Abundance And Niche Study Of The Main Rat Species In The Highland Region In The Northwest Of Hebei Province

The highland in the northwest of Hebei province is the transitional region of Mogolia altiplano and the plain of North China. Correspondently, the combination of the Mogolia district and the North China district characterizes the formation of the zoogeographical region.There is important significance in studying the abundance and diversity of the rat species to investigate the fundamental theories of animal biology. At the same time, this region is the natural defense and the main water resource conservation of North China and its biological variation influences the human environment of Beijing and Tianjin district. Moreover, Rats is the species which are sensitive to the biological change, so studying the rats biologically is very meaningful to master the biological change of the highland region in the northwest of Hebei province theoretically and practically. This study was carried out from Janurary of 2006 to May of 2008 and the outdoor investigation time is from May of 2006 to September of 2007, and Guyuan County, which is typical of the transitional region of the highland, was chosen as the investigated area. The main rat species are studied from the different aspects of abundance, diversity, niche metrics methods and n-dimensional suitability. The results are:1. The abundance and the diversity of the rat species in the highland: according to the geogrophical features, the investigated area can be divided into:The mountainous region in the edges of the highland; the low hills and dry grassland; and the plain and the wet grassland. Seven species of rats were captured in the research, and the ordination (from high level to low level) of the abundance of these three regions is: the mountainous region in the edges of the highland, the low hills and dry grassland, the plain and the wet grassland. In terms of fauna composition, the type of Northeast-North of China is typical in the mountainous region in the edges of the highland; and the type of Mogolia altiplano is typical in the low hills and dry grassland and the plain and the wet grassland, which reflects the transitional features of the dominant rat species. Of the fourteen habitat types, the ordination of rat diversity index (from high level to low level) is: young larch woodland, farmland, returned plowland and young woodland, grazing wet grassland, barren slope and low hills, grazing half-wet grassland, sparse larch woodland, herd prohibited half-wet grassland, adult poplar woodland, herd prohibited returned plowland=herd prohibited wet grassland, grazing dry grassland, natural woodland, adult larch woodland. The ordination of the individual richness (from high level to low level) is: the low hills and dry grassland, the mountainous region in the edges of the highland, the plain and the wet grassland. Connected with the alteration of the productive style in the last ten years, the general changing tendency of the rat species is analyzed during the present study.2. Niche metrics methods:a. In terms of the study of the niche metrics methods, niche breadth is divided into absolute niche breadth and comparative niche breadth. The concept and the metrics approach of the absolute niche breadth are put forward in this study. Based on the resource utilization curve put forward by MacArthur and the features of the normal distribution function curve, combined with the common use statistic estimation reference cost 0.6826,0.05 and 0.01, absolute niche breadth is defined as the corresponding scope of the resource variable when the utilization probability of one-dimensional resource by species is equal to 0.99; optimum niche is defined as the corresponding resource variable point(x=u) when the probability density is maximum. Further more, the absolute niche is divided into adequate niche, sub-adequate niche and boundary niche; and adequate niche is defined as the corresponding resource variable scope of [u-σ,u+σ] between the two inflecxions of the probability density function curve; sub-adequate niche is defined as the corresponding resource variable scope of [u-1.96σ,u-σ] and [u+σ,u+1.96σ]; boundary niche is defined as the corresponding resource variable scope of [u-2.576σ,u-1.96σ] and [u+1.96σ,u+2.576σ]. With the examples of the main rats in the highland, these methods are discussed respectively.b. In terms of the study of the niche metrics models, the concept of species-amount saturation is advanced, based on which, niche metrics model is established. And they are: one-dimensional niche breadth metrics model, one-dimensional niche breadth metrics model including the resource information factors. N-dimensional niche breadth model, symmetry and asymmetry model of niche overlapping and the niche model of one species overlapping with other species are also put up during the present study.c. In terms of the study of the species compitition index, niche competition modulus restricted by species density (α), resource utilization niche competion modulus (β) and niche competition modulus (γ) models are suggested and put up. These models are used to analyse the competition relationship of the main rat species in the highland. It turns out that niche competition modulus model, which can be cooperated with niche breadth and niche overlapping model, is better than the niche overlapping model in describing the interspecific relationship. 3. Combining the n-dimensional niche theory put forward by Hutchinson with the Habitat Suitability Index put forward by USFWS, the n-dimensional niche suitability model of Citellus dauricus Brandt is established, and the habitat suitability of the highland for Citellus dauricus Brandt is evaluated. N-dimensional niche suitability model is applied to the habitat evaluation of the rats, the forecast of the amount of the population, and the evaluation of the risk of biology invasion. All in all, this research provides a new approch to the biological study of rats.