Evolutionary biology: adaptive developmental plasticity in snakes

The morphology of organisms is generally well matched to their environment, presumably because expression of their genes is tailored either at the population or the individual level to suit local conditions: for example, snake populations that persistently encounter large prey may accumulate gene mutations that specify a large head size, or head growth may be increased in individual snakes to meet local demands (adaptive developmental plasticity). Here we test the relative contributions of genetics and environment to the jaw sizes of two tiger snake populations: one that consumes small prey on the mainland, and an island population that relies on larger prey and has a larger jaw size. Although the idea of adaptive plasticity in response to environmental pressures is controversial, we find that both factors influence the difference in jaw size between the two populations, and the influence of developmental plasticity is greater in the island population.     

具有避难所的非自治差分修正Leslie-Gower捕食-食饵系统的动力学行为研究

研究一类具有避难所的非自治差分修正Leslie-Gower捕食-食饵系统,通过对系统动力学行为的详细分析,得到保证系统持久和全局渐近稳定的充分性条件,发现只要避难所足够大就可以保证食饵种群持久生存.借助差分不等式获得一组保证食饵种群绝灭而捕食者种群持久的充分性条件,发现当避难所较小时,食饵种群会由于捕食者的捕食而最终绝灭,但此时捕食者由于拥有其他的食物来源仍可持久生存.     

Allometric degree distributions facilitate food-web stability

In natural ecosystems, species are linked by feeding interactions that determine energy fluxes and create complex food webs. The stability of these food webs enables many species to coexist and to form diverse ecosystems. Recent theory finds predator-prey body-mass ratios to be critically important for food-web stability. However, the mechanisms responsible for this stability are unclear. Here we use a bioenergetic consumer-resource model to explore how and why only particular predator-prey body-mass ratios promote stability in tri-trophic (three-species) food chains. We find that this 'persistence domain' of ratios is constrained by bottom-up energy availability when predators are much smaller than their prey and by enrichment-driven dynamics when predators are much larger. We also find that 97% of the tri-trophic food chains across five natural food webs exhibit body-mass ratios within the predicted persistence domain. Further analyses of randomly rewired food webs show that body mass and allometric degree distributions in natural food webs mediate this consistency. The allometric degree distributions hold that the diversity of species' predators and prey decreases and increases, respectively, with increasing species' body masses. Our results demonstrate how simple relationships between species' body masses and feeding interactions may promote the stability of complex food webs.     

Patterns of predation in a diverse predator-prey system

There are many cases where animal populations are affected by predators and resources in terrestrial ecosystems, but the factors that determine when one or the other predominates remain poorly understood. Here we show, using 40 years of data from the highly diverse mammal community of the Serengeti ecosystem, East Africa, that the primary cause of mortality for adults of a particular species is determined by two factors--the species diversity of both the predators and prey and the body size of that prey species relative to other prey and predators. Small ungulates in Serengeti are exposed to more predators, owing to opportunistic predation, than are larger ungulates; they also suffer greater predation rates, and experience strong predation pressure. A threshold occurs at prey body sizes of approximately 150 kg, above which ungulate species have few natural predators and exhibit food limitation. Thus, biodiversity allows both predation (top-down) and resource limitation (bottom-up) to act simultaneously to affect herbivore populations. This result may apply generally in systems where there is a diversity of predators and prey.     

陕西省歧山地区纵纹腹小鸮的食性研究

文章报道了纵纹腹小鸮在陕西省,歧山县京当地区的捕食行为及其在不同季节的食性变化.它在冬季(1—2月)主要活动于晚上.繁殖期活动时间延长,并越来越接近昼行性.在食物组成上,也有明显的季节性和地区性差异.冬季在取食频次上以鼠类为主,占整个猎物出现频次的66.7%(其中大仓鼠Cricetulus triton占25.6%),昆虫类仅占20.5%;繁殖前期(3—5月)鼠类占34.5%,昆虫类 62%;繁殖后期(6一8月)食鼠占2.47%;食昆虫占96,9%.在同一生境内,它与大型鸮类——雕鸮BuboO bubo的营养生态位发生部分重叠(重叠指数C为0.324),只是前者偏食小型鼠类和昆虫,而后者们食大、中型啮齿类.在不同地区和生境下表现出与地区的食源丰富程度有关.在饲养过程中,发现它取食一些植物果实,剖胃时也发现胃内偶有植物枝叶,同时,我们还观察到,小鸮在野外或饲养情况下,有食同类尸体的现象,但并未发现其活体相残.     

Biomechanics (Communication arising): prey attack by a large theropod dinosaur

Prey-capture strategies in carnivorous dinosaurs have been inferred from the biomechanical features of their tooth structure, the estimated bite force produced, and their diet. Rayfield et al. have used finite-element analysis (FEA) to investigate such structure-function relationships in Allosaurus fragilis, and have found that the skull was designed to bear more stress than could be generated by simple biting. They conclude that this large theropod dinosaur delivered a chop-and-slash 'hatchet' blow to its prey, which it approached with its mouth wide open before driving its upper tooth row downwards. We argue that this mode of predation is unlikely, and that the FEA results, which relate to an 'overengineered' skull, are better explained by the biomechanical demands of prey capture. Understanding the mechanics of predation is important to our knowledge of the feeding habits of carnivorous dinosaurs and for accurate reconstruction their lifestyles.     

Coexistence of two sympatric and mOrpho1ogically similar bat species Rhinolophus affnis and Rhinolophus pearsoni

Ecologists have long focused on the coexistence of sympatric species.Here,we investigated two horseshoe bat species,Rhinolophus affinis and Rhinolophus pearsoni inhabited in the same cave,for their foraging strategies,niche differentiation,prey selection,and their coexistence status.These two species of horseshoe bats were ditierent in the dominant frequency of their echolocation calls.but similar in their morphology.We found evidence for prey selectivity although there was a high degree of overlap in prey categories and sizes.R affinis and R pearsoni foraged on 16 and 7 categories insects,respectively,with Pyralidae,Geometridae,Melolonthidae dominating their diets.The degree of trophic niche overlap was 0.69.Pairwise comparisons suggested that there was no obvious differentiation in prey categories and size.However,high prey availability in the environment(Simpson diversity index=0.79 and Margalef richness index=4.121 contributed to their coexistence by dampening the interspecific competition.Since there are one or more mechanisms facilitating species coexistence in a community,our results suggest that the spatial niche differentiation in foraging microhabitats and in foraging habitats at landscape scale may promote the coexistence of the two bat species.However,additional field data are needed to confirm this speculation.     

Coexistence of two sympatric and morphologically similar bat species Rhinolophus affinis and Rhinolophus pearsoni

Ecologists have long focused on the coexistence of sympatric species. Here, we investigated two horseshoe bat species, Rhinolophus affinis and Rhinolophus pearsoni inhabited in the same cave, for their foraging strategies, niche differentiation, prey selection, and their coexistence status. These two species of horseshoe bats were different in the dominant frequency of their echolocation calls, but similar in their morphology. We found evidence for prey selectivity although there was a high degree of overlap in prey categories and sizes. R. affinis and R. pearsoni foraged on 16 and 7 categories insects, respectively, with Pyralidae, Geometridae, Melolonthidae dominating their diets. The degree of trophic niche overlap was 0.69. Pairwise comparisons suggested that there was no obvious differentiation in prey categories and size. However, high prey availability in the environment （Simpson diversity index = 0.79 and Margalef richness index = 4.12） contributed to their coexistence by dampening the interspecific competition. Since there are one or more mechanisms facil- itating species coexistence in a community, our results suggest that the spatial niche differentiation in foraging rnicrohabitats and in foraging habitats at landscape scale may promote the coexistence of the two bat species. However, additional field data are needed to confirm this speculation.     

具有父母照顾的捕食者捕食模型分析

分析了一个描述生态系统的反应扩散方程组.在此系统中,捕食者被分成不成熟和成熟两部分,不成熟的捕食者不能捕获猎物而是靠父母喂养;假设不成熟的捕食者的成熟率是食物的函数,研究了该系统的耗散性以及常数稳态解的局部稳定性.     

Coexistence of two sympatric and morphologically similar bat species Rhinolophus affinis and Rhinolophus pearsoni

Ecologists have long focused on the coexistence of sympatric species. Here, we investigated two horseshoe bat species, Rhinolophus affinis and R. pearsoni inhabited in the same cave, for their foraging strategies, niche differentiation, prey selection, and their coexistence status. These two species of horseshoe bats were different in the dominant frequency of their echolocation calls but similar in their morphology. We found evidence for prey selectivity although there was a high degree of overlap in prey categories and sizes. R. affinis and R. pearsoni foraged on 16 and 7 categories insects, respectively, with Pyralidae, Geometridae, Melolonthidae dominating their diets. The degree of trophic niche overlap was 0.69. Pairwise comparisons suggested that there was no obvious differentiation in prey categories and size. However, high prey availability in the environment (Simpson diversity index = 0.79 and Margalef richness index ＝ 4.12) contributed to their coexistence by dampening the interspecific competition. Since there are one or more mechanisms facilitating species coexistence in a community, our results suggest that the spatial niche differentiation in foraging microhabitats and in foraging habitats at landscape scale may promote the coexistence of the two bat species. However, additional field data are needed to confirm this speculation.     

Energetic constraints on the diet of terrestrial carnivores

Species in the mammalian order Carnivora exhibit a huge diversity of life histories with body sizes spanning more than three orders of magnitude. Despite this diversity, most terrestrial carnivores can be classified as either feeding on invertebrates and small vertebrates or on large vertebrates. Small carnivores feed predominantly on invertebrates probably because they are a superabundant resource (sometimes 90% of animal biomass); however, intake rates of invertebrate feeders are low, about one tenth of those of vertebrate feeders. Although small carnivores can subsist on this diet because of low absolute energy requirements, invertebrate feeding appears to be unsustainable for larger carnivores. Here we show, by reviewing the most common live prey in carnivore diets, that there is a striking transition from feeding on small prey (less than half of predator mass) to large prey (near predator mass), occurring at predator masses of 21.5-25 kg. We test the hypothesis that this dichotomy is the consequence of mass-related energetic requirements and we determine the predicted maximum mass that an invertebrate diet can sustain. Using a simple energetic model and known invertebrate intake rates, we predict a maximum sustainable mass of 21.5 kg, which matches the point where predators shift from small to large prey.     

Evidence of intra-specific competition for food in a pelagic seabird

The factors affecting the population dynamics of seabirds have long intrigued biologists. Current data suggest that density-dependent depletion of prey during the breeding season may regulate population size. However, much of the evidence for this has been circumstantial, and the underlying mechanisms are unclear. Here, we show that the per capita population growth rates of northern gannet Morus bassanus at colonies in Britain and Ireland have declined with increasing population size. Furthermore, direct observations reveal that the mean foraging trip duration of breeding gannets is positively correlated with colony size, both among colonies of different sizes in the same year, and within colonies as they change in size. To understand this phenomenon, we have developed a model which demonstrates that disturbance of fish alone can readily generate conditions under which gannets at larger colonies have to travel further to obtain food.     

Group formation stabilizes predator-prey dynamics

Theoretical ecology is largely founded on the principle of mass action, in which uncoordinated populations of predators and prey move in a random and well-mixed fashion across a featureless landscape. The conceptual core of this body of theory is the functional response, predicting the rate of prey consumption by individual predators as a function of predator and/or prey densities. This assumption is seriously violated in many ecosystems in which predators and/or prey form social groups. Here we develop a new set of group-dependent functional responses to consider the ecological implications of sociality and apply the model to the Serengeti ecosystem. All of the prey species typically captured by Serengeti lions (Panthera leo) are gregarious, exhibiting nonlinear relationships between prey-group density and population density. The observed patterns of group formation profoundly reduce food intake rates below the levels expected under random mixing, having as strong an impact on intake rates as the seasonal migratory behaviour of the herbivores. A dynamical system model parameterized for the Serengeti ecosystem (using wildebeest (Connochaetes taurinus) as a well-studied example) shows that grouping strongly stabilizes interactions between lions and wildebeest. Our results suggest that social groups rather than individuals are the basic building blocks around which predator-prey interactions should be modelled and that group formation may provide the underlying stability of many ecosystems.     

庇护所效应对一类三种群食物链稳定性的影响

研究了一类具有食饵保护的三种群食物链模型,得到了各平衡点存在的充分条件,并且分析了各平衡点的局部性态,结合Hurwitz判据和Liapunov函数得到正平衡点全局渐近稳定的充分条件,首次分析并得到了庇护所效应对三种群食物链系统持久生存性的影响。     

Predators increase the risk of catastrophic extinction of prey populations.

There has been considerable research on both top-down effects and on disturbances in ecological communities; however, the interaction between the two, when the disturbance is catastrophic, has rarely been examined. Predators may increase the probability of prey extinction resulting from a catastrophic disturbance both by reducing prey population size and by changing ecological traits of prey individuals such as habitat characteristics in a way that increases the vulnerability of prey species to extinction. We show that a major hurricane in the Bahamas led to the extinction of lizard populations on most islands onto which a predator had been experimentally introduced, whereas no populations became extinct on control islands. Before the hurricane, the predator had reduced prey populations to about half of those on control islands. Two months after the hurricane, we found only recently hatched individuals--apparently lizards survived the inundating storm surge only as eggs. On predator-introduction islands, those hatchling populations were a smaller fraction of pre-hurricane populations than on control islands. Egg survival allowed rapid recovery of prey populations to pre-hurricane levels on all control islands but on only a third of predator-introduction islands--the other two-thirds lost their prey populations. Thus climatic disturbance compounded by predation brought prey populations to extinction.     

食虫有袋类食性选择与猎物质量的相互关系

食虫有袋类是捕食多种昆虫的泛食性动物．同域的不同食虫有袋类同样选择鞘翅目、蜚蠊目、直翅目和膜翅目昆虫作为主要猎物但对同种昆虫猎物的捕食频率明显不同．食虫有袋类的食性具有季节转变现象．不同猎物昆虫质量之间的差异大多不显著但猎物昆虫的质量具有季节变化．食虫有袋类的食性选择与猎物质量、食性季节转变与猎物质量季节变化之间不存在显著相关关系．根据该结果以及最佳摄食理论,食性选择有可能受猎物可获得量或猎物体形大小的影响,值得今后进一步加以研究．     

食饵具有存放周期性制约的捕食者-食饵系统模型及其动态行为的数值模拟研究

基于对自然界捕食系统实际情况的分析出发。对模型进行了扩展，并建立了受时变环境周期激励、食饵具有常数存放率以及食饵具有周期存放等情况下的捕食者--食饵系统的新模型，通过模拟计算相平面轨线(迹)、时程图、极限集状态、截面、功率谱等若干系统指标，分析研究了几个新捕食模型随参数变化时表现出的动态行为以及行为所发生的质的变化．结果表明周期激励强度、食饵常数存放率的大小、食饵周期存放以及周期存放的频度对系统行为都有很大的影响，当食饵存放率为零时，系统随周期激励强度的增大经历了稳定、周期波动、准周期波动和灭绝四种状态；当周期激励强度和频度恒定时，系统随食饵常数存放率的增大经历了周期(准周期)波动、分岔后的周期(准周期)波动和灭绝等状态；而在周期激励强度和频度恒定时，食饵周期存放可能引起系统出现混沌行为；当周期存放的强度较大时，食饵存放频度的变小不利于系统的稳定．     

Reconciling complexity with stability in naturally assembling food webs

Understanding how complex food webs assemble through time is fundamental both for ecological theory and for the development of sustainable strategies of ecosystem conservation and restoration. The build-up of complexity in communities is theoretically difficult, because in random-pattern models complexity leads to instability. There is growing evidence, however, that nonrandom patterns in the strengths of the interactions between predators and prey strongly enhance system stability. Here we show how such patterns explain stability in naturally assembling communities. We present two series of below-ground food webs along natural productivity gradients in vegetation successions. The complexity of the food webs increased along the gradients. The stability of the food webs was captured by measuring the weight of feedback loops of three interacting 'species' locked in omnivory. Low predator-prey biomass ratios in these omnivorous loops were shown to have a crucial role in preserving stability as productivity and complexity increased during succession. Our results show the build-up of food-web complexity in natural productivity gradients and pin down the feedback loops that govern the stability of whole webs. They show that it is the heaviest three-link feedback loop in a network of predator-prey effects that limits its stability. Because the weight of these feedback loops is kept relatively low by the biomass build-up in the successional process, complexity does not lead to instability.     

基于主成分分析法的中国城镇居民消费结构研究

以2009年全国31个省、市、自治区的城镇居民家庭平均每人全年消费性支出的食品、衣着、居住、家庭设备用品及服务、医疗保健、交通与通讯、娱乐教育文化服务、其它商品和服务等8个指标数据为依据,利用R统计软件,采用主成分分析法对当前城镇居民消费结构进行分析,结果显示:娱乐教育文化服务、交通通讯、家庭设备用品、居住、食品是影响消费大小变动的主要因素,而衣着、医疗保健、居住、食品是影响消费结构变动的主要因素;各省市城镇居民消费大小与其经济发达程度密切相关;相邻省市消费结构比较相似;沿海地区与内地消费结构有较大的差别.