Social Organizations In Relation To Vegetation Cover In Tibetan Ground Tits

Animal social organizations typically include cooperative breeding and extra-pair paternity(EPP).The former refers to the phenomenon that a sexually mature individual in a population abandons the chance of independent reproduction and chooses to delay dispersal and stay in the nest to help other individuals,especially relatives.The latter refers to the phenomenon that females copulate with individuals other than social mates and result in offspring in social monogamous birds.Tibetan ground tits Pseudopodoces humilis are a facultatively cooperatively breeding bird distributed over the Tibetan Plateau,in which extra-pair mating routinely occurs.Because the social organization of birds is closely related to their ecological environment,ecological factors must play a key role in the evolution of social organization.This study selected vegetation cover as an ecological factor,calculated vegetation index by analyzing remote sensing satellite images,combined with field work in 15 research sites in Gansu,Qinghai,Sichuan and Tibet Autonomous Region from 2016 to 2017,applied molecular biological techniques for gender and paternity identification of the collected tits blood samples,and used the least square regression combined with the AIC model screening method to preliminarily explore the relationship between vegetation covers on Tibetan Plateau and the social organization of Tibetan ground tits.The results showed that the square of mean vegetation index of June,July and August of the previous year could predict the proportion of nests with helpers with19%R~2.In the relationship between proportion of nests with extra-pair offspring and vegetation index,and the relationship between proportion of offspring and vegetation index,the square of mean vegetation index in June,July and August of the previous year was the best predictor with 24%R~2.Food abundance reflected by vegetation index is the key to understanding this result.The lack of food resources in the plateau is an important ecological factor restricting the survival and reproduction of Tibetan ground tits.It is speculated that in poor vegetation conditions,Tibetan ground tits tend to refuse cooperative breeding in order to avoid relatives'competition,and long-distance foraging increases the probability of extra-pair copulation.And when vegetation conditions are good,sexually mature individuals tend to reproduce independently,meanwhile,higher reproductive density increases the probability of extra-pair copulation.In the future,we should pay more attention to the life history of the insects that the Tibetan ground tits feed on and their relationship with environment.Besides,further understanding of extrapair mating patterns are important,and we should synthesize more population data to research the relationship between social organizations of Tibetan ground tits and vegetation cover.