1. Introduction
The interaction between frugivorous and fleshy-fruited plants is an important ecological process that links successive generations of plants and influences vegetation dynamics (García et al., 2018; Rumeu et al., 2020). Many fleshy-fruited plants rely on birds for seed dispersal because of their high diversity, mobility, diversified habitat selection (Carlo & Morales, 2016; Camargo et al., 2020), and differences in body characteristics that can concurrently remove a variety of fruit species (Wang et al., 2019). The relationship between fleshy-fruited plants and frugivorous birds can form a complex interaction network. Therefore, unraveling the structure and dynamics of the interaction network can provide novel insights into co-evolution theory (Schleuning et al., 2015), and can be used to describe the diversity of interactions, reveal ecological patterns, and plan conservation efforts (Ramos-Robles et al., 2016; Beal-Neves et al., 2020).
Rapid urbanization has had significant effects on ecosystem structure, leading to habitat loss, degradation, and homogenization (Kiers et al., 2010). Changes in landscape configuration and composition affect the movement and community diversity of bird (Pena et al., 2017), and ultimately reduce the stability of the interaction network structure and ecosystem service function, leading to serious consequences in ecological and evolutionary processes (Harrison & Winfree, 2015; Guenat et al., 2019). For instance, urbanization can negatively affect plant-bird interactions by decreasing bird richness and increasing interaction evenness (Schneiberg et al., 2020). Urban green spaces are a multitude of different open spaces in cities, such as patched native vegetation and artificially managed parks, which play a crucial role in maintaining species diversity and act as ecological corridors by connecting natural vegetation remnants (Daniels et al., 2020; Zhang et al., 2022). Urban green spaces comprise a range of garden plants, which not only provide sufficient food resources and suitable alternative habitats for birds but also influence the dispersal behavior of birds that can connect different patches (Silva et al., 2016; He et al., 2022). For instance, 19 bird species foraged on 21 fleshy-fruited plants in the Nanjing Botanical Garden Mem. Sun Yat-Sen during autumn and winter and then dispersed these seeds to different types of habitats (Li et al., 2001).
With the decline in urban bird diversity and the continuous enrichment of urban green space vegetation types, the characteristics of plant-frugivore networks in urban green spaces have aroused great interest. Previous studies have further shown that the richness and diversity of bird-plant interaction networks are affected by different factors, as suggested by changes across phenology, fruit size, color, and crop of plants that directly affect the foraging choice of frugivore birds (Plein et al., 2013; Zhang et al., 2022), while the body size, mouth-beak length, and tail length of frugivore birds are associated with feeding amount, mode, and flight ability, and this variability in functional characteristics might increase the functional complementarity within networks (Dehling et al., 2016; Sebastián‐González, 2017).
The Guilin Botanical Garden, located in the Guilin city, Guangxi Zhuang Autonomous Region, Southwest China, serves as a typical ex-situ plant protection base in an urban green space (Tang et al., 2009). It has more than 300 endangered plants, and these plants produce large amounts of fruit every year, providing an adequate source of food for birds. However, very little information is available regarding the interaction network structure and characteristics between birds and fruit plants. In this study, we report the structure of the plant-frugivore network and the trophic relationships between the network roles and functional traits of two trophic species in the Guilin Botanical Garden. We aimed to answer the following questions: (1) whether seasonal variation affects interactions between frugivorous birds and plant species and (2) whether species traits influence the functional roles of plants and animals in interaction networks. We predicted that (i ) the network is more complex in autumn and winter because of sufficient fruit resources and (ii ) the role of species in interaction networks is affected by their traits.