中国典型草原放牧草场蝗虫为害损失及经济阈值的估算(英语)

传统上估算蝗虫在放牧草场为害损失的方法几乎都是用来测定对牧草秋季产量的影响,而实际上,在估算放牧草场蝗虫为害损失及经济阈值时,牧草的现存量而非秋季产量是更应考虑的因素.本文提出了一种适合测定蝗虫对牧草现存生物量影响的新方法,即野外挂笼饲养与蝗虫种群动态相结合的估算方法,并在此基础上组建了放牧草场蝗虫种群经济阈值模型;α_0 α_1M_1_α_2M_2_ α_3S_1 α_4S_2=C其中,M_1:狭翅雏蝗生物量;M_2:宽须蚁蝗生物量;S_1:狭翅雏蝗平均个体重量,S_2:宽须蚁蝗平均个体重量;α_0-α_4:常数.同时引入蝗虫种群数量和生物量两项参数来表达蝗虫种群的发生程度.     

FORAGE LOSSES CAUSED BY GRASSHOPPER CHORTHIPPUS DUBIUS (ZUB.1 ON GRASSLAND IN INNER MONGOLIA OF CHINA

Abstract To quantitatively assess the losses of forage, we conducted experiments to determine the average amount of forage destroyed (forage consumed plus forage cut-off and dropped to the ground) per day by the grasshopper, Chorthippus dubius (Zub.), at its different life stages in laboratory and then extrapolated estimates of losses caused by the field grasshopper population from these results and the population densities of this grasshopper. The main results are as follows:

• 1 Ch. dubius is a late-occurring species of grasshoppers in Inner Mongolian grassland. It occurred from June to October. The duration for each instar and the longevity of the adult under natural conditions ranged from 9. 09–9. 81 fdays) and 17. 65–19. 441days) respectively.
• 2 Both consumption and forage defoliation rates by Ch. dubius increase with its developemnt. The consumption rates had significantly linear relationships with the grasshopper's body weights.
• 3 Average losses caused by one grasshopper in its whole lifespan were 487. 55–784. 4 mg (dry weight) and the average amount of forage consumed and wasted per day was 7. 64–11. 45 mg.
• 4 Total losses caused by Ch. dubius population in 1990 ranged from 0. 762–1. 647 g/m² in the three types of vegetation, and the largest value was found in restorative type. The seasonal courses of cumulative forage losses would fit logistic equations in the three vegetation types.
• 5 Population densities (18. 5, 194., 11. 8/m², 4th instar nymph predominantly) were suggested as the levels at which control should be initiated on the three types of pastures respectively.

     

Effects of large herbivore grazing on grasshopper behaviour and abundance in a meadow steppe

1. Adaptive phenotypic plasticity has been a major subject in evolutionary ecology, but how a species' behaviour may respond to certain environmental change is still not clear. In grasslands worldwide, large herbivores are increasingly used as a tool for grazing management, and occur to interact with grasshoppers that dominate grassland insect communities. Previous studies have been well-documented about grazing effects on diversity and abundance of grasshoppers. Yet, how grazing may alter grasshopper behaviour, and potential effects on their abundance remains elusive. 2. We conducted a field experiment by manipulating grazing using sheep, cattle, and their mix to examine the behavioural responses and abundance of the grasshoppers (Euchorthippus unicolor) to grazing in a Leymus chinensis-dominated grassland. 3. Results showed that the grasshoppers spent less time on feeding and resting on grasses, but more time on switching and resting on forbs under cattle grazing and mixed grazing with cattle and sheep. In contrast, the grasshoppers spent more time on feeding but less time on switching and resting on forbs under sheep grazing. The behavioural changes were also potentially linked to grasshopper abundance in the context of grazing management. 4. The responses of grasshopper behaviour and abundance to grazing may be largely triggered by altered vegetation and microclimates. Such behavioural flexibility of grasshoppers must be considered when large herbivores are recognised as a management tool for influencing grasshopper abundance, and grazer species should be paid more attention both individually and jointly for better grassland conservation.     

内蒙古草原三种植物群落中狭翅雏蝗造成的牧草损失(英文)

狭翅雏蝗Chorthippus dubius是我国北方草原的重要蝗种之一,在大发生年对牧草的威胁很大。它对牧草的损失至今尚无较准确的定量估算。本文通过测定不同发育阶段狭翅雏蝗的取食率、掉落毁损率,结合野外自然种群数据,对内蒙古草原三种植物群落中狭翅雏蝗造成的牧草损失进行了估测,并对三种草场蝗虫的经济阈值进行了计算。主要研究结果如下: 1.狭翅雏蝗对羊草、冷蒿、大针茅的取食率相似;取食率与虫体体重存在显著的线性相关。 2.狭翅雏蝗每个个体在一生中平均造成牧草损失487.55—784.4mg(干重),每日消耗与浪费的牧草为7.64—11.45mg。 3.狭翅雏蝗种群造成的牧草损失在冷蒿群落、羊草-大针茅-羊草群落、羊草-大针茅群落分别为1.52,1.65,0.76g/m,占地上初级生产量的2.96％、1.18％、0.42％,表现为越退化的草场,狭翅雏蝗对牧草的压力越大。其累积损失量的季节程式可以刚logisuc方程拟合。 4.狭翅雏蝗的经济阈值在羊草、羊草+大针茅+冰草、冷蒿草原分别为每平方米18.5、19.4、11.8头四龄为主个体。     

不同放牧强度下的内蒙古草原蝗虫群落动态

本文研究了内蒙古草原蝗虫群落在不同放牧强度下的动态变化。植物和蝗虫的取样涉及3种植物群落类型。每一种群落类型又根据放牧强度的不同,划分为5个放牧梯度。随着放牧强度的增加,蝗虫群落的组成和结构均发生了明显的变化。使用贴近度分析及择近原则的方法,阐明了蝗虫种的优势度变化及替代种的替代次序。通过灰色关联及系统聚类分析方法的结合,分析了11个蝗虫种对不同放牧强度的反应。对应性分析和多元逐步回归分析说明,蝗虫群落的变化是与某些植被因子和土壤因子密切相关,特别是植物种类数、生物量、高度以及土壤硬度和含水量等。某些蝗虫种的生态指示意义也在文中进行了讨论。     

Relationships among the Stem, Aboveground and Total Biomass across Chinese Forests

Forest biomass plays a key role in the global carbon cycle. In the present study, a general allometric model was derived to predict the relationships among the stem biomass Ms, aboveground biomass MA and total biomass MT, based on previously developed scaling relationships for leaf, stem and root standing biomass. The model predicted complex scaling exponents for MT and/or MA with respect to Ms. Because annual biomass accumulation in the stem, root and branch far exceeded the annual increase in standing leaf biomass, we can predict that MT ∝MA ∝ Ms as a simple result of the model. Although slight variations existed in different phyletic affiliations （i.e. conifers versus angiosperms）, empirical results using Model Type Ⅱ （reduced major axis） regression supported the model＇s predictions. The predictive formulas among stem, aboveground and total biomass were obtained using Model Type I （ordinary least squares） regression to estimate forest biomass. Given the low mean percentage prediction errors for aboveground （and total biomass） based on the stem biomass, the results provided a reasonable method to estimate the biomass of forests at the individual level, which was insensitive to the variation in local environmental conditions （e.g. precipitation, temperature, etc.）.     

Leaf meristems: an easily ignored component of the response to human disturbance in alpine grasslands

Grazing and fencing are two important factors that influence productivity and biomass allocation in alpine grasslands. The relationship between root (R) and shoot (S) biomass and the root:shoot ratio (R/S) are critical parameters for estimating the terrestrial carbon stocks and biomass allocation mechanism responses to human activities. Previous studies have often used the belowground:aboveground biomass ratio (M_b/M_a) to replace the R/S in alpine ecosystems. However, these studies may have neglected the leaf meristem biomass, which belongs to the shoot but occurs below the soil surface, leading to a significant overestimation of the R/S ratio. We conducted a comparative study to explore the differences between the R/S and M_b/M_a at both the species (Stipa purpurea, Carex moorcroftii, and Artemisia nanschanica) and community levels on a Tibetan alpine grassland with grazing and fencing management blocks. The results revealed that the use of the M_b/M_a to express the R/S appeared to overestimate the actual value of the R/S, both at species and community levels. For S. purpurea, the M_b/M_a was three times higher than the R/S. The M_b/M_a was approximately two times higher than the R/S for the species of C. moorcroftii and A. nanschanica and at the community level. The relationships between the R‐S and M_b‐M_a exhibited different slopes for the alpine plants across all the management practices. Compared to the fenced grasslands, the plants in the grazing blocks not only allocated more biomass to the roots but also to the leaf meristems. The present study highlights the contribution of leaf meristems to the accurate assessment of shoot and belowground biomasses. The R/S and M_b/M_a should be cautiously used in combination in the future research. The understanding of the distinction between the R‐S and M_b‐M_a may help to improve the biomass allocation mechanism response to human disturbances in an alpine area.     

DYNAMICS OF GRASSHOPPER COMMUNITIES UNDER DIFFERENT GRAZING INTENSITIES IN INNER MONGOLIAN STEPPES

Abstract Vegetation and grasshopper community variables were monitored on the natural steppes grazed by livestock in Inner Mongolia, China. The sites sampled belong to 3 vegetation types laid separately in 3 continuums from different grazing intensities. Each continuum consisted of 5 plots along grazing gradients. Within the plots, the species composition, population number and population calorific value of grasshoppers that was converted from their biomass varied sensitively with increase of grazing intensities. The methods of neartude and choosing rules of fuzzy mathematics were used to analyze successive populations of grasshoppers. By combining the gray relation with hierarchic cluster analysis, eleven grasshopper species were divided into 3 grazing guilds based on their responses to grazing. The results from detrended correspondence and the multivariate regression analysis proved that there were close successive relationships among the grasshopper species that varied with the changes of plant species, biomass, height and coverage. The importance of some grasshopper indicators to grassland change is discussed.     

Changes in western wheatgrass foliage quality following defoliation: consequences for a graminivorous grasshopper

We determined the effects of defoliation by a graminivorous grasshopper on the foliage quality of the C3 plant, western wheatgrass (Pascopyrum smithii [Rydb] A. Love). Additionally, we determined the effects of this defoliation upon the subsequent feeding of the graminivorous grasshopper Phoetaliotes nebrascensis Thomas (Orthoptera: Acrididae). In field and greenhouse studies, graminivorous grasshopper herbivory altered the quality of remaining western wheatgrass foliage. In the greenhouse, severe (50% foliage removal) grasshopper grazing (638 grasshoppers/m² for 72h) resulted in decreased foliar nitrogen (–12%), carbohydrate (–11%) and water (–2.5%) concentrations, and increased phenolic concentrations (+43%). These changes were associated with decreased adult female grasshopper mass gain, consumption rate, approximate digestibility, and food conversion efficiencies. In the field, moderate (14% foliage removal) grasshopper grazing (20 grasshoppers/m² for 20 days) led to a 10% reduction in foliar nitrogen concentrations. Foliage quality changes in the field were not associated with any reductions in grasshopper mass gain, consumption rates, food digestibility, or conversion efficiencies. The results presented here are consistent with the hypothesis that defoliation leads to a reallocation of carbon and nitrogen compounds within the plant such that foliage quality for P. nebrascensis is reduced.     

Persistence of <Emphasis Type="Italic">Paranosema</Emphasis> (<Emphasis Type="Italic">Nosema</Emphasis>) <Emphasis Type="Italic">locustae</Emphasis> (Microsporidia: Nosematidae) among grasshopper (Orthoptera: Acrididae) populations in the Inner Mongolia Rangeland,China

Paranosema (Nosema) locustae Canning has persisted in grasshopper populations in the Inner Mongolia Rangeland since spore treatment was applied in 1993. In the treatment year, a 58.32–71.43% reduction of grasshoppers was recorded and 59.26–80.36% of surviving grasshoppers of various species were infected. In the years following application, prevalence of P. locustae varied from 13.65% to 60.71%, demonstrating that P. locustae remains in grasshopper populations for many years. Infection prevalence was more than 60.00% for Dasyhippus barbipes (F.-W.), Bryodema luctuosum luctuosoma (Stoll) and Angaracris barabensis (Pall.) in 1993 but was very variable, ranging from 20.00% to 60.71% over the subsequent nine years. Disease prevalence was 43.72–60.71% in 1993 and 1994 for Oedaleus asiaticus B.-Bienko and Myrmeleotettix palpalis (Zub.) but gradually declined to approximately 20%, where it remained. Persistence of P. locustae in grasshopper populations may be important in keeping densities below economic thresholds for a number of years after application. Handling Editor: Helen Roy.     

放牧干扰下的蝗虫－植物相互作用关系

本文研究了内蒙古典型草原植物和蝗虫群落在不同放牧强度影响下的多样性、均匀性和丰盛度变化。比较了蝗虫群落与植物群落在放牧梯度上的相互作用关系。研究发现,放牧干扰活动会明显地影响植物和蝗虫群落结构,但蝗虫群落结构的变化趋势并非与植物完全同步。蝗虫与植物间的联系更多地表现在植物起着蝗虫栖息地条件的作用,而并不完全是食料植物的作用。文中对放牧实践与多样性保护的关系进行了讨论。     

Grasshopper fecundity responses to grazing and fire in a tallgrass prairie

Grasshopper abundance and diversity vary with management practices such as fire and grazing. Understanding how grasshopper life history traits such as fecundity respond to management practices is key to predicting grasshopper population dynamics in heterogeneous environments. Landscape-level experimental fire and bison grazing treatments at the Konza Prairie Biological Station (Manhattan, KS) provide an opportunity to examine how management affects grasshopper fecundity. Here we report on grasshopper fecundity for nine common species at Konza Prairie. From 2007 to 2009, adult female grasshoppers were collected every 3 wk from eight watersheds that varied in fire and grazing treatments. Fecundity was measured by examining female reproductive tracts, which contain a record of past and current reproductive activity. Body size was a poor predictor of fecundity for all species. Despite large differences in vegetation structure and composition with management regime (grazing and fire interval), we observed little effect of management on grasshopper fecundity. Habitat characteristics (grasshopper density, vegetation biomass, and vegetation quality; measured in 2008 and 2009) were better predictors of past fecundity than current fecundity, with species-specific responses. Fecundity increased throughout the summer, indicating that grasshoppers were able to acquire sufficient nutritional resources for egg production in the early fall when vegetation quality is generally low. Because fecundity did not vary across management treatments, population stage structure may be more important for determining population level reproduction than management regime at Konza Prairie.     

Herbivore phenology can predict response to changes in plant quality by livestock grazing

Livestock grazing can have a strong impact on herbivore abundance, distribution and community. However, not all species of herbivores respond the same way to livestock grazing, and we still have a poor understanding of the underlying mechanisms driving these differential responses. Here, we investigate the effect of light intensity cattle grazing on the abundance of two grasshoppers (Euchorthippus cheui and E. unicolor) that co-occur in the same grasslands and feed on the same food plant (the dominant grass Leymus chinensis). The two grasshopper species differ in phenology so that their peak abundances are separated into early- and late-growing seasons. We used an exclosure experiment to monitor grasshopper abundance and food quality in the field under grazed and ungrazed conditions, and performed feeding trials to examine grasshopper preference for grazed or ungrazed food plants in the laboratory. We found that the nitrogen content of L. chinensis leaves continuously declined in the ungrazed areas, but was significantly enhanced by cattle grazing over the growing season. Cattle grazing facilitated the early-season grasshopper E. cheui, whereas it suppressed the late-season grasshopper E. unicolor. Moreover, feeding trials showed that E. cheui preferred L. chinensis from grazed plots, while E. unicolor preferred the leaves from ungrazed plots. We conclude that livestock grazing has opposite effects on the two grasshopper species, and that these effects may be driven by grazing-induced changes in plant nutrient content and the unique nutritional niches of the grasshoppers. These results suggest that insects that belong to the same guild can have opposite nutrient requirements, related to their distinct phenologies, and that this can ultimately affect their response to cattle grazing. Our results show that phenology may link insect physiological needs to local resource availabilities, and should be given more attention in future work on interactions between large herbivores and insects.     

Interspecific competition among grasshoppers and their effect on plant abundance in experimental field environments

Summary We tested whether grasshoppers in experimental field environments, i.e. cages (40×40 cm) placed on existing old field vegetation, (1) were limited in density by plant abundance and/or nitrogen content, (2) exhibited interspecific competition, and (3) altered the relative abundance of different plant species. We examined interactions among a pair of early season grasshopper species (May–June; Arphia conspersa and Pardalophora apiculata) and a late season pair (July–August; Melanoplus femur-rubrum and Melanoplus bivittatus). Each grasshopper species was placed in cages by itself and with another grasshopper species. Grasshoppers generally survived at higher density in fertilized cages and they reduced plant abundance relative to empty cages, suggesting that grasshoppers may be food limited at these densities. In unfertilized plots, early season grasshoppers preferred grasses (Schizachyrium scoparium and Poa pratensis) and favored the growth of forbs (especially Solidago spp.). However, late in summer, Melanoplus spp. preferred Solidago spp. and favored the growth of grasses.The pattern of grasshopper survivorship and plant reduction within these experimental environments provide preliminary support for some of the predictions of resource competition theory. Grasshoppers exhibited interspecific competition only if they significantly reduced plant biomass. If two species competed, a grasshopper species was eliminated only if the superior competitor, when living by itself, could reduce plant biomass to a significantly lower level than the inferior competitor. Competitors persisted only if they did not differ in their ability to reduce plant biomass or reduced the abundance of different plant species.     

Stem, branch and leaf biomass-density relationships in forest communities

Defining and quantifying biomass?Cdensity relationships in dense plant stands has been a long-standing issue in both theoretical and empirical studies. Most existing/traditional studies focus on whole plant individuals, without considering different plant components (e.g., stem, branch and leaf). However, the analysis of biomass?Cdensity relationships for different plant parts is linked to those for whole plants, and thus important for understanding plant strategies for utilizing resources and community dynamics. In our study, we investigated standing stem (M _S), branch (M _B) and leaf (M _L) biomass?Cdensity relationships, across a range of forest communities in China. The results showed that there was no constant predicted value (e.g., ?1/2 or ?1/3 for M _S; ?1/2, ?1/3 or 0 for M _B and M _L) that can describe all the relationships, and that the scaling exponents for stem, branch and leaf biomass varied across different forest types. In particular, standing leaf biomass (leaf biomass per unit area) was not constant in these forest communities. Furthermore, stem biomass?Cdensity lines were steeper than corresponding branch and leaf lines across most of these forest communities.     

中国北方草地蝗虫学研究概况

<正> 就目前所知,我国严重为害草地的害虫约计40余种(田畴等,1988),其中主要为蝗虫类。其为害遍布我国北方草地。仅在内蒙古,每年发生面积约500～1000万亩,在为害严重的局部地区其虫口密度达200头/m~2。蝗虫的大发     

Insect herbivory and vertebrate grazing impact food limitation and grasshopper populations during a severe outbreak

1. Competition between herbivores often plays an important role in population ecology and appears strongest when densities are high or plant production is low. Phytophagous insects are often highly abundant, but relatively few experiments have examined competition between vertebrates and phytophagous insects. 2. In grassland systems worldwide, grasshoppers are often the dominant phytophagous insect, and livestock grazing is a dominant land use. For this study, a novel experiment was conducted examining competition between vertebrates and invertebrates, where both grasshopper densities and sheep grazing were manipulated inside 10‐m² caged mesocosms during a grasshopper outbreak. We examined how grasshopper densities and the timing of vertebrate herbivory affected grasshopper densities, if the effects of vertebrates on survival and reproduction changed with grasshopper density, and how a naturally occurring grasshopper outbreak affected grasshopper populations in the following year. 3. Densities of grasshoppers at the site peaked at 130 m^–2. Food‐limited competition was stronger in treatments with higher grasshopper densities and repeated or late livestock herbivory, leading to reduced survival, femur length, and functional ovarioles, a measure of future reproduction. Strong food‐limited density‐dependent reproduction and survival led to reduced hatching densities in 2001. 4. As competition was typically stronger with high grasshopper densities than with livestock grazing, competition from vertebrates could be relatively less important for phytophagous insect population dynamics during outbreaks. The experiment provides insights into how competition between insect and vertebrate herbivores influences insect population dynamics, and indicates that severe outbreaks can rapidly subside with strong competition from vertebrate and insect herbivores.     

Predictions of species interactions from consumer-resource theory: experimental tests with grasshoppers and plants

We tested the ability of consumer-resource theory to predict direct and indirect interactions among species, using an experimental system of insect herbivores and herbaceous plants. Specifically, we examined interactions among three species of grasshoppers (Melanoplus femur-rubrum, Spharagemon collare, andPhoetaliotes nebrascensis; Orthoptera, Acrididae) and herbaceous plants in experimental field cages placed over existing fertilized or unfertilized vegetation in a Minnesota old field. For the conditions inside these cages, we addressed whether (1) grasshopper diet predicted the presence of competition among grasshopper species, and (2) direct effects of grasshoppers on plants produced indirect interactions among plants, grasshoppers and soil nitrogen. Overall,M. femur-rubrum ate a greater proportion of forbs in cages, while the other two species ate primarily grasses. As expected, a pair of grasshopper species competed if they had similar diets. However, there were important exceptions that could be explained from observed indirect effects, although alternative explanations were also possible. First, all three grasshopper species significantly shifted their diets in the presence of other species, and these shifts occurred most often when competition was expected or occurred. Second, the two grassfeeding species reduced the biomass of the dominant grass (Schizachyrium scoparium) and increased available soil nitrogen and biomass of forbs. This effect may explain why the grass-feedingP. nebrascensis had a positive effect on the forb-feedingM. femur-rubrum on unfertilized plots. Overall, we show that direct effects of consumers on resources can predict competition and other important indirect interactions within a community.     

Impact of grazing regime on a Mongolian forest steppe

Question: What is the impact of grazing regime on plant species abundance, plant growth form, plant productivity and plant nutrient concentrations in a forest steppe? Location: Hustai National Park in the forest steppe region of Mongolia. Methods: On the Stipa steppe we applied three different grazing regimes by using; (1) one type of exclosure which excluded grazing by large mammalian herbivores, mainly takh (Przewalski horse), (2) another type of exclosure that excluded both large and small (Siberian marmots) mammalian herbivores, and (3) control plots which were freely grazed. We measured species frequencies, tiller densities, plant biomass and nitrogen concentrations of the vegetation. Results: Exclusion from grazing by takh and marmots significantly increased plant standing crop, but marmot grazing and full grazing did not show significant differences. Protection from grazing decreased forage quality, shown by a lower N-concentration of the standing crop. However, this was solely the result of the lower live-dead ratio of the vegetation. The frequency of the rhizomatous Leymus chinensis decreased under reduced grazing, as did the frequency of the total of rhizomatous species. The frequency of Stipa krylovii increased under reduced grazing, as did its basal areas, tiller density and tussock height. Conclusion: Reduced grazing leads to a lower abundance of rhizomatous species and an increase in tussock species.     

Patch choice of avian herbivores along a migration trajectory–From Temperate to Arctic

Migratory waterfowl species seem to track temporal and spatial pulses of optimal forage availability on their way from temperate wintering to arctic breeding sites. In order to unravel the relative contribution of forage quality and forage biomass to foraging choices in avian herbivores, we experimentally manipulated biomass and quality of main forage plants through fertilisation and grazing exclusion at three sites along the flyway of barnacle geese, Branta leucopsis. Fertilisation increased the nitrogen content of the forage and grazing exclusion increased biomass levels. Manipulated plots were offered to wild geese in a random block experimental design and goose visitation was measured through dropping counts. At all sites there was a trend towards a higher preference of plots with increased quality and average biomass above plots with an average quality and increased biomass. Generally, geese preferred plots with highest standing crop of nitrogen. The numerical response of the geese to forage changes was supported by behavioural observations at the Baltic site. We conclude that for migrating barnacle geese the bottlenecks in the standing crop of nitrogen appear to lie in the limited biomass availability at the Baltic stopover site and the limited nutrient content of food in the Arctic breeding site, restricting the potential nutrient intake on these sites.