How dispersal capacity makes non-dispersal functional traits of animal
communities diverge or converge depending on spatial scale
Community assembly theory proposed a hierarchy by which local
composition is determined by both regional processes, e.g. dispersal and
migration, and local processes, e.g. local filtering by environmental
conditions and competition. How these factors interact and combined
govern local species assembly and trait composition is poorly known.
Thereto, we propose a conceptual model in which strong dispersal ability
(linked to low environmental tolerance) is fitness-dependent, promoting
species to track environmental changes; weak dispersal (linked to high
tolerance) should be fitness-independent, enhancing the influence of
competition. Conquently, local trait dissimilarity should have a
positive humpback shape, while regional trait dissimilarity should have
an upturned-humpback relationship with a dispersal trait gradient. We
found strong empirical support for this concept in trait distribution
patterns of stream macroinvertebrates from five basins across China.
These findings are discussed in terms of metacommunity theory and merit
further testing of our concept across ecosystems and organism worldwide.