植食性哺乳动物觅食功能反应模型机制的检验

植食性哺乳动物在食物密集斑块的觅食为 型功能反应。在新鲜苜蓿叶片构成的食物密集斑块上 ,以高原鼠兔作为实验动物 ,检验植食性哺乳动物的觅食功能反应及其模型机制。食物大小可调节高原鼠兔的口量 ,尽而控制其瞬时摄入率 ;高原鼠兔觅食叶片的口量 S与瞬时摄入率 I存在渐近的函数关系 ,为 型功能反应 ;高原鼠兔的食物收获率 B随口量 S的增加呈非线性递减 ;最大处理速率 Rmax的测定值与模型的预测值极为近似 ;瞬时摄入率 I的测定值与模型的预测值线性回归显著 ( P<0 .0 1 )。研究结果充分验证了提出的假设 :植食性哺乳动物 型功能反应模型能有效地预测其摄入率的动态 ;植食性哺乳动物收获与咀嚼间的竞争能调其收获率和摄入率     

根田鼠几种觅食功能反应模型的比较

植物组织空间排列对植食性哺乳动物功能反应的作用,是觅食生态学的热点问题之一。以新鲜紫花苜蓿叶片为食物,改变苜蓿叶片大小调控根田鼠口量,改变叶片间距调控叶片密度,设置叶片空间异质性斑块。在空间异质性斑块上测定根田鼠的觅食行为及其参数,检验植食性哺乳动物4种功能反应模型的预测性。除复合模型参数Rmax、h和Vmax及口量模型参数Rmax的最大似然估计值与测定值近似外,其它模型参数的估计值与测定值均存在较大差异。根田鼠摄入率测定值与4种模型预测值的线性回归均显著(P0.01),但与复合模型预测值的线性拟合效果最佳。表明,复合模型能很好地解释根田鼠觅食与行走的竞争对摄入率调节的动态。根田鼠复合模型存在调节其功能反应机制转变的距离临界值(d)。叶片间距大于该值时,叶片密度调节摄入率;叶片间距小于该值时,口量调节摄入率。结果充分地验证了提出的特定假设:在植物密集条件下,植物大小能调节植食性小型哺乳动物根田鼠的摄入率;在植物稀疏条件下,植物密度调节其摄入率。     

根田鼠瞬时摄入率对植物可利用性变量集功能反应的格局

在实验室条件下,以随机区组设计的新鲜紫花苜蓿叶片斑块,测定苜蓿叶片可利用性变量,叶片密度,生物量密度和叶片大小对根田鼠瞬时摄入率的作用格局。苜蓿叶片大小对根田鼠摄入率具有显作用（P＜0．01）,而叶片密度与生物量作用则不显（P＞0．05）;根田鼠摄入率对其口量变化能作出2倍以上的反应（P＜0．01）;观测摄入率与模型预测摄入率的回归显（P＜0．01）,研究结果证明,以叶片大小替代根田鼠口量是影响其摄率的独立变量;检验了植物大小是替代植食性哺乳动物口量的有效变量,以及植物大小是影响植食性哺乳动物摄入率潜在独立变量的假设。     

东方田鼠警觉对其功能反应的作用格局

植食性哺乳动物功能反应描述了摄入率与植物可利用性变量的动态关系。动物警觉因占用了处理食物时间即觅食中断时间而延迟与下一口食物相遇,引致摄入率降低,进而对功能反应构型产生影响。在新鲜白三叶叶片构成的各类食物密集斑块上,测定东方田鼠觅食行为,建立功能反应函数模型,检验觅食中断对功能反应的作用格局及机制。结果发现,除小叶片斑块觅食中断时间在觅食活动中所占的比例较低外,在大、中型叶片斑块的觅食中断时间比例均达到15.42%-26.82%;尽管,觅食中断使摄入率降低了33%,但东方田鼠功能反应仍为Ⅱ型功能反应。除东方田鼠采食时间及觅食回合时间随叶片重增大保持相对稳定外,处理时间及觅食中断时间均随叶片重增大呈线性递增趋势;采食时间、处理时间及觅食中断时间随口量的增大呈线性递增趋势;采食率随叶片重和口量增大呈指数递减趋势。研究结果揭示,东方田鼠因警觉引起的觅食中断事件是导致采食率及摄入率降低的主要因子。摄入率测定值与模型预测值的线性回归极显著(P < 0.01),表明,新建立的功能反应模型具有良好的可预测性。推测,东方田鼠因警觉引起采食率及摄入率减小的代价,是以延长觅食时间来补偿的。研究结果充分验证了,在可利用性植物密集斑块,由植物大小调控的动物口量决定其摄入率,且受采食和处理食物竞争及觅食中断的制约,其功能反应为Ⅱ型功能反应的假说。     

捕食风险对东方田鼠功能反应格局的作用

植食性哺乳动物对食物斑块的选择和利用不仅取决于食物的可利用性,且与觅食环境潜存的各种风险紧密关联。捕食风险是否通过作用于动物觅食活动中的警觉影响其功能反应格局。在新鲜白三叶叶片构成的各类食物密集斑块上,测定东方田鼠觅食行为,建立功能反应模型,检验捕食风险对其功能反应格局的作用。结果发现,捕食风险能显著地延长东方田鼠的觅食决定时间,但其摄入率保持稳定,功能反应构型亦未发生改变,仍为Ⅱ型功能反应;除了对照组个体的采食时间随叶片大小增大无明显变动规律外,处理组个体的采食时间及对照组和处理组个体的处理时间、觅食中断时间均随叶片大小及口量的增大呈线性增高趋势,处理组个体的觅食中断时间明显大于对照组个体的;对照组和处理组个体的采食率均随叶片大小及口量呈非线性渐近递减趋势,但处理组个体的采食率较对照组个体的略有降低。结果揭示,在捕食风险压力下,虽然上述觅食参数变异能潜在地降低摄入率,但个体能通过改变觅食活动中各种警觉行为动作如降低嗅闻和静听监视动作的发生频次,增大视觉监视动作比重,以此缓冲捕食风险压力,维持摄入率。摄入率测定值与模型预测值的线性回归极显著,表明,功能反应模型具有良好的预测性。在可利用植物密集斑块,动物觅食活动中的警觉能缓冲捕食风险压力;动物摄入率是由植物大小调控的口量决定的,且受采食与处理食物竞争及觅食中断的制约;其功能反应仍属Ⅱ型功能反应。     

植食性哺乳动物能量收益增长减速机制的检验

能量收益函数描述了植食性哺乳动物在植物斑块的食物摄入量与在斑块停留时间的函数关系,为觅食生态学理论的重要组成部分。在新鲜白三叶叶片构成的各类叶片斑块上,测定东方田鼠的觅食行为,建立其能量收益函数模型,分析植食性哺乳动物能量收益增长减速的机制。研究结果表明,东方田鼠觅食大叶片时,叶片干物质收益与停留时间呈非线性渐进函数关系,能量收益函数为渐进函数;觅食中、小型叶片时,叶片干物质收益与停留时间呈线性函数关系,能量收益函数为线性函数;没有检测到东方田鼠的能量收益动态呈分段线性函数或S型函数增长。东方田鼠在大、中型叶片斑块觅食时,随停留时间的增大,口量呈线性或指数递减,而处理时间则呈线性或指数递增,采食时间、间隔时间及咀嚼频次保持相对稳定,瞬时摄入率呈减小趋势;东方田鼠在小叶片斑块觅食时,觅食行为参数口量、摄入率、采食时间、间隔时间、处理时间及咀嚼频次均保持相对稳定。研究结果充分验证了,植食性哺乳动物在消费植被过程中,大型可利用性植物减少,受植物大小调控的动物口量减小,处理时间增加,引起瞬时摄入率降低,导致其能量收益增长减速的假说。     

植食性哺乳动物能量收益函数模型的预测性及适用性

以东方田鼠喜食的白三叶叶片作为食物,在保持叶片生物量不变的条件下,改变叶片大小,配置东方田鼠觅食的各类食物大小异质斑块,测定东方田鼠觅食的行为。通过比较几种植食性哺乳动物能量收益函数模型的预测性,评价其适用性。结果发现,没有检测到东方田鼠食物摄入量动态呈S型能量收益函数增长。线性函数模型能准确地预测东方田鼠在中、小型食物斑块的停留时间;在大型食物斑块,尽管,分段线性函数及渐进函数均能很好地拟合东方田鼠的食物摄入量动态,但仅分段线性函数模型能准确地预测其停留时间。线性函数模型及分段线性函数模型是在功能反应机制模型-口量模型基础上建立的,反映了调节摄入率动态的机制,为机制性模型。因此,此2种模型是在口量及摄食站尺度上,探讨动物在食物斑块的能量收益动态及停留时间;而渐进函数模型及S型函数模型均为实验性模型,是在斑块尺度上预测动物能量收益动态及停留时间,未能反映动物摄入率动态,故其预测效果较差。由于此4种模型均未考虑动物在食物斑块搜寻食物及非觅食活动如警觉和逃跑等花费的时间,因而,限制了模型的广泛应用。建议,发展新的模型,促进觅食生态学斑块模型理论研究的深入发展。     

东方田鼠家族群对成员个体觅食行为的影响

植食性哺乳动物在分享社群觅食带来好处的同时,是否因个体间的相互干扰而影响其摄入率。在新鲜马唐叶片构建的均质密集食物斑块上,测定东方田鼠家族群成员个体在食物斑块上的觅食行为序列过程及行为参数,检验家族群存在对成员个体觅食行为的影响。结果发现,东方田鼠家族群雌、雄成员个体的觅食行为参数均无显著差异。然而,与单只个体相比,家族群觅食尽管能显著地缩短成员个体的觅食决定时间,但却显著地降低了成员个体的摄入率。分析觅食行为参数觅食中断时间发现,相较于单只个体,家族群成员个体间因相互干扰而引起的觅食中断时间的增加,不但增大了收获每口食物的时间,而且导致其摄入率下降。检测家族群成员个体各警觉行为动作参数,发现,成员个体间的相互干扰能引致个体的一般扫视、盯视及嗅闻动作时间比例显著增大,尽管直立扫视和静听动作时间比例减少显著,但并未使个体的觅食中断时间减小。结果充分说明,东方田鼠家族群成员个体间的相互干扰能使个体觅食行为参数发生变异,导致觅食中断时间增加,摄入率降低。     

饥饿和食物单宁酸对东方田鼠(Microtus fortis)食物摄入量和觅食行为的影响

实验室条件下,测定饥饿和食物单宁酸对东方田鼠食物摄入量和觅食行为的影响。结果表明,饥饿使实验个体的食物总摄入量增加,食物摄入率及口量大小随饥饿强度的增大而增加,而觅食频次则无显著改变,实验个体每取食回合的觅食时间呈缓慢增加的趋势,与对照组比较,觅食时间差异不显著。东方田鼠优先选择0％单宁酸食物,次为3%单宁酸食物,而对6%单宁酸食物的摄入量最少。在饥饿条件下,东方田鼠食物摄入率的增加主要源于其口量大小,觅食频次和觅摄食时间对食物摄入量增加的贡献不显著。在饥饿条件下,植食性小哺乳动物并未通过延长觅食时间,降低用于防卫、繁殖活动时间来增加食物摄入量,而是通过增加口量大小,提高其食物摄入率来满足其营养需要。验证了饥饿与植物次生化合物共同作用引起田鼠类动物生理的改变,能影响其食物摄入量及觅食行为的假设。     

饥饿和食物单宁酸对东方田鼠(Microtus fortis)食物摄入量和觅食行为的影响

实验室条件下,测定饥饿和食物单宁酸对东方田鼠食物摄入量和觅食行为的影响。结果表明,饥饿使实验个体的食物总摄入量增加,食物摄入率及口量大小随饥饿强度的增大而增加,而觅食频次则无显著改变,实验个体每取食回合的觅食时间呈缓慢增加的趋势,与对照组比较,觅食时间差异不显著。东方田鼠优先选择0%单宁酸食物,次为3%单宁酸食物,而对6%单宁酸食物的摄入量最少。在饥饿条件下,东方田鼠食物摄入率的增加主要源于其口量大小,觅食频次和觅摄食时间对食物摄入量增加的贡献不显著。在饥饿条件下,植食性小哺乳动物并未通过延长觅食时间,降低用于防卫、繁殖活动时间来增加食物摄入量,而是通过增加口量大小,提高其食物摄入率来满足其营养需要。验证了饥饿与植物次生化合物共同作用引起田鼠类动物生理的改变,能影响其食物摄入量及觅食行为的假设。     

温度对三品系角突臂尾轮虫生活史策略的影响

应用群体累积培养法 ,以浓度为 6 .0× 10 6cells/mL蛋白核小球藻 (Chlorellapyrenoidosa)为食物 ,研究了温度(2 0℃、2 5℃和 30℃ )对青岛、广州与芜湖等品系的角突臂尾轮虫 (BrachionusangularisGosse)的种群增长、个体大小和卵大小的影响。结果表明 ,温度对各品系轮虫的种群增长率和个体大小等均有显著影响。青岛品系和广州品系轮虫种群增长的最适温度分别为 30℃和 2 5℃ ,芜湖品系轮虫则在 30℃下不能生存。青岛品系和广州品系的种群增长率均与温度呈曲线相关 ,回归方程分别为 :Y =0 .0 0 0 9X2 - 0 .0 0 6 1X 0 .4 0 90和Y =- 0 .0 14 4X2 0 .74 12X - 8.375 1。各品系轮虫个体大小和卵大小均随温度的升高而呈现出下降趋势。在本研究的温度范围内 ,广州、青岛和芜湖各品系轮虫个体变异分别达 4 2 .90 %、14 .4 3%和 6 .2 3% ;2 0℃和 2 5℃下芜湖品系分别高出青岛品系达 74 .91%和87.98%。在温度和品系两因素中 ,品系对轮虫个体体积有较大的影响     

DENSITY-DEPENDENT NATURAL SELECTION IN DROSOPHILA: EVOLUTION OF GROWTH RATE AND BODY SIZE

Drosophila melanogaster populations subjected to extreme larval crowding (CU lines) in our laboratory have evolved higher larval feeding rates than their corresponding controls (UU lines). It has been suggested that this genetically based behavior may involve an energetic cost, which precludes natural selection in a density-regulated population to simultaneously maximize food acquisition and food conversion into biomass. If true, this stands against some basic predictions of the general theory of density-dependent natural selection. Here we investigate the evolutionary consequences of density-dependent natural selection on growth rate and body size in D. melanogaster. The CU populations showed a higher growth rate during the postcritical period of larval life than UU populations, but the sustained differences in weight did not translate into the adult stage. The simplest explanation for these findings (that natural selection in a crowded larval environment favors a faster food acquisition for the individual to attain the same final body size in a shorter period of time) was tested and rejected by looking at the larva-to-adult development times. Larvae of CU populations starved for different periods of time develop into comparatively smaller adults, suggesting that food seeking behavior in a food depleted environment carries a higher cost to these larvae than to their UU counterparts. The results have important implications for understanding the evolution of body size in natural populations of Drosophila, and stand against some widespread beliefs that body size may represent a compromise between the conflicting effects of genetic variation in larval and adult performance.     

APPARENT SELECTIVE NEUTRALITY OF MITOCHONDRIAL DNA SIZE VARIATION: A TEST IN THE DEEP-SEA SCALLOP PLACOPECTEN MAGELLANICUS

Animal mitochondrial DNA (mtDNA) is believed to have evolved under intense selection for economy of the size of the molecule. Among scallop species mtDNA size may vary by a factor of two and among conspecific individuals by as much as 25%. We have examined the possibility that large mtDNA size differences may be associated with fitness in the deep sea scallop Placopecten magellanicus by comparing shell lengths of individuals with different copy numbers of a large mtDNA repeated sequence. Among juvenile cohorts of same age, shell length is known to be a good index of overall fitness in marine bivalves and it is shown here to be affected by differences in nuclear genotype, expressed as the degree of enzyme heterozygosity. We have observed no correlation between shell length and mtDNA length and interpreted this to mean that variation in the size of animal mtDNA is effectively neutral to the forces of natural selection acting on the individual. This type of mtDNA variation must, therefore, be explained in terms of biases in the molecular mechanisms causing expansion or contraction of the molecule, differential replication rates of mtDNA molecules of different size, and the stochastic assortment of mtDNA size classes among individuals.     

INFLUENCE OF CELL VOLUME ON THE GROWTH AND SIZE REDUCTION OF MARINE AND ESTUARINE DIATOMS1

The maximal growth rate (μ_max) of 19 marine and estuarine diatoms decreased with increasing cell volume (V). The relationship between log μ_max (Y) and log V (X) was calculated. Statistical analyses showed that the slope of the equation was not significantly different from those obtained by other researchers and that the 95% confidence intervals of mean μ_max at cell volumes of 10³–10⁵μm³ were not significantly different from those cited in most studies. A new regression line for diatoms was calculated as follows: log μ_max= 0.47–0.14 log V; r =–0.69. The rate of size reduction per generation of the 19 diatom species ranged from 0.03 to 0.87 μm per generation. The rate increased with increasing cell length and cell volume and with decreasing maximum division rate. Statistical analyses showed that the rate was closely related to the cell volume and to the reciprocal of the growth rate. The relationships between maximal growth rate and cell volume and between rate of size reduction and cell volume showed that a diatom with a large volume had a smaller maximal growth rate and a larger rate of size reduction than a diatom with a small volume. The estimates using the equation for the regression line between the rate of size reduction and the reciprocal of maximum division rate indicated that a diatom with a high maximum division rate would need more generation equivalents for a certain size reduction than a diatom with a low maximum division rate, but the periods required for reduction would be approximately equal irrespective of maximum division rate.     

NEW LIGHT ON THE SCALING OF METABOLIC RATE WITH THE SIZE OF ALGAE

The scaling of metabolic rate with the size of algae has been discussed and researched at length. The observation that algae usually have exponents b in the equation R = a· W ^{− b} (where R is the specific growth rate, W is the organism [cell] biomass, and a and b are constants) equal to or higher than the value of −0.25 for many other organisms is generally related to resource-saturated (maximal) values of R. Recent work has shown that the exponent b for light-limited growth is more negative than −0.25. This was predicted from considerations of the package effect in photon absorption, as modulated by the volume-specific pigment content of the cells, and the photosynthetic unit size. Further work is needed to extrapolate these findings to fluctuating light environments. This minireview puts the recent work into a broader context and suggests how further work could quantify the roles of optical thickness and of spatial and temporal variations in the radiation field in determining metabolic rates.     

SIZE DEPENDENCE OF GROWTH RATE,RESPIRATORY ELECTRON TRANSPORT SYSTEM ACTIVITY,AND CHEMICAL COMPOSITION IN MARINE DIATOMS IN THE LABORATORY1

The dependence of growth, electron transport system activity and chemical composition on the size of diatoms was examined during the exponential phase of growth. The six different marine centric species compared ranged in volume from 7.7 μm³ to 62 × 10⁵μm³. A size dependence was observed for growth, ¹⁴C uptake, respiration and the productivity index (¹⁴C/chl a). Although the size dependence of all parameters was similar, the results indicate that on a carbon basis, growth efficiency decreases with increasing size. The C/N and C/chl a ratios were not size dependent. The importance of the surface area to cell volume ratio, and the importance of carbon per unit volume in determining the observed size dependence are discussed.     

长江中、上游铜鱼的生长特性

铜鱼是长江中上游的重要经济鱼类和天然捕捞对象,1990—1995年作者利用在长江中上游收集的1030尾标本,对铜鱼的生长特性进行了研究。其体重和体长的关系为W=0.005413L~(3.113)(r=0.9982),生长方程为L_t=60.0229[1-e~(-0.2325(t 0.6108))];W_t=3261.9137[1-e~(-0.2325(t 0.6108))]~(3.113),体重生长拐点t=4.2龄,相应的体长41.05cm、体重973.03g。按生长指标值分析,阶段生长可明显地划分为两个时期,即4龄前的生长迅速期和4龄后的生长减缓期。因此,天然渔业的捕捞规格应控制在约1000g以上的个体,目前在葛洲坝以下的中游江段主要捕捞幼鱼的现状应该改变。     

田野小家鼠种群特征研究

近年,关于种群特征的研究,当首推夏武平等(1982)对长爪沙鼠的种群动态及其调节的研究,国内对种群特征间关系的进一步探研尚不多见,而该工作对动物种群动态的预测是至关重要的。 小家鼠(Mus musculus L.)的种群特征包括诸多方面,如性比、年龄结构、胎仔数、怀孕率和身体大小等,它们的变化均与一定的种群数量相联系,今在过去工作的基础上作一些新的探求。     

On-station comparative analysis of reproductive and survival performance between Red Maasai,Dorper, and Merino sheep breeds

The reproductive performance of ewes and the survivability of lambs to weaning have a critical economic impact on sheep farming worldwide. Further, knowledge of major mortality causes allows an opportunity for improved flock management to evade financial losses. The maximum likelihood estimates for generalised linear mixed models and chi-square test methods were used to examine 971 mating records, 839 and 763 lambs born and weaned (singles or twins) from the Naivasha Sheep and Goats station in Kenya for the years 2011 to 2020 consisting of Dorper, Red Maasai (RedM), and Merino breeds. The RedM (P < 0.05) outperformed Dorper and Merino in weaning rate, whereas reproductive performance between the three breeds was not significantly different (P > 0.05) in litter size and multiple lambings per ewe lambing. On the one hand, Dorper significantly (P < 0.05) outperformed the other two breeds only in weaning weight per lamb born. In addition, among all the major causes of death, pneumonia appeared to be the one to which Dorper breeds were most susceptible (chi-square test, P < 0.05). According to the findings of this study, neither the Dorper nor the Merino sheep breeds were reproductively superior to the RedM in an extensive semi-arid production environment. In addition, Dorper's susceptibility to the leading causes of mortality, particularly pneumonia and sheep pox, were relatively high compared to other breeds and could be a precursor to massive economic losses for Dorper sheep producers. In contrast to the indigenous RedM breed, imported sheep breeds appeared to be more susceptible to major mortality-related under an extensive production system. Therefore, regardless of weaning weight, RedM breed production appears to be a more viable investment for small-scale farmers, particularly in semi-arid regions.     

THE EFFECTS OF PREDATION ON THE AGE AND SIZE OF MATURITY OF PREY

The effects of nonselective predation on the optimal age and size of maturity of their prey are investigated using mathematical models of a simple life history with juvenile and adult stages. Fitness is measured by the product of survival to the adult stage and expected adult reproduction, which is usually an increasing function of size at maturity. Size is determined by both age at maturity and the value of costly traits that increase mean growth rate (growth effort). The analysis includes cases with fixed size but flexible time to maturity, fixed time but flexible size, and adaptively flexible values of both variables. In these analyses, growth effort is flexible. For comparison with previous theory, models with a fixed growth effort are analyzed. In each case, there may be indirect effects of predation on the prey's food supply. The effect of increased predation depends on (1) which variables are flexible; (2) whether increased growth effort requires increased exposure to predators; and (3) how increased predator density affects the abundance of food for juvenile prey. If there is no indirect effect of predators on prey food supply, size at maturity will generally decrease in response to increased predation. However, the indirect effect from increased food has the opposite effect, and the net result of predation is often increased size. Age at maturity may either increase or decrease, depending on functional forms and parameter values; this is true regardless of the presence of indirect effects. The results are compared with those of previous theoretical analyses. Observed shifts in life history in response to predation are reviewed, and the role of size-selective predation is reassessed.