Résumé
Dispersal is a central life-history trait for most animals and plants: it
allows to colonize new habitats, escape from competition or avoid
inbreeding. Yet, not all species are mobile enough to perform sufficient
dispersal. Such passive dispersers may use more mobile animals as
dispersal vectors. If multiple potential vectors are available, an active
choice can allow to optimize the dispersal process and to determine the
distribution of dispersal distances, i.e. an optimal dispersal kernel. We
explore dispersal and vector choice in the neotropical flower mite
Spadiseius calyptrogynae using a dual approach which combines experiments
with an individual-based simulation model. Spadiseius calyptrogynae is
found in lowland rainforests in Costa Rica. It inhabits inflorescences of
the understorey palm Calyptrogyne ghiesbreghtiana and is phoretic on a
number of flower visitors including bats, beetles and stingless bees. We
hypothesised that the mites should optimise their dispersal kernel by
actively choosing a specific mix of potential phoretic vectors. In a
simple olfactometer setup we showed that the flower mites do indeed
discriminate between potential vectors. Subsequently we used an
individual-based model to analyse the evolutionary forces responsible for
the observed patterns of vector choice. The mites combine vectors
exhibiting long-distance dispersal with those allowing for more localized
dispersal. This results in a fat-tailed dispersal kernel that guarantees
the occasional colonization of new host plant patches (long distance)
while optimizing the exploitation of clumped resources (local dispersal).
Additionally, kin competition results in a preference for small vectors
that transport only few individuals at a time. At the same time, these
vectors lead to directed dispersal towards suitable habitat, which
increases the stability of this very specialized interaction. Our findings
can be applied to other phoretic systems but also to vector-based seed
dispersal, for example.