|Other Abstract||Lake Fuxian is an oligotrophic and deepwater lake in the Yunnan plateau lake groups. During the survey of the catches from 2002 to 2005, 42 species of fishes belonging to 18 families were collected and identified. 18 species of 24 were locally successfully established. The nonnative Pelteobagrus fulvidraco was the object of the present study. The life history characteristics were studied, such as age, growth, reproduction and mortality. Lake Fuxian was considered as a fundamental geographical units where was invaded by the nonnative fishes, and was representative in fish composition and community structure of the plateau lake. The common life-history strategies were explored on the basis of the contrast between successful and failed fishes. The risk assessment system of alien fishes was founded based on the relative factor of invasiveness in order to forecast and keep away the invasion in the highland river system. The main result summarized as:
Ages were determined based on the annuli of vertebrae. The estimated age range was between 0+-5+ years for females and 0+-7+ years for males. The age groups of 3+-4+ years old were predominant in the catches. The growth parameters used to fit the Von Bertalanffy equation were L∞＝294.68 mm, k＝0.2476 year-1, t0＝-0.0298 year, W∞＝209.93 g for male and L∞＝257.13 mm, k＝0.2219 year-1, t0＝-0.3329 year, W∞＝184.45 g for female. The growth performance indices were φ♂ = 4.3324 and φ ♀ = 4.1665. The inflexion point of age and body weight was estimated at 3.1 years and 60.98 g for males, correspondingly, 3.6 years and 54.47 g for female. There was the significant difference in the sex ratio in favor of male (1:2.55). The estimated age of the first mature was 2+ year. The Mean absolute fecundity (F) was 2374 oocytes, ranging from 431 to 7169. The evolvements of eggs were batch-synchronous. The reproductive activity extended from pre-May to end of August, with peaks in June. The type of reproduction was a batch spawner. The aforementioned life-history characteristic demonstrated P. fulvidraco is one of equilibrium strategist of the adaptive stable habitat. Comparing with the data of other source distribution populations, these results suggested there were typical characters of a complex age structure, relatively slow growth, low individual fecundity and delay in the first maturity age.
Growth of newly introduced populations is a process of the stochastic differential equation models. Allee effects and propagule pressure may restrict establishment of introduced species. Invasive process in a fluctuating environment could represent a lag time. It is negligible for the long-term persistence model to demographic and environmental stochasticity and Allee effects. Fishing is an important factor in population dynamics of species. The instantaneous coefficients of total mortality (Z) and natural mortality (M) were assessed 0.99 year-1and 0.43 year-1 for male, 1.22 year-1 and 0.40 year-1 for female, respectively. The maximum value of Y'/R occurred at Emax = 0.634 for males and Emax = 0.719 for females, Ecur < Emax. Therefore, on the supposition that capturel length was not changed, population dimension will maintain at a high level in the following years.
We compared the overlap of native and exotic fishes in habitat spaces, feeding types and reproductive season. The native fish of diverse niche was differed in responding to invasion of alien species. The endemic and spawning fish in spring and summer were more prone to become extinct, and the threatened rate of the special in habitat space and carnivores was lower. The results suggested the invasion resistance decreased by disruption and less of resident functional group richness. The niche opportunities may be key factors to explain community invisibility.
The variables of 14 biological and ecological attributes for 18 alien species were analyzed. The results suggested that the opportunistic strategists with small-bodied, early maturation, short lifespan, low fecundity per spawning event, and low egg diameter, and the equilibrium strategists with small- to medium-bodied, moderate maturation age, low fecundity per spawning event, protracted spawning season and high juvenile survivorship (greater parental care), were successful invader. The breeding migration of the periodic strategists did not be satisfied because of the obturated property of Lake Fuxian, thus establishment was failed despite of repetitive introduces. In general, it is very high for the alien fishes with wide geographical distribution, intended fishery introduction and prior invasion success to invade successfully. Our expectation was that nonnative equilibrium strategists would spread most rapidly because of niche opportunities created by extensive environmental change and minimal niche overlap with native species. In addition, we expected rapidly declining native species to be either opportunistic or periodic strategists.
We brought forward 36 universal problems in correlation to the invasive factors for the plateau water body, which included geography and domestic history, biological and ecological characteristics, genetics characteristics, human interest and community characteristics. Quantitative risk assessments protocol was constituted based on the descriptive enquiries that species was potentially invader. The proposed system would be identified risk for the recent introduction of nonnative species, and then take the corresponding management measures (accepts, declines or needs to further study).|