Arbuscular mycorrhizal fungi alter plant community composition along a grazing gradient in Inner Mongolia Steppe

Arbuscular mycorrhizal fungi (AMF) have a significant influence on plant productivity and diversity in non-grazing grassland. However, the interactive effects between grazing intensity and AMF on plant community composition in natural grassland communities are not well known. We conducted a field experiment that manipulated AMF colonization and grazing intensity to study the impact of AMF suppression on plant community composition and nutrient status over 2 years (2015–2016) with contrasting rainfall levels. We found that AMF root colonization was significantly reduced by the application of the fungicide benomyl as a soil drench. Grazing intensity regulated plant community composition and aboveground biomass mainly by reducing the growth of Leymus chinensis over 2 years. AMF suppression increased the growth of Chenopodium glaucum, but it did not alter other plant species across all grazing intensities. The effects of AMF suppression on plant community composition changed along a grazing gradient considerably between years: AMF suppression increased the biomass of C. glaucum across all grazing intensities in 2015, but slightly increased it in 2016. Interactions between AMF suppression and grazing intensity altered the phosphorus concentration of Stipa grandis and Cleistogenes squarrosa in 2015 but not in 2016. AMF suppression decreased the shoot phosphorus content of L. chinensis but increased that of C. glaucum across all grazing intensities. Our results indicate that grazing intensity substantially alters aboveground community biomass and affects growth of dominant species; AMF by itself have limited effects on plant communities along a grazing gradient in typical steppe.     

Forage quality in relation to long-term grazing history,current-year defoliation,and water resource

Forage nitrogen concentrations, nitrogen yields, and in vitro digestibilities were assessed in shortgrass steppe that had been ungrazed, lightly, or heavily grazed for 50 years. Caged plots were defoliated in amounts based upon removals observed in naturallygrazed reference plots or not defoliated. This was done in a year of average precipitation and with a supplemental water treatment to simulate a wet year. In general, current-year defoliation had positive effects, and longterm grazing and supplemental water had negative effects, on forage nitrogen concentrations and digestibilities. However, defoliation interacted with long-term grazing in determning forage nitrogen concentrations, and with grazing and with watering in determining digestibilities. Nitrogen concentration and digestibility increased with defoliation in lightly, but not in heavily, grazed treatments. The dilution effect of supplemental water an digestibilities through increased plant growth was offset by defoliation. The negative effects of long-term grazing on forage quality were small, equally or more than compensated for by defoliation in a year of average precipitation, but more pronounced in the simulated wet year. Nitrogen yields and digestible forage production were usually increased by defoliation, but this depended upon grazing and watering treatments. Increased nitrogen and digestible forage yields and concentrations in response to defoliation were greater than the biomass response in lightly grazed grassland. For both nitrogen and digestibility, yields were greater in grazed than ungrazed treatments in the year of average precipitation, but less in the simulated wet year. Optimizing quantity and year-to-year stability of nitrogen and digestible forage yield may best be achieved with light grazing rather than no or heavy grazing. Clipping was conducted in a manner closely resembling the natural pattern and intensity of defoliation by the cattle, and confirms the potential for a positive feedback of increased forage quality with defoliation observed in pot experiments. Long-term heavy grazing can diminish this response. Quantily (aboveground primary production, ANPP), quantity of quality (digestible and N yields), and quality (concentrations) do not necessarily respond similarly in interactions between current-year defoliation, long-term grazing history, and level of water resource.     

Morphological features and viability of Scrippsiella trochoidea cysts isolated from fecal pellets of the polychaete Capitella sp.

To investigate the impact of grazing by the polychaete Capitella sp. on the two cyst morphotypes of Scrippsiella trochoidea, the typical morphotype with short calcareous spines (spiny-type cyst) and artificially induced the transparent type without calcareous spines (naked-type cyst), we examined the morphological features and germination capability of the two cyst morphotypes isolated from fecal pellets of the polychaete Capitella sp. produced in a restricted habitat. The morphological destruction was observed in both spiny- and naked type cysts after passage through the gut of Capitella sp., and this seemed to occur rapidly for naked-type cysts. In addition, the germination of both spiny- and naked-type cysts isolated from fecal pellets on day 2 of harvesting was significantly reduced and subsequently completely abolished, in contrast to previous findings from ingestion studies. Our results indicate that continual grazing by Capitella sp. within a restricted habitat can compromise the survival of S. trochoidea cysts.     

Seed banks of grazed and ungrazed Baltic seashore meadows

Abstract. The seed banks of three grazed and three ungrazed seashore meadows were studied on the west coast of Finland. 8486 seedlings (mean 13 669 seedlings/m²) germinated from cold-treated samples (n = 343; depth = 10 cm). Most seedlings and species were monocots and perennials. The seed bank flora included 54 dicots vs. 28 monocots and 66 perennials vs. 16 annuals. The most abundant species were Juncus gerardii, Schoenoplectus tabernaemontani, Eleocharis uniglumis, Agrostis stolonifera, Juncus bufonius and Carex nigra, which made up 73% of the seed bank. Numbers of species and seedlings differed between elevation classes. Species richness was highest in elevation class 50–70 cm. The highest seed density occurred in class 20–50 cm. A model for size and species composition of the seed bank in relation to elevation is presented. The seed bank was larger and richer in species in the ungrazed than in the grazed sites, but not so in the upper elevations and closest to the open sea. Grazing reduced the size of the seed bank of Agrostis stolonifera, A. capillaris, Calamagrostis stricta, Elymus repens, Juncus bufonius, Limosella aquatica and Schoenoplectus tabernaemontani, but increased that of J. gerardii. 32 species germinated only from ungrazed samples and 11 species only from grazed ones. Multivariate classification resulted in nine sample groups. The ordination scatter was best explained by the flooding stress variables, elevation, the distance from the water line and the number of helophyte species in samples. 75 species were found both in the seed bank and in the vegetation, but there was a significant lack of resemblance (in the Mantel test) due to over-representation of some species. Eight species occurring only in the seed bank were mainly annuals or biennials (63%); those occurring only in the established vegetation (86 species) were mainly perennials (86%).     

草原植物的放牧抗性

放牧抗性是指在放牧系统中,草原植物生存和生长的相对能力,包括避食性和耐牧性两部分,放牧避食性是指植物降低被牧食的机率和强度等机制,而耐牧性是指植物被牧食以后刺激植物再生长的机制,对物种抗性阈值和耐牧性阈值的研究将有利于解释放牧演替理论的原因和机制,不同的物种其抗性阈值和耐牧性阈值不同,这主要起决于它们放牧抗性策略,在草地管理中,认识植物将避食性和／或耐牧性机制作为诱导物种组成变化的优先抗性策略具有重要的理论和实践意义。     

Restricting dairy cow access time to pasture in autumn: The effects on milk production,grazing behaviour and DM intake of late lactation dairy cows

Extending the grazing season in pasture based systems of dairy production can increase farm profitability; poor weather and soil conditions can reduce the number of grazing days. The study objectives were to (i) examine the effect of restricted access to pasture in the autumn on the milk production, grazing behaviour and DM intake (DMI) of late lactation spring-calving dairy cows and (ii) establish the effect of alternating restricted and continuous access to pasture on dairy cow production, DMI and grazing behaviour. Cows were randomly assigned to one of four grazing treatments: (i) 22 h (full-time) access to pasture (22H; control); (ii) Two 5-h periods of access to pasture (2×5H); (iii) Two 3-h periods of access to pasture (2×3H); and (iv) alternating between full-time and 3-h access to pasture with no more than three continuous days on any one regime, e.g. Monday – full-time access, Tuesday − 2x3H access, Wednesday − 2x3H access; Thursday – full-time access, etc. (2×3HV). Restricted access to pasture was offered after a.m. and p.m. milking. Swards of similar quality and pregrazing herbage mass were offered. Treatment had no effect on milk yield (13.2 kg/day), milk fat (48.2 g/kg), protein (39.0 g/kg) or lactose content (42.6 g/kg) and milk solid yield (1.15 kg/day). Similarly, there was no effect of treatment on final BW (483 kg) or final BCS (2.66). There was no significant difference in DMI (15.1 kg DM/cow/day) between treatments. There was an effect on daily grazing time, 22H cows (565 min/cow/day) grazed for longest time, however, when the 2x3HV treatment had full-time access to pasture, they had a similar grazing time (543 min/cow/day) to the 22H cows and were similar to the 2x3H treatment on days with restricted access to pasture (357 min/cow/day). The 22H and 2x5H animals had similar grass DMI/min (29.2 g/min), the 2x3HV were higher (33.9 g/min) but were similar to the comparable treatment when offered 2x3H access time (41.6 g/min) and when offered 22H access time (27.7 g/min). The results from this study show how when offered a grass only diet of autumn pasture grazing behaviour can be modified by restricting pasture access time without reducing dairy cow production in late lactation at low production levels. There was also no effect of alternating access time between 22H and 2x3H on milk production and DMI in the 2x3HV treatment. Restricted access time to pasture in autumn may be a strategy which farmers can use to extend the grazing season.     

Dynamic response of woody vegetation on fencing protection in semi-arid areas; Case study: Pilot exclosure on the Firmihin Plateau,Socotra Island

Woody vegetation dynamics and Dracaena cinnabari regeneration have been studied for five years in the conditions of Socotra Island. Woody plants were measured regularly inside and outside the exclosure area, and the growth and survival of D. cinnabari seedlings were observed. In the exclosure of about 1000 m² a total of 49 species were identified, including 23 endemics, growing in the average density of 3.82 specimens per m². The fenced area was overgrown relatively rapidly by dense grass cover – reaching approx. 2.7 t/ha. Species growth dynamics inside and outside the exclosure shows that grazing had a marked impact, leading to the elimination of trees and shrubs. All grazed species grew noticeably in the exclosure, in the average of 50 cm in 5 years. D. cinnabari as the dominant flagship species of Socotra has been studied with regards to regeneration dynamics. Observations indicate that probability of its seedlings survival increases with their age. No seedlings germinated from the seeds sown in the experiment, however, outplanted seedlings performed relatively well. Field observations show that D. cinnabari seed germination is triggered when the seed reaches a protected micro-habitat with a developed humus layer and high relative humidity in the soil lasts for at least two days.     

Configuration of daily grazing and searching of growing beef cattle in grassland: observational study

Many of the studies in Campos grasslands focus on management aspects such as the control of herbage allowance, and application of nutrients and/or overseeding with legumes. However, there is little literature on how the Campos grassland resource is utilised, especially regarding the grazing pattern and the relationship between pasture quantity and quality on daily grazing activities. The study of the ingestive behaviour in species-rich and heterogeneous native grasslands during daylight hours, and understanding how animals prioritise quality or quantity of intake in relation to pasture attributes, are important to comprehend the ingestive-digestive processes modulating the energy intake of animals and to achieve a better grazing management. Therefore, the objective was to describe and quantify the daily grazing behaviour of growing cattle grazing native pasture with different structures as a result of different management practices, and study the relationship of pasture attributes and intake through multivariate analysis. The study was carried out at the Faculty of Agronomy, Paysandú, Uruguay. Treatments were native grassland, overseeding with Trifolium pratense and Lotus tenuis + phosphorus, and native pasture + nitrogen-phosphorus. Grazing activities were discriminated into grazing, searching (defined when animals take 1–2 bites in one feeding station and then change to another feeding station and so on), ruminating and idling. The probability of time allocated to each activity was continuously measured during daylight hours (0700–1930) and was related to pasture structure and forage quality using regression tree models, while the bite rate was determined every 2 h. The diurnal pattern of growing cattle showed grazing and searching sessions, followed by ruminating and idling sessions. The length of sessions (as the probability of time allocated to each activity) varied throughout the day. The grazing probability was greater during afternoon than morning and midday (0.74 vs 0.45 vs 0.46, respectively), and it was associated with higher bite rate (34.2 bites/min). Regression tree models showed different grazing, searching and ruminating strategies according to pasture attributes. During the morning, animals modified grazing, searching, ruminating and idling strategies according to bite rate, crude protein in diet and herbage allowance. At midday, they only adjusted ruminating and idling, while during afternoon sessions, grazing activities were modified by pasture quantity attributes such as herbage mass and herbage allowance. By controlling the herbage allowance, herbage mass and pasture height, animals prioritise quality in the morning and quantity in the afternoon, integrating and modifying the grazing-searching and ruminating-idling pattern.     

Food patch size, food concentration and grazing efficiency of the harpacticoid Paramphiascella fulvofasciata (Crustacea, Copepoda)

Harpacticoid copepods are known as important grazers on primary producers. The underlying factors for their food selectivity and grazing efficiency are however far from well known. For instance, their patchy distribution in the marine environment is well documented but how meiofaunal organisms cope with the spatial distribution/accessibility of the available food resources is less clear.In the present study a laboratory experiment was conducted to test the grazing efficiency of Paramphiascella fulvofasciata (Copepoda, Harpacticoida) on the epipelic diatom Seminavis robusta applied in recipients of different area and in various concentrations. Diatoms were enriched in the stable isotope ¹³C in order to trace food uptake and copepods were left to graze for 4 days.We found that the grazing efficiency of P. fulvofasciata was diatom concentration-dependent. A lower diatom uptake at lower diatom densities illustrated this clear functional response. On the contrary, there was no significant effect of the area per se where the copepods could graze upon. The lack of a significant effect of area is mainly due to the high variability in uptake that was recorded in some treatments. Although P. fulvofasciata is a very motile copepod, known as endobenthic and epibenthic species, it was able to concentrate on food uptake at the bottom of the experimental unit as there was no significant difference in uptake between treatments with different water heights in the units. In addition, it was found that a diatom concentration of about 140 000 cells/cm² favours egg production of P. fulvofasciata.     

夏季胶州湾微型浮游动物摄食初步研究

2002年6月至7月间对胶州湾内、外和港口3个典型站位进行了微型浮游动物对浮游植物的摄食研究．按陆基半现场方式进行了4次稀释法实验,对湾外相同的站位进行了两次实验,对湾内和港口各进行了一次实验,获取了研究站位浮游植物和微型浮游动物种类、丰度、体积转换浮游植物碳含量、碳／叶绿素比率、浮游植物净生长率、微型浮游动物摄食率、对潜在初级生产力的摄食压力、对浮游植物现存量的摄食压力以及碳摄食通量等参数．湾外和湾内站位的浮游植物组成相似,优势种为新月柱鞘藻(Cylindrotheca closterium)和中肋骨条藻(Skeletonema costatum),港口浮游植物优势种类为中肋骨条藻、浮动湾角藻(Eucampia zodiacus)和旋链角毛藻(Chaetoceros curvisetus)．湾外微型浮游动物的优势种为百乐拟铃虫(Tintinnopsis beroidea),而在湾内为百乐拟铃虫和急游虫(Strombidium sp．),港口主要为急游虫,也有少数的百乐拟铃虫．微型浮游动物对浮游植物的摄食率和对潜在初级生产力的摄食压力,在湾内最高,其次在湾外,港口最低．微型浮游动物对浮游植物的摄食率,在湾外,分别为0．96和1．20d^-1,在湾内为1．33d^-1,在港口为0．36d^-1．微型浮游动物对潜在初级生产力的摄食压力,在湾外,分别为74％和84％,在湾内为93％,在港口为53％．微型浮游动物的碳摄食通量在港口最高达到281mgC·m^-3·d^-1,在湾内为102mgC·m^-3·d^-1,在湾外最低范围在31～49mgC·m^-3·d^-1．浮游植物的细胞大小和两种微型浮游动物的摄食习性的不同是造成研究站位微型浮游动物摄食率和摄食压力不同的主要原因．同世界其它内湾相比,胶州湾微型浮游动物的摄食压力处于中等水平。     

内蒙古草原草场放牧退化模式研究及退化监测专家系统雏议

本文将定位研究与路线考察相结合,将放牧影响下草原的动态演替及其在牧压梯度上的空间变化相对比,研究了内蒙古主要草原草场的放牧退化模式,并在此基础上初步探讨了判别草场退化的数量指标和退化监测专家系统。1)植物种与牧压关系的分析,区别出放牧的定性和定量指示植物及宜中牧植物,并划分植物为不同的放牧生态种组。2)退化草原恢复过程的研究表明,根茎禾草的恢复快于丛生禾草;群落恢复过程是单稳态的,且恢复演替动态与其牧压梯度上的空间变化相对应。3)内蒙古高原主要草原草场在持续放牧影响下均趋同于冷蒿(Artemisia frigida)草原。冷蒿是最可靠的正定量放牧指示植物,但同时又是优良牧草和草原退化的阻击者。4)讨论了草原草场退化的概念,论述了草原逆向演替与草场退化的区别和联系,提出了区分草原的逆向演替为草场熟化和退化两个过程,并依草场群落与牧压的关系建立了判定草场是否退化及退化程度的数量指标。5)初步设计了草原草场退化监测—决策专家系统,包括监测、判别和决策三个步骤。     

Feeding and survival rates of the copepods Euterpina acutifrons Dana and Acartia grani Sars on the dinoflagellates Alexandrium minutum Balech and Gyrodinium corsicum Paulmier and the Chryptophyta Rhodomonas baltica Karsten

Here we studied the feeding performances and survival rates of the copepods Euterpina acutifrons and Acartia grani exposed to cultures of the toxic dinoflagellates Alexandrium minutum and Gyrodinium corsicum and the nontoxic Chryptophyta Rhodomonas baltica. The presence of hemolysins in G. corsicum was also analysed. For both copepod species, high ingestion rates on A. minutum and lower but similar rates on G. corsicum and R. baltica were found. After 120 h, only the E. acutifrons that grazed on G. corsicum or R. baltica showed 100% survival, whereas survival of the copepods that grazed on A. minutum was significantly lower. A. grani was more sensitive to the dinoflagellates, and at 120 h showed survival rates of 70% on G. corsicum and 60% on A. minutum. These results support the hypothesis that the feeding interactions between copepods and toxic dinoflagellates are highly species-specific. Long-term observations indicated that E. acutifrons can graze on G. corsicum without impairing their feeding or growth performances. Both copepod species consumed A. minutum in the short-term, but their long-term impact on this and other toxic marine dinoflagellates would be limited by the toxic effects of these flagellates. We did not find any evidence of haemolytic activity in extracts of G. corsicum. Toxins other than haemolysins may be responsible for the deleterious effects observed on A. grani.     

Simulated long-term vegetation response to alternative stocking strategies in savanna rangelands

Increasing cover by woody vegetation, prevalent in semiarid savanna rangelands throughout the world, is a degrading process attributed to the grazing impact as a major causal factor. We studied grazing effects on savanna vegetation dynamics under alternative stocking strategies with a spatially explicit grid-based simulation model grounded in Kalahari (southern Africa) ecology. Plant life histories were modeled for the three major life forms: perennial grasses, shrubs, annuals. We conducted simulation experiments over a range of livestock utilization intensities for three alternative scenarios of small scale grazing heterogeneity, and two alternative strategies: fixed stocking versus adaptive stocking tracking herbage production. Additionally, the impact of the duration of the management planning horizon was studied, by comparing community response and mean stocking rates after 20 and 50 years. Results confirmed a threshold behavior of shrub cover increase: at low, subcritical utilization intensity little change occurred; when utilization intensity exceeded a threshold, shrub cover increased drastically. For both stocking strategies, thresholds were highly sensitive to grazing heterogeneity. At a given critical utilization intensity, the long term effect of grazing depended on the level of grazing heterogeneity: whereas under low heterogeneity, shrub cover remained unchanged, a large increase occurred under highly heterogeneous grazing. Hence, information on spatial grazing heterogeneity is crucial for correct assessment of the impact of livestock grazing on vegetation dynamics, and thus for the assessment of management strategies. Except for the least heterogeneous grazing scenario, adaptive stocking allowed a more intensive utilization of the range without inflating the risk of shrub cover increase. A destabilizing feedback between rainfall and herbage utilization was identified as the major cause for the worse performance of fixed compared to adaptive stocking, which lacks this feedback. Given the usually high grazing heterogeneity in semiarid rangelands, adaptive stocking provides a management option for increasing herbage utilization and thus returns of livestock produce without increasing degradation risks.     

Herbivory resistance traits in populations of Poa ligularis subjected to historically different sheep grazing pressure in Patagonia

Seeding selected populations with high grazing resistance may foster recovery of plant populations threatened by overgrazing. Resistance to grazing depends on grazing avoidance (escape from grazers) and grazing tolerance (ability to growth after defoliation). Many studies of grazing tolerance defoliate plants at a fixed height instead of removing the same proportion of biomass and therefore confound tolerance with avoidance. For this reason, the information on evolution of tolerance to defoliation at the intraspecific level is remarkably scarce despite the abundance of papers published that evaluate responses to defoliation. The estimation of the cost of tolerance is also troublesome because current methods usually include spurious correlations due to correlation between variables that share common terms. The objectives of this paper were to assess the intraspecific variation in tolerance and in traits associated with avoidance and growth in populations with different sheep grazing histories. We also estimated the percentage of biomass removed when the defoliation treatment was imposed at fixed height in order to separate tolerance and avoidance. Finally, we estimated the cost of tolerance using a new method proposed for spurious correlations. Results of a greenhouse experiment indicated no difference in tolerance among the three compared populations. However, the populations from overgrazed fields had more prostrate growth form, higher specific leaf area, and higher tillering rate (when no defoliated) than populations from exclosures. We confirmed that fixed height defoliation would have removed a higher proportion of shoot biomass from taller than from shorter individual plants, confounding grazing tolerance and avoidance. Regarding the cost of tolerance, we found no differences from a null model of no cost, indicating that the evolution (or future breeding) of more tolerant genotypes would not be constrained by this cost.     

Is diatom size selection by harpacticoid copepods related to grazer body size?

Copepods are known as important consumers of primary production and are eaten by larger animals. They therefore form a main link to higher trophic levels. While feeding pathways and specificity of planktonic copepods have been well studied, the selectivity of the benthic harpacticoid copepods is far less documented. A better knowledge of the functional ecology of harpacticoids as important grazers on primary producers may have consequences for the re-evaluation of basic energy flow in benthic ecosystems.We tested whether size selectivity for diatoms exists in harpacticoid copepods. We hypothesized that size selectivity of harpacticoid copepod species is strongly related to body size. Because of morphological constraints, we expected smaller copepods to prefer smaller diatoms while larger copepods should be able to consume both small and large diatoms. We tested this hypothesis in four harpacticoid copepod species of varied body size: Tigriopus brevicornis, Harpacticus obscurus, Amphiascus minutus and Paramphiascella fulvofasciata. As food source we used two ¹³C labelled strains of the benthic diatom Seminavis robusta with a four-fold difference in cell biovolume.Three out of four harpacticoid species showed size selectivity: H. obscurus and A. minutus preferred the larger Seminavis cells, while P. fulvofasciata selected the smaller Seminavis cells. Based on monoclonal treatments, there was no clear preference found for T. brevicornis although there was a small preference for large cells in the mixed treatments. Except for P. fulvofasciata, all species showed a lower uptake when offered the mixed diet (both small and large cells). Although most species showed a size selectivity, our results suggest that this selectivity was not related to their body size. However, the only species that ate significantly more of small diatoms was characterised by comparatively small mouthparts in relation to its body size.     

Review: Assessment of dairy cow welfare at pasture: measures available,gaps to address,and pathways to development of ad-hoc protocols

Pasture is generally perceived as positive for dairy cow welfare, but it nevertheless exposes cows to heat, parasites, and other challenges. This review is intended for people ready to design comprehensive protocols for assessing the welfare of dairy cows at pasture. We provide an overview of the benefits and risks of pasture for cows, and then go on to identify the available and feasible measures for assessing cow welfare at pasture and the gaps that need to be addressed to develop specific welfare measures. Some of the measures from on-farm welfare assessment protocols designed for indoor use (e.g. Welfare Quality®) are relevant for cows at pasture (e.g. lameness scoring). However, the timing, location and/or method for certain measures (e.g. observation of social behaviour) need to be adapted to the pasture context, as cows at pasture can roam over a large area. Measures to address specific pasture-related risks (e.g. heat stress, biosecurity) or benefits (e.g. expression of a wide range of behaviours) should be implemented in order to capture all dimensions of cow welfare at pasture. Furthermore, cow welfare is liable to vary over the grazing season due to changes in weather conditions, grass quality and pasture plots that induce variations in lying surface conditions, food availability, distance to walk to the milking parlour, and so on. It is therefore important to investigate the variability in different welfare measures across the pasture season to check whether they hold stable over time and, if not, to determine solutions that can give an overview across the grazing season. Sensors offer a promising complement to animal and environment observations, as they can capture long-term animal monitoring data, which is simply not possible for a one-day welfare-check visit. We conclude that some measures validated for indoor situations can already be used in pasture-based systems, while others need to be validated for their fitness for purpose and/or use in pasture conditions. Furthermore, thresholds should probably be determined for measures to fit with pasture contexts. If all measures can be made adaptable to all situations encountered on farms or variants of the measures can at least be proposed for each criterion, then it should be possible to produce a comprehensive welfare assessment protocol suitable for large-scale use in near future.     

Predation on barnacles of intertidal and subtidal mussel beds in the Wadden Sea

Balanids are the numerically dominant epibionts on mussel beds in the Wadden Sea. Near the island of Sylt (German Bight, North Sea), Semibalanus balanoides dominated intertidally and Balanus crenatus subtidally. Field experiments were conducted to test the effects of predation on the density of barnacle recruits. Subtidally, predator exclusion resulted in significantly increased abundances of B. crenatus, while predator exclusion had no significant effects on the density of S. balanoides intertidally. It is suggested that recruitment of B. crenatus to subtidal mussel beds is strongly affected by adult shore crabs (Carcinus maenas) and juvenile starfish (Asterias rubens), whereas recruits of S. balanoides in the intertidal zone are mainly influenced by grazing and bulldozing of the very abundant periwinkle Littorina littorea, which is rare subtidally. Thus, not only do the barnacle species differ between intertidal and subtidal mussel beds, but the biotic control factors do so as well. Electronic Publication     

The propagation of disturbance in savannas through food webs

Abstract. Savanna-grassland ecosystems are highly interactive due to effects among interconnected trophic elements. This can cause disturbance at one level in the trophic web to be propagated through that web to have effects far removed from the initial locus of disturbance. The reconstructed effects of rinderpest upon African savannas, acting directly upon susceptible grazers and browsers but in directly upon many other ecosystem components, are used as a case history illustrating the propagation of disturbance in savanna ecosystems.     

A cautionary note: Examples of possible microbial community dynamics in dilution grazing experiments

Dilution experiments are used commonly to provide estimates of grazing pressure exerted on phytoplankton and bacterioplankton as well as estimate their growth rates. However, very little attention has been given to the dynamics of grazers, especially heterotrophic nanoflagellates (HNF), in such experiments. We found temporal changes in concentrations of ciliates and HNF in a dilution experiment using water from the oligotrophic N.W. Mediterranean Sea. Ciliates decreased markedly over 24 h when held in seawater diluted with particle-free water (60% and 20% final conc whole seawater) while HNF increased in concentration in the same treatments. Using a time-course approach in a second experiment, we monitored changes in HNF and bacterioplankton concentrations in 20% whole seawater (80% particle-free seawater). Both HNF and heterotrophic bacteria displayed stable concentrations for the first 12 h and then grew rapidly, especially HNF, from 12 to 24 h. Examination of bacterial community composition using denaturing gel gradient electrophoresis (DGGE) showed a change in community composition over the 24 h incubation period. Dilution can have differential effects on the distinct components of the marine microbial food web.