黑龙江省完达山东部林区马鹿种群遗传多样性的微卫星分析

黑龙江省完达山东部林区是东北马鹿(Cervus elaphus xanthopygus)种群密度较高的分布区之一,本文对2年冬季采集的167份马鹿粪便进行了7个微卫星座位的个体识别,评价了马鹿种群遗传多样性,并分析近期马鹿数量的急剧下降对种群遗传结构的影响。结果表明:167份粪便DNA分属66只个体;种群平均等位基因数9.00±2.77;平均有效等位基因数3.97±0.99;平均多态信息含量0.69±0.09;平均期望杂合度0.74±0.08;平均观察杂合度0.69±0.08。整个种群显著偏离Hardy-Weinberg平衡,但种群固定系数Fis为0.060,没有显著偏离零。可见,完达山东部林区马鹿种群遗传多样性较高,数量的急剧下降近期还没有表现在种群遗传结构上。     

景观破碎化对东北虎主要猎物种群动态影响的模拟

以完达山东部地区的现实景观为背景,采用空间直观种群模型LAPS和情景模拟相结合的"虚拟实验"途径,模拟了在10个不同破碎化程度的景观情景中东北虎的主要猎物于1992-2011年间的种群动态,评价了完达山东部地区当前的景观破碎化程度对东北虎主要猎物种群动态的影响。结果表明:LAPS模型准确刻画了研究区东北虎主要猎物种群数量急剧下降的趋势,2002年模拟的东北虎主要猎物的种群数量和实测值之间没有显著差异,马鹿、野猪和狍子的P值分别为0.8651、0.9534和0.2836;不同生境类型的种群密度数据与实测值之间均没有显著差异,其中阔叶林生境中的马鹿、野猪和狍子的P值分别为0.8521、0.9447和0.3152;在灌丛生境中的马鹿、野猪和狍子的P值分别为0.8846、0.9576和0.2415。斑块类型和景观水平上的格局指标变化趋势表明由于农田扩张导致10个景观情景的破碎化程度逐渐增加,景观水平的破碎化程度低于斑块类型水平。方差分析显示10个景观情景中的种群数量没有显著差异,马鹿、野猪和狍子的P值分别为0.8516、0.2624和0.7636,说明研究区当前的景观破碎化程度对种群动态影响并不显著。完达山东部地区存在盗猎等人为干扰,导致了东北虎主要猎物的数量远低于环境容纳量,景观破碎化虽然在局部地区较为严重,但完达山东部地区整体上景观破碎化并不强烈,该地区景观破碎化的效应尚未显现。认为控制盗猎等人为干扰是增加该地区东北虎主要猎物的数量、实现东北虎种群恢复所应优先采取的措施。     

黑龙江省完达山东部林区东北虎猎物生物量

研究一个地区猎物种群生物量能否满足捕食动物种群数量的需求,这对于了解濒危大型食肉动物是否受到来自于食物缺乏的威胁和制定相应的保护措施极其重要。为了掌握黑龙江省完达山东部林区东北虎食物需求与猎物生物量之间的关系,于2008年冬季至2009早春积雪覆盖期采用随机布设样线,通过收集有蹄类动物在雪地上留下的足迹等活动的方法,在东方红林业局和迎春林业局管辖境内3 692.06 km²的区域布设大样方48个,并在大样方里共布设样线240条开展有蹄类动物种群数量调查,确定东北虎猎物生物量。调查结果表明:研究地区野猪(成体502 606只,亚成体209 210只)、马鹿(成体331 357只,亚成体67 72只)和狍子(成体810 815只,亚成体202 203只)的生物量分别为74 767.50 87 825.00 kg、79 744.50 85 984.50 kg 和 31 337.00 31 525.50 kg,3种有蹄类动物生物量共计1 85 849.00 205 335.00 kg。研究地区猎物总生物量为209 619.89 231 598.24 kg。如果按8%的生物提供给东北虎,3种主要猎物生物量可满足5.22 6.92只东北虎个体的食物需求,研究地区猎物总生物量则可满足5.89 7.81只东北虎个体的食物需求。此外,对足迹遇见率与抽样强度、抽样强度与足迹遇见率的均值标准误差之间关系的分析表明,在完达山东部林区布设120条样线(抽样距离600 km)、150条样线(抽样距离750 km)和115条样线(抽样距离675 km)能满足野猪、马鹿、狍子种群数量调查准确性的最低需求。     

黑龙江凤凰山国家级自然保护区野猪冬季容纳量及最适种群密度

近年黑龙江省凤凰山国家级自然保护区野猪数量不断增长,人猪冲突加剧,保护区资源保护管理工作面临较大管理压力.为确定野猪种群的实际数量,同时评估该保护区的野猪的容纳量水平,以便为保护区管理局针对野猪的管理提供相关指导意见.2009-2010年冬季,在保护区采用样带调查、雪地足迹链跟踪和观察食痕的方法,并结合已有野猪生态研究确定野猪食性.野猪主要食物种类包括:木贼(Equisetum hiemale)、红松(Pinus koraiensis)果实松籽、胡桃楸(Juglans mandshurica)果实核桃、蒙古栎(Quecusmongolica)果实橡子、稠李(Padus racemosa)、榛子(Corylus heterophlla)、苔草(Carex spp.)、辽东葱木(Aralia elata).研究期间共布设长3-5km、单侧宽度50m、总长134 km的样带30条.调查中,每隔200 m布设10 m×10 m的大样方,并在每个大样方中央及四角布设1 m×1 m的小样方,共布设大样方350个,小样方1 750个.通过样方调查,统计野猪栖息生境当年可食植物枝条及其食物种类,然后计算其食物的总供给量,再结合食物营养成分,通过粗蛋白、粗纤维、粗脂肪的能量转换,按照每克粗蛋白和粗纤维的能量转换系数为16.74kJ、每克粗脂肪的能量转换系数为37.66 kJ,确定野外生境食物总能量供给.结合野猪冬季日营养需求,以能量为基础估算保护区野猪的营养容纳量.在种群密度调查过程中,通过足迹链判断个体方法为:单一清晰足迹链确定为一个体所留,30m内多条足迹穿越同一样带被认为是一个野猪群所留,调查中根据个体分开时的足迹链数确定野猪个体数,同时将粪便、卧迹、啃食痕迹作为个体判断的辅助信息.研究结果表明:凤凰山保护区内能够提供的总能量为7.375 ×107MJ,冬季平均每头野猪生存所需能量为(14 677.698±409.92) MJ,野猪营养容纳量为(1 006±28)头,种群密度为(3.79±0.11)头/km2.此外,调查中发现30余个野猪套及2头野猪被猎杀现场,反应出当地的人猪冲突较为严重.结合调查中发现的野猪套数量及野猪被猎杀概率,对野猪种群数量引入20％的死亡风险系数.最终确定凤凰山野猪种群的最适数量在(603±17)头左右,最适密度为(2.27±0.06)头/km2.通过样带法调查得出凤凰山自然保护区实际野猪种群数量为(596±155)头,密度(2.24±0.58)头/km2,已趋近营养容纳量.因此,野猪并未过量,不能采取狩猎等降低种群数量的措施,同时保护区也应对野猪种群进行持续监控,防止野猪种群过度繁殖以至成灾.     

张广才岭南部东北虎猎物种群冬季营养容纳量研究

猎物匮乏是影响东北虎（Panthera tigris altaica）种群恢复的关键因素之一。容纳量研究是开展东北虎猎物恢复工作的必要前提。通过Maxent模型、聚类分析和训练随机树分类等方法,结合调查数据,预测了吉林省张广才岭南部黄泥河林业局东北虎主要猎物的适宜栖息地空间分布,解译了植被类型,在此基础上基于不同植被类型动物可采食部分代谢能、不同生境等级食物可利用率、马鹿（Cervus elaphus）和狍（Capreolus capreolus）生境等级重叠情况以及动物冬季能量需求,分析了东北虎猎物的冬季营养容纳量。结果表明：黄泥河林业局狍、野猪（Sus scrofa）和马鹿的适宜栖息地分别占研究区域总面积的52.8%、40.7%和25.4%;从猎物获取能量来看,以山杨（Populus davidiana）、桦树（Betula）、核桃楸（Juglans mandshurica）为主的植被类型是马鹿、狍可获得能量较多的生境,以蒙古栎（Quercus mongolica）、核桃楸为主的植被类型是野猪可获得能量较多的生境。东北虎猎物种群的综合冬季营养容纳量为574只马鹿（0.29只/km²）,7016只狍（3.54只/km²）,4785只野猪（2.38只/km²）。     

黑龙江省老爷岭南部穆棱林区马鹿种群分布数量及生境适宜性评价

开展野生动物种群分布数量和生境适宜性评价研究是制定物种科学保护决策的基础和关键。以东北马鹿(Cervus canadensis xanthopygus)为研究对象,于2015—2020年在黑龙江省老爷岭南部穆棱林区,采用大样方调查方法收集马鹿在雪地留下的足迹信息分析马鹿种群数量;通过相机监测、足迹链跟踪和大样方调查3种方法综合收集马鹿活动点信息,利用最大熵(MaxEnt)建模分析马鹿生境适宜性。马鹿种群分布数量研究结果表明,穆棱林区马鹿种群密度为(0.0645±0.009)只/km~2,种群数量为47—61只,主要分布在研究地区南部的和平、龙爪沟和共和林场。生境分析结果表明：人为干扰因子中,居民区对MaxEnt模型的贡献率为44%,马鹿主要在距居民区距离约5 km和10—15 km的区域活动,在偏僻的林间小道和乡村道路马鹿生境适宜性较高,其对模型贡献率分别为16.8%和10.2%;植被因子中,在距常绿针叶林和针阔混交林距离4 km范围内,随距离增加马鹿生境适宜性逐渐降低。生境适宜性分析结果表明,研究地区马鹿适宜生境和次适宜生境面积为87.09 km~2,仅占研究区域的10.39%,主要...     

基于生境可获得性的完达山地区马鹿(Cervus elaphus xanthopygus)冬季生境选择

于2004～2005年冬季研究了完达山地区马鹿的生境利用和选择。在野外调查的基础上,获取了研究地区马鹿种群水平上的生境利用数据;利用地理信息系统和遥感技术,从区域尺度上测度了各类生境因子的可获得性。通过比较被利用生境与可获得生境,测度了马鹿冬季对各类生境或生态因子的选择。结果表明,马鹿对植被类型、海拔、坡向、NDVI等级、到公路距离表现出非比例利用,对坡度的利用与其可获得性则没有显著性差异。马鹿选择采伐迹地,低郁闭度生境（第2、3NDVI等级）,200～300m海拔区间,南坡,距离公路600～700m的区间。马鹿采食生境和卧息生境对各类因子具有不同的选择性,表现出不同功能生境分离的特征。对于采食生境,马鹿选择采伐迹地、阔叶疏林,低郁闭度（第2、3NDVI等级）,南坡;对于卧息生境,马鹿仅选择采伐迹地,低郁闭度（第2、3、4NDVI等级）。根据马鹿活动样点的出现与否,建立了马鹿冬季生境选择的逻辑斯谛回归模型。模型回判结果表明,该模型对马鹿活动样方与对照样方的总体正确预测率为74．4％,对马鹿活动样方的正确预测率为84．2％,对对照样方的正确预测率为62．4％,能够较好的预测生境利用概率。     

内蒙古森林—草原交错带中野生东北马鹿冬季食物组成模式

分布于内蒙古森林—草原交错带的东北马鹿(Cervus elaphus xanthopygus)种群,受冬季低温和雪被的影响,对营养和能量的需求发生变化,同时,交错带内植物区系复杂,草本植物覆盖率高,而野生东北马鹿冬季主要以木本植物的嫩枝为食,因此分布于该地区的野生东北马鹿种群将面临食物资源短缺、营养缺乏的潜在威胁。本研究于2019年和2020年冬季,在内蒙古高格斯台罕乌拉国家级自然保护区内,采集野生东北马鹿粪便样本共98份。采用粪便显微分析法了解内蒙古森林—草原交错带中东北马鹿冬季的食物组成,结合去趋势分析法揭示了东北马鹿冬季食物组成模式。对东北马鹿粪便残渣分析发现,东北马鹿冬季共采食22种(科)植物,其中2020年冬季发现东北马鹿大量采食云杉(Picea asperata,9.88%)为其新食物。对东北马鹿食物组成进行去趋势分析发现,两年冬季中多数东北马鹿呈现出以蒙古栎(Quercus mongolica)、山杏(Armeniaca sibirica)、细叶沼柳(Salix rosmarin? ifolia)和家榆(Ulmus pumila)等落叶乔木和灌木为主要食物,同时采食高比例禾本科(Poaceae spp.)植物的食物组成模式;少数个体因食物短缺而呈现出以云杉为主要食物的特殊组成模式。禾本科和云杉是引起东北马鹿冬季食物组成变化的主因。本研究揭示了内蒙古森林—草原交错带中东北马鹿冬季的食物组成模式,为该地区东北马鹿营养生态学的进一步研究与保护管理提供参考依据。     

穆棱林区野生东北马鹿种群冬季食物组成模式与植物代谢产物的关系

高纬度地带,在冬季食物资源有限的环境中,野生大型有蹄类动物满足营养需求的同时,需要对植物中次生代谢产物进行平衡,回避有害物质并选择对机体有益的成分,从而形成特定的食物组成模式。以东北马鹿（Cervus elaphus xanthopygus）为研究对象,于2020年11月,在黑龙江穆棱东北红豆杉国家级自然保护区境内,采集东北马鹿粪便和植物样本。通过粪便显微分析法确定保护区内马鹿冬季食物组成,采用k-means聚类分析揭示马鹿冬季食物组成模式。应用广泛靶向代谢组技术对部分植物中次生代谢产物的含量进行全覆盖定性和相对定量检测,将食物组成与次生代谢产物数据整合,进行曼特尔检验（Mantel test）分析,以探究植物次生代谢产物对马鹿种群内食物组成模式的影响。结果表明,林区内马鹿种群冬季共采食30种植物,其中木本植物占92.48%;且种群内分别呈现出以东北红豆杉（Taxus cuspidata）,簇毛槭（Acer barbinerve）,毛榛子（Corylus mandshurica）为主要食物的不同食物组成模式。广泛靶向代谢组技术共检测出638种次生代谢产物,有25种代谢物与马鹿采食频率显著相关,其中多数萜类物质抑制马鹿采食,而鞣质类物质对马鹿的采食选择有一定的正向作用;Mantel test结果显示,上述25种物质中黄酮、鞣质、萜类化合物相对含量与不同马鹿个体食物组成显著相关,说明这些代谢物相对含量和性质的差异会造成种群内不同个体食物组成的差异,是种群内形成不同食物组成模式的原因之一。从植物次生代谢产物角度揭示了该地区东北马鹿种群冬季食物组成模式呈现差异的可能因素,为进一步研究大型有蹄类营养策略和植物化学防御关系提供基础依据。     

小兴安岭南麓马鹿冬季适宜生境评价

通过2014-2015年两次冬季野外调查, 将收集的79处马鹿(Cervus elaphus)出现信息作为分布点数据, 选取地形、景观类型、植被特征和人类干扰4类19种因子作为环境变量, 利用最大熵(maximum entropy, MaxEnt)模型, 分析了小兴安岭铁力林业局辖区马鹿种群冬季潜在适宜生境分布特征和主要环境因子对马鹿分布的影响。结果显示: 模型预测精度较高, 训练集与验证集的平均AUC(area under the curve, 受试工作者曲线下面积)值分别为0.949和0.958; Jackknife检验结果表明: 景观类型因子对马鹿生境选择的影响较大; 坡向、距大路距离、距混交林距离、距灌草地距离和距农田距离是影响马鹿生境分布的主要环境因子, 其综合贡献值依次为27.8%、23.9%、19.5%、15.3%和10.4%; 距小路距离对马鹿分布影响较小。我们依据MaxEnt模型最大约登指数, 找到最佳中断点0.22作为阈值将马鹿冬季栖息地划分为适宜和不适宜两个等级, 其面积分别为663.49 km²和1,378.85 km², 分别占研究区总面积的32%和68%。马鹿的适宜生境主要分布在铁力林业局辖区的东部山地和中部林地等区域; 南部地区接近铁力市区, 人类活动频繁, 不适宜马鹿栖息。对马鹿种群的保护管理措施提出3点建议: 控制人为干扰; 构建多样性景观; 优先保护马鹿的潜在适宜生境分布区。     

基于粪便DNA的马鹿种群数量和性比

为分析黑龙江省完达山林区马鹿种群生存状态,制定科学有效地保护措施,从分子水平研究了种群数量和性比。2006、2007两年冬季跟踪马鹿足迹链,于五泡林场共搜集210份粪便,以成功提取DNA的167份作为分析样本。通过多态性较高的7个微卫星位点进行了基因分型分析,显示167份粪便DNA分属66只个体。基于非损伤性标志重捕法,统计出林场内马鹿数量2a平均47(39—60)只,密度0.302(0.251—0.386)只/km2,与2002年大样方法调查结果相比有减无增。SRY基因性别鉴定显示,种群雌雄性比1.00∶2.00(22♀,44♂),存在较多雄性个体,分析认为偷猎是导致性比失衡的最主要原因。数量的持续下降和性比失衡提示完达山林区马鹿种群数量的恢复需要更好地保护工作。     

In vitro digestibility of seasonal forages used by wapiti and roe deer in northeastern China

Seasonal changes in in vitro dry matter digestibility (IVDMD) of five forage classes (browses, sedges, forbs. ferns and the bark of Ulmus spp.) used by wapiti and roe deer were determined in relation to chemical composition, using the two-stage technique of in vitro trial with rumen inocula from one wapiti and one roe deer captured in winter. Wapiti and roe deer showed remarkable fluctuation in IVDMD among seasons and forage classes. IVDMD decreased from 43.8-64.3% in spring to 29.4-40.5% in winter for wapiti, and from 52.4-77.4% in spring to 25.9-36.5% in winter for roe deer. There was significant variation in IVDMD among species of browses for wapiti and roe deer. IVDMD ranged from 28.5% to 58.7% in twigs and from 39.8% to 58.2% in leaves for wapiti, and from 24.1% to 67.7% in twigs and from 40.0% to 71.7% in leaves for roe deer. Roe deer had higher IVDMD (40.0-71.7%) in both leaves and twigs of browses than wapiti (35.9-58.7%) during snow-free seasons, but IVDMD of twigs was lower for roc deer (25.9-36.5%) than wapiti (29.4-38.4%) in winter. Significant multiple correlation was found between NDF and ADF, and IVDMD in sedges, forbs and ferns for both wapiti and roe deer, whereas only roe deer showed the significant multiple correlation for leaves of browses.     

Determination of Foraging Thresholds and Effects of Application on Energetic Carrying Capacity for Waterfowl

Energetic carrying capacity of habitats for wildlife is a fundamental concept used to better understand population ecology and prioritize conservation efforts. However, carrying capacity can be difficult to estimate accurately and simplified models often depend on many assumptions and few estimated parameters. We demonstrate the complex nature of parameterizing energetic carrying capacity models and use an experimental approach to describe a necessary parameter, a foraging threshold (i.e., density of food at which animals no longer can efficiently forage and acquire energy), for a guild of migratory birds. We created foraging patches with different fixed prey densities and monitored the numerical and behavioral responses of waterfowl (Anatidae) and depletion of foods during winter. Dabbling ducks (Anatini) fed extensively in plots and all initial densities of supplemented seed were rapidly reduced to 10 kg/ha and other natural seeds and tubers combined to 170 kg/ha, despite different starting densities. However, ducks did not abandon or stop foraging in wetlands when seed reduction ceased approximately two weeks into the winter-long experiment nor did they consistently distribute according to ideal-free predictions during this period. Dabbling duck use of experimental plots was not related to initial seed density, and residual seed and tuber densities varied among plant taxa and wetlands but not plots. Herein, we reached several conclusions: 1) foraging effort and numerical responses of dabbling ducks in winter were likely influenced by factors other than total food densities (e.g., predation risk, opportunity costs, forager condition), 2) foraging thresholds may vary among foraging locations, and 3) the numerical response of dabbling ducks may be an inconsistent predictor of habitat quality relative to seed and tuber density. We describe implications on habitat conservation objectives of using different foraging thresholds in energetic carrying capacity models and suggest scientists reevaluate assumptions of these models used to guide habitat conservation.     

Nutritional estimate of populations of some wild free-ranging African ungulates in grassland (Nechisar national park, Ethiopia) in dry season

The amount and nutritive value of forage plants, diet composition, digestibility of dry matter and nutrients were recorded for zebra. Grant's gazelle, Swayne's hartebeest and hippopotamus in November-December 1991 Besides, daily egest of feces, the level of food and nutrient consumption, energy and protein requirements were recorded for zebra and Grant's gazelle The digestibility of pasture forage was determined as a ratio of lignin concentration in food to the concentration m feces (lignin tracer technique), a daily intake was calculated on the basis of the daily feces egest Protein percentage m the diet of zebra and hartebeest consuming dry parts of grasses did not exceed 5% Gazelle diet consists of green parts of plants and included 18% of protein The digestibility of dry matter in nonruminants (zebra, hippopotamus) was 40-45%, in hartebeest - 50%, in gazelle - 60% Due to the abundance of dry grasses (3 7 ton ha^-1) the daily food consumption of zebra was high - 7 2 kg ind^-1 (dry weight), the metabolizable energy intake (ME) being 51 MJ Adult gazelles consumed 15-25 kg ind^-1 of food and 14-24 MJ of ME The energy requirements of adult males and non-lactating females of zebras and gazelles (48 and 13 MJ respectively) were met, the energy balance berig negative for lactating animals The daily protein requirement was not met in zebra (392-704 g md^-1 vs 134 g ind^-1 of intake) and in lactating gazelles (250 g ind^-1 vs 197 g md^-1) Non-lactating gazelles consume sufficient amount of both energy and protein due to the high feeding selectivity of the species and thanks to the abundance of burnt areas with young green after-grass m the dry period     

Diets of giants: the nutritional value of sauropod diet during the Mesozoic

A major uncertainty in estimating energy budgets and population densities of extinct animals is the carrying capacity of their ecosystems, constrained by net primary productivity (NPP) and its digestible energy content. The hypothesis that increases in NPP due to elevated atmospheric CO₂ contributed to the unparalleled size of the sauropods has recently been rejected, based on modern studies on herbivorous insects that imply a general, negative correlation of diet quality and increasing CO₂. However, the nutritional value of plants grown under elevated CO₂ levels might be very different for vertebrate megaherbivores than for insects. Here we show plant species‐specific responses in metabolizable energy and nitrogen content, equivalent to a two‐fold variation in daily food intake estimates for a typical sauropod, for dinosaur food plant analogues grown under CO₂ concentrations spanning estimates for Mesozoic atmospheric concentrations. Our results potentially rebut the hypothesis that constraints on sauropod diet quality were driven by Mesozoic CO₂ concentration.     

Effects of human disturbance on movement,foraging and bed selection in red deer<Emphasis Type="Italic">Cervus elaphus xanthopygus</Emphasis> from the Wandashan Mountains,northeastern China

We characterized 716 sites (including 22 beds, 60 foraging and 604 movement sites) used by red deerCervus elaphus xanthopygus Milne-Edwards, 1867 in the Wandashan Mountains, northeastern China in the winter period. We used covariates for vegetation, topography, disturbances by other ungulates, and disturbance by humans to develop movement, forage and bed site resource-selection models. We used an information-theoretic approach to select the top 5 models for movement, forage and bed site occurrences respectively. The three most parsimonious autologistic models were good predictors of movement, forage and bed occurrence of this species. Vegetation covariates were important components of all models. We recorded avoidance responses by the behaviours of species to each disturbance type (ie, villages, forest roads and abandoned roads); bed site occurrences were most sensitive to all human disturbances for their lowest odds encountered. Across all parsimonious models, villages have the largest negative effect on movement, foraging and bed occurrences. Movement and bedding behaviours were also affected by other ungulate disturbances. Altitude had slightly negative effect on movement and foraging behaviours. Ridges, topographic aspect and shrub stands were all correlated with bed-site selection. Although different behaviours may be associated with different microhabitat features, behaviours of red deer responded similarly to the same human disturbance on a broad scale. Based on the observations above, we believe that red deer are avoiding human-altered habitat for movement, bedding and foraging because of disturbances during the critical late winter period. Furthermore, various behavioural resource selection models and corresponding graphs of important habitat disturbances can be used to guide and evaluate future development proposals.     

Diet selection of African elephant over time shows changing optimization currency

Multiple factors determine diet selection of herbivores. However, in many diet studies selection of single nutrients is studied or optimization models are developed using only one currency. In this paper, we use linear programming to explain diet selection by African elephant based on plant availability and nutrient and deterrent content over time. Our results indicate that elephant at our study area maximized intake of phosphorus throughout the year, possibly in response to the deficiency of this nutrient in the region. After adjusting the model to incorporate the effects of this deficiency, elephant were found to maximize nitrogen intake during the wet season and energy during the dry season. We reason that the increased energy requirements during the dry season can be explained by seasonal changes in water availability and forage abundance. As forage abundance decrease into the dry season, elephant struggle to satisfy their large absolute food requirements. Adding to this restriction is the simultaneous decrease in plant and surface water availability, which force the elephant to seek out scarce surface water sources at high energy costs. During the wet season when food becomes more abundant and energy requirements are satisfied easier, elephant aim to maximize nitrogen intake for growth and reproduction. Our study contributes to the emerging theory on understanding foraging for multiple resources.