应用红外相机监测结果估计小型啮齿类物种的种群密度

红外相机(或称相机陷阱)技术可以提供物种组成、种群数量和行为等信息,广泛应用于野生动物的监测与管理。对于可以个体识别的物种,红外相机结合标志重捕法可准确估计其种群密度。但对于不可个体识别的动物,目前尚无成熟方法来估计其种群密度。建立了一个新方法,通过模拟个体运动并匹配红外相机监测数据来估计动物的种群密度。在长白山国家级自然保护区25hm2森林动态监测样地中,以每公顷一台的密度布设红外相机,调查小型啮齿动物的种群数量。在2011年和2012年冬季分别监测41d和40d。然后,设计模型模拟不同密度下啮齿类物种的运动过程,同时记录它们在25hm2的区域内被25台相机拍摄的次数。应用随机森林算法建立回归模型来匹配模拟结果与监测结果,估计啮齿类物种在样地内的密度及其置信区间。这是一种全新的利用红外相机监测数据估计种群密度的方法,可以填补对不可个体识别物种密度估计方法的空缺。     

基于红外相机的不可个体识别动物种群密度估算方法

种群密度估计对野生动物的保护和管理至关重要,也是动物生态学和保护生物学备受关注的研究热点,但对大中型兽类种群数量的准确估算一直面临挑战。红外相机是哺乳动物调查中普遍采用的工具,也是克服这一挑战的一种经济有效的方法。目前国际上已有多种方法采用红外相机数据估算不可个体识别动物的种群密度,但相关技术在我国的应用案例较少,本文旨在为国内研究者应用红外相机数据估算动物种群密度提供参考。首先,我们介绍了随机相遇模型(randomencounter model, REM)、随机相遇与停留时间(random encounter and staying time, REST)模型、相机前停留时间(time in front of the camera,TIFC)模型以及红外相机距离取样(cameratrapdistancesampling,CTDS)这四种模型的基本原理和假设;其次,描述了这些模型在野外调查中的技术要点,并给出数据处理与分析的建议;最后,总结了每个模型的数据需求、优点和缺点。虽然我国目前拥有估算种群密度的大量红外相机数据源,但有很多物种的数量尚未知晓,也没有一种方法对所有红外相机数据都是...     

长爪沙鼠的肝毛细线虫感染率与鼠类及猛禽密度的关系

为研究鼠类密度和猛禽密度对鼠类肝毛细线虫(Capillaria hepatica)感染率的影响,作者于2004年7月在内蒙古锡林郭勒盟阿巴嘎旗北部和东乌珠穆沁旗西南部典型草原草场选取了14个实验样地,采用洞口计数法(四分之一圆面积法)调查估计各实验样地内长爪沙鼠(Meriones unguiculatus)密度,同时采用夹线调查法捕获鼠类样本,进行常规解剖获取肝毛细线虫的感染数据。采用目测计数法统计猛禽的出现频次,并以其出现频次作为猛禽的相对密度指标。实验样地共捕获长爪沙鼠1 058只,观察到鹰隼类活动69只次。数据分析结果表明,长爪沙鼠肝毛细线虫感染率与鼠类密度之间存在极显著的正相关关系(P0.01,R~2=0.926),长爪沙鼠肝毛细线虫感染率与猛禽密度之间亦存在极显著的正相关关系(P0.01,R~2=0.853)。该结果说明,长爪沙鼠是肝毛细线虫的主要宿主,鼠类密度和猛禽密度的升高均会增加长爪沙鼠肝毛细线虫感染率,猛禽密度和鼠类密度之间还存在叠加效应,猛禽的捕食作用会加快肝毛细线虫病的传播周期,加重肝毛细线虫病疫情。     

典型草原区鹰隼类密度对啮齿动物密度的数值响应

捕食者与猎物的关系是动物生态学研究的热点之一,捕食者应对猎物密度的变化往往呈现出特定的数值响应特征。为研究典型草原区鹰隼类对其猎物——啮齿动物密度变化的数值响应关系,于2005年7月在内蒙古自治区锡林郭勒盟阿巴嘎旗白音图嘎苏木选取15个实验样地,采用标准夹线法调查了啮齿类密度,同时采用目视方法调查了鹰隼类密度。本次实验共捕获鼠类2 675只,主要为布氏田鼠(Lasiopodomys brandtii),观察到鹰隼类活动450只次。回归分析结果表明,鼠类密度和鹰隼类密度的数值反应关系符合S型曲线,可用Gompertz方程W=22.765 e-3.735 e-0.078 t来拟合,拟合优度R2达0.984,表明鼠类密度对鹰隼类密度有显著影响,验证了Holling所提出的脊椎动物捕食者和猎物数量关系属于S型反应曲线的观点。从本文的结果看,鹰隼类数量对鼠类数量的反应可分为三个阶段:(1)平缓期,随着鼠类密度的逐渐增加,鹰隼类活动频次增长非常缓慢;(2)快速反应期,当鼠类密度达到5只/hm2时,鹰隼类活动频次随鼠类密度的增加迅速增长,期间出现一个增长拐点值;(3)稳定平台期,当鼠类的密度达到40只/hm2左右时,鼠类密度虽然继续增加,但鹰隼类活动频次保持稳定,不再增加。本研究可为草原鼠害的天敌控制方法提供参考。     

基于LULUCF温室气体清单编制的浙江省杉木林生物量换算因子

以杉木林为研究对象,在12个县市选取浙江省2009年CFI体系的95个杉木林样地,根据样地平均木,在样地外围相似地段确定解析木共计95株,联立树高曲线方程和生物量模型,同时使用已公开发表的20个杉木生物量模型进行估算,由单株累加获得CFI系统样地的生物量,计算样地生物量与蓄积之比即BEF,建立BEF与林分蓄积之间的关系.根据2009年浙江省CFI体系数据,推算全省杉木林BEF为0.7453t/m3,杉木林总生物量为3721.54万t,不确定性为5.739％;使用IPCC(1996)的碳密度缺省值(0.50)计,生长1 m3杉木吸收CO2 1.3663 t.     

亚热带地区马尾松林碳储量的遥感估算——以长汀河田盆地为例

全球气候的变化已使得人类日益关注森林生态系统的碳储量变化.以福建省长汀县河田盆地为例,开展马尾松林碳储量估算模型的研究.通过2010年的野外样地调查获得了马尾松林的实测数据,并将其与同年的ALOS遥感影像对应样地的植被光谱信息进行比较.通过研究5种遥感植被指数与马尾松林碳储量之间的相关关系,从中选取了基于归一化植被指数(NDVI)的研究区最佳马尾松林碳储量反演模型.精度分析表明,该模型平均相对误差为-1.95％,均方根误差为3.01 t/hm2,因此可以有效地用于反演研究区的马尾松林碳储量.利用该模型反演出河田盆地2010年马尾松林的总碳储量为114.58×104 t,碳密度为34.92 t./hm2.     

基于红外相机数据评估华南地区豹猫的种群密度和活动节律

可靠的种群密度数据对野生动物的保护和管理十分重要。豹猫(Prionailurus bengalensis)是中国分布最广且常见的猫科动物, 但野生种群密度估算的研究并不多。本研究于2020年6月至2021年5月在香港新界嘉道理农场暨植物园开展红外相机调查, 利用空间标记-重捕法估算当地豹猫的种群密度并用核密度估计方法分析其活动节律。本次调查以网格方式布置红外相机, 在约1.5 km²的研究范围之内设置了19个相机位点, 每个位点安装2台相机以获取豹猫身体两侧花纹来进行个体识别。连续12个月调查共捕获113次有效的豹猫拍摄事件, 当中仅61次事件的照片足够清晰以进行个体识别。基于种群封闭的要求, 我们以2个月为单位将12个月的数据分为6个采样期去分析豹猫种群密度, 结果显示仅两个采样期的估算值最为准确, 分别为0.64 ± 0.31 (0.26-1.55)只/km²和0.87 ± 0.48 (0.31-2.40)只/km², 是已知全球豹猫密度最高的地点之一。结果还发现, 雨季研究地点的豹猫并无明显的日活动节律, 在旱季则偏夜行-晨昏行性多一些, 但也有一定的日间活动; 雨季和旱季的日活动节律无显著差异。本研究是首次以个体识别配以空间标记-重捕模型对中国大陆地区豹猫种群密度调查的研究; 我们也提出一些关于红外相机架设方法的建议, 以提高照片个体识别的准确度并增加重捕次数, 最后提高密度估算的准确度。本研究也进一步证明豹猫适应性极强, 在活动节律上表现出极高的可塑性, 在严格保护下可以恢复健康的种群。     

试论赤尾噪鹛指名亚种的受胁程度

本文作者近期曾梳理赤尾噪鹛指名亚种(Garrulax milnei milnei)自戴维神父1874年命名以来的相关报道,揭示出该鸟近数十年来在野外的高稀缺性。为此,2015年3月至10月,江西武夷山国家级自然保护区对赤尾噪鹛指名亚种展开专项野外调查达20余次,并在保护区海拔1 700 m以上地带29个位点安放了57台红外触发相机,以期发现该鸟的现存证据。遗憾的是,无论是野外调查还是本次红外触发相机的照片/录像记录,并扩延至保护区自2009年10月以来300余台红外触发相机的全部记录,均未能发现或甄别出赤尾噪鹛指名亚种的存在。据此,作者提出赤尾噪鹛指名亚种当前的受胁程度当在极危(CR)与野外(功能性)灭绝(EW)之间。     

红外相机技术在陕西观音山自然保护区兽类监测研究中的应用

国外使用红外相机技术开展野生动物调查研究已有较长的历史,最早的报道见于Champion(1927),在20世纪90年代逐渐发展成熟,广泛用于动物种群数量和密度的研究.如应用红外相机和种群捕获模型(Capture-recapture)对印度Nagarahole国家公园的孟加拉虎(Panthera tigris)的种群数量和密度的研究(Karanth,1995;Karanth和Nichols;1998),验证了红外相机技术与种群捕获模型的结合在孟加拉虎种群预测方面的优势,有效解决了监测中孟加拉虎数量稀少、活动隐秘等问题.     

鼎湖山马尾松林群落生物量生产对人为干扰的响应

通过处理 (根据当地习惯收割凋落物和林下层 )和保护 (无任何人为干扰 )样地的比较 ,在 10 a时间里研究了鼎湖山生物圈保护区马尾松 (Pinus massoniana)林群落生物量生产对人为干扰的响应。 1990～ 1995年 ,由于人为干扰活动而直接从处理样地取走的有机质总量为 2 1.2 1t/hm2 。 1990～ 2 0 0 0年 ,保护样地林下层生物量以 34%～ 5 3%的年增长速率从 2 .2 3t/hm2 逐年提高 ,至 1995年达到高峰 (11.10 t/hm2 ) ,之后因与乔木层马尾松生长竞争原因而下降至 9.4 4 t/hm2 ;地表凋落物主要来源于林下层植物且地表凋落物量变化与林下层生物量变化相类似。在整个试验过程 ,尽管保护样地和处理样地乔木层马尾松个体总数均随时间而减少 ,但它们的总生物量则随时间而增加且其增加的速率随时间和样地不同而异。 1990～ 1995年 ,保护样地总生物量增加了 38.3% (从 81.2 t/hm2增至 112 .3t/hm2 ) ,较处理样地 (收获林下层和凋落物 )总生物量增加的百分比高 4 .7个百分点 (33.6 % ,从 98.8t/hm2增至 132 .0 t/hm2 )。然而 ,1995～ 2 0 0 0年 ,保护样地总生物量增加的百分比为 2 9.1% (从 112 .3t/hm2 增至 14 5 .0 t/hm2 ) ,较处理样地 (1995～ 2 0 0 0年也停止人为干扰 )增加的百分比却低 3.2个百分点 (32 .3% ,从 13     

Demystifying the Sundarban tiger: novel application of conventional population estimation methods in a unique ecosystem

Conserving large populations with unique adaptations is essential for minimizing extinction risks. Sundarban mangroves (>10,000 km²) are the only mangrove inhabited by tigers. Baseline information about this tiger population is lacking due to its man-eating reputation and logistic difficulties of sampling. Herein, we adapt photographic capture-mark-recapture (CMR) and distance sampling to estimate tiger and prey densities. We placed baited camera stations in a typical mangrove in 2010 and 2012. We used telemetry based tiger home-range radius (5.73 km, SE 0.72 km) to estimate effective trapping area (ETA). An effort of 407 and 1073 trap nights were exerted to photocapture 10 and 22 unique tigers in 2010 and 2012. We accounted for use of bait by modelling behaviour and heterogeneity effects in program MARK and secr package in program R. Using traditional CMR, tiger number was estimated at 11 (SE 2) and density at 4.07 (SE range 3.09–5.17) in 2010 while in 2012, tiger number was 24 (SE 3) and density 4.63 (SE range 3.92–5.40) tigers/100 km². With likelihood based spatially explicit CMR, tiger densities were estimated at 4.08 (SE 1.51) in 2010 and 5.81 (SE 1.24) tigers/100 km² in 2012. Using distance sampling along water channels, we estimated chital density at 5.24/km², SE 1.23 which could potentially support 4.68 tigers/100 km² [95 % CI (3.92, 5.57)]. Our estimates suggest that Sundarban tiger population is one of the largest in the world and therefore merits high conservation status.     

陆桥岛屿环境下社鼠种群数量的估算方法

根据2010年3月—11月在千岛湖地区2个岛屿上社鼠(Niviventer confucianus)的标志重捕数据,分别用Jolly-Seber法、修正Lincoln指数法、Schnabel法和MNA法计算两个岛屿上社鼠种群数量,并深入探讨在陆桥岛屿环境下估算社鼠种群数量的适用方法。研究结果显示,在满足Jolly-Seber法的条件下,通过该方法计算的结果与修正Lincoln指数法无显著差异。但在野外实验中,并不是所有的重捕数据都满足Jolly-Seber法的条件,而且该方法不能估算头尾两月的数量。因此,修正Lincoln指数法更适于估算陆桥岛屿环境下社鼠的种群数量。可为今后开展陆桥岛屿环境下鼠类种群生态学研究奠定基础。     

The effects of rearing density on growth,size heterogeneity and inter-individual variation of feed intake in monosex male Nile tilapia Oreochromis niloticus L.

The growth dispersion of farmed fish is a subject of increasing interest and one of the most important factors in stocking density. On a duration of 60 days, the effect of stocking density on the growth, coefficient of variation and inter-individual variation of feed intake (CV_FI) of juvenile Nile tilapia Oreochromis niloticus L. (14.9 ± 1.2 g) were studied in an experimental tank-based flow-through system. Groups of fish were stocked at four stocking densities: 200, 400, 600 and 800 fish/m³, corresponding to a density of ∼3, 6, 9 and 12 kg/m³ and referred to as D₁, D₂, D₃ and D₄, respectively. Each treatment was applied to triplicate groups in a completely randomized design. No treatment-related mortality was observed. The fish densities increased throughout the experiment from 3 to 23.5, 6 to 43.6, 9 to 56.6 and 12 to 69 kg/m³. Results show that mass gain and specific growth rate (SGR, %M/day) were negatively correlated with increased stocking density. Groups of the D₁ treatment reached a mean final body mass (FBM) of 119.3 g v. 88.9 g for the D₄ groups. Feed conversion ratios (FCRs) were 1.38, 1.54, 1.62 and 1.91 at D₁, D₂, D₃ and D₄ treatments, respectively. Growth heterogeneity, expressed by the inter-individual variations of fish mass (CV_M), was significantly affected by time (P < 0.001), stocking density (P < 0.001) and their interaction (P < 0.05). The difference in CV_M was particularly conspicuous towards the end of the experiment and was positively correlated with stocking density. Similarly, radiographic study shows that CV_FI was also found to be significantly greater for groups reared at high stocking densities (D₃ and D₄) than the other treatments (D₁ and D₂). These differences in both CV_M and CV_FI related to the stocking density need to be taken into account by husbandry practices to assure the production of more homogeneous fish size. A simple economic analysis indicates a parabolic relationship between profit and density with optimal final density at the peak of the curve. Given reasonable assumptions about production costs, the optimal final density (D_opt) is 73.7 kg/m³. A sensitivity analysis shows that changes in the fixed cost have no effects on the optimal final density. However, small change in variable costs, such as feed and juvenile costs, may have substantial effect on the optimal density.     

Edge Effect on Density Estimates of a Radiotracked Population of Yellow-Necked Mice

ABSTRACT Density estimates for small-mammal populations from capture-mark-recapture (CMR) data have played an important role in many studies of theoretical and applied ecology. Defining effective trapping area (ETA) is one of the main issues affecting accuracy of density estimates. Our objective was to assess sensitivity of CMR density estimates to correctors based on movement parameters calculated from trapping and radiotelemetry data. From May to November 2005, we conducted monthly CMR trapping in a beech (Fagus sylvaticus) forest of the province of Trento, northern Italy. In conjunction with CMR, we radio-marked 32 yellow-necked mice (Apodemus flavicollis) captured from July to October and located them daily using radiotelemetry. We estimated population size (N) by model averaging with Program MARK. We calculated ETA using several definitions of the boundary strip, including full and half mean maximum distance moved (MMDM) from capture-recapture and telemetry data and mean radius of mean monthly home ranges. The boundary strip (W) increased with the amount of behavioral information embodied in the estimates. The largest W and lowest density values were based on radius of mean home ranges followed by MMDM calculated from telemetry data. The ETA based on movement distances increased more than proportionally when N decreased, suggesting that low population density combined with scarce resources results in rodents moving more in search of food, thus leading to overestimated ETA and underestimated density values. Although robust behavioral information would certainly improve density estimates, we suggest caution in relating ranging movements to capture probability and hence in using correctors based on movement distances to infer density values.     

The Lyme Disease Pathogen Has No Effect on the Survival of Its Rodent Reservoir Host

Zoonotic pathogens that cause devastating morbidity and mortality in humans may be relatively harmless in their natural reservoir hosts. The tick-borne bacterium Borrelia burgdorferi causes Lyme disease in humans but few studies have investigated whether this pathogen reduces the fitness of its reservoir hosts under natural conditions. We analyzed four years of capture-mark-recapture (CMR) data on a population of white-footed mice, Peromyscus leucopus, to test whether B. burgdorferi and its tick vector affect the survival of this important reservoir host. We used a multi-state CMR approach to model mouse survival and mouse infection rates as a function of a variety of ecologically relevant explanatory factors. We found no effect of B. burgdorferi infection or tick burden on the survival of P. leucopus. Our estimates of the probability of infection varied by an order of magnitude (0.051 to 0.535) and were consistent with our understanding of Lyme disease in the Northeastern United States. B. burgdorferi establishes a chronic avirulent infection in their rodent reservoir hosts because this pathogen depends on rodent mobility to achieve transmission to its sedentary tick vector. The estimates of B. burgdorferi infection risk will facilitate future theoretical studies on the epidemiology of Lyme disease.     

Image analysis of the leaf vascular network: physiological considerations

The study of leaf vascular systems is important in order to understand the fluid dynamics of water movement in leaves. Recent studies have shown how these systems can be involved in the performance of photosynthesis, which is linked to the density of the vascular network per unit of leaf area. The aim of the present study was to highlight the correlation between a leaf vein density (V_D) and net photosynthetic rate (P_N), which was undertaken using a digital camera, a stereoscopic microscope, and a light source. The proposed hypothesis was tested, for the first time, on the leaves of two cultivars of Vitis vinifera (L.). A significant difference was found between the V_D of mature leaves of the two cultivars. V_D was also significantly correlated with the maximum leaf P_N. These findings support the hypothesis that the vascular system of grape leaves can be correlated with leaf photosynthesis performance.     

Theoretical investigations on the structure, density, thermodynamic and performance properties of amino-, methyl-, nitroso- and nitrotriazolones

We have studied herein the effect of position and the number of -NO, -NO₂, -NH₂ and -CH₃ groups on the structure, stability, impact sensitivity, density, thermodynamic and detonation properties of triazolones by performing density functional theory calculations at the B3LYP/aug-cc-pVDZ level. The optimized structures, vibrational frequencies and thermodynamic values for triazolones have been obtained in their ground state. Kamlet-Jacob equations were used to calculate the detonation velocity and detonation pressure of model compounds. The detonation properties of NNTO (D 8.75 to 9.10 km/s, P 34.0 to 37.57 GPa), DNTO (D 8.80 to 9.05 km/s, P 35.55 to 38.27 GPa), ADNTO (D 9.01 to 9.42 km/s and P 37.81 to 41.10 GPa) and ANNTO (D 8.58 to 9.0 km/s, P 30.81 to 36.25 GPa) are compared with those of 1,3,5-trinitro-1,3,5-triazine (RDX) (D 8.75 km/s, P 34.70 Gpa) and octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) (D 8.96 km/s, P 35.96 GPa). The designed compounds satisfy the criteria of high energy materials.     

The effect of translocation on movement behaviour—A test of the assumptions of behavioural studies

Animal movement behaviour is intensively investigated with capture-mark-recapture studies. For the analysis of such experiments, the influence of marking technique, handling and translocation of marked animals on movement pattern is of crucial importance since it may mask or overrule the effects of the main research question. Here we present a capture-mark-recapture experiment on the movement behaviour of the blue-winged grasshopper Oedipoda caerulescens. We analyzed the influence of translocation of individuals from familiar to unfamiliar sites. Our study clearly demonstrates a significant influence of translocation to unfamiliar sites on the movement behaviour of O. caerulescens. Translocated individuals moved longer distances, showed smaller daily turning angles, and thus movements were more directed than those of resident individuals. The effect of translocation on daily moved distances was most pronounced on the first day of the experiment. We thus conclude that at least for the first day after translocation, movement behaviour is significantly influenced by translocation itself. Data ignoring this influence will be unsuitable for the prediction of dispersal behaviour, habitat detection capability or habitat preference.     

Mate-Searching Behaviour of Common and Rare Wasps and the Implications for Pollen Movement of the Sexually Deceptive Orchids They Pollinate

Pollinator behaviour directly affects patterns of pollen movement and outcrossing rates in plants. In orchids pollinated by sexual deception of insects, patterns of pollen movement are primarily determined by the mate-searching behaviour of the deceived males. Here, using a capture-mark-recapture study (CMR) and dietary analysis, we compare mate-searching behaviour in relation to local abundance of two pollinator species and explore the implications for pollen movement in sexually deceptive Drakaea (Orchidaceae). Drakaea are pollinated solely by the sexual deception of male thynnine wasps. The rare Drakaea elastica and widespread D. livida occur sympatrically and are pollinated by the rare but locally common Zaspilothynnus gilesi, and the widespread and abundant Z. nigripes, respectively. Local abundance was significantly different with Z. nigripes twice as abundant as Z. gilesi. For the 653 marked wasps, there was no significant difference in median movement distance between Z. gilesi and Z. nigripes. However, the maximum movement distance was twice as high for Z. gilesi (556 m) compared with Z. nigripes (267 m). This is up to three times greater than previously reported for thynnines in CMR studies. Recapture rates were six times higher in Z. gilesi (57%) compared to Z. nigripes (9%). Pollen loads and wasp longevity were similar, suggesting that this difference in recapture rate arises due to differences in the number of males moving at a scale >500 m rather than through diet or mortality. Differences in the frequency of longer movements may arise due to variation in the spatial distribution of the wingless females. We predict that pollen movement will largely be restricted to within populations of Drakaea (<500 m), with few movements between populations (>500 m).     

The use of non-standard CT conversion ramps for Monte Carlo verification of 6 MV prostate IMRT plans

Monte Carlo (MC) dose calculation algorithms have been widely used to verify the accuracy of intensity-modulated radiotherapy (IMRT) dose distributions computed by conventional algorithms due to the ability to precisely account for the effects of tissue inhomogeneities and multileaf collimator characteristics. Both algorithms present, however, a particular difference in terms of dose calculation and report. Whereas dose from conventional methods is traditionally computed and reported as the water-equivalent dose (D_w), MC dose algorithms calculate and report dose to medium (D_m). In order to compare consistently both methods, the conversion of MC D_m into D_w is therefore necessary.This study aims to assess the effect of applying the conversion of MC-based D_m distributions to D_w for prostate IMRT plans generated for 6 MV photon beams. MC phantoms were created from the patient CT images using three different ramps to convert CT numbers into material and mass density: a conventional four material ramp (CTCREATE) and two simplified CT conversion ramps: (1) air and water with variable densities and (2) air and water with unit density. MC simulations were performed using the BEAMnrc code for the treatment head simulation and the DOSXYZnrc code for the patient dose calculation. The conversion of D_m to D_w by scaling with the stopping power ratios of water to medium was also performed in a post-MC calculation process.The comparison of MC dose distributions calculated in conventional and simplified (water with variable densities) phantoms showed that the effect of material composition on dose-volume histograms (DVH) was less than 1% for soft tissue and about 2.5% near and inside bone structures. The effect of material density on DVH was less than 1% for all tissues through the comparison of MC distributions performed in the two simplified phantoms considering water. Additionally, MC dose distributions were compared with the predictions from an Eclipse treatment planning system (TPS), which employed a pencil beam convolution (PBC) algorithm with Modified Batho Power Law heterogeneity correction. Eclipse PBC and MC calculations (conventional and simplified phantoms) agreed well (<1%) for soft tissues. For femoral heads, differences up to 3% were observed between the DVH for Eclipse PBC and MC calculated in conventional phantoms. The use of the CT conversion ramp of water with variable densities for MC simulations showed no dose discrepancies (0.5%) with the PBC algorithm. Moreover, converting D_m to D_w using mass stopping power ratios resulted in a significant shift (up to 6%) in the DVH for the femoral heads compared to the Eclipse PBC one.Our results show that, for prostate IMRT plans delivered with 6 MV photon beams, no conversion of MC dose from medium to water using stopping power ratio is needed. In contrast, MC dose calculations using water with variable density may be a simple way to solve the problem found using the dose conversion method based on the stopping power ratio.