Dispersal-mediated coexistence and extinction dynamics in three archetypal food webs

Species dispersal is a fundamental process governing the spatial structure, stability, and persistence of ecological communities. While previous studies have elucidated the role of dispersal in simple food webs and omnivorous systems, a systematic comparison of how species-specific dispersal patterns affect coexistence across different trophic interaction modules - simple food web, exploitative competition, and apparent competition - remains lacking. Here, we extend a spatially structured patch-dynamic framework to investigate how dispersal range and mode influence species persistence in three archetypal three-species food webs subject to habitat loss and fragmentation. Our model incorporates trophic level-dependent dispersal, with basal species exhibiting neighbor dispersal, intermediate species exhibiting within-fragment local dispersal, and top predators exhibiting global dispersal, consistent with empirical observations that dispersal range increases with trophic level. Using pair-approximation techniques, we analyze the steady-state patch occupancy dynamics across gradients of habitat loss and fragmentation. Our results reveal three key findings: (1) In simple food web, higher trophic levels exhibit greater sensitivity to both habitat loss and fragmentation due to bottom-up resource constraints, confirming the trophic rank hypothesis; (2) In exploitative competition systems, a dispersal-competition trade-off generates non-monotonic diversity patterns, with maximum species coexistence at intermediate fragmentation levels where inferior competitors gain refuge via superior dispersal; (3) In apparent competition systems, the shared predator mediates coexistence through source-sink dynamics, with the inferior prey species benefiting from lower dispersal rates that reduce predator encounter frequency. Our findings demonstrate that dispersal effects are contingent on food web architecture, challenging the notion that increasing dispersal connectivity universally promotes biodiversity. These results provide theoretical guidance for conservation strategies in fragmented landscapes, emphasizing the need to consider both trophic structure and species-specific dispersal traits when predicting community responses to habitat destruction.