关键词： competition   grazing facilitation   livestock-wildlife interactions   nutrient-rich foraging hotspots   Odontotermes   resource selection  

摘要： African savanna termite mounds function as nutrient-rich foraging hotspots for different herbivore species, but little is known about their effects on the interaction between domestic and wild herbivores. Understanding such effects is important for better management of these herbivore guilds in landscapes where they share habitats. Working in a central Kenyan savanna ecosystem, we compared selection of termite mound patches by cattle between areas cattle accessed exclusively and areas they shared with wild herbivores. Termite mound selection index was significantly lower in the shared areas than in areas cattle accessed exclusively. Furthermore, cattle used termite mounds in proportion to their availability when they were the only herbivores present, but used them less than their availability when they shared foraging areas with wild herbivores. These patterns were associated with reduced herbage cover on termite mounds in the shared foraging areas, partly indicating that cattle and wild herbivores compete for termite mound forage. However, reduced selection of termite mound patches was also reinforced by higher leafiness of Brachiaria lachnantha (the principal cattle diet forage species) off termite mounds in shared than in unshared areas. Taken together, these findings suggest that during wet periods, cattle can overcome competition for termite mounds by taking advantage of wildlife-mediated increased forage leafiness in the matrix surrounding termite mounds. However, this advantage is likely to dissipate during dry periods when forage conditions deteriorate across the landscape and the importance of termite mounds as nutrient hotspots increases for both cattle and wild herbivores. Therefore, we suggest that those managing for both livestock production and wildlife conservation in such savanna landscapes should adopt grazing strategies that could lessen competition for forage on termite mounds, such as strategically decreasing stock numbers during dry periods.

关键词： Tree cavities   Forestry   Conservation planning   Hollow-using fauna   Management prescriptions   Habitat trees  

摘要： Hollow-using fauna are thought to be particularly vulnerable to timber harvesting, and habitat for these species is often managed by retaining single hollow-bearing trees or patches of hollow-bearing trees within the harvested area. This study examined tree retention, survival and use by arboreal mammals in 27 small clumps of trees (0.04-0.21 ha) retained at ten partial harvest sites and 24 clumps of trees in nearby unharvested sites in Tasmania, Australia. Harvested sites were assessed on three occasions (1999, 2005-06 and 2014) and unharvested sites on two occasions (2005-06 and 2014). Of the retained clumps in harvested areas, 96% contained at least two habitat trees at the time of first survey (one year after harvest) which is the minimum required under the Tasmanian Forest Practices Code. Loss of retained trees in clumps between 2005-06 and 2014 was higher in harvested sites (average of 11.7% of all trees and 1.5% of habitat trees per clump) than unharvested sites (average of 2.8% of all trees and 0.3% of habitat trees per clump), but was comparable to or lower than rates of loss in many other studies. Trees were more likely to fall if they were dead and had little burn damage at the time of last survey. Factors found to influence tree death included the interaction between burn damage and the size of the tree, with the likelihood of a heavily burnt, average sized tree dying being twice that of an unburnt tree. Scratch marks from arboreal mammals were more prevalent in large trees with visible hollows, particularly in the clumps in harvested areas. In conclusion, the Tasmanian Forest Practices Code provisions were generally implemented as required and the evidence suggests the retained clumps of trees survive and are effective to some degree at providing habitat and promoting recolonisation by fauna in partial harvest coupes. However, further work is required to assess the adequacy of the clump provisions, when combined with management for other values in produ

关键词： agriculture   cropland   epigaeic spider species   food security   food web   functional diversity   functional traits   pest control  

摘要： Predators play a disproportionately positive role in ensuring integrity of food webs, influencing ecological processes and services upon which humans rely. Predators tend to be amongst the first species to be affected by anthropogenic disturbance, however. Spiders impact invertebrate population dynamics and stabilise food webs in natural and agricultural systems (potentially mitigating against crop pests and reduced yields). Africa's savannas are undergoing continent-wide conversion from low-density rangelands to villages and croplands, as human populations burgeon. Despite limited research, and evidence of deleterious impacts to biodiversity, African savannas are earmarked by prominent international organisations for conversion to cropland. Given the key role of spiders in food webs, they can have beneficial impacts in agroecosystems. Furthermore, functional diversity (FD) reflects ecosystem pattern and processes better than species diversity, so we evaluated impacts of large-scale landuse change on both species richness and FD. We surveyed spiders using pitfall traps at 42 sites (14 replicates each in rangeland, cropland, and villages) in South African savannas, investigating effects of landuse, season, and habitat variables on spider species diversity and FD. Species richness was lowest in villages. FD was lowest in cropland, however, with reduced representation of traits associated with hunting of larger invertebrates. Furthermore, there were fewer specialists in croplands. These findings suggest that even when cropland does not impact species diversity, loss of FD can still occur. As savanna systems transform, impacts on invertebrate population dynamics may increase the possibility of a breakdown in pest control in natural and agricultural systems, given changes in FD of invertebrate predators.

关键词： Pastoralism   Coexistence   Rangelands   Heterogeneity   Community based conservation   Resilience  

摘要： Wildlife and livestock have coexisted across East African rangelands for millennia, tracking seasonal forage availability across large landscapes. More recently however, free-ranging movements have been increasingly restricted by land use changes, reducing the ability of livestock and wildlife to access necessary grazing resources, leading to both homogenization and degradation of the rangeland. This in turn has led to losses in productivity of both livestock and wildlife. This study describes wildlife and livestock interactions in response to pasture in one of the few remaining areas of mixed wildlife-livestock use with unrestricted movements. We ask if pastoral management systems can create and maintain spatial and temporal heterogeneity of pasture, through the seasonal movement of livestock. Furthermore, does this heterogeneity create a diverse, productive and resilient assemblage of both domestic and wild ungulates? Our results provide evidence to support the notion that traditional pastoral systems which continue to manage for heterogeneity of pasture can still support not only livestock but also substantial numbers of wildlife. The results highlight the need for wildlife and livestock to retain both mobility and access to both wet and dry season areas to maintain ecosystem resilience and promote coexistence in mixed livestock-wildlife landscapes.

关键词： 树鼩   病毒感染性疾病   动物模型  

摘要： 病毒感染是我国传染病致死的主要病因。建立一种能有效模拟人类感染病毒的动物模型,对病毒感染性疾病的致病机制和防治研究具有重要意义。树鼩作为灵长类动物的近亲,是近年建立和发展起来的新型动物模型,在病毒感染性疾病模型研究中突显优势和潜能。本文从树鼩的分类学、生理学和免疫学等生物学特征方面阐述了其应用于病毒感染性疾病动物模型研究的优势,并对树鼩在肝炎病毒、单纯疱疹病毒、流感病毒、肠道病毒等多种人类病毒感染性疾病模型应用中的最新研究进展予以比较和概述。

关键词： Chromatin-based mechanisms   Genotypic variation   Insect herbivore   Phenotypic plasticity   Tree defence  

摘要： The interaction of plants and their herbivorous opponents has shaped the evolution of an intricate network of defences and counter-defences for millions of years. The result is an astounding diversity of phytochemicals and plant strategies to fight and survive. Trees are specifically challenged to resist the plethora of abiotic and biotic stresses due to their dimension and longevity. Here, we review the recent literature on the consequences of phytochemical variation in trees on insect-tree-herbivore interactions. We discuss the importance of genotypic and phenotypic variation in tree defence against insects and suggest some molecular mechanisms that might bring about phytochemical diversity in crowns of individual trees.

关键词： Acacia nilotica   digestibility   nitrogen balance   protozoa   rumen enzymes   sheep  

摘要： This study was conducted to evaluate the effect of supplying two levels of Acacia nilotica (***) pods to rations of sheep on nutrient digestibility, nitrogen balance and rumen liquor parameters (pH, total protozoa count, protein concentration and enzymes activity). Twelve mature rams (50 +/- 1.25 kg B.W.) were distributed into three groups, each with four rams. Animals in group one were considered as a control which fed a basal diet, consisting of concentrate mixture and Egyptian clover. The second group and the third one received the same basal diet with supplying the concentrate mixture by 1.5% and 3.0% of *** pods meal respectively. The experiment lasted for 3 weeks. It was found that supplementation of *** pods to the concentrate mixture at a rate of 1.5% and 3.0% significantly improved the total feed intake compared to the control. The digestibility of dry matter and crude fibre was significantly reduced with *** supplements, whereas the digestibility of crude protein was significantly improved. All of nitrogen intake and N-retained were significantly increased in rams fed on concentrates with 1.5% and 3.0% A. nilotica pods when compared to the control. The pH of ruminal fluid was not affected by the dietary treatments. Nevertheless, the total rumen protozoa count was significantly decreased in *** pods supplemented groups. Also, the rumen protein concentration and the ruminal enzymes activity, especially alpha-amylase, cellulase and protease, were lower in *** pods supplemented treatments. In conclusions, inclusion of low levels of *** pods (1.5% and 3.0%) in the concentrates can be used as a natural protein protectant in ruminants by forming tannin protein complexes in the rumen to maximize the amino acids available in the lower digestive tract. Also, these levels can increase the protein digestibility as well as the N-retained in the body .

关键词： RNA-seq   PLANARIA   TRANSCRIPTOMES  

摘要： Flatworms of the species Schmidtea mediterranea are immortal-adult animals contain a large pool of pluripotent stem cells that continuously differentiate into all adult cell types. Therefore, single-cell transcriptome profiling of adult animals should reveal mature and progenitor cells. By combining perturbation experiments, gene expression analysis, a computational method that predicts future cell states from transcriptional changes, and a lineage reconstruction method, we placed all major cell types onto a single lineage tree that connects all cells to a single stem cell compartment. We characterized gene expression changes during differentiation and discovered cell types important for regeneration. Our results demonstrate the importance of single-cell transcriptome analysis for mapping and reconstructing fundamental processes of developmental and regenerative biology at high resolution.

关键词： competition   fire   rodents   savanna ecosystem   shrews   small mammals   Zambia  

摘要： While niche separation and relationships with environmental conditions of large mammals of the African savanna have been studied intensively, less conspicuous components have not received similar attention. This is the case of Kafue National Park (KNP), Zambia, where mechanisms supporting coexistence among rodent and shrew species remain unclear, much less the influence of fire on their dietary resource use. Here, we use stable carbon and nitrogen isotopes to assess dietary resource use and partitioning among rodents and shrews found in three vegetation formations of KNP. According to the nitrogen isotope signatures, rodents are one to two trophic levels above primary production, save for Mus triton that is above by two to three. Shrews are two trophic levels above primary production. Among shrews, factors allowing coexistence of similar sized species could not be resolved. Rodent species of the same assemblage either differ in body mass by a factor of two (following Hutchinson's rule) or similar sized species occupy different trophic levels or dietary guilds based on their isotopic nitrogen or carbon signatures. At sites with frequent fires, rodents have broader dietary niches than at sites with low fire frequencies. This could either indicate relaxed competition under high fire frequencies as rodent populations do not reach the carrying capacity of the habitat, or it could reflect reduced competition due to lower species numbers under high versus low fire recurrence regimes. The results indicate competition as an important component structuring rodent communities in Zambian savannas, thus suggesting limited resources.

关键词： Below and aboveground interactions   Arbuscular mycorrhizal fungi   Simulated herbivory   Local adaptation   Kenya Long-term Exclosure Experiment (KLEE)  

摘要： The functional relationship between arbuscular mycorrhizal fungi (AMF) and their hosts is variable on small spatial scales. Here, we hypothesized that herbivore exclusion changes the AMF community and alters the ability of AMF to enhance plant tolerance to grazing. We grew the perennial bunchgrass, Themeda triandra Forssk in inoculum from soils collected in the Kenya Long-term Exclosure Experiment where treatments representing different levels of herbivory have been in place since 1995. We assessed AMF diversity in the field, using terminal restriction fragment length polymorphism and compared fungal diversity among treatments. We conducted clipping experiments in the greenhouse and field and assessed regrowth. Plants inoculated with AMF from areas accessed by wild herbivores and cattle had greater biomass than non-inoculated controls, while plants inoculated with AMF from where large herbivores were excluded did not benefit from AMF in terms of biomass production. However, only the inoculation with AMF from areas with wild herbivores and no cattle had a positive effect on regrowth, relative to clipped plants grown without AMF. Similarly, in the field, regrowth of plants after clipping in areas with only native herbivores was higher than other treatments. Functional differences in AMF were evident despite little difference in AMF species richness or community composition. Our findings suggest that differences in large herbivore communities over nearly two decades has resulted in localized, functional changes in AMF communities. Our results add to the accumulating evidence that mycorrhizae are locally adapted and that functional differences can evolve within small geographical areas.