关键词： HABITAT (Ecology)   HERBIVORES   FOREST fires   SAVANNA animals   VEGETATION & climate   ANIMAL feeding  

摘要： Discusses studies on resprouting vegetation initiated by fire, and reinforced by herbivory. Attraction of herbivores to the same areas in a feedback loop; Examination of the habitat after burning occurred; Test of whether herbivores prefer burnt areas in subsequent growing seasons.

关键词： ARTHROPODA   LAND settlement   BIOTIC communities   EARTH (Planet)   CRUST  

摘要： The colonization of continental environments (land and fresh water) has focused historically on a major event during the mid-Paleozoic Era characterized by the relatively sudden emergence of megascopic embryophytes, fungi, arthropods and tetrapods. A significant earlier phase of Precambrian (Archean and Proterozoic Eons) terrestrialization extends to the first 80% of the history of life and records the colonization of subaerial soils or rock surfaces predominantly by cyanobacterial mats and crusts. These two phases are separated by a similar to 90-million-year early Paleozoic interlude of minimal terrestrial colonization. Trophically modern ecosystems appeared during the Late Silurian-Middle Devonian (425-375 million years ago), consisting of complex symbiotic, parasitic and other trophic associations, including detritivory and limited herbivory. The integration of these two historically disparate fields (Precambrian microorganisms and their biochemical and sedimentological signatures, and the paleoecology of mid-Paleozoic ecosystems) has resulted in a wider perspective on terrestrialization. Here, I present an ecological and evolutionary context for the emergence of terrestrial ecosystems and examine associations among organisms, from the endosymbiotic capture of organelles by eukaryotes to modes of metazoan nutrition on land. Such studies now enable the tracking, in ecological detail, of the invasion of continental environments during the past 3.5 billion years of life.

关键词： structure   X-Ray Computed Tomography   Laboratory mice   Lung   Canine species  

摘要： Quantitative analysis of intrathoracic airway tree geometry is important for objective evaluation of bronchial tree structure and function. Currently, there is more human data than small animal data on airway morphometry. In this study, we implemented a semi-automatic approach to quantitatively describe airway tree geometry by using high-resolution computed tomography (CT) images to build a tree data structure for small animals such as rats and mice. Silicon lung casts of the excised lungs from a canine and a mouse were used for micro-CT imaging of the airway trees. The programming language IDL was used to implement a 3D region-growing threshold algorithm for segmenting out the airway lung volume from the CT data. Subsequently, a fully-parallel 3D thinning algorithm was implemented in order to complete the skeletonization of the segmented airways. A tree data structure was then created and saved by parsing through the skeletonized volume using the Python programming language. Pertinent information such as the length of all airway segments was stored in the data structure. This approach was shown to be accurate and efficient for up to six generations for the canine lung cast and ten generations for the mouse lung cast.

关键词： species coexistence   optimal patch use   giving-up densities   Kalahari desert   Africa   rodents   habitat selection   resource abundance  

摘要： The operation of five different mechanisms of species coexistence in a community of rodents was examined in a semi-arid Kalahari savanna in southern Africa. The two most common species were Tatera leucogaster (bushveld gerbil) and Rhabdomys pumilo (striped mouse). The mechanisms examined were habitat selection in a mosaic, microhabitat selection, spatial variation in resource abundance, temporal variation in resource abundance, and diet partitioning. The rodents were censused using mark-recapture live trapping, activity measured using sand-tracking, and foraging efficiency measured using giving-up densities (GUDs;the amount of food remaining following patch exploitation) in experimental food patches. There was no support for any of the five mechanisms: T leucogaster tended to be a more efficient and mobile forager than R. pumilio. It is suggested that coexistence maybe based on a sixth mechanism, seasonal variation in resource abundance and a tradeoff of maintenance efficiency versus foraging efficiency. Further, it appears that R. pumilio is more efficient at maintaining harvest potential, not by maintaining high consumer biomass, but rather by having a high intrinsic rate of increase.

关键词： 动物类药材   三棵树药市   中药   市场分析  

摘要： 阳春三月，三棵树药市进入热销期。与2004年同期相比，生意活跃，南北方各类品种的大货陆续入市，投交顺畅，产销两旺；小批量与零星交易频繁，一些品种已经供不应求。由于各类品种的价格趋于稳定，其中部分品种价格稳中有升，居高不下，提升销售与效益呈现了“双赢”的喜人景象。进入2005年后，

关键词： complex life history   density-mediated indirect effect   non-additive multiple predator effects   phenotypic plasticity   stage-specific predation  

摘要： While theoretical studies of the timing of key switch points in complex life cycles such as hatching and metamorphosis have stressed the importance of considering multiple stages, most empirical work has focused on a single life stage. However, the relationship between the fitness components of different life stages may be complex. Ontogenetic switch points such as hatching and metamorphosis do not represent new beginnings-carryover effects across stages can arise when environmental effects on the density and/or traits of early ontogenetic stages subsequently alter mortality or growth in later stages. In this study, I examine the effects of egg- and larval-stage predators on larval performance, size at metamorphosis, and post-metamorphic predation in the African tree frog Hyperolius spinigularis. I monitored the density and survival of arboreal H. spinigularis clutches in the field to estimate how much egg-stage predation reduced the input of tadpoles into the pond. I then conducted experiments to determine: (1) how reductions in initial larval density due to egg predators affect larval survival and mass and age at metamorphosis in the presence and absence of aquatic larval predators, dragonfly larvae, and (2) how differences in mass or age at metamorphosis arising from predation in the embryonic and larval environments affect encounters with post-metamorphic predators, fishing spiders. Reduction in larval densities due to egg predation tended to increase per capita larval survival, decrease larval duration and increase mass at metamorphosis. Larval predators decreased larval survival and had density-dependent effects on larval duration and mass at metamorphosis. The combined effects of embryonic and larval-stage predators increased mass at metamorphosis of survivors by 91%. Larger mass at metamorphosis may have immediate fitness benefits, as larger metamorphs had higher survival in encounters with fishing spiders. Thus, the effects of predators early in ontogeny ca

摘要： Animal models are invaluable in preclinical research on human psychopathology. Valid animal models to study the pathophysiology of depression and specific biological and behavioral responses to antidepressant drug treatments are of prime interest. In order to improve our knowledge of the causal mechanisms of stress-related disorders such as depression, we need animal models that mirror the situation seen in patients. One promising model is the chronic psychosocial stress paradigm in male tree shrews. Coexistence of two males in visual and olfactory contact leads to a stable dominant/subordinate relationship, with the subordinates showing obvious changes in behavioral, neuroendocrine, and central nervous activity that are similar to the signs and symptoms observed during episodes of depression in patients. To discover whether this model, besides its "face validity " for depression, also has "predictive validity," we treated subordinate animals with the tricyclic antidepres, sant clomipramine and found a time-dependent recovery of both endocrine function and normal behavior. In con-. trast, the anxiolytic diazepam was ineffective. Chronic psychosocial stress in male tree shrews significantly decreased hippocampal volume and the proliferation rate of the granule precursor cells in the dentate gyrus. These stress-induced changes can be prevented by treating the animals with clomipramine, tianeptine, or the selective neurokinin receptor antagonist L-760,735. In addition to its apparent face and predictive validity, the tree shrew model also has a "molecular validity" due to the degradation routes of psychotropic compounds and gene sequences of receptors are very similar to those in humans. Although further research is required to validate this model fully, it provides an adequate and interesting non-rodent experimental paradigm for preclinical research on depression.

关键词： lizards   ecosystems   disturbance   reptiles   biodiversity   human impact   savanna   traditional medicine   South Africa  

摘要： Habitat degradation through over-grazing and wood collection is especially prevalent in developing countries such as South Africa. As human populations expand and the demand for land increases, the traditional idiom of setting aside protected areas for conservation is insufficient and assessment and protection of diversity outside these areas is needed. We assessed the impact of land use on lizard assemblages in communal rangelands in South Africa by comparing abundance, species richness and species diversity between degraded communal lands with a protected area. We first quantified vegetation differences between the study areas and found marked differences. Communal lands had significantly fewer large trees and less ground cover. Contrary to prediction, we found no evidence that any species of lizard was negatively affected by habitat disturbance. Some species were more common in communal lands, and species richness and diversity were also higher using certain sampling techniques. Terrestrial diversity was likely enhanced due to the preference of many terrestrial lizards for open, sparsely grassed areas. We discuss other reasons for increased diversity such as the intermediate disturbance hypothesis and/or reduced numbers of predators and competitors. We also conducted surveys of households and traditional healers to investigate the relationship between human uses of reptiles and abundance. The predominant users of reptiles were traditional healers. The most commonly used species were not encountered in our field surveys, and respondents indicated that they appeared to be declining. Our results emphasise the importance of integrating local knowledge into biodiversity assessment and conservation planning. Although we did not identify a negative impact of disturbance on lizard communities, community structure was different and this likely influenced ecosystem integrity and function in some way. (C) 2004 Elsevier Ltd. All rights reserved.

关键词： tree frog   mitochondrial genome   LA-PCR   rearrangement   timescale  

摘要： In this study, we have determined the complete sequence of the mitochondrial genome of an Old World tree frog Polypedates megacephalus (Anura: Rhacophoridae) by using a long polymerase chain reaction (PCR) technique and shotgun strategy of sequencing. The entire mtDNA sequence is 16,473 nt long with a novel mitogenomic gene organization in amphibians. Unlike other neobatrachian frogs, the transfer ribonucleic acid (tRNA)-Leu(CUN) and tRNA-Thr genes exchange their positions in P. megacephalus and form a Thr-Leu(CUN)-Pro-Phe tRNA gene tetrad. Moreover, we found that the ATP8 gene was replaced by a noncoding sequence of 853 nt long and that the ND5 gene was absent in the new mitogenome. These peculiar features of P. megacephalus mtDNA were further studied among related anuran species by PCR amplification. The new sequence data was used to assess the phylogenetic relationships of the three living amphibian orders using neighbor joining, maximum likelihood, and Bayesian methods. In agreement with most morphological studies, phylogenetic analyses of a whole mitochondrial genome data set suggest a close relationship between salamanders and frogs. Moreover, using a molecular clock-independent Bayesian approach for inferring dating information from molecular phylogenies, we have provided a rough timescale for living amphibian evolution. This timescale provides a working framework for future paleontological researches on amphibian evolution and improves our understanding of the evolutionary history of modern amphibians. (c) 2004 Elsevier B.V. All rights reserved.

关键词： canopy   microarthropods   Cryptomeria japonica   oribatida   collembola  

摘要： In a Cryptomeria japonica plantation, we examined the composition and seasonal abundance of micro-arthropods in communities associated with "habitat substrates" in the canopy (defined as dead leaves, dead branches, and living leaves) and compared them with those in soil communities. Habitat substrates and microarthropods were periodically collected by the branch-clipping and washing method from the canopy and by the Tullgren method from the soil. Oribatida, Collembola, and larvae of the Chironomidae, most of which are detritivorous or fungivorous, were dominant in the canopy. The dominant oribatid and collembolan families differed markedly between the canopy and the soil. Numbers of all microarthropods per unit dry weight of leaf or per unit area of branch ranged from 4.2 to 11.7g(-1) dry wt on dead leaves, 0.13-0.48 cm(-2) on dead branches, and 1.3-6.4g(-1) dry wt on living leaves. In the soil, the number of individuals per unit ground area ranged from 24000 to 220000m(-2). The total abundances of microarthropods on dead leaves and dead branches were almost constant throughout the year. These results suggest that the arboreal litter characteristic of C japonica canopies is utilized consistently by large numbers of detritivorous and fungivorous microarthropods, and that the decomposition of dead foliage and branches is initiated in the canopy.