| Chinese giant salamander(Andrias davidianus;hereafter referred to as giant salamander)was once widely distributed in the basin freshwater ecosystem of Yangtze river,Yellow River,and Pearl River.However,in the past few decades,the wild population of giant salamander almost disappeared due to human overhunting,the deterioration of natural environment,habitat fragmentation,and other reasons.Although these reasons have been considered to cause serious damage to the wild giant salamander population,there is still a lack of systematic research on the ecological risk factors threatening this animal.According to the previous studies,we predicted that habitat change and human disturbance are important factors for the decrease of the wild population of giant salamander.Meanwhile,researches in recent decades have evidenced that climate change has a significant impact on living organisms.Considering that giant salamander is a poikilothermic animal with a special life history,we predict that climate change may also be an important ecological risk factor for this animal.In order to study these ecological risk factors systematically,we first investigated the microhabitat environmental indexes of wild giant salamander populations.We also investigated the population size of giant salamander by net cage trapping and/or field encounter.Then,we conducted maximum entropy(MAXENT)model,combined with preference temperatures of giant salamander acclimated to different temperatures,to 1)predict the potential distribution pattern of wild giant salamander populations in the future;2)identify the main climate factor affect their distribution pattern;and 3)analyze the change of their climate niche with the variance of future climate change.These results may provide potential suggestions and protocols for the protection of wild giant salamander in a changing climate.Results are detailed as follows:(1)Our field work was carried out in Shangcheng county of Henan province,Tongjiang county of Sichuan province and Kaihua county of Zhejiang province.A combination of net cage trapping,field encounter,questionnaire survey and field observation were conducted to investigate the microhabitat environmental factors and population size of giant salamander.A total of 42 sample points was set,and each sample point was measured for 9 microhabitat environmental indicators.A total of 48 giant salamanders were captured in these sites.According to the results of GLM model,the number of individuals is negatively correlated with water depth,vegetation coverage,hydropower facilities construction,water temperature,pH,conductivity,humidity and total alkalinity,while positively correlated with total phosphorus.The abundance of giant salamander is negatively correlated with water depth,vegetation coverage,water temperature,conductivity and humidity,while positively correlated with turbidity.Water temperature(ranging between 17? to 22?)and humidity are the common significant environmental factors in both model.(2)In order to reveal the influence of temperature domestication on giant salamander,the preference temperature of this animal was determined after long-term acclimation to different temperatures(5 ?,5 ? and 25 ?).The results showed that thermal acclimation for 4 weeks could not change the temperature preference of giant salamander.5? domestication and 15? domesticated strain after 4 weeks,there is no significant difference between the preferences of both temperature(P=0.8281);5? domestication and 25? domesticated strain after 4 weeks,there is no significant difference between the preferences of both temperature(P=0.7263).15? domestication and 25? domesticated strain after 4 weeks,no significant difference between the preferences of both temperature(P=0.3782).During the 42 weeks of acclimation,giant salamanders acclimated at different temperatures developed intergroup difference in ontogeny gradually.Those acclimated at higher temperatures grow faster than those acclimated at lower temperatures.(3)The MAXENT model was used to predict the effects of climate change on the distribution pattern of Chinese giant salamander.Then the climatic niche was constructed by principal component analysis,and the significant differences of future climatic niche changes were compared by calculating niche overlap and similarity index.Our results showed that the main areas that were suitable for the distribution of giant salamander were Q inling Mountain,Daba Mountain,Wushan Mountain,Xuefeng Mountain,Wuling Mountain,Nanling Mountain,Wuyi Mountain,middle reaches and lower plains of Yangtze river were.Our results also demonstrated that the suitable area for Chinese giant salamander distribution will decrease obviously in the future because of climate change.The comparison between the present climatic niche and that of 2050 showed that the whole climatic niche of Chinese giant salamander moved in the positive direction of the principal component 1(PC1)and the negative direction of the principal component 2(PC2).The comparison between the current climatic niche and that of 2070 showed that the whole climatic niche of Chinese giant salamander moved more obvious in the positive and negative direction of PC1 and PC2,respectively.Combined with the relationships between bioclimatic factors and PC1 and PC2,our results revealed that in the future,the climatic environment of the suitable habitat of Chinese giant salamander will present an annual average temperature rise trend,the annual temperature difference will decrease,and the rainfall will increase during the rainy season.26% and 34% of the climate niche of Chinese giant salamander will change until 2050 and 2070,respectively.Overall,some suggestions for the protection of giant salamander are raised in this paper,based on our investigation on the wild habitat environment,population size,temperature preference,temperature-depended growth,and the change of the distribution pattern and climatic niche of Chinese giant salamander in a varying climate.Firstly,in order to know the distribution of the wild Chinese giant salamander population in China more accurately,we suggested that a comprehensive survey on the wild giant salamander population should be organized by relevant departments and scientific researchers conduct in China.These include drawing a more accurate distribution chart of giant salamander population in China by means of questionnaire survey,regional visit and field survey,surveying potential habitats suiting for,but have not been observed of,giant salamander,comprehensively,e.g.,helan mountain area.Secondly,we should strengthen the management system of protective areas,improve the relevant protection laws,strengthen management,and prohibit behaviors destructing wild giant salamander populations strictly.Relevant protection departments should pay attention to discover and manage potential habitat suiting for giant salamander.Human activities should be minimized in the habitat of giant salamander,and more effort should be mad on the advertisement of their protection.Finally,reintroduction of giant salamander should be scientific and followed by subsequent... |
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