关键词： 完全基因组   系统发育树   组合向量   熵密度分布   对数关联距离  

摘要： 线粒体完全基因组是一种构建脊椎动物系统发育树的非常重要的数据资源.该文中我们应用基于非序列比对的熵密度分布方法结合对数关联距离对64种脊椎动物的线粒体完全基因组进行分析处理并构建系统发育树,产生的树将所选择的生物体分为三个大类:哺乳类(Mammalia)、鱼类(Fish)和初龙下纲(包括鸟类(Birds)和爬行类(Reptiles)),其拓扑结构与当前已知的用传统方法产生的树相似.

关键词： body size   carbon quality   ecological stoichiometry   herbivory   leaf chemistry   nitrogen   phosphorus   plant-insect interactions   Quercus  

摘要： 1. Environmental heterogeneity created by prescribed burning provided the context for testing whether the distribution of an oak specialist (the lace bug, Corythuca arcuata) could be explained by stoichiometric mismatches between herbivore and host plant composition. 2. Field observations showed that lace bug density was seven-fold higher in frequently burned than in unburned units. 3. Lace bug density did not increase with leaf nutrient concentrations, but was instead associated with higher light levels, higher concentrations of leaf carbon (C), lignin and total phenolics, and lower levels of cellulose. In addition, lace bugs reared on high-light leaves had higher levels of survivorship than those fed on low-light leaves. 4. Sampling restricted to full-sun leaves was used to test whether fire-related changes in leaf nitrogen (N) and phosphorus (P) concentrations have a secondary influence on lace bug success. This sampling provided only limited evidence for nutrient limitation, as decreases in leaf N and P were associated with an increase in lace bug mass but a decrease in density. 5. It is concluded that burning probably promotes lace bug population growth by increasing canopy openness, light penetration, and the availability of C-based metabolites, and thus simple stoichoimetric mismatches between herbivores and host plants are not of primary importance in this system.

关键词： key resource   population regulation   rainfall   savanna   waterholes  

摘要： In arid and semiarid environments surface-water strongly constrains the distribution and abundance of large herbivores during the dry season. Surprisingly, we know very little about its variability in natural ecosystems. Here we used long-term data on the dry-season occurrence of water at individual waterholes to model the surface-water availability across Hwange National Park, Zimbabwe, under contrasted climatic and management scenarios. Without artificial pumping only 19.6% of the park occurred within 5 km of water under average climatic conditions. However surface-water availability was strongly influenced by annual rainfall, and over 20 years the variability of the surface area of the park occurring within 5 km of water was slightly larger than the variability of rainfall. This contrasts with the usual buffered response of vegetation production to rainfall fluctuations, and suggests that the variability in dry-season foraging range determined by surface-water availability could be the main mechanism regulating the population dynamics of large herbivores in this environment. Artificial pumping increased surface-water availability and reduced its variability over time. Because changes in surface-water availability could cause the greatest changes in forage availability for large herbivores, we urge ecologists to investigate and report on the variability of surface-water in natural ecosystems, particularly where rapid climate changes are expected.

关键词： phenotype   species diversity   phylogeny   evolutionary change   phototransduction evolution   tree-thinking perspective  

摘要： Biologists are amazed by the intricacy and complexity of biological interactions between molecules, cells, organisms, and ecosystems. Yet underlying all this biodiversity is a universal common ancestry. How does evolution proceed from common starting points to generate the riotous biodiversity we see today? This "novelty problem "-understanding how novelty and common ancestry relate-has become of critical importance, especially since the realization that genes and developmental processes are often conserved across vast phylogenetic distances. In particular, two processes have emerged as the primary generators of diversity in organismal form: duplication plus divergence and co-option. In this article, we first illustrate how phylogenetic methodology and "tree-thinking" can be used to distinguish duplication plus divergence from co-option. Second, we review two case studies in photoreceptor evolution-one suggesting a role for duplication plus divergence, the other exemplifying how co-option can shape evolutionary change. Finally, we discuss how our tree-thinking approach differs from other treatments of the origin of novelty that utilized a "linear-thinking" approach in which evolution is viewed as a linear and gradual progression, often from simple to complex phenotype, driven by natural selection.

关键词： BIOLOGICAL INVASIONS   PHEIDOLE-MEGACEPHALA   RAIN-FOREST   ANT   HOMOGENIZATION   CONSEQUENCES   IMPACT  

摘要： Palmyra Atoll, in the Line Islands of the equatorial Pacific, supports one of the largest remaining native stands of Pisonia grandis forest in the tropical Pacific Ocean. In 2003, we surveyed terrestrial arthropods to document extant native and introduced species richness, compare these lists with historical records, and assess potential threats to native species and ecosystem integrity. In total, 115 arthropod taxa were collected, bringing the total number of taxa recorded since 1913 to 162. Few native species were collected;most taxa were accidental introductions also recorded from the Hawaiian Islands, the presumed main source of introductions to Palmyra. The overlap with previous historical Surveys in 1913 and 1948 was low (<40%), and new species continue to establish, with one species of whitefly reaching pest status between 2003 and 2005. We observed numerous dead or dying large Pisonia grandis, and the green scale Pulvinaria. urbicola (Coccidae) was particularly abundant on trees of poor health. Abundant introduced ants, particularly Pheidole megacephala, tended this and other hemipterans feeding on both native and introduced plants. We hypothesize that the Pheidole-Pulvinaria facultative mutualism is causing the decline of Pisonia grandis. Because of the unique properties of Pisonia grandis forest on oceanic atolls, its importance for nesting seabirds, and its alarming global decline, immediate conservation efforts should be directed at controlling introduced Hemiptera and disrupting their mutualisms with normative ants on Palmyra Atoll.

关键词： bagging   biomonitoring   boosting   decision tree   ecological modelling   habitat suitability   river assessment   tree-pruning  

摘要： In this study, decision tree models were induced to predict the habitat suitability of six macroinvertebrate taxa: Asellidae, Baetidae, Caenidae, Gammaridae, Gomphidae and Heptageniidae. The modelling techniques were applied on a dataset of 102 samples collected in 31 sites along the river Axios in Northern Greece. The database consisted of eight physical-chemical and seven structural variables, as well as the abundances of 90 macroinvertebrate taxa. A seasonal variable was included allowing the description of potential temporal changes in the macroinvertebrate taxa. Rules relating the presence/absence of six benthic macroinvertebrate taxa with the 15 physical-chemical and structural river characteristics and the seasonal variable were induced using the J48 algorithm. In order to improve the performance and the interpretability of the induced models, three optimisation techniques were applied: tree-pruning, bagging and boosting. The predictive performance of the decision tree models was assessed on the basis of the percentage of Correctly Classified Instances (CCI) and the Cohen's kappa statistic. The results of the present study demonstrated that although the models had a relatively high predictive performance, noise in the dataset and inappropriate input variables prevented to some extent, the models from making reliable predictions. Although tree-pruning did not improve significantly the reliability of the induced models, it reduced considerably the tree complexity and in this way increased the transparency of the trees. Consequently, the induced models allowed for a correct ecological interpretation. The effect of bagging and boosting on the other hand varied considerably between the different models, as well as within different repetitions of 10-fold cross-validation in an individual model. In some cases the predictive performance was improved, in others stable or even worsened. The effect of bagging and boosting seemed to be strongly dependent on the dataset o

关键词： embryo behaviour   hatching   inducible defence   phenotypic plasticity   predation  

摘要： Risk-sensitive hatching is adaptive for species facing a trade- off between egg-stage and post-hatching risks, and environmental variation in one or both stages. Such plasticity has been found in amphibians, fishes, reptiles and spiders, with red-eyed treefrogs (Agalychnis callidryas) being the best-studied case. We assessed hatching plasticity and egg- and larval-stage risks in a closely related, syntopic species, the gliding leaf-frog (Agalychnis spurrelli). We found a lower hatching response to egg-eating snakes in A. spurrelli (9-28% of embryos escaped) than in A. callidryas (59-80% escaped). Levels of snake predation were similarly high for clutches of both species monitored at a pond in Costa Rica, and in fish predation experiments early-hatched A. spurrelli tadpoles were more vulnerable than later hatchlings, as has been shown for A. callidryas. A. spurrelli thus face a risk trade-off similar to A. callidryas, and likely would benefit from predator-nduced hatching;their lower responsiveness to snakes appears nonadaptive. A. spurrelli embryos showed a stronger hatching response (57% hatched in 1 h) to submergence underwater than to snake attacks even though submergence is a less frequent risk. This suggests they have a greater capacity for early hatching than is expressed in the context of snake attacks, but have much lower sensitivity to snake cues than to flooding cues. Development in A. spurrelli is accelerated compared to syntopic A. callidryas, and spontaneous hatching is earlier and more synchronous. This is congruent with predictions based on selection by egg predators in the absence of a strong escape hatching response.

关键词： carnivore   faeces   hair   herbivore   Kruger Park  

摘要： This paper characterizes predator - prey interactions amongst African mammals from C-4 savanna environments using stable carbon and nitrogen isotope proxies for diet. Stable carbon (delta C-13) and nitrogen (delta N-15) isotope data from hair and faeces of large African mammal carnivores, and herbivores as potential prey, are presented for a diverse range of taxa. Carbon- isotope data imply that most carnivores from the "lowveld" savanna of South Africa form part of C-4 grass-based food webs. Nitrogen isotope data show clear differences between trophic levels, although it appears that the magnitude of these differences varies between predators feeding on invertebrates and vertebrates, respectively. Whilst the number of carnivore samples for which data are available is relatively few, and data for prey are restricted mainly to large ungulate herbivores, results clearly demonstrate the potential for future applications of this technique to predator-prey food webs in African savannas. In tandem with traditional approaches, stable isotopes can help elucidate patterns of predator impacts on prey populations, domestic livestock, and resolving similar food webs in palaeoenvironmental contexts.

关键词： discriminant analysis   decision trees   neural networks   protozoa   metazoa   image analysis  

摘要： Protozoa and metazoa are considered good indicators of the treatment quality in activated sludge systems due to the fact that these organisms are fairly sensitive to physical, chemical and operational processes. Therefore, it is possible to establish close relationships between the predominance of certain species or groups of species and several operational parameters of the plant, such as the biotic indices, namely the Sludge Biotic Index (SBI). This procedure requires the identification, classification and enumeration of the different species, which is usually achieved manually implying both time and expertise availability. Digital image analysis combined with multivariate statistical techniques has proved to be a useful tool to classify and quantify organisms in an automatic and not subjective way. This work presents a semi-automatic image analysis procedure for protozoa and metazoa recognition developed in Matlab language. The obtained morphological descriptors were analyzed using discriminant analysis, neural network and decision trees multivariable statistical techniques to identify and classify each protozoan or metazoan. The obtained procedure was quite adequate for distinguishing between the non-sessile protozoa classes and also for the metazoa classes, with high values for the overall species recognition with the exception of sessile protozoa. In terms of the wastewater conditions assessment the obtained results were found to be suitable for the prediction of these conditions. Finally, the discriminant analysis and neural networks results were found to be quite similar whereas the decision trees technique was less appropriate. (c) 2007 Elsevier B.V. All fights reserved.

关键词： Africa   wildlife   monitoring   conservation   non-protected areas  

摘要： Ecosystem processes in African savannas can be better conserved if management is based on a mechanistic understanding of wildlife dynamics in livestock-dominated landscapes. For Laikipia District, a non-protected savanna region in northern Kenya, we used spatially explicit estimates of density to characterize factors influencing the dynamics of large herbivores on three land-use types: commercial ranches that favor wildlife, communal 'group ranches' practicing pastoralism, and the remainder ('transitional' properties). For 21-year time series of nine wild and two domestic species, linear model selection was used to ascribe between 45% (Grant's gazelle) and 95% (plains zebra) of observed variation in biomass density to land use, rainfall-dependence, density-dependence, and trends over time. Strongly opposing patterns of variation across the landscape in wildlife and livestock densities affirmed the primacy of land use among factors influencing wildlife abundance in non-protected areas. Rainfall limited densities of only the dominant grazing species throughout the monitoring period (plains zebra and cattle), and of most other species while their densities were high. Regulating effects of density were detected only for the dominant wild grazing and browsing species (zebra and giraffe). All but two wild species (zebra and Grant's gazelle) declined on at least one land-use type, for reasons that varied among land uses. Where favored, diverse and abundant wild herbivores (mean of 1.7 t km(-2) on pro-wildlife ranches) can thrive even when sharing the landscape with a slightly higher biomass density of livestock (mean of 2.7 t km-(12)). Where not favored, only a few resilient wild species (e.g. gazelles and plains zebra) persist with high densities of livestock (mean of 4.6 t km(-2) on transitional ranches). Maintaining higher wild species diversity in the landscape will depend on the creation of a network of unfenced conservation areas in which livestock densities are pers