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1.
Fewster RM Buckland ST Burnham KP Borchers DL Jupp PE Laake JL Thomas L 《Biometrics》2009,65(1):225-236
Summary . The dominant source of variance in line transect sampling is usually the encounter rate variance. Systematic survey designs are often used to reduce the true variability among different realizations of the design, but estimating the variance is difficult and estimators typically approximate the variance by treating the design as a simple random sample of lines. We explore the properties of different encounter rate variance estimators under random and systematic designs. We show that a design-based variance estimator improves upon the model-based estimator of Buckland et al. (2001, Introduction to Distance Sampling. Oxford: Oxford University Press, p. 79) when transects are positioned at random. However, if populations exhibit strong spatial trends, both estimators can have substantial positive bias under systematic designs. We show that poststratification is effective in reducing this bias. 相似文献
2.
The introduction of alien species is one of the main threats to the conservation of native species, especially in island ecosystems.
Here, we report on the population growth of 15 species of mammals introduced in 1983 on the island of Anchieta, an 828 ha
land-bridge island in southeastern Brazil. We estimated the density of mammals through 296 km of line transect census. Five
species introduced became extinct (coypu, brocket deer, six-banded armadillo, nine-banded armadillo, maned three-toed sloth);
six became over-abundant (marmoset, coati, agouti, seven-banded armadillo, and capybara); one has a stable population (capuchin
monkey). Anchieta Island has the highest density of mammals in the entire Atlantic forest (486.77 ind/km2), especially nest predators (232.83 ind/km2) and herbivores (253.58 ind/km2). Agoutis (Dasyprocta spp.) and marmosets (Callithrix penicillata) were, by far, the species with the highest population growth. The high density of mammals in this island may have strong
consequences for plant recruitment and bird diversity. 相似文献
3.
Cutting straight line transects through dense forest is time consuming and expensive when large areas need to be surveyed for rare or highly clustered species. We argue that existing paths or game trails may be suitable as transects for line transect sampling even though they will not, in general, run straight. Formulas and software currently used to estimate local density using perpendicular distance data can be used with closest approach distances measured from curving transects. Suitable paths or trails are those for which the minimum radius of curvature is rarely less than the width of the shoulder in the detection probability function. The use of existing paths carries the risk of bias resulting from unrepresentative sampling of available habitats, and this must be weighed against the increase in coverage available. 相似文献
4.
When using bivariate line transect methods to estimate the biomass density of a tightly clustered biological population, it is generally assumed that both the perpendicular distance from the trackline to the cluster and the cluster size, or biomass, are measured without error. This is unlikely to be the case in practice. In this article, assuming additive mean zero errors in distance and multiplicative errors in size, we develop an estimator of density that corrects for these errors. We use the method of moments for the case of gamma cluster size, randomly placed transect lines, and the generalized exponential detection function. We derive results that show that it may not be necessary to correct for errors in distance or size when the distance and size estimates are not biased. When the size estimates are biased, the biomass density estimate has approximately the same bias as the size estimates. The work is illustrated in the context of annual aerial surveys for juvenile southern bluefin tuna in the Great Australian Bight. 相似文献
5.
Interest in surveys for monitoring plant abundance is increasing, due in part to the need to quantify the rate of loss of biodiversity. Line transect sampling offers an efficient way to monitor many species. However, the method does not work well in some circumstances, for example on small survey plots, when the plant species has a strongly aggregated distribution, or when plants that are on the line are not easily detected. We develop a crossed design, together with methods that exploit the additional information from such a design, to address these problems. The methods are illustrated using data on a colony of cowslips. 相似文献
6.
Summary . We consider a fully model-based approach for the analysis of distance sampling data. Distance sampling has been widely used to estimate abundance (or density) of animals or plants in a spatially explicit study area. There is, however, no readily available method of making statistical inference on the relationships between abundance and environmental covariates. Spatial Poisson process likelihoods can be used to simultaneously estimate detection and intensity parameters by modeling distance sampling data as a thinned spatial point process. A model-based spatial approach to distance sampling data has three main benefits: it allows complex and opportunistic transect designs to be employed, it allows estimation of abundance in small subregions, and it provides a framework to assess the effects of habitat or experimental manipulation on density. We demonstrate the model-based methodology with a small simulation study and analysis of the Dubbo weed data set. In addition, a simple ad hoc method for handling overdispersion is also proposed. The simulation study showed that the model-based approach compared favorably to conventional distance sampling methods for abundance estimation. In addition, the overdispersion correction performed adequately when the number of transects was high. Analysis of the Dubbo data set indicated a transect effect on abundance via Akaike's information criterion model selection. Further goodness-of-fit analysis, however, indicated some potential confounding of intensity with the detection function. 相似文献
7.
Melville and Welsh (2001, Biometrics 57, 1130-1137) consider an approach to line transect sampling using a separate calibration study to estimate the detection function g. They present a simulation study contrasting their results with poor results from a traditional estimator, labeled the \"Buckland\" estimator and referenced to Buckland et al. (1993, Distance Sampling: Estimating Abundance of Biological populations). The poor results from the \"Buckland\" estimator can be explained by the following observations: (i) the estimator is designated for untruncated distance data, but was applied by Melville and Welsh to truncated distance data; (ii) distance data were not pooled across transects, contrary to standard practice; and (iii) bias of the estimator was evaluated with respect to a fixed rather than a randomized grid of transect lines. We elaborate on the points above and show that the traditional methods perform to expectation when applied correctly. We also emphasize that the estimator labeled the \"Buckland\" estimator by Melville and Welsh is not an estimator recommended by Buckland et al. for practical survey applications. 相似文献
8.
Summary . Double-observer line transect methods are becoming increasingly widespread, especially for the estimation of marine mammal abundance from aerial and shipboard surveys when detection of animals on the line is uncertain. The resulting data supplement conventional distance sampling data with two-sample mark–recapture data. Like conventional mark–recapture data, these have inherent problems for estimating abundance in the presence of heterogeneity. Unlike conventional mark–recapture methods, line transect methods use knowledge of the distribution of a covariate, which affects detection probability (namely, distance from the transect line) in inference. This knowledge can be used to diagnose unmodeled heterogeneity in the mark–recapture component of the data. By modeling the covariance in detection probabilities with distance, we show how the estimation problem can be formulated in terms of different levels of independence. At one extreme, full independence is assumed, as in the Petersen estimator (which does not use distance data); at the other extreme, independence only occurs in the limit as detection probability tends to one. Between the two extremes, there is a range of models, including those currently in common use, which have intermediate levels of independence. We show how this framework can be used to provide more reliable analysis of double-observer line transect data. We test the methods by simulation, and by analysis of a dataset for which true abundance is known. We illustrate the approach through analysis of minke whale sightings data from the North Sea and adjacent waters. 相似文献
9.
Fewster RM 《Biometrics》2011,67(4):1518-1531
Summary In spatial surveys for estimating the density of objects in a survey region, systematic designs will generally yield lower variance than random designs. However, estimating the systematic variance is well known to be a difficult problem. Existing methods tend to overestimate the variance, so although the variance is genuinely reduced, it is over‐reported, and the gain from the more efficient design is lost. The current approaches to estimating a systematic variance for spatial surveys are to approximate the systematic design by a random design, or approximate it by a stratified design. Previous work has shown that approximation by a random design can perform very poorly, while approximation by a stratified design is an improvement but can still be severely biased in some situations. We develop a new estimator based on modeling the encounter process over space. The new “striplet” estimator has negligible bias and excellent precision in a wide range of simulation scenarios, including strip‐sampling, distance‐sampling, and quadrat‐sampling surveys, and including populations that are highly trended or have strong aggregation of objects. We apply the new estimator to survey data for the spotted hyena (Crocuta crocuta) in the Serengeti National Park, Tanzania, and find that the reported coefficient of variation for estimated density is 20% using approximation by a random design, 17% using approximation by a stratified design, and 11% using the new striplet estimator. This large reduction in reported variance is verified by simulation. 相似文献
10.
This article develops an approach to estimating population abundance from line transect surveys that uses a calibration survey to estimate the detection function, which is then employed as a weight function in constructing the abundance estimate. Nonparametric methods of estimating the detection function via local regression and via a kernel density estimator are considered. The proposed methods are evaluated using a set of Western Australian plant data and weed enumeration data. 相似文献
11.
哺乳类动物数量调查中的截线抽样法与逆向截线法 总被引：5，自引：2，他引：5
文本介绍了可用于哺乳动物数量调查的一种新方法--截线抽样法,并在此方法的基础上,结合我国动物调查实践,提出了逆向截线法。逆向截线法在贺兰山自然保护区马鹿数量调查中,取得了较好效果。 相似文献
12.
13.
An implicit assumption of standard line transect methodology is that detection probabilities depend solely on the perpendicular distance of detected objects to the transect line. Heterogeneity in detection probabilities is commonly minimized using stratification, but this may be precluded by small sample sizes. We develop a general methodology which allows the effects of multiple covariates to be directly incorporated into the estimation procedure using a conditional likelihood approach. Small sample size properties of estimators are examined via simulations. As an example the method is applied to eastern tropical Pacific dolphin sightings data. 相似文献
14.
The likelihood function for data from independent observer line transect surveys is derived, and a hazard model is proposed for the situation where animals are available for detection only at discrete time points. Under the assumption that the time points of availability follow a Poisson point process, we obtain an analytical expression for the detection function. We discuss different criteria for choosing the hazard function and consider in particular two different parametric families of hazard functions. Discrete and continuous hazard models are compared and the robustness of the discrete model is investigated. Finally, the methodology is applied to data from a survey for minke whales in the northeastern Atlantic. 相似文献
15.
用距离取样技术估算森林生境中的梅花鹿密度 总被引：5，自引：0，他引：5
YuchunLI MasaakiKOGANEZAWA 《动物学报》2004,50(1):27-31
作者于 1999年 9、 10月在日本国日光国立公园的一个梅花鹿 (Cervusnippon)高密度区域实施了 16次夜间探照样带距离法取样调查。采用车载探照记数和激光测距仪测距 ,记录了梅花鹿的结群大小和距样带中心样线的垂直距离。应用距离取样技术 (Distancesamplingtechnique ,DST)计算的结果表明 ,梅花鹿的密度为12 5 8头 /km2 (95%CI 10 0 7-157 3 ) ,在两侧 80m宽度的调查样带内梅花鹿的总发现率为 52 5% ;对线样带法的传统动物密度计算方法 (King s ,Hayne s ,Leopold s ,Gates sⅠ ,Gates sⅡ ,Gates sⅢ和Frye s方法 )的结果验证表明 ,这些传统密度计算方法过高估算梅花鹿的密度 ,其结果为距离取样技术 (DST)计算结果的 1 76(Frye′s法 ) -6 10 (Hayne′s法 )倍。因此 ,作者建议在使用线样带法测定动物密度时应尽量避免使用这些传统计算方法 ;不同地区间及同一地区不同季节间应用线样带法调查得到的动物个体记数值之间的比较存在偏差 ,应该使用距离取样技术计算动物的密度 相似文献
16.
西藏羌塘自然保护区与人类活动有关的藏羚、藏野驴和藏原羚密度 总被引：6，自引：0，他引：6
1999年,2000年和2002年,在西藏西北部的西藏羌塘自然保护区分别沿三条横跨该自然保护区的长度为750-860km的东西向样线估计了藏羚(Pantholopshodgsoni)、藏野驴(Equuskiang)和藏原羚(Procaprapicticaudata)密度(每平方公里个体数)和遇见率(每平方公里遇见个体数)。在低海拔(4500-4700m)地区,藏羚、藏野驴和藏原羚数量很少,在那些人类活动强度高或中等的地区,藏羚、藏野驴和藏原羚的数量也极少,以致无法估计密度或遇见率。在高海拔(4700-5200m)地区,藏羚和藏野驴数量在那些人类和家畜活动强度低的地区,数量总比那些中等人类活动强度的地区高,尽管藏羚的数量差别比藏野驴小。藏原羚的情形不一样,在人类活动强度低或中等的地区的遇见率相仿。在某种程度上,这种差别可能与这些动物的生境偏好有关。看起来,藏原羚、其次是藏野驴比藏羚更能耐受人类和家畜的活动。注意到这三种动物在人类和家畜活动低的地区的结果方差都大,表明三种动物在有人类和家畜活动低的地区与在那些中等人类和家畜活动地区的分布相反的成群分布。三年中有蹄类动物遇见率的模式都相似,在调查期间有蹄类动物种群没有波动的趋势 相似文献
17.
Adaptive line transect sampling offers the potential of improved population density estimation efficiency over conventional line transect sampling when populations are spatially clustered. In adaptive sampling, survey effort is increased when areas of high animal density are located, thereby increasing the number of observations. Its disadvantage is that the survey effort required is not known in advance. We develop an adaptive line transect methodology that, by varying the degree of adaptation, allows total effort to be fixed at the design stage. Relative to conventional line transect surveys, it also provides better survey coverage in the event of disruption in survey effort, e.g., due to poor weather. In analysis, sightings from the adaptive sections are downweighted in proportion to the increase in effort. We evaluate the methodology by simulation and report on surveys of harbor porpoise in the Gulf of Maine, in which the approach was compared with conventional line transect sampling. 相似文献
18.
Zhensheng Liu Xiaoming Wang Liwei Teng Duoying Cui Xinqing Li 《Ecological Research》2008,23(2):393-400
The monitoring of animal populations is necessary to conserve and manage the rare or harvest species and to understand the population change over several years. We used distance sampling methods to estimate seasonal density of blue sheep in a 2,740 km2 area of Helan Mountain region by walking along 32 transect lines from winter 2003 to autumn 2005. In all, 367–780 blue sheep were observed in 91–143 groups in the surveys during the seasons. Observed mean group size ranged from 3.42 to 8.35 individuals; encounter rate, the number of groups detected per kilometre, varied from 0.19 to 0.30 during the seasons. A hazard rate key function with cosine series expansion and a half-normal key function with either cosine or simple polynomial series expansion were the best fitting models based on the lowest value of Akaike’s information criterion (AIC). Density estimates varied between 3.627 sheep per square kilometre in spring 2004 and 4.635 per square kilometre in summer 2005. There were no detectable differences in estimated density among seasons (P = 0.887). The estimated density of blue sheep was negatively correlated with the total number of deaths (P < 0.05), number of sub-adult males’ deaths (P < 0.05), number of sub-adult females’ deaths (P < 0.05), and number of male lambs’ deaths (P < 0.05). We concluded that distance sampling surveys should be used to monitor long-term population trends to provide the best quantitative estimates of blue sheep populations in the Helan Mountains region. 相似文献
19.
东海水域瓶鼻海豚种群数量和分布的初步研究 总被引：3，自引：2，他引：3
运用截线抽样法调查了北纬２５°～３０°,东经１２５°以西的东海水域中瓶鼻海豚在夏季７～９月间的种群密度和数量,得出的最小估计值分别为０．１４００头／ｋｍ２和９９４０头。瓶鼻海豚在该水域的分布特点为：随纬度增加（由南向北）密度逐渐减少,而在经度方向上则没有明显的密度变化规律。 相似文献
20.
D. R. Anderson K. P. Burnham B. R. Chain 《Biometrical journal. Biometrische Zeitschrift》1980,22(6):513-524
ANDERSON and POSPAHALA (1970) investigated the estimation of wildlife population size using the belt or line transect sampling method and devised a correction for bias, thus leading to an estimator with interesting characteristics. This work was given a uniform mathematical framework in BURNHAM and ANDERSON (1976). In this paper we show that the ANDERSON-POSPAHALA estimator is optimal in the sense of being the (unique) best linear unbiased estimator within the class of estimators which are linear combinations of cell frequencies, provided certain assumptions are met. 相似文献