哺乳类动物数量调查中的截线抽样法与逆向截线法

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。     

Feral donkey Equus asinus populations on the Karpaz peninsula, Cyprus

Numerous researchers have documented the adverse effects of feral donkeys Equus asinus introduced to semi-arid ecosystems. With the release of feral donkeys and potential increasing populations in natural habitats in northern Cyprus, there is concern for negative impacts on vegetation and native species. In the north of the island, there has been only one published study of feral donkey populations, and population estimators were relatively subjective. We estimated feral donkey populations on the Karpaz Peninsula using line transect surveys and quantitative distance sampling estimators. We stratified the sampling by using 11 sample units within the study area. We evaluated potential biases associated with habitat, topography, and perpendicular distance from the transect line and found that these variables did not bias donkey detections during our surveys. Using program DISTANCE, we found that a hazard rate cosine model was the best model that described our distance data based on model selection criterion (Akaikes Information Criteria adjusted for small sample bias). Estimated effective strip width was 280.19 m and detection probability was 0.47 with this model. Estimated donkey density was 6.7 donkeys/km², and estimated total abundance was 800 donkeys for the entire 132.5 km² study area. Of 95 donkey groups detected: 16% were detected in agricultural habitats with flat topography, 9% were detected in agricultural habitats with sloped topography, 24% were detected in shrub/forest habitats with flat topography, and 51% were detected in shrub/forest habitats with sloped topography. Of 102 behavioral observations recorded (multiple behaviors were detected in groups), frequencies of behaviors were 1% bedded, 70% standing, 22% grazing, 6% moving, and 2% other. Our estimated donkey population density in the Karpaz Peninsula was >2 times densities reported in arid regions of the United States and Australia, but slightly lower than earlier density estimates reported for the Karpaz region. These estimates of feral donkey populations in the Karpaz Peninsula provide a quantitative baseline from which to make population management decisions.     

Variance estimation for systematic designs in spatial surveys

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.     

Density and population size of mammals introduced on a land-bridge island in southeastern Brazil

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.     

关于使用样线法估计种群密度

样线法是在大范围内估计野生动物种群密度的优良方法这一。我们在本文中说明了使用以平均垂直距离作为有效样带宽度来计算种群密度的简单数学公式一般不会得到可靠的效果。即使野外实施方式正确,使用该数学计算式估计出的密度结果也往往过于偏高。因此,我们建议最好合作计算机软件DISTANCE调查野生动物种群密度,并能熟悉样线距离取样法的理论基础。     

First record of Alicia mirabilis (Anthozoa: Actiniaria) from the Aegean Sea and density assessment with distance sampling in a site of high abundance

The occurrence of the actiniarian Alicia mirabilis in the Aegean Sea is documented for the first time from five sites in the Saronikos Gulf. The density of A. mirabilis was assessed in one site (Lychnari bay) with line transects (underwater distance sampling with SCUBA). Its density ranged between 0 and 4.3 individuals are^-1 (1 are=100 m²) with a mean of 1.1±0.5 individuals are^-1. The species was found in a variety of substrates (sandy bottoms, weeds, seagrass beds, rocks, litter) and its distribution was aggregated. Distance sampling was an efficient way to estimate the density of A. mirabillis and is proposed as a good choice for density estimations of actiniarians and other benthic fauna.     

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

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     

Some comments on anderson and pospahala's correction of bias in line transect sampling

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.