Functional zeta diversity can better reveal fish metacommunity assembly process in a transitional floodplain

Comprehending the mechanisms governing metacommunity assembly holds pivotal importance for effective conservation strategies. Amidst diverse theories in explaining metacommunity assembly processes, ecologists are progressively delving into the interplay between ecological stochasticity and determinism in shaping species assemblages. Given the ease of measurement, three null model-based methodologies have been widely employed to measure the stochastic and deterministic process, i.e., dispersal-niche continuum index (DNCI), elements of metacommunity structure (EMS), and zeta diversity calculations. However, it is still in doubt which approach can better detect the dominant ecological process governing metacommunity assembly. In this study, we concurrently utilized these three approaches to reveal the fish metacommunity assembly processes in a transitional floodplain among different habitats between high- and low-water levels. In general, our results recognized functional zeta diversity as indicative measurement in this study case since it uniquely unveiled the significant assembly transitions from stochasticity to determinism in response to water receding. Specifically, fish metacommunity in high-water periods was governed by stochastic processes, which can be ascribed to connectivity and easier dispersal in the flooding period. In contrast, the deterministic process shaped fish metacommunity in low-water phase since the stringent environmental loading enhance environmental filtering. This phenomenon is more pronounced in lotic habitats due to the more intricate environments there. It is worth noting that EMS and DNCI approaches showed blind response to this shift. In consequence, our findings advocate for favoring zeta diversity in resolving stochastic and deterministic contributions in governing metacommunity assembly. In addition, our findings also highlight the superiority of functional diversity over traditional taxonomic diversity, since we recorded a more reasonable metacommunity assembly process revealed by the functional group approach, which emphasizes the significance of incorporating functional traits in community ecology.