| Nestedness is an important pattern frequently reported for species assemblages on islands or fragmented systems.However,to date,there are few studies that comprehensively investigated faunal nestedness and underlying processes in urbanized landscapes.Our study has 3 main objectives as follows:(1)to evaluate whether bird assemblages in Nanjing urban parks conforms to the taxonomic,phylogenetic and functional nested subset pattern;(2)to determine the causal mechanisms underlying the taxonomic,phylogenetic and functional nestedness of bird assemblages;(3)to apply the nestedness theory to direct urban park planning and protect bird diversity in our system.From April 2019 to January 2020,we conducted10 surveys of bird communities in 37 city parks in Nanjing using the transect method,and a total of 76 bird species were found.Our results showed that(1)bird assemblages in urban parks were significantly taxonomically nested;(2)park area,habitat diversity,building index,habitat specificity,and minimum area requirement of birds were significantly correlated with nestedness.Therefore,the nestedness of bird assemblages was caused by selective extinction,habitat nestedness,and urbanization.However,the nestedness of bird assemblages did not result from passive sampling,selective colonization,or human disturbance;(3)tree NODF analysis revealed that bird assemblages in urban parks were significantly and phylogenetically and functionally nested;(4)phylogenetic and functional nestedness were significantly affected by park area,isolation and building index.The number of habitat types also had a significant impact on functional nestedness.Overall,to maximize the number of species preserved in our system,conservation priority should be given to parks with large area,rich habitat diversity,and lower levels of urbanization(less building index).From a species perspective,we should focus on species with large area requirement and high habitat specificity for their effective conservation. |
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