Niche Dynamics And Environmental Adaptation Of Feirana Species In The Qinling Mountains

Animals'niche reflects the multi-dimensional utilization of resources,and niche variation can represent species'response strategy to environmental conditions.Amphibians have unique physical structure and life history characteristics,which make them very sensitive to environmental change and become an ideal indicator species.Environmental change caused by human activities is one of the important factors for the population decrease of amphibian.However,it is still unclear how the niche characteristics of amphibian species will change under human disturbance and how the resource utilization strategy differ in different spatial and temporal scales.Here,we used the stable isotope technique to analyze the niche dynamics of Feirana species at the community,species and individual levels within the Qinling Mountains,aiming to explore the multiple environmental adaptation mechanism of amphibians and provide scientific support for the protection plans.The main results are as follows:1.Niche variation of Feirana species in different habitat typesThe process of urbanization may change community structure and even cause species extinction,affecting the position construction of animals in the ecosystem.According to the vegetation coverage and the intensity of human activities,we quantified the niche characteristics of Feirana species in natural,rural and urban habitat types separately by using stable isotope technology,evaluating the impact of environmental differences on the niche construction under the urbanization gradients.The niche width of genus Feirana in different habitat types is significantly different.Species in urban habitats has broader niche width?SEA_B=6.14?than rural?SEA_B=4.31?and natural habitats?SEA_B=1.34?,indicating that species may evolve a more diverse diet structure in the process of urbanization adaption.?¹³C values are significantly different among the three habitat types?Kruskal-Wallis test:H=9.58,P<0.01?,urban habitats have highest?¹³C value?Means±SD=-22.34±1.80?.The results indicate that the composition of vegetation might be variable in different habitats,and there is more C₄ resource in the food chain of Feirana in urban condition.Niche overlap is observed in different habitats,but there is no significant difference in?¹⁵N?H=1.83,P=0.40?,demonstrating that different populations may have similar taxa resources and occupy roughly the same trophic level in the ecosystem.2.Niche differentiation among species of the same habitat typeThere is only F.quadranus found in urban habitats.The individual specialization degree WIC/TNW=0.99 indicates that all individuals make nearly full use of the overall niche of the population,and the niche expansion of urban species is achieved by increasing the individual generalization of resource utilization.Niche overlap exists in different species occupying the same habitat type,and the overlap probability is 1.7%to70.9%.Species in rural environment has more similar resource utilization and higher overlap probability than their natural counterparts,which may be explained by the deduction of resource heterogeneity and the increasing competition stress among species that caused by the decreasing of food diversity in the environment.The?¹⁵N value is significantly different among species in the same habitat?natural environment:Z=2.41,P=0.02;rural environment:H=17.45,P<0.01?,indicating that competition among species leads different resource utilization strategies and segregated trophic niches.3.Ontogenetic niche variation of Feirana speciesTadpole muscle,adult muscle and bone collagen represent different ontogenetic period,stable isotope ratio is significant different among these tissue(?¹³C:F=22.88,P<0.01;?¹⁵N:H=7.24,P=0.03).Tadpoles have the highest value of both?¹³C and?¹⁵N.These results illustrate that there are differences in environmental resource utilization in Feirana species at different life history stages,and the niche variation is discontinuous during the transition from tadpole to adult frogs,the adults assimilate lower proportion of energy from C4 plants.Considering the environmental conditions of sampling sites,the high value of?¹⁵N in tadpoles may be caused by the cumulative effect of human domestic water.With the increasing body length,the?¹³C value showed a decreasing tendency in both bone collagen and muscle tissue of adult Feirana frogs,and the?¹⁵N value increased,which may be related to the change of food assimilation during the ontogenesis.Since there is small difference of niche width between bone collagens and adult muscle tissues?muscle:SEA_B=5.65;bone collagen:SEA_B=5.57?,we speculate that the nutritional structure and ecological function of Feirana species are basically stable in the ecosystem.In conclusion,by comparing the niche variation of Feirana species in spatiotemporal dynamics within the Qinling Mountains,we show that the niche width changes with the ontogenetic process,while the interspecific competition may cause niche differentiation.Besides,urbanization and human disturbance will lead to the expansion of niche width by forming generalization species.This study can help us understand species'adaptation mechanism to the environment,and it is also useful for learning the community structure and functional variation in the ecosystem,so as to provide scientific support for amphibians protection strategy and population restoration action in the urbanization process.