In addition to differences in the mean dispersal distance
associated with each dispersal syndrome, there may be differences
in the relationship between dispersal distance and seed
mass and ⁄or plant height between dispersal syndromes. We
predicted that seed mass and dispersal distance would be positively
related for species dispersed by ants and seed-caching
vertebrates and negatively related for species that are ballistically
or wind dispersed or dispersed through ingestion by vertebrates.
We predicted that there would be no relationship
between seed mass and dispersal distance for species dispersing
by attachment or with unassisted dispersal. The reasoning
behind these predictions is explained in Appendix S1 in Supporting
Information. For plant height and dispersal distance,
we predicted positive relationships for wind and unassisted
dispersal because greater release heights increase dispersal
distances and taller species may have wider canopies than
shorter species, thereby increasing fall distance. We predicted
no relationship for ballistic species because Beer & Swaine
(1977) demonstrated in a theoretical paper that release height
had little influence on seed dispersal distance. Lastly, for species
using biotic dispersal (ants, seed-caching ingestion and
attachment), we predicted no relationship between plant height
and dispersal distance. Changes in animal vector traits are
more important than variation within a particular species for
dispersal kernels (Will & Tackenberg 2008), and we predicted
that this would extend to cross-species relationships.