Morphological Ecology And Coexistence Mechanism Of Two Sympatric Species Of Eremias

In the natural environment,niche differentiation is one mechanism for species coexistence.Species that are distributed in sympatry and have a close evolutionary relationship will regulate their ecological similarities to reduce competition.In this study,we analyzed the morphological indices,food composition and locomotor performance of two sympatric species of Eremias,and discussed the morphological ecology and co-existence mechanism of the two lizards.The main findings are as following:(1)Both Eremias grammica and Eremias velox shown male-biased sexual dimorphism.The head morphology index,tail base width and tail length of male E.grammica were significantly larger than the females,and the head width had an allometric growth.The head length,head width/head length and head depth/head length of male E.velox were significantly larger than the female lizard.The pattern of sexual dimorphism in body size and the relative head size of the two lizards were similar,which conforms to the prediction of the sexual selection hypothesis.In addition,the relative axilla-groin length of females in both species were significantly larger than that of males,which was consistent with the prediction of fecundity selection hypothesis.(2)The main food types of two lizards were Coleoptera and Orthoptera insect,and the nutritional niche overlap between male and female individuals was higher,and the intraspecies competition was greater.The ratio of hard food of the male E.grammica was higher than the male E.velox,and the medium food of both sexes E.velox was higher than the E.grammica.These results suggest that the two species may be differentiated in other niche dimensions such as microhabitat or activity time,which needs further study.(3)Both sexes of E.grammica exhibited the best maximum sprint speed and acceleration on sand substrate,and the females also showed the best endurance performance.The maximum sprint speed of male E.velox on soil substrate was significantly higher than that of female,while the endurance of female E.velox on soil substrate was significantly higher than that of male.In conclusion,in terms of endurance,both female lizards chose the “home field advantage” hypothesis.On the maximum sprint speed,E.grammica are adapted to the “home field advantage” hypothesis on sand substrate,female E.velox is “jack of all trades and master of none”,the male E.velox performs as the “home field advantage” hypothesis on soil substrate.There was a trade-off between maximum sprint speed and endurance of E.velox,and the influence of substrate type on the locomotor performance between sex was significantly different.(4)The developed bilateral toe fringe and large abdominal area of E.grammica increased the contact area between the lizard's body and the substrate,which was beneficial to the lizard's maximum sprint speed and acceleration.There was a significant positive correlation between head shape and sprinting speed,and a negative correlation between head shape and endurance.The model of sprint speed includes several indexes such as contact area,substrate type and weight.The best model of endurance was substrate type,which indicated that habitat was an important factor affecting endurance of lizards rather than morphology.In short,the morphological and functional relationship of intra-species and inter-species between the two Eremias species shows plasticity due to different selection pressures and is conducive to species coexistence.