关键词： Grassland intensification   Grazing   Pasture degradation   Process-based model  

摘要： Process-based modelling is needed to assess potential ecological impacts of large-scale intensification of African savanna rangelands and to investigate major processes involved, that cannot be tested on appropriate temporal and spatial scales at field level. To date, modelling conversion or integration of crop-and pasture-based systems in savanna ecosystems is not possible at the necessary level of detail. The Land Use Change Impact Assessment tool (LUCIA) dynamically simulates spatially explicit impacts of land-use change on ecosystem functions within a grid-based landscape. We added a physiologically detailed source-sink plant growth module with growth reserves, dynamic biomass partitioning, and dormancy to LUCIA to simulate a grazed rangeland vegetation in Borana, Ethiopia. Grass and tree growth, validated against measured above-ground biomass time series were most sensitive to dormancy break or induction parameters that control the growing period under strong rainfall seasonality. A moderate stocking rate of cattle allowed pasture persistence and continuous fodder production. Overgrazing caused depletion of root and tree stem growth reserves that were needed for seasonal regrowth. Consequently, pasture degraded due to reduced regrowth capacity and reserve replenishment. Physiological processes are well represented, laying the foundation for integration of further ecological processes, such as tree recruitment, bush encroachment, and plant community shifts.

关键词： Scale of response   Tree cover   Spatial scale   Multi-scale model   Mammal   Herbivore   Brazil  

摘要： Context Determining the appropriate scale at which to study species' interactions with their environment is a great challenge. Objective We investigated the spatial extent at which landscape structure affects the occurrence of four species of terrestrial mammalian herbivores in the Brazilian savannas and examined whether those scales could be explained by species ecological traits and how forest habitat was operationally defined. Methods Using maps of forest cover, camera trapping and occupancy modelling, we determined the relations between three landscape metrics (percentage of forest cover, patch density and edge density) and the occurrence of four species. To determine the optimal scale of effect for each species, we computed landscape metrics at different spatial extents (from 0.5 to 10 km radius) from camera trap locations and for three forest maps, each using different operational definitions of a forest pixel: minimum of tree cover of 25, 50 or 75%. Results The occupancy models revealed scales of effect of 0.5 to 2 km with the scale of effect being similar among three of the species. However, the probability of a scale of effect being detected depended upon how forest is operationally defined, being greater when forest was defined with greater tree cover, particularly for forest-specialist species. Conclusions Besides biological traits, the way habitat is operationally defined shapes our ability to detect the scale of effects. Thus, it is necessary not to adopt a multi-scale approach, but also to use multiple operational definitions of habitat, considering particularities of how each species interact with their environment.

关键词： Harvesting intensity   Arthropod herbivory and guild diversity   Native tree plantation   Nothofagus spp   Austrocedrus chilensis   Sustainable woodland management  

摘要： Sustainable forest management should optimise the balance between tree productivity and biodiversity conservation. One strategy to achieve both is the use of native plantations in biomass extraction systems. However, it is unknown how different native tree species and their herbivores respond to a gradient of biomass extraction. In a Patagonian woodland, we planted six native tree species of high wood value and contrasting physiological traits, in plots with increasing harvesting intensities (HI: 0, 30, 50 or 70% of basal area removal), and measured herbivory rates, herbivore guild diversity, and sapling survival and growth. To understand whether herbivore diversity in non-planted wild species was affected by harvesting intensity, we performed the same herbivore measures in six wild woodland plant species. Herbivory rates and herbivore guild diversity showed similar responses to HI, being highest on saplings growing at 30% (N. dombeyi, N. antarctica, N. pumilio and N. alpina) or 30% and 50% (N. obliqua) HI. Deciduous tree species were consumed at a higher rate and held more diverse guilds, whereas evergreen species were consumed at a lower rate or barely damaged. Differences among species seem to be mostly driven by leaf habit and nitrogen content. In turn, higher HI increased the heterogeneity of arthropod guild composition, being N. alpina and N. pumilio the species with most variation in guild composition across HI. Contrariwise, regarding the non-planted wild woodland species, there was no effect of HI on herbivory rates or guild diversity. Finally, planted tree species survived and grew more at 30% and 50% HI despite supporting higher leaf damage, except for N. antarctica which showed a similar survival rate across all HI. Species with highest performance were A. chilensis and N. obliqua;but differences regarding plant performance among species were not explained by their physiological traits. Approximately one-third to mid harvesting intensities in this Patago

关键词： Arthropod   Herbivore   Mycorrhizal fungi   Mycorrhizal type   Predator  

摘要： Ectomycorrhizal (EcM) tree species often become more dominant than arbuscular mycorrhizal (AM) tree species in temperate forests, but they generally coexist. Theory predicts that ecological feedback mediated by aboveground herbivory and/or belowground microbes could explain these dominance/coexistence patterns. An experimental test of how aboveground/belowground organisms associated with AM/EcM trees mediate ecological feedbacks has been lacking at the community-level. By establishing AM and EcM tree sapling assemblages in mesocosms and then introducing seedlings of each type in a reciprocal planting experiment, we compared seedling performance under varying sapling species (conspecifics, heterospecifics within the same and different mycorrhizal types), using traits that reflect either aboveground herbivory-mediated feedback or belowground fungal-mediated feedback or both. When examining seedling traits that reflect aboveground herbivory-mediated feedbacks (i.e., foliar damage), AM plants tended to experience less foliar damage and EcM plants more damage under conspecific versus heterospecific saplings within the same mycorrhizal types, and aboveground herbivory-mediated feedback was species-specific rather than mycorrhizal type-specific. Conversely, when examining traits that reflect belowground fungal-mediated feedbacks, both AM and EcM plant species often exhibited mycorrhizal type-specific feedbacks (e.g., greater aboveground biomass under the same versus different mycorrhizal-type saplings) rather than species-specific feedbacks. Furthermore, tree species affected by herbivory-mediated feedback were less affected by belowground feedback, indicating that the relative importance of the feedbacks varied among plant species. Analysis of plant-associated organisms verified that the feedback outcomes corresponded with species accumulation of belowground fungi (but not of aboveground herbivores). Thus, aboveground herbivores drive stronger plant species-specific feedb

关键词： Aggregated retention   Forest structural complexity   Microtus oregoni   Neotamias townsendii   Pacific Northwest   Peromyscus   Retention forestry   Small mammals  

摘要： Retention forestry, the practice of maintaining stand legacies in harvested forests, is used to create more complex forest structure and positive biodiversity outcomes in managed forests. However, the relative effectiveness of different retention strategies at increasing forest structural complexity and populations of dependent wildlife species is not well understood. We used an experimental study to evaluate changes in the population density of three small mammal species in response to different size and location (riparian or upland) of retention tree patches within harvested forests in the Pacific Northwest, USA. We further assessed whether small mammal density varied in relation to differences in structural complexity within retention patches among experimental retention stands. Within stands, deer mice (Peromyscus spp.) population density did not differ between retention and harvested areas (beta =-0.05, SE = 0.06), Townsend's chipmunk (Neotamias townsendii) density was higher in retention compared to clearcut areas (beta = 1.61, SE = 0.10), and creeping vole (Microtus oregoni) density was highest in clearcut areas (beta =-0.68, SE = 0.10). At the stand-scale, deer mouse density and chipmunk density were lowest in stands with large upland patches of retention (mean = 83, SD = 28 trees) and highest in stands with multiple small patches of upland retention (mean = 8, SD = 2 trees). Creeping vole density followed the opposite pattern, highest in stands with large upland patches and lowest in stands with multiple small patches. Densities of each species were intermediate in stands where at least a portion of the retention trees were connected to forested riparian buffers. Relating the density of each species to structural complexity within stands revealed that Townsend's chipmunk density increased with increasing retention tree blowdown (beta = 0.39, SE = 0.08), a proxy for downed wood resources, whereas creeping vole density decreased (beta =-0.51, SE = 0.12), and

关键词： cattle   essential oil   natural compounds   natural extract   plant extract   vegetable oil  

摘要： There is a growing public concern on the use of antibiotics and ionophores in livestock and emerging antimicrobial resistance. Plant extracts and essential oils are natural alternatives having antimicrobial and antioxidant properties. This study evaluated the effects of a mixture of baccharis (Baccharis dracunculifolia) leaves and stems, tamarind (Tamarindus indica L.) seed, cashew (Anacardium occidentale) nut shell liquid, and clove (Syzygium aromaticum) essential oil on animal performance, feed intake, feed efficiency, apparent digestibility, molar concentration of volatile fatty acids and feeding behavior of bulls finished in the feedlot and fed high-grain diets. A total of 32 bulls (1/2 Angus vs. 1/2 Nellore) with a mean age of 24 +/- 2.0 months and a mean body weight of 418 +/- 4.51 kg were distributed in a completely randomized design with four diets and eight replications per diet. The four experimental diets were as follows: CONT - basal diet;MIX2 - basal diet and 2 g/animal/d of extracts from baccharis, tamarind, cashew nut shell liquid, and clove;MIX4 - basal diet and 4 g/animal/d of extracts from baccharis, tamarind, cashew nut shell liquid, and clove;MIX6 - basal diet and 6 g/animal/d of extracts from baccharis, tamarind, cashew nut liquid shell liquid and clove. Animal performance, dry matter, and other nutrients intake were similar among diets. Dry matter, neutral detergent fiber, and organic matter digestibilities were greater for the MIX2 when compared to other diets. There was an increase in propionate and a decrease in the acetate/propionate ratio when MIX6 was used. A similar effect was observed when orthogonal contrasts comparing the CONT diets with the addition of MIX was used. Feeding behavior was similar among the four diets. Our findings indicated that supplementation of baccharis, tamarind, cashew nut shell liquid, and clove oil (2, 4, and 6 g/animal/d) may be fed to beef cattle once it showed no adverse effects on feed intake and nutrient d

关键词： Benthic macroinvertebrates   Bioindicators   Change points   Local stressors   Thresholds   Traits  

摘要： Riparian zones ensure freshwater ecosystem processes such as microclimate regulation, organic matter inputs, and fine substrate retention. These processes illustrate the importance of riparian zones for freshwater ecosystem functioning, maintaining biodiversity, and mitigating the effects of anthropogenic pressures on aquatic ecosystems. We aimed to determine the freshwater invertebrate biological traits that are most affected by anthropogenic stressors in the riparian zones of 210 Neotropical savanna headwater streams. We assessed % canopy cover over the streambed, % fine bottom substrate, % leaf pack, substrate heterogeneity, and water temperature. Firstly, we identified bioindicator taxa in response to each local metric gradient. We assessed the functional response, based on biological traits of bioindicators previously selected. We identified 324,015 specimens belonging to 84 freshwater invertebrate taxa. Fifty-one taxa (60%) were bioindicators of anthropogenic stressors. We found three main sets of traits. (1) a set of traits linked to increased disturbance (higher percentage of fine sediments), consisting of organisms with aquatic adult stages, spherical body shape, and long adult life stages. (2) A set of traits linked to lower disturbance (higher substrate heterogeneity), including taxa with short or very short lifespans that live attached to substrates. (3) A set of traits linked to higher water temperature, including organisms with short adult lifespans and lower body flexibility. These patterns suggest that the stressors act as environmental filters and do not act independently on single traits, but rather, selecting sets of biological traits that facilitate taxa surviving and persisting in local environmental conditions. Our results support the development of powerful evaluation tools for environmental managers and decision makers. Because degraded freshwater communities respond in similar ways across large biogeographic areas, these sets of traits can b

关键词： 智慧树   慕课资源   动物生理学  

摘要： 动物生理学是整个生命科学相关专业的核心基础课程,该课程知识点繁多、内容抽象、机制复杂,对于很多学生来说有一定难度,特别是理解能力稍弱的少数民族学生。传统的灌注式教学模式效果一般,为提高教学质量和教学效果,探索新的教学模式迫在眉睫。本文主要介绍基于智慧树平台将慕课资源融入到传统教学之中的探索应用及教学效果评价,充分利用“互联网+”现代网络教学方法来弥补传统教学模式的不足,提高教学效果和教学质量。

关键词： Litter decomposition   Soil fauna   Ephemeral herb litter   Mixture effect   Understorey   Temperate forest  

摘要： Leaf litter from forest understorey species has very different characteristics (e.g. a higher nutrient content) which are regarded to be more palatable and digestible for the decomposer community compared to litter from the overstorey trees. Consequently, the decomposition of tree litter may show different dynamics when mixed with litter from herb species. To study the effect of understorey litter on tree litter decomposition, we set up a litterbag experiment in a temperate mixed deciduous forest in Belgium. We investigated the effect of spring (Anemona nemorosa) and summer (Aegopodium podagaria) herb litter on the litter decomposition of five native tree species that differ in litter quality. The spring and summer withering herb litters were added above the tree litters. After 742 days of in situ incubation, mass loss (40%-100%) and the decomposition rate (0.27-1.68 yr(-1)) of the litter from the five tree species were positively correlated with litter quality. The addition of summer herb litter resulted in increased mass loss and decomposition rates (kappa) of the underlying recalcitrant tree litter. In addition, summer herb litter increased nutrient concentration in the short-term as well as the abundance of soil fauna during litter decomposition. In contrast, spring herb litter slightly inhibited tree litter decomposition. Structural equation models showed that the effect of understorey litter on decomposition rates of tree litter acted via nutrient leaching towards the tree litter layer rather than via the alteration of soil fauna (detritivores and omnivores) abundance. Our results show that litter from understorey vegetation can alter nutrient availability in recalcitrant litters (Fagus sylvatica and Quercus robur) via increased nitrogen (N), calcium (Ca), magnesium (Mg), phosphorus (P) and potassium (K) concentrations by 9%, 21%, 22%, 41%, and 315% respectively after the summer herb litter addition. The effect on tree litter decomposition strongly depends on

关键词： Color index   Goat   Growth performance   Meat   Sensory quality   Tannin  

摘要： The objective of this study was to determine the optimum level of condensed tannins (CTs), delivered as Acacia mearnsii extract, for inclusion in the diet of goats for enhancing growth, commercial cuts, the physicochemical composition and fatty acid (FA) profile of the meat and meat sensory attributes. Thirty-two castrated crossbreed Boer goats with a mean age of four months and a mean body weight (BW) of 19.7 +/- 2.05 kg were distributed in a completely randomized design. The diets varied in level of CTs [0, 16, 32 and 48 g/kg dry matter (DM)] from an Acacia mearnsii extract. Final BW;acid detergent fiber (ADF);shoulder, neck and rib weight;and loin yield increased quadratically (P <= 0.05) with the amount of CTs in the diet. Except for a trend of a quadratic reduction in luminosity color (P = 0.07) and a linear reduction in collagen deposition (P = 0.03) with increasing level of dietary CTs, the meat physicochemical parameters were unaffected by CTs inclusion. With increasing amount of CTs from Acacia mearnsii extract in the diet, the concentrations of C17:1 and C18:1 cis-9 in the longissimus lumborum of goats linearly decreased, whereas those of C18:0, C18:2 cis-9, cis-12 and C18:3 cis-9, cis-12, cis-15 (P <= 0.05) linearly increased. In addition, the values of total saturated FA (SSFA), polyunsaturated FA (Sigma PUFA), ratio of Sigma PUFA:Sigma SFA and Sigma PUFA:monounsaturated FA (Sigma MUFA) increased (P <= 0.05) with increasing CTs level;in contrast, Sigma MUFA and the Sigma MUFA/Sigma SFA ratio decreased. Other FA sums and ratios were not affected by the inclusion of CTs in the diet. The inclusion of dietary CTs tended to unfavorably reduce the FA index and enzymatic activity of Delta 9-desaturase C16 (P <= 0.10). However, there was a linear decrease (P <= 0.05) in Delta 9-desaturase C18 and elongase enzymatic activities and the hypocholesterolemic to hypercholesterolemic FA ratio (h:H) index with increasing level of dietary CTs, and the atherogenicity inde