| Grasshoppers are the most important primary consumers among invertebrates and are often functionally dominant phytophagous insects in temperate grassland ecosystems( Anderson 1964; Joem 1979; Rodell et al 1977) . The feeding of grasshoppers forms a key link in the material circulation and energy conversion in a grassland ecosystem. While outbreaks of grasshoppers can cause severe defoliation of grasses and forbs, it also severely hinders the development of animal husbandry. Several volume of studies have been conducted on individual species of Acridoidea at home and abroad(e.g Uvrov 1966 1977; Chapman & Joem 1990; Guo Fu et.al. 1992),but these only aimed at the bioecology and control methods of several pests, locusts and grasshoppers. In the past few years, many detailed studies were made on the grasshopper community ecology on the typical steppe in Nei Monggol(Kang et al 1992,1994a, 1994b, 1994c, 1995a, 1995b). However, ocurrence and distribution of grasshoppers are influenced exceedingly by variable environmental factors such as vegetation type and structure, geographical characters, climatic conditions in microhabitat and so on (Torell 1978) . Little work has been done on the community ecology of grasshoppers on .desert steppes, which make up the main part of grasslands in the Northwestern China, the author has studied some grasshopper community patterns, and effects of environmental factors on these patterns, as well as their models in the desert steppe ecosysem in 1986 ~ 1996.1 Physical environment of the grasslands in NingxiaNingxia grasslands are situated in the middle - eastern Asia belonging to inland region at N 35° 17' ~ 39°22' and E 104°17' ~ 107°39' with an area of around 30100km2, and it includes 11 different types of grassland, that is, meadow steppe, arid steppe, desert steppe, siccideserta, prairie deserta, montane meadow, moistand bottemland meadow, shrub meadow, shrub steppe, swamp meadow, steppe savanna, and several larger areas which, include meadon steppe, arid steppe, desert steppe,siccideserta. These were distributed zonally in horizon from the south to the north. Among them the desert steppe is the largest in area, about 55% of total natural grassland area in Ningxia; and the arid steppe, 37.0%; the siccideserta, 1.8%; the others are of smaller area.In the grassland region, the topology ranges from 1090 m in the northern, to 3350 m in the southern region. The complex and diversified natural environment and vegetation forms on which the variety number of grasshopper species and population depended for their existence is caused by topographic patterns and widely irrgular distribution of mountains, plains, plateaus, deserts, sand dune and water area etc.In spite of small areas of grassland in Ningxia, it has evident climatic characteristics of the three major natural regions, e. g. , the monsoon climatic region, Nei Monggol - Xinjiang plateau region and Qinghai - Xizang plateau region, as well as the general wind in our country. Effects of temperature factors on vegetation types and distribution with increase in latitude are not obvious because that the topography in the region is falling from the south to the north. The annual precipitation is dropping from the southern region, e. g. the rangeland of Liupan mountains, 450mm - 700mm of precipitation, belonged to semihumia climate, to the northern region, e.g. the middle and northern region of Helan mountains, 220mm ~ 400 mm, below 200 mm of precipitation, and belongs to the arid - semi arid climate; the index of gridity (Ratio of aporation/ precipitation) is increasing from 1 to 5.5 times and the vegetative landscapes are changing from the forest type to the desert steppe type from the south to the north.There are more than one thousand natural plants in Ningxia grasslands, of which there are approximately one hundred species of good forage grass and 200 species of major forage plant, among them species of grass and legume are 1/5 and 1/ 3 of total forage plants respectively. Summed species of Compositae, Liliaceae.Cyperaceae, Iridaceae, Chenopodiaceae, are 1/4; of which 1/6 can not be adapted to feed for cattle. After all, Ningxia grasslands are good grasslands for foraging animals.2. The community structure of grasshopper in Ningxia and its property of environmetal adaptation.Based on the looking through speciments of grasshoppers in 4 Insect Collections of such as Ningxia Agricultural College, Ningxia Academy of Agriculture, and Institute of Zoology, Shaanxi Teacher' s University etc. The grasshoppers having been examined include 2 superfamilies, 8 families, 38 genera and 91 species or subspecies according to the taxonomic system of grasshopper published by Xia Kailing (Zheng Zheming 1992,1995).5 distribution regions were divided based on the geographical ranges of Ningxia by Zheng Zhemin( 1992), that is, the regions of Liupian mountains, of Loss plateau, and of sicci - semi deserta, then 3 subregions were divided in the last region, for example, subregions of Helan and Luo mountains, of sicci - semi deserta and of irrigated terrace.11 types of grasslands were incorporated into the following 7 main natural subregions, such as, forest steppe, meadow steppe, arid steppe(typical steppe), desert steppe, prairie deserta, siccideserta(typical desert), swamp and bentland meadow, based on the area and the geographic distribution of these grasslands. The community compositions of grasshopper on these subregions having been classified and counted showed that the most species of grasshopper were in the desert steppe and the largest population of grasshopper was found in the arid steppe.The results being computerized on the community compositions of grasshopper on 7 types of grassland (subregions mentioned above) by the Principal Components analysis showed that the community compositions were influenced by the topogrophic characteristics and climatic regime in their distributional subregions. The distribution of 91 grasshopper species were divided into 3 geographical faunaes and 5 subfaunaes, which agree with the conclusions of Prof. Zheng Zhenmin in 1992.The quanitative indices, such as, "non anyone, 0", "individuals, +", "medium, ++","most, + + +", presented the distributional states in insect classification, for 91 grasshopper species were transformed into ecological quantitative data such as that "0","1", "2", "3". The ecological distribution of 91 species of grasshopper were classifized by using the mean of Euclidean distance to analyse the transformed data into 3 large ecological groups and 16 subgroups( Fig. 3.5) , some of the rules are given as follows:(1) Species which are distributed extensively in all 5 large topographical regions and 7 types of grassland including Chorthippus albonemus, Sphingonotus mongolicus, Oedaleus inferenalisetc, with a total of 11 species (12% of total species) belonging to 5 families.In this group, 11 species of grasshopper can be clustered into 3 subgroups in greater detail, that is, the group of Chorthippus spp., of Sp. mongolian and of Oe. infemalis, and of Ep. coerulipes and of Tr. annulate.(2) Species that can be distributed in three topographical regions and two or three types of grassland, such as Pseudetmethis alashanicus, Angaracris rhodopa, Spingonotus ningsianus, Compabhipis dauidianoetc, with an approximate total of 50 species ( > 50%) belonging to 10 families. Similarly, 50 species can be classified into 8 subgroups.(3) Species that can be distributed only in one or two types of grassland, most of which are those new species or the species distributed in the special habitat, e.g. Ps. rubimarginls, Sp. yenchinus etc. The species were divided into seven subgroups based on their specieal distributional districts or habitats, such as, specieal species of Liupan Mountains, Oasis, Sandland, Desert steppe, Arid steppe,Brush meadow and Helan mountains.Community composition of grasshoppers is influenced by variation in altitude of their distributional regions. Using increments of 200 m altitude the vertical distribution, 56 species of grasshopper, were divided by the Optimum partitiontechnique into 4 altitudinal belts, such as, wildland in agrarian zone( 1000m - 1200 m); desert steppe zone( 1200m ~ 1500 m) ; mountain steppe zone( 1500m - 2200 m) and alipine meadow zone( > 2300 m) .3. Studies on spatial pattern for grasshopper communities and sampling models.(1) Studies on spatial pattern and interspecific relationships of distribution for grasshopper communities in Ningxia.On the desert steppe near the farm of Luanchuan, Helan county, on the east side of Helan mountains, grasshoppers were sampled using a sampler of 1m × 1m × 0.5m made by the author with nylon net and metal wire. The model of species - area relationship for grasshoppers on the desert steppe was used to compute minimum quadrant area based on the sum of species and area sampled;Poin correlation coefficients and Correlation coefficients, which resulted from the four- fold table, were used to analyse interspecific distribution. Six aggregation indices, e. g., c = s2/x; Index of clumping (I) (David and Moore 1954); Parameter of negative binomial distribution (K)( Waters 1959); Index of dispersion(Iσ) of Morisita( 1959); M* , mean crowding( Lloyd 1967), were used to analyse the spatial patternes of the community and 9 dominant species of grasshopper. Based on frequences of species and individuals of grasshopper presented in the sampler, the author proposed a new formula of mix index as follow:in here, Ai, n is the frequency of the ith species and it' s number of individual present in each separate sampler separately; j is numbers of samples taken(j ≤minimum quadrant area/area of sample); F is the mid index for diffrent species of grasshopper. The heigher the F value for a population, the more mixed the population with the others. Based on F values, the effects of each population on the spatial pattern of the community can be determinted.Based on the equations above, results being computed from sampled data showed that:(1) Species - area relationship can be fitted with following equation:in here, Sq is the summed area sampled with q number of grasshopper species.The minimum quadrant area is 1400 m2 and 13 species of grasshopper corresponding to the area made up 68 percentage of total species in the region.(2) The interspecific distributions of grasshoppers showed group habit of distribution and can be clustered into 4 group with the Fuzzy combinative.(3) The aggregation indices and the mixed indexes were tested, the results showed that the patterns of grasshopper communities and each dominant species were aggregated distribution of varying degrees, 3 classes were clustered from the PCA ordination for the aggregations.(4) A new concept of "key distribution patterns" was put forward based on population number, mix indexes and the similarity of population of grasshoppers to the community in its distribution pattern. The pattern of Sphingonotus ningxianus Zheng is recognized as the key distribution pattern for the community of grasshoppers on the desert steppe on the east side of Helan mountains.(2) Studies on sampling procedures for grasshoppers on desert steppeOver a range of densities from 0.5 to 8.5 grasshoppers per m2, a set of wire rings (0.02, 0.05, 0.10, 0.20, 0. 35 m2 respectively) were thrown to count grasshoppers within the rings on the desert steppe.Grasshopper numbers per m2 being converted from each identical rings were tested for goodness of fit with that from Night - Cages(Anderson al.et., 1952) treated as the "true" value by using a paired T - tested. The results showed that the optimum area for typical densities is among 0.05, 0.10, 0.20 m2 and the accuracy of sampling changes slightly with the mean numbers of grasshopper in the area investigated. A random spatial distribution has been confirmed for grasshoppers on the desert steppe in Ningxia. Poissonconfidence intervals and Binomial sampling therefore are appropriate. Two binomial models, Poisson probability density function and Nachman binomial regressions, were fitted for the proportion of grasshoppers counted within into 0.10 m2 ring to predict mean density and vice versaPoisson modelNachman modelResults tested for two models showed that under 35/m2 of densities for grasshopers, two models gave higher precision, under 5% of error probability. Finally,based on the random sampling model, the theoretical subsamples(Table 4. 9) were developed from poisson confidence intervals.4. Analysis of community diversties of grasshoppers and their ecological adaptation to environmental factors(1) Ecological adaptation of grasshoppers to environmental factors.Based on 8 environmental factors of the seven grassland types stated above, that is, altitude(100 m), annual median temperature (℃ ), accumulated temperature of ≥10 ℃, annual precipitation(mm) , annual relative humidity(%), length of day light(h), aridity index and vegetational cover( % ) , effects of environmental factors on occurence of graahoppers were determined by the Path Coefficiency. Positive effects of seven environmental factors on occurence of grasshoppers were showed from the direct coeffients as following: annual median temperature(℃) > aridity index > accumulated temperature of ≥ 10 ℃ > length of day > annual relative humidity (%) > annual precipitation(mm) > vegetational cover(%) > altitude( 100 m) . These helped to explain why most grasshoppers on the steppe in Ningxia adapted to the arid climate of higher temperatures and lower humidity, and habitats of simpler structure and lower cover of vegetation, as well as richness of sunlight. Effects of the indirect path coeffcients showed that negative effects of the environmental factors on occurrence of grasshoppers are related mostly to the aridity index and annual median temperature(℃ ) .(2) Adaptation of grasshoppers to environmental humidity.Taking aridity index mentioned above as the distinguishing criteria, 91 grasshopper species could be clustered into 5 grades, that is, xeric species, xeric and mesoxeric species,mesic species,mesichygro species and hygro species.(3) Changes in community diversities and the mathematical analysis for the effects of environmental factors on the diversity for grasshoppers in several grasslands in Ningxia.The seven ecological parameters of plant communities and eight paramaters of grasshopper communities were investigated through systematic and random sampling in five types of grassland, that is, meadow steppe, typical steppe, desert steppe, typical desert and bent and bottomland in the farm area. The results showed that varied diversities of grasshopper communities in the different types of grassland, the most diversity of species in the desert steppe and the most number of individuals in the typical steppe for grasshopper. The abundence of grasshoppers changes over the mothes, the most diversity being in august.Based on mathematical methods such as Canonical analysis and Double Screening for Stepwise Regression, in which 15 paramaters for environmental factors ( 8 paramaters of them for plant communities)were taken as independent variables, and 7 paramaters for grasshopper communities were taken as dependent variables.The results showed that the diversity of grasshopper species were positively correlated with the aridity index in the habitat of insects and the plant communities with a greater complexity in its family/species composition; that the diversity of grasshopper individuals were positively correlated with the plant community, with a greater complexity in it' s vertical structure; In various families of grasshopper, some species were closely associated with forb grasslands and arid habitats, while some species were associated with good floral conditions. However, in the relationship between plant and grasshopper, the effcts on some grasshoppers of a good habitablecondition formed from the structure of plant communities may be more important than that of the food plants.(4) Mathematical analysis of changes in grasshopper and plant community diversity and the relationships between them in the desertification of the steppe in Ningxia.Grasshopper population had been monitored on the different desertifized gradients of arid steppe in Yanchi county, Ningxia, and correlated with floral biomass in these gradients. Grasshopper and plant sampling were conducted in two types of steppe. Each steppe was divided into five plots that showed different desertifized gradients of the steppe. Abundance and diversity of plant and grasshopper communities in the plots were compared. The results showed that changes in plant communities directly affected the community structure of grasshoppers, however, the diversity of vegetation was not entirely parallel to those of grasshopper species. Diversity of plant and grasshopper species were significantly higher in moderately desertifized plots, while diversity of grasshopper species was significantly higher in lightly desertifized plots.Population biomass of grasshopper in two families Arcypteridae and Gomphoceridae were positively correlated with grasses and negatively correlated with forbs and the other plants, while the values of grasshoppers in two families Oedipodidae and Pamphagidae were negatively correlated with grasses and total plant biomass and positively correlated with forbes and luguminous plants. Soil compactness and water content also significantly affected grasshopper species biomass and community complexity. There are a devasting effects of environmental factors on community diversities of grasshoppers and plants in the desertification of steppe.(5) The changes of the composition and diversity of grasshopper community in different stages of succession in the regions of artificial fixed sandBased when the regions were closed 4 stages of succession, that is, closed region of 1 ~ 2 years, of 3 ~ 10 years, of 11 ~ 20 years and over 21 years, were divided in the artifical fixed sand of Sapuotou. The number of species and indivaiduals were analysed. The results showed that there are different species of grasshopper with the different stage of succession. As the plants are recovering, the community composition of grasshopper are diversifing, but the obvious different in the species.5. Mathematical analysis of the position of the population, temporal and spatial heterogeneities of grasshoppers on desert steppe in Ningxia.In the desert steppe on the east side of Helan mountains, the investigation sites were divided into 5 different types based on the characters of vegetational structure and topographic and geological features. During June to September in each year, on each type of steppe the density of each grasshopper population was investigated once with the sampler mentioned above every 15 days. Using the population biomass as a quantitative index, the PCA ordination was used to make the a comparison of population positions for 15 species of grasshopper on the desert steppe, and the population chronosequence of grasshoppers in time and in space was discussed from the perspective of temporal and spatial heterogeneities. The population positions of 15 grasshoppers on the desert steppe were divided quantitatively. The model of successional series for the dominant species were put forward as changes in the season and the types of grassland.(1) Biomass of grasshopper population give more accurate results than numbers of grasshopper populations when taking quantitative data as interpreting position and function for each grasshopper species as well as interrelationships among grasshopper species on the desert ecosystem.(2) There are obvious differences of individual biomass among different species as well as in the different stages of development in the same species.(3) On the basis of biomasses of grasshopper population from field, 15 species of grasshopper are classified into 3 groups, such as, dominant species, subordinate species and rare species, by the method of multivariant analysis.(4) Based on the analysis of temporal heterogeneity for grasshoppers on the desert grassland, 15 species of grasshopper could be classified into 3 temporal groups, they are, species occuring in early period, medium period and late period.The partition of sequential development for 5 dominant species was very obvious.(5) The results showed that spatial heterogeneity of grasshopper community were influenced by the geographic and geomorphic variations, however, replacement among the grasshopper species seemed not to be much more sensitive than those invegetations.(6) Based on comprehensive analysis for the temporal and spatial heterogeneities of grasshopper communities, the partition of utilization in time and space resources for 15 grasshopper species was very obvious. Species groupings are different on varant grasslands and there are obvious partitions among populations for same species group in time.6. Intra- and interspecific competition in adults of three abundent grasshoppers from a desert grassland.Recognizing the existence and importance of intra - and interspecific competition in natural populations of insect herbivore remains problematical.The auther performed artificial field - cage expriments to detect the presence of both intra -and interspecific competition among adults of three common, mixed grass - feeding grasshoppers, Sphingonotus ningsianus Zheng et Cow, Compsorhipis davidiana (Sauss), Pseudotmethis alashanicus B. - Bienko on the desert grassland on the east side of Helan mountains in Ningxia. Based on increased mortality and lowed fecundity at higher densities, strong evidence for intraspecific compesition among species existed. Interspecific competition was weaker than intraspecific competition in this study. When interspecific competition existed, it was complex in its effects, of which the largest was more an increase in mortality, but little difference was found in reproduction from the species of smaller size. Although there was little evidence for an influence on the pattern of both intra - and interspecific effects on mortality and egg production, sinificant density -dependent depression of available food was observed for the intraspecies. Interspecific effects were influenced by food limitation or self adaptation. Because experiments were run at high density levels only irregularly reached under natural conditions, interspecific competition among these three species may occur only intermittently, or potentially.7.Studies on multidimensional niches of grasshoppers on the desert steppe in Ningxia.A study was conducted in the desert steppe area on the eastern side of Helan mountains to determine resource utilization in time, space and food by grasshopper assemblages. The pattern of use for these resources was analyzed from population biomasses simpled on the five vegation types presented in the preceding chapter once every 15 days during June to September by examining species - specific niche breadths and overlaps. Comparison in niche breadthes indicated that species which had a similar broad niche along one dimension at least had a separate niche along another one. there were sufficient differences between species for overall overlap associated with resource use to explain coexistence in the assemblages by resource segregation.Microscopic examination of crop contents was used to determine the food preference of grasshoppers on the desert steppe in Ningxia. Results from the dietary analysis of 12 grasshoppers showed that 42 species of vascular plants served as food source (Table 8.5). The utilization ratio of available plants eaten by most grsshoppers is less than 30% of total plants. The overlap and breadth of trophic niches among these grasshopper species were studied by the popoular indices (Table 8.6). The results showed that these grasshoppers have a limited niche breadth in trophic utilization( ≤0.25). Species of broader niche breadth mostly distributed where circumstance are adverse, and species of narrower niche breadth generelly distributed where grasses, or mixed xeric forbs grow luxuriantly. The high niche overlap occurs mostly among species that have similar habitats. 12 species of grasshopper can be clustered into 2 groups, that is, species group on desert, and that on steppe.On the basis of partition in utilization of resources, 12 grasshopper species were clustered into 4 groups by the Principal Component Analysis: forbivorous, mixed forbivorous, mixed graminivorous, mixedo- trophicus species (Fig. 8.5).The author proposes sevaral new equations for measurement of potential compatitive interaction for food among grasshopper species by combining the average biomass of individual species with index of food preference:here, a : index of potential compative interaction for food; → the direction of compatitive interaction; Ui1 and Ui2 : feeding preference for the first and second grasshopper on the ith species of food plant; M : average individual biomass of the grasshopper; n: species of plant being fed on by grasshoppers.In reality, competitive interaction for food amongst grasshopper species is influenced by their population numbers. Equations measuring realistic competitive interaction for food were found through combining population numbers with equation5 and 6:P1 and P2 are average densities on the field for the first and the second species of grasshopper respectively.The potential and realistic compative interactions among 12 grasshopper species were given (Table 8.6).8. Studies on the consumption injury and the economic threshold for grasshoppers on desert grassland in Ningxia.(1) Effects of grasshopper density and plant composition on growth and destruction of grasses.A study was conducted to determine the effects of grasshopper density and plant composition on grass growth and destruction by the mixed grass - and forb - feeding grasshopper, Oedaleus infernalis Sauss. Using a completely randomized design, 0.5 × 0.5× 0.5 m3 cages of 60 were placed on plots on mixed - grass rangeland on the eastern side of Helan mountains and stocked with 0, 4, 8, 16, or 32 adults of O. infernalis. Grasshopper densities within the cages were calculated for each cage for 56 days. Before adding grasshoppers, biomasses of grasses and forbs within the cages were estimated visually, then, estimated weekly. After 56 days, the final biomass of vegetation was determined.Results from analysis of variance with regression and multiple regression analysis indicated there is a double effects of the feeding of grasshoppers on the growth of plants. The effects would be advantageus on the growth of the plant from less consumption by a lower population density of grasshoppers, and conversely, as the population numbers of the grasshoppers increases, a sharp growth of forbs would be caused due to grasses being consumed, and then the utilization of grassland would be losed.The damage of grasshoppers on the growth of plants is affected by growth period and community composition of the plants. Appropriate rain in the growing period of plant and proper management of grassland would reduce the damage of grasshoppers on grasses.(2) Studies on the equivaence consumption injury and the multiple economic threshold for grasshoppers on rangelands in Ningxia.Microscopic examination of crop contents was used to determine the food preference of 12 grasshopper species. The results from the dietary analysis showed that 42 species of vascular plants (Table 8.5) were served as food sources. The artificial cages were placed under the natural conditions of field to determine average weights of the individual food consumption, days of feeding and individual biomass of grasshoppers. The linear regression equation, F = 29.95 + 0.0728 M ± 0.0015 (9), is proposed, in which, F is average weight of individual foods consumed and M is the individual biomass of grasshoppers.It was pointed by Tian Zhang et. al that the weights of cut off are related to the food consumption, the linear regression equation: D = 0.0129 + 1.066F r = 0.5384 F = 17.552 > F0.05= 9.28 , in which, D is average weight of cut off;F is food consumption.First of all, based on the parameters mentioned above and the plant value index which is converted from the forage qualitative grades for the plants species being invistigated, a formula from potential damaging valune of insects was proposed as follow:here, Svj is potential value of damage by grasshoppers; Tj is food consumption of individual grasshoppers per day, which can be substituted for equation (9); Pi is the relative frequency of the ith plant of the crop content, C; is thequalitative forage grade of the ith plant species and G , average value of the grades, s is numbers of plant species, i and j represent each species of plant and insect respectively. The potential damage values for 12 grasshoppers were calculated (Table 9.4).Secondly, we used the forage ratio losses from grasshoppers for the criterion of control decision, and the model of economic threshold was proposed as follow:Another simple and easy formula can be used too:here, D is the mixed population density at the grasshoppers when the forage loss was started, or the value when action must be taken; L is the loss rate of plant biomass by feeding of the grasshopper, and the others are descriptive in equation (10).The results calculated with formula (11) show the mixed population density to be 5.46 and 10.24 when the loss rate of grass is given as 8% and 15% respectively from the damage effect of grasshoppers.Considering types of grassland affecting the occurrence of grasshoppers, the mixed population density was converted into an equivalent damage with the fomulaas follow:The calculated IE are 12.8 and 24.01 g/m2 when D are 5.46 and 10.24 separately.Finally, new index of equivalent damage( IE = 5. 46 ) and equivalent economic threshold (IE = 10.24 ) mentioned above were tested against the population density of grasshopper in reality on the 3 types of grassland in Helan mountain rangeland.9. Studies on the biological specificity and the control of the dominant species of grasshopper in Mingxia The biological properties of 10 dominant species of grasshopper were given, such as, the occurrence and development, the habitus of infection and so on. Then, the general control methods of grasshoppers, that is, transfamation of habitats, chemical control, biological control and mechanical control, were introducted.
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