关键词： island rule   mammals   dwarfism   gigantism   biogeography   decision tree  

摘要： Many hypotheses have been proposed to explain size changes in insular mammals, but no single variable suffices to explain the diversity of responses, particularly within Rodentia. Here in a data set on insular rodents, we observe strong consistency in the direction of size change within islands and within species but (outside of Heteromyidae) little consistency at broader taxonomic scales. Using traits of islands and of species in a classification tree analysis, we find the most important factor predicting direction of change to be mainland body mass (large rodents decrease, small ones increase);other variables (island climate, number of rodent species, and area) were significant, although their roles as revealed by the classification tree were context dependent. Ecological interactions appear relatively uninformative, and on any given island, the largest and smallest rodent species converged or diverged in size with equal frequency. Our approach provides a promising framework for continuing examination of insular body size evolution.

关键词： TREE seedlings   NORWAY spruce   EUROPEAN beech   SILVER fir   EXCLOSURES   FOREST dynamics  

摘要： Predation of tree seeds can be a major factor structuring plant communities. We present a three year study on tree seed survival on experimental dishes in an old-growth forest in central Europe in Austria. We addressed species specific, spatial and temporal aspects of post-dispersal seed predation. Seeds of Norway spruce Picea abies, European beech Fagus sylvatica, and silver fir Abies alba were exposed on dishes in different types of exclosures which allowed access only to specific guilds of seed predators. Removal experiments were carried out in two old-growth forests and a managed forest (macro-sites), including micro-sites with and without cover of ground vegetation. We conducted the experiment in three consecutive years with a mast year of beech and spruce before the first year of the study. The seed removal experiments were combined with live trapping of small mammals being potential seed predators. Our experiments showed a distinctly different impact of different predator guilds on seed survival on the dishes with highest removal rates of seeds from dishes accessible for small mammals. We observed differing preferences of small mammals for the different tree species. Seed survival in different macro- and micro-habitats were highly variable with lower seed survival in old growth forests. In contrast to our assumption, and in contrast to the satiation hypothesis which assumes higher seed survival in and directly after mast years, seed survival was lower in the year following the mast year of beech when a population peak of small mammals occurred and higher in intermast periods when subsequently small mammal population crashed. This suggests a higher importance of sporadic masting shortly after mast years in intermast periods for establishment of forest trees provided that pollination efficiency is high enough in such years. Combined with the high seed mortality observed after the mast year, this corroborates the important role of seed predation for forest dynam

关键词： Humanoid robots   Multirobot systems   Robot dynamics   Robotic self-replication   On-line pattern recognition  

摘要： We have proposed a new repetition framework for vision-based behavior imitation by a sequence of multiple humanoid robots, introducing an on-line method for delimiting a time-varying context. This novel approach investigates the ability of a robot "student" to observe and imitate a behavior from a "teacher" robot;the student later changes roles to become the "teacher" for a naive robot. For the many robots that already use video acquisition systems for their real-world tasks, this method eliminates the need for additional communication capabilities and complicated interfaces. This can reduce human intervention requirements and thus enhance the robots' practical usefulness outside the laboratory. Articulated motions are modeled in a three-layer method and. registered as learned behaviors using color-based landmarks. Behaviors were identified on-line after each iteration by inducing a decision tree from the visually acquired data. Error accumulated over time, creating a context drift for behavior identification. In addition, identification and transmission of behaviors can occur between robots with differing, dynamically changing configurations. ITT, an on-line decision tree inducer in the C4.5 family, performed well for data that were similar in time and configuration to the training data but the greedily chosen attributes were not optimized for resistance to accumulating error or configuration changes. Our novel algorithm, OLDEX identified context changes on-line, as well as the amount of drift that could be tolerated before compensation was required. OLDEX can thus identify time and configuration contexts for the behavior data. This improved on previous methods, which either separated contexts off-line, or could not separate the slowly time-varying context into distinct regions at all. The results demonstrated the feasibility, usefulness, and potential of our unique idea for behavioral repetition and a propagating learning scheme.

关键词： Grassland   Rodents   Seed predators   Woody invaders  

摘要： Woody plant invasion in grassland ecosystems is a worldwide phenomenon, and biotic interactions as competition and predation have been invoked as a possible barrier to woody encroachment in many ecosystems. We evaluated the role of rodents as seed predators in Pampean grasslands, and we assessed the differences in removal by rodents between one native species, Prosopis caldenia (Cald,n) and one exotic species, Gleditisia triacanthos (Honey locust). The experiment was conducted at different phases of the rodent population cycle in two grassland communities, a remnant of a native grassland and a post agriculture grassland (old field). The amount of seed loss caused by predation was estimated by a bait-removal experiment in foraging stations. We estimated the frequency of foraging stations with consumption, the overall amount of seed predation and the individual rate of seed predation. The total amount of seed removal and the individual rate of seed removal were higher for P. caldenia than for G. triacanthos, in the native grassland than in the old field, and in autumn when rodent density was maximum. Overall, the role of rodents on woody seed removal varied according to the plant species and depending on the local conditions that vary through time and space.

关键词： assemblage   browse   elephant   long-term exclusion   species richness  

摘要： The Nkuhlu large-scale long-term exclusion experiment in Kruger National Park was designed to study the long-term effects of large herbivores on vegetation. One treatment excludes elephants, another excludes all herbivores larger than hares and another one comprises an open, control area. Vegetation monitoring was implemented in 2002 when a baseline survey was conducted prior to exclusion. Monitoring was repeated 5 years after exclusion. Data from the surveys were analysed to establish how structure and composition of woody vegetation had changed 5 years after herbivore exclusion. The analysis showed that neither plant assemblage nor mean vegetation height had changed significantly since exclusion. However, both species richness and density of woody plants increased 5 years after exclusion of all large herbivores, but not after the exclusion of elephants alone. One already common species, Dichrostachys cinerea, became more common after excluding all large herbivores compared with either no exclusion or elephant exclusion, possibly leading to competitive suppression of other species. Species other than D. cinerea tended to either increase or decrease in density, but the changes were insufficient to induce significant shifts in the overall assemblage of woody plants. The results indicate that after 5 years of exclusion, the combined assemblage of large herbivores, and not elephants alone, could induce changes in species richness and abundances of woody plants, but the effect was so far insufficient to induce measureable shifts in the assemblages of woody plants. It is possible that assemblages will change with time and increasing elephant numbers may amplify future changes.

关键词： bark beetle   Dendroctonus brevicomis   Entomocorticium spp.   herbivory   local adaptation   monoterpenes   mutualism   phenotype   phytochemistry   phytophagy   Pinus ponderosa   symbiosis  

摘要： Many herbivores consume microbial food sources in addition to plant tissues for nutrition. Despite the ubiquity of herbivore-microbe feeding associations, few studies examine how host plant phenotypes affect microbial symbionts of herbivores. We tested the hypothesis that chemical polymorphism in a plant population mediates the performance of nutritional microbial symbionts. We surveyed the composition of ponderosa pine resin in northern Arizona, USA, for variation in six monoterpenes, and we approximated four chemical phenotypes. We reared populations of an herbivorous tree-killing beetle (Dendroctonus brevicomis) in ponderosa pine host material, controlling for three monoterpene compositions representing an alpha-pinene to Delta-3-carene gradient. Beetles were reared in host material where the dominant monoterpene was alpha-pinene, Delta-3-carene, or a phenotype that was intermediate between the two. We isolated nutritional fungal symbionts (Entomocorticium sp. B) from beetle populations reared in each phenotype and performed reciprocal growth experiments in media amended to represent four "average'' monoterpene compositions. This allowed us to test the effects of natal host phenotype, chemical polymorphism, and the interaction between natal host phenotype and chemical polymorphism on a nutritional symbiont. Three important findings emerged: (1) fungal isolates grew 25-32% faster when acquired from beetles reared in the intermediate phenotype;(2) the mean growth rate of nutritional fungi varied up to 44% depending on which monoterpene composition media was amended with;and (3) fungal isolates uniformly performed best in the intermediate phenotype regardless of the chemical composition of their natal host. The performance of nutritional fungi related to both the chemical "history'' of their associated herbivore and the chemical phenotypes they are exposed to. However, all fungal isolates appeared adapted to a common chemical phenotype. These experiments argue in fa

关键词： Ant-plant interaction   Context-dependency   Brazil   Caatinga   Cerrado   Natural selection   Nectar glands  

摘要： Despite the general belief that the interaction between extrafloral nectaries (EFNs) and ants is mutualistic, the defensive function of EFNs has been poorly documented in South American savannas. In this article, we evaluate the potential impact of EFNs (benefits and costs) on two species of plants from the dry areas of Central Brazil, Anemopaegma album and Anemopaegma scabriusculum (Bignoniaceae). In particular, we characterize the composition of substances secreted by the EFNs, test whether EFNs attract ants, and whether ants actually present a defensive role, leading to reduced herbivory and increased plant fitness. Histochemical analyses indicated that EFNs from both species of Anemopaegma secrete an exudate that is composed of sugars, and potentially lipids and proteins. Furthermore, EFNs from both species were shown to present a significant role in ant attraction. However, contrary to common expectations, ants were not found to protect plants against herbivore attack. No effect was found between ant visitation and flower or fruit production in A. album, while the presence of ants led to a significant decrease in flower production in A. scabriusculum. These results suggest that EFNs might present a similar cost and benefit in A. album, and a higher cost than benefit in A. scabriusculum. Since the ancestor of Anemopaegma occupied humid forests and already presented EFNs that were maintained in subsequent lineages that occupied savannas, we suggest that phylogenetic inertia might explain the presence of EFNs in the species of Anemopaegma in which EFNs lack a defensive function.

关键词： Phylogenetic analysis   Mitochondria   Animal phylogenetics   Genetic loci   Speciation   Mitochondrial DNA   Mammals   Population genetics  

摘要： An important challenge for phylogenetic studies of closely related species is the existence of deep coalescence and gene tree heterogeneity. However, their effects can vary between species and they are often neglected in phylogenetic analyses. In addition, a practical problem in the reconstruction of shallow phylogenies is to determine the most efficient set of DNA markers for a reliable estimation. To address these questions, we conducted a multilocus simulation study using empirical values of nucleotide diversity and substitution rates obtained from a wide range of mammals and evaluated the performance of both gene tree and species tree approaches to recover the known speciation times and topological relationships. We first show that deep coalescence can be a serious problem, more than usually assumed, for the estimation of speciation times in mammals using traditional gene trees. Furthermore, we tested the performance of different sets of DNA markers in the determination of species trees using a coalescent approach. Although the best estimates of speciation times were obtained, as expected, with the use of an increasing number of nuclear loci, our results show that similar estimations can be obtained with a much lower number of genes and the incorporation of a mitochondrial marker, with its high information content. Thus, the use of the combined information of both nuclear and mitochondrial markers in a species tree framework is the most efficient option to estimate recent speciation times and, consequently, the underlying species tree.

关键词： 后生动物   古生物学家   系统演化   研究员   化石生物   螺旋星系   系统树   仙女座  

摘要： 发现于华南贵州的一类5．8亿年前的化石让我们开始，怀疑已知的动物系统树。因为形体像极了螺旋星系仙女座。这类被命名为“八臂仙母虫”的化石生物，将重新排序生命系统树的最早期分支。相关论文在2011年9月21日美国出版的《进化和发育》杂志以封面文章形式发表。

关键词： 油桐饼(粕)   蛋白质   脱毒方法   畜牧生产  

摘要： 本文主要介绍油桐饼(粕)资源的特点、营养价值、脱毒方法及其在畜牧生产上的应用。