the rate of decline is unknown.     

Simulation of seasonal changes in microbial activity of maritime antarctic peat

Seasonal variations in temperature and moisture in moss peat were monitored in the field at Signy Island, Antarctica. When simulated in intact peat cores in vitro after frozen storage, these variations caused changes on O₂-uptake which closely reproduced the results for fresh samples. Respiration rate was used as a measure of aerobic decomposer activity. Supplements of sugars indicated the predominance of microbial respiration and its dependence on the availability of dissolved organic C (DOC). Low temperatures of 0° to 1°C were not rate-limiting for respiration in vivo or in vitro, and O₂-uptake was detected at ?1°C. Repeated peaks of O₂-uptake under wet conditions resulting from simulated spring freeze-thaw cycles, and a solitary peak during an autumn simulation, suggested release of DOC substrates from frost-damaged cells. Desiccation, microfaunal predation and microaerophily were thought to contribute to respiratory declines. O₂-uptake and CO₂-evolution were equivalent in peat beneath Polytrichum sampled in autumn. Peat respiration was not generally proportional to microbial biomass, but saccharolytic yeasts were dominant during the respiratory maximum in spring and correlated with O₂-uptake in a mixed culture of indigenous microflora. Yeasts grew exponentially in freezethaw cycle simulations but percolated into the peat profile in the field. The basal O₂-uptake, which may be attributable to the decomposition of redalcitrant molecules such as cellulose, was lower in simulations of spring than autumn. Although bacterial biomass increased and diversified during summer, the ratio of fungal-to-bacterial contributions to O₂-uptake in an incubated homogenate of peat sampled in autumn was 4:1.     

Modeling co-occurrence of northern spotted and barred owls: Accounting for detection probability differences

Barred owls (Strix varia) have recently expanded their range and now encompass the entire range of the northern spotted owl (Strix occidentalis caurina). This expansion has led to two important issues of concern for management of northern spotted owls: (1) possible competitive interactions between the two species that could contribute to population declines of northern spotted owls, and (2) possible changes in vocalization behavior and detection probabilities of northern spotted owls induced by presence of barred owls. We used a two-species occupancy model to investigate whether there was evidence of competitive exclusion between the two species at study locations in Oregon, USA. We simultaneously estimated detection probabilities for both species and determined if the presence of one species influenced the detection of the other species. Model selection results and associated parameter estimates provided no evidence that barred owls excluded spotted owls from territories. We found strong evidence that detection probabilities differed for the two species, with higher probabilities for northern spotted owls that are the object of current surveys. Non-detection of barred owls is very common in surveys for northern spotted owls, and detection of both owl species was negatively influenced by the presence of the congeneric species. Our results suggest that analyses directed at hypotheses of barred owl effects on demographic or occupancy vital rates of northern spotted owls need to deal adequately with imperfect and variable detection probabilities for both species.     

植物化感作用研究概况

近年来植物化感物质的提取、纯化、鉴定及其生物检测方法的研究取得很大进展。化感作用物质主要来自植物的次生代谢产物，它通过影响植物膜系统、激素水平、矿质吸收、呼吸和光合作用等对植物的生长产生影响。并阐述了植物化感作用及其机理、化感作用的研究方法，指出植物化感作用研究中存在的问题和研究方向。     

南极磷虾等径滚轴挤压剥壳工艺优化

该文采用响应面分析法对南极磷虾滚轴挤压剥壳工艺参数进行优化,以剥壳得肉率为试验指标,以滚轴转速、滚轴间隙、旋转圈数为自变量,在单因素试验的基础上进行响应面分析。获得最佳工艺条件为：滚轴转速1.6 r/s、滚轴间隙0.5 mm、旋转圈数1.7 r,预测的得肉率为36.44%,此参数条件下的实测平均得肉率为35.17%。在最佳工艺参数下,试验放置时间与剥壳得肉率的关系,结果表明：随着放置时间的增加,剥壳得肉率逐渐降低;手工剥壳得肉率从35.29%降至29.73%,机器剥壳得肉率从34.71%降至21.08%。机器剥壳得肉率较手工剥壳相对较低,且降幅更为明显。研究结果可为南极磷虾剥壳装备的研制提供参考。     

Hierarchical modeling of cluster size in wildlife surveys

Clusters or groups of individuals are the fundamental unit of observation in many wildlife sampling problems, including aerial surveys of waterfowl, marine mammals, and ungulates. Explicit accounting of cluster size in models for estimating abundance is necessary because detection of individuals within clusters is not independent and detectability of clusters is likely to increase with cluster size. This induces a cluster size bias in which the average cluster size in the sample is larger than in the population at large. Thus, failure to account for the relationship between detectability and cluster size will tend to yield a positive bias in estimates of abundance or density. I describe a hierarchical modeling framework for accounting for cluster-size bias in animal sampling. The hierarchical model consists of models for the observation process conditional on the cluster size distribution and the cluster size distribution conditional on the total number of clusters. Optionally, a spatial model can be specified that describes variation in the total number of clusters per sample unit. Parameter estimation, model selection, and criticism may be carried out using conventional likelihood-based methods. An extension of the model is described for the situation where measurable covariates at the level of the sample unit are available. Several candidate models within the proposed class are evaluated for aerial survey data on mallard ducks (Anas platyrhynchos).     

HPLC analysis of rosmarinic acid in feed enriched with aerial parts of Prunella vulgaris and its metabolites in pig plasma using dual-channel coulometric detection

This paper describes a sensitive isocratic HPLC/ECD method developed for the determination of rosmarinic acid (RA) in plant material, animal feed, and pig plasma. The plasma sample preparation only includes protein precipitation and adjustment of the pH. The applicability of the method was tested on plasma samples of pigs that were exposed to a 91-day oral intake of RA via feed enriched by aerial parts of Prunella vulgaris. The plasma was directly analyzed using the method described as well as after enzymatic hydrolysis. When no hydrolysis step was included, RA and caffeic acid (CA) were quantified in the plasma. In hydrolyzed plasma samples, several other metabolites were determined, including dihydrocaffeic, ferulic, and dihydroferulic acid. The dual-channel coulometric detection employed, as an alternative to mass spectrometry, offers good selectivity and sensitivity owing to the electrochemical properties of the phenolic constituents.     

Depositional seals in polyacrylamide-amended soils of varying clay mineralogy and texture

Purpose  

Depositional seals, formed when turbid waters infiltrate into soils, lead to a reduction in soil hydraulic conductivity (HC) and enhance runoff and soil erosion. Since clay size particles constitute a dominant proportion of depositional seals, soil texture and clay mineralogy play a significant role in determining the seal’s hydraulic characteristics. Presence of high molecular weight anionic polyacrylamide (PAM) in suspension flocculates fine sediments, and therefore, its application to the soil surface may modify the characteristics of the depositional seal. The impact of PAM on the latter is expected to be influenced by soil properties. The aim of this study was to elucidate the effects of PAM application on clay flocculation and the HC of depositional seals formed in four soils varying in texture (ranging from loamy sand to clay loam), and diverse proportions of clay mineral constituents (kaolinite, smectite, and vermiculite).     

Large-scale reclamation of barren lands in Iceland by aerial seeding

Catastrophic soil erosion has resulted in the desertification of vast areas in Iceland. Barren lands are revegetated on a large scale by aerial broadcasting of commercial grass seed of Festuca rubra cv. Leik (red fescue) and subsequent regular fertilizer application for five years. Vegetation cover following aerial seeding of F. rubra was recorded in three reclaimed sites, which were two, ten and 25 years old, in an inland area in southern Iceland. As a comparison, vegetation cover was also recorded on barren land. Plant succession was inferred from these records. Vegetation cover was recorded using the point-intercept method. Spores of arbuscular mycorrhizae fungi (AMF) were recorded from each site. Barren lands have characteristically low (<5%) vegetation cover. The highest cover of F. rubra was found two years after revegetation was initiated. Non-dependent AMF forbs also colonized and increased their cover rapidly in the second year due to fertilizer application, but after a decade their cover declined. Ten years after the aerial seeding, F. rubra disappeared and the area was dominated by the native grass Agrostis stolonifera (creeping bent grass). A cover of mosses and plant litter was also recorded on the ten-year-old site. AMF spores were low in all studied sites, and colonization of AMF was only found in the roots of A. stolonifera. After 25 years, it appeared that the cover of native forbs started to increase again and salix bushes were established. Aerial seeding of F. rubra failed to create a long-lasting cover to facilitate natural rapid succession. Alternative revegetation practices, taking into consideration the dynamics of the mutualistic microorganisms (Rhizobium and AMF)/plant association, are suggested for a better and more economic management of reclamation strategies. Copyright © 1999 John Wiley & Sons, Ltd.     

Quantification of saponins in aerial and subterranean tissues of Medicago truncatula

Triterpene saponins from aerial and subterranean organs of Medicago truncatula cv. Jemalong A-17 were qualitatively profiled and quantified using reverse-phase HPLC with on-line photodiode array detection and electrospray-ionization mass spectrometry (HPLC/PDA/ESI/MS). Absolute quantifications were performed for 3-O-beta-D-glucopyranosyl-medicagenic acid and soyasaponin 1 (3-O-[alpha-L-rhamnopyranosyl(1-->2)-beta-D-galactopyranosyl(1-->2)-beta-D-glucuronopyranoside] soyasapogenol B), whereas relative quantifications were determined for 29 other saponins in root, stem, leaf, seedpod, and seed. Roots contained the greatest total amount of saponins followed by leaf and seed, respectively. The quantitative data also reveal the differential accumulation of triterpene saponins in the various organs of M. truncatula. Specifically, relatively higher quantities of medicagenic acid conjugates accumulated in leaf and seed, whereas relatively higher levels of soysapogenol conjugates were observed in root. The differential accumulation of specific triterpene saponins is suggestive of spatially differentiated biosynthesis and/or biological function.     

Terraces in arid stream valleys a probability model

A model which generates stream terraces in extreme arid environments is developed on the basis of the random occurrence of superfloods in time and in space. The probability of occurrence of the number of terraces in a given desert valley at any point in time is evaluated in relation to varying rates of terrace obliteration. It is shown on theoretical grounds that, if the number of superfloods necessary for obliteration (NSFNFO) is one, the probability for having no terrace is one third, and for having one terrace is two thirds. These findings agree well with computer-generated frequencies.Some geomorphic implications of the analysis are discussed, and the potential for future research based on the approach employed is evaluated.     

The use of land form-soil associations in irrigation soil surveys in northern Nigeria

The problems of soil mapping for irrigated agriculture on the savanna landscapes near Kano are discussed. Using data from a detailed soil survey, the possibility of establishing the major variations in soil properties relevant to irrigation by landform-soil association mapping is considered. In the landform classes identified, some soil textural and colour properties have within-class variances somewhat lower than their between-class variances, and moderate interclass correlations. The magnitude of the between-class differences in these properties is great enough to indicate whether the soils can be irrigated successfully and to help determine the irrigation method. Other soil properties including infiltration rate and topsoil available water capacity also differ significantly between landform classes, but their within-class variabdity is still relatively high, indicating the need for further investigations. The variability of most soil chemical properties across the area is not successfully accounted for by landform-soil association mapping. The results suggest that landform-soil association mapping can be a useful means of establishing imgability a feasibility survey level.     

Altered selection probabilities caused by avoiding the edge in field surveys

When field plots are prevented from overlapping the boundary of the tract being sampled, the selection probabilities of population elements near the edge differ from what they are when plots are permitted to overlap the boundary. In both situations, selection probabilities of edge elements differ from those of elements located far to the interior of the tract. An analytical expression and graphical depiction of the altered selection probabilities are presented, accompanied by an empirical study of the consequences on estimation for the situation where plots are pulled back from the edge until just tangent with the boundary.