关键词： Bottom-up versus top-down effects   Functional divergence   Functional evenness   Functional richness   Spatial heterogeneity   Termitaria  

摘要： Spatially heterogeneous habitats often promote woody plant species and functional diversity (FD). Ungulate herbivory can have the opposite effect. Across the globe, the type and intensity of herbivory is changing, as domestic livestock replace wild ungulates, which are increasingly confined to protected areas. Despite recognition of the importance of FD for ecosystem functioning, the interactive effect of soil-related fine-scale heterogeneity and larger-scale ungulate herbivory on woody plant FD is little-known. In miombo woodland of Zimbabwe, we investigated (1) how bottom-up fine-scale heterogeneity created by Macrotermes termitaria interacts with top-down effects of herbivore foraging-guilds on woody plant FD;and (2) whether browsing combined with grazing impacts FD more than grazing alone. The three different herbivore treatments (grazing, combined browsing-and-grazing, and exclusion) had been maintained for 50 years. We surveyed 10 termite mound-matrix plots within three sites per treatment. We assessed woody plant traits and FD across treatments (herbivore feeding-guild) and position (mound or woodland-matrix), and interactive effects between these. Woody plant FD was greater on mounds, and lowest overall with browsing-and-grazing. Specific traits were associated with position (e.g. palatability was greater for mounds), and treatment (e.g. spinescence increased with grazing). Long-term enclosure of ungulate herbivores (browsing-and-grazing, and grazing alone) decreased woody FD, but this was mitigated by termitaria. The novel finding is that at regional scales, mounds can enhance woody plant FD despite the impacts of herbivory. At broader scales encompassing the miombo system, potential exists for mounds to stabilise woody plant FD from livestock-induced impacts.

关键词： fire   herbivory   Mali   savannah   tree harvest   West Africa  

摘要： Theory and empirical evidence for the impacts of fire and herbivory in savannahs is well established - they are top-down disturbances that maintain savannahs in disequilibrium states away from potential tree cover. In African savannahs, the demand for fuelwood is extremely high, so tree harvest likely also has an impact, both directly and indirectly, on tree cover, density and biomass. Many savannah trees resprout vigorously from the base after harvest. However, harvested trees regenerate as saplings susceptible to fire and browsing, so harvest may have important demographic consequences. Here, we report the effects of tree harvest, and its interaction with fire and herbivory, on savannah dynamics by analysing woody regrowth following a harvest in arid Sahelian and mesic Guinean savannahs in Mali, West Africa. Tree harvest resulted in an overall reduction in wood production per tree compared to growth in nonharvested trees. Regrowth, either biomass or height, did not differ among fire and herbivory treatments. Our results suggest that the resprouting abilities that savannah trees have evolved to cope with frequent fire are essential for surviving tree harvest and subsequent disturbance. In these savannahs, regrowth is rapid enough in the first growing season to escape the impact of dry season fires.

关键词： PREDATORY animals   FICTION  

关键词： Polysaccharide   Anacardiaceae   Diarrheal models   Cholera   Castor oil  

摘要： Ethnopharmacological relevance: Anacardium occidentale L. (Anacardiaceae) is commonly known as the cashew tree. It is native to tropical America and extracts of the leaves, bark, roots, chestnut net and exudate have been traditionally used in northeast Brazil for the treatment of various diseases. The exudate of the cashew tree (cashew gum) has been exploited by locals since ancient times for multiple applications, including the treatment of diarrheal diseases. Aim of the study: The primary aim of the present study is to evaluate the antidiarrheal activity of cashew gum (CG), a complex heteropolysaccharide from the exudate of the cashew tree, using various models. Materials and methods: The antidiarrheal activity of cashew gum (CG) against acute diarrhea was investigated using the castor oil-induced diarrhea model. The effects of CG on gastrointestinal transit and castor oil- and PGE(2)- induced enteropooling were also examined in rodents. In addition, the effect of CG against secretory diarrhea was investigated using a model of fluid secretion in cholera toxin-treated intestinal closed loops in live mice. Results: Cashew gum (30, 60, and 90 mg/kg, p.o.) showed a significant (P <0.05-0.01) antidiarrheal effect in rats with castor oil-induced diarrhea, inhibiting the total amount of stool and diarrheal stools. The 60 mg/kg dose of CG exhibited excellent antidiarrheal activity and significantly reduced the severity of diarrhea (diarrhea scores) in rats. CG (60 mg/kg) significantly (P < 0.05) decreased the volume of castor oil- and PGE(2)-induced intestinal fluid secretion (enteropooling). In addition, similar to loperamide (standard drug, 5 mg/kg, p.o.), CG treatment reduced the distance traveled by a charcoal meal in the 30-mm gastrointestinal transit model by interacting with opioid receptors. In cholera toxin-induced secretory diarrhea, CG (60 mg/kg) significantly inhibited the intestinal fluid secretion and decreased Cl- ion loss in the cholera toxin treated isola

关键词： browsing megaherbivores   compounded disturbances   context-dependent responses   contingency   controlled burning   ecosystem engineers   habitat facilitation   keystone species   large mammalian herbivores   transiently synergistic indirect effects  

摘要： Disturbance is a crucial determinant of animal abundance, distribution and community structure in many ecosystems, but the ways in which multiple disturbance types interact remain poorly understood. The effects of multiple-disturbance interactions can be additive, subadditive or super-additive (synergistic). Synergistic effects in particular can accelerate ecological change;thus, characterizing such synergies, the conditions under which they arise, and how long they persist has been identified as a major goal of ecology. We factorially manipulated two principal sources of disturbance in African savannas, fire and elephants, and measured their independent and interactive effects on the numerically dominant vertebrate (the arboreal gekkonid lizard Lygodactylus keniensis) and invertebrate (a guild of symbiotic Acacia ants) animal species in a semi-arid Kenyan savanna. Elephant exclusion alone (minus fire) had negligible effects on gecko density. Fire alone (minus elephants) had negligible effects on gecko density after 4months, but increased gecko density twofold after 16months, likely because the decay of fire-damaged woody biomass created refuges and nest sites for geckos. In the presence of elephants, fire increased gecko density nearly threefold within 4months of the experimental burn;this occurred because fire increased the incidence of elephant damage to trees, which in turn improved microhabitat quality for geckos. However, this synergistic positive effect of fire and elephants attenuated over the ensuing year, such that only the main effect of fire was evident after 16months. Fire also altered the structure of symbiotic plant-ant assemblages occupying the dominant tree species (Acacia drepanolobium);this influenced gecko habitat selection but did not explain the synergistic effect of fire and elephants. However, fire-driven shifts in plant-ant occupancy may have indirectly mediated this effect by increasing trees' susceptibility to elephant damage. Our findings

关键词： animal model   cardiac transplantation   Chinese tree shrews   xenograft rejection   xenotransplantation  

摘要： Since -1,3-galactosyltransferase knockout (GalT-KO) pigs became available, there has been an increasing interest in non-Gal natural antibody (nAb)-mediated xenograft rejection. To better understand mechanisms of non-Gal nAb-mediated rejection, a simple small animal model without gene manipulation would be extremely valuable. Here, we tested whether the Chinese tree shrew (CTS), which is a small-sized mammal that is phylogenetically close to primates, could serve as a model for discordant xenograft rejection. MethodsStudy 1: Expression of -Gal antigens in hearts and kidneys of CTSs and rats was assessed by IB4 lectin binding. Presence of anti-Gal and anti-non-Gal IgM and IgG nAb in CTS sera was tested by FACS using Gal+ and GalTKO PBMC as well as BSA-ELISA. Study 2: Rat hearts were transplanted into CTS recipients (group 1, n = 7), and CTS hearts were transplanted in rats [n = 10;seven received no immunosuppression (group 2) and three received FK506 + leflunomide (group 3)]. ResultsStudy 1: Both CTSs and rats had -Gal expression in hearts and kidneys. ELISA showed CTSs do not have anti-Gal nAb, and flow cytometry indicated CTSs have anti-non-Gal IgM and IgG nAb in serum. Study 2: Rat hearts in CTSs were uniformly rejected within 35 mins, while CTS hearts in rats continued beating until day 5 without immunosuppression, and up to day 8 with immunosuppression. ConclusionRat-to-CTS heart transplantation is a discordant xenotransplant model, CTS-to-Rat heart transplantation is a concordant xenotransplant model. CTSs are valuable small animals to study mechanisms and strategies to avoid non-Gal nAb-mediated xenograft rejection.

关键词： Herbivores   Insect-plant relationships   Plant diversity   Plant genetics   Tree growth  

摘要： [ Although the effects of plant diversity on herbivores are contingent upon herbivore traits and the source of plant diversity (e.g. intra-and interspecific), most studies have analyzed these effects separately. We compared the effects of genotypic diversity of big-leaf mahogany Swietenia macrophylla with that of tree species diversity on two specialist caterpillars (Hypsipyla grandella stem borers and Phyllocnistis meliacella leaf miners) and three generalist leafhoppers (Cicadellidae) feeding on mahogany in a large-scale (7.2 ha) forest diversity experiment in southern Mexico. The experiment consisted of fifty-nine 21 x 21-m plots, with 64 tree saplings each (3-m spacing between plants). Plots were either mahogany monocultures or species polycultures of four species (including mahogany) and - within each of these two plot types - mahogany was represented by either one or four genotypes. Throughout a five-month period, beginning six months after planting, we measured mahogany growth and monitored herbivore and predator (spider) abundance. We found no effect of mahogany genotypic diversity on either specialist caterpillars or generalist leafhoppers, and this result was consistent across levels of tree species diversity. In contrast, species diversity had significant effects on both specialists but neither of the generalist herbivores. Specifically, species diversity lowered H. grandella attack at the middle of the sampling season, but increased attack at the end of the season, whereas P. meliacella abundance was consistently reduced. Such effects were not mediated by effects of species diversity on plant growth (of which there were none), but rather through resource heterogeneity. Diversity did not influence spider abundance. This study is one of few to directly compare sources of plant diversity, and uniquely compares such effects among herbivores with contrasting life histories (e.g. diet breadths). Overall, we demonstrate that plant species diversity effects outw

关键词： Acacia mortality   Introduced species   Nature conservation   Seed viability   Ungulate herbivores   Wildlife reservation  

摘要： Acacia trees are keystone species of drylands. The recruitment of Acacia seedlings is regulated by large herbivores. The study objective was to investigate the effect of several large herbivore species on Acacia germination and recruitment. These species include the addax (Addax nasomaculatus), Arabian oryx (Oryx leucoryx), Asiatic wild ass (Equus hemionus), African wild ass (Equus africanus), and dorcas gazelle (Gazella dorcas). Feces of these herbivore species were collected in a safari reservation in the hyper-arid Arava Valley, where Acacia raddiana and Acacia tortilis trees are widespread. The study was implemented in a net house, where the feces were laid in small piles on the ground and irrigated. Two batches of the feces were studied: one in the winter and one in the spring of 2012. The winter batch encompassed only the feces of the addax, oryx, and Asiatic ass, and it was found that the addax feces generated a significantly greater number of seedlings than the feces of other species. Of this batch, only 13 % of seedlings were alive similar to 250 days later. The spring batch encompassed all five species and revealed a germination rate in the feces according to the following order: addax > oryx > Asiatic ass > gazelle > African ass. Of this batch, 46 % of seedlings were alive similar to 200 days later. This study provides new knowledge regarding the effect of each of the ungulate species on recruitment capacity of new trees to the Acacia population. The results propose that the two most significant factors affecting recruitment are rumination and size of herbivores.

关键词： Research Article  

摘要： With grasslands and savannas covering 20% of the world's land surface, accounting for 30-35% of worldwide Net Primary Productivity and supporting hundreds of millions of people, predicting changes in tree/grass systems is priority. Inappropriate land management and rising atmospheric CO2 levels result in increased woody cover in savannas. Although woody encroachment occurs world-wide, Africa's tourism and livestock grazing industries may be particularly vulnerable. Forecasts of responses of African wildlife and available grazing biomass to increases in woody cover are thus urgently needed. These predictions are hard to make due to non-linear responses and poorly understood feedback mechanisms between woody cover and other ecological responders, problems further amplified by the lack of long-term and large-scale datasets. We propose that a space-for-time analysis along an existing woody cover gradient overcomes some of these forecasting problems. Here we show, using an existing woody cover gradient (0-65%) across the Kruger National Park, South Africa, that increased woody cover is associated with (i) changed herbivore assemblage composition, (ii) reduced grass biomass, and (iii) reduced fire frequency. Furthermore, although increased woody cover is associated with reduced livestock production, we found indigenous herbivore biomass (excluding elephants) remains unchanged between 20-65% woody cover. This is due to a significant reorganization in the herbivore assemblage composition, mostly as a result of meso-grazers being substituted by browsers at increasing woody cover. Our results suggest that woody encroachment will have cascading consequences for Africa's grazing systems, fire regimes and iconic wildlife. These effects will pose challenges and require adaptation of livelihoods and industries dependent on conditions currently prevailing.

关键词： Research Article  

摘要： Biological invasions are a major threat to biodiversity;however, the degree of impact can vary depending on the ecosystem and taxa. Here, we test whether a top invader at a global scale, the tree Robinia pseudoacacia (black locust or false acacia), which is known to profoundly change site conditions, significantly affects urban animal diversity. As a first multitaxon study of this kind, we analyzed the effects of Robinia dominance on 18 arthropod taxa by pairwise comparisons of woodlands in Berlin, Germany, that were dominated by R. pseudoacacia or the native pioneer tree Betula pendula. As a negative effect, abundances of five arthropod taxa decreased (Chilopoda, Formicidae, Diptera, Heteroptera, Hymenoptera);13 others were not affected. Woodland type affected species composition of carabids and functional groups in spiders, but surprisingly did not decrease alpha and beta diversity of carabid and spider assemblages or the number of endangered species. Tree invasion thus did not induce biotic homogenization at the habitat scale. We detected no positive effects of alien dominance. Our results illustrate that invasions by a major tree invader can induce species turnover in ground-dwelling arthropods, but do not necessarily reduce arthropod species abundances or diversity and might thus contribute to the conservation of epigeal invertebrates in urban settings. Considering the context of invasion impacts thus helps to set priorities in managing biological invasions and can illustrate the potential of novel ecosystems to maintain urban biodiversity.