Drivers of metacommunity dynamics in river-floodplain fish: A path modeling approach

Metacommunity theory offers a compelling framework for understanding the
processes that govern biodiversity patterns across space and time. Yet, a
persistent challenge remains: integrating the wide array of ecological
drivers into a unified model using observational data from complex,
dynamic ecosystems. In this study, we present a novel, process-explicit
path modelling approach that bridges recent theoretical advances in
metacommunity ecology with empirical data. Focusing on fish communities in
the floodplains of the Danube River, we leverage environmental DNA (eDNA)
metabarcoding to characterize community composition across a
spatio-temporal network of sites. We partition beta diversity into its
species replacement and richness difference components and apply
structural equation modelling to evaluate the relative influence of
multiple ecological drivers—including spatial and temporal dispersal,
demographic stochasticity, abiotic filtering and interspecific
interactions. Our results reveal that river-floodplain fish
metacommunities are shaped by a complex web of interacting processes.
Notably, we find that species replacement is primarily driven by spatial
distance and environmental filtering, while richness differences are more
influenced by biotic interactions and community size. Lateral hydrological
connectivity emerged as a pivotal landscape feature, governing beta
diversity both directly and indirectly through its modulation of local
environmental conditions. This connectivity acted as a structural conduit,
mediating dispersal, environmental heterogeneity, and biotic interactions.
By disentangling the contributions of multiple processes, our model
underscores the dominant role of spatial structuring and abiotic filtering
over temporal dynamics and biotic interactions in shaping metacommunity
assembly. The model also demonstrates improved explanatory power and
stronger model fit, outperforming previous studies. These findings
underscore the need for integrative frameworks that consider the
simultaneous influence of multiple ecological processes, particularly in
highly dynamic systems like river-floodplains. Our conceptual and
modelling approach advances metacommunity theory by offering a robust,
data-driven means to assess complex assembly mechanisms and by emphasizing
the critical role of connectivity and habitat complementarity in
sustaining biodiversity within dynamic landscapes.