Seasonal dynamics of waterbird assembly mechanisms revealed by patterns in phylogenetic and functional diversity in a subtropical wetland

Abstract

Despite growing interest in using phylogenetic and functional methods to understand community assembly, few studies have examined how these methods can be used to assess seasonal variation in assembly mechanisms among migrant species.Migration can rapidly alter the relative influence of stochastic processes, species interactions, or environmental factors in shaping communities across seasons. Here, we describe seasonal dynamics in the phylogenetic and functional diversity of waterbirds in Mai Po Wetland, a subtropical region with significant and predictable temporal variation in climate and migratory bird density. Phylogenetic α diversity varied seasonally, exhibiting a clustered structure (indicative of environmental filtering) in summer, and over-dispersed structure (indicative of biotic filtering) in winter.Phylogenetic diversity in spring and autumn exhibited a more intermediate, random structure, consistent with stochastic arrivals and departures of migrants. Functional diversity was clustered in spring but showed over-dispersion in the other three seasons. Phylogenetic β diversity in summer and winter assemblages was characterized by two distinct groups, while spring and autumn assemblages were mixed. Our results suggest that waterbird assemblages were primarily shaped by interspecific competition in winter, while random processes tended to shape assemblages in spring and fall. Environmental factors played a more important role in summer, during periods of high heat stress. In addition, species co-occurrence patterns were significantly more strongly related to phylogenetic similarity in winter than in summer. Our results suggest that the relative importance of assemblage mechanisms can vary seasonally in response to changing environmental conditions, suggesting that studies attempting to infer a single dominant assembly mechanism may ignore important assembly processes. Temporal shifts in assembly mechanisms may play an important role in maintaining diversity in subtropical and temperate wetlands and perhaps also in other dynamic systems.

Changes in functional composition and diversity of waterbirds: The roles of water level and submerged macrophytes

“…Environmental filtering would result in negative SESFRic and SESFDis values by allowing only a set of species with certain functional traits to persist and by forcing most of the biomass into a small trait space (Liu, Swenson, Zhang, & Ma, 2013; Mason et al., 2005). These findings were also in concordance with some of the previous studies on waterbirds that reported functionally clustered waterbirds communities (the western populations in Che et al., 2018; summer season in Che et al., 2019; Li et al., 2019). For organisms like waterbirds, which have high‐dispersal capabilities and can respond to changes in the environment quickly, priority effects (Chase, 2003) and stochastic processes (Hubbell, 2001) are less likely to be dominant players in community assembly (Daniel et al., 2019; Fukami, 2015; Li et al., 2019).…”

“…Furthermore, in permanent and large lakes such as our study lakes, environmental filtering is expected to be more prominent in community assembly as compared to smaller and temporary wetlands, where stochastic events and priority effect are expected to be major determinants of assembly (Daniel et al., 2019; Li et al., 2019). However, it should also be noted that there have been other studies reporting neutrally assembled waterbird communities (spring and autumn populations in Che et al., 2019; populations of temporary wetlands in Daniel et al., 2019; de Arruda Almeida et al., 2019) and functionally over‐dispersed waterbird communities (the eastern populations in Che et al., 2018; winter populations in Che et al., 2019). Overall, various factors including climate, wetland age, wetland size, season of the year, population densities, and trophic states of wetlands seem to be capable of influencing waterbird community assembly.…”

Water-level controlled reservoir as refugia for waterbirds in an urban landscape

“…The lowest abundance during the rainy season, when most birds breed, is possibly due to reproductive displacement (Sick 1997). Indeed, Ardeidae offspring frequently disperses locally after maturation (Che et al 2019).…”

Nonlinear Regression Applications in Modeling Over-Dispersion of Bird Populations

“…As previously well-documented, seasonality (Caula et al, 2008;Chen et al, 2019;Gomes et al, 2017;Girma et al, 2017;Katuwal et al, 2016) and habitat (Caula et al, 2008;Chen et al, 2018;Chen et al, 2019;Durmuş et al, 2018;Girma et al, 2017) influence the species richness and population size. The present results of the study are consistent with the previous reports given above.…”