Dispersal-related traits
Studies used a wide range of traits as proxies for dispersal ability,
which, unsurprisingly, vary substantially with the taxon and system
studied (Table 2). For marine animals, traits that allow dispersal
during the larval stage (which is often pelagic) are most commonly used.
Type of larvae (e.g., pelagic vs. non-pelagic) and egg (e.g., pelagic
vs. non-pelagic), and the duration of the pelagic larval stage have
generally been considered as proxies of dispersal for fishes,
echinoderms and molluscs. Body size has also been used as a proxy for
dispersal for crustaceans and fishes. For terrestrial animals, body size
has been the main trait used as a proxy for dispersal ability. In
addition, traits related to flight ability have been used in taxa for
which flight is present (e.g., birds, bats, insects), either as a binary
trait (presence vs. absence of wings) or a continuous variable
(hand-wing index, wing load or size) reflecting flight potential (Table
2). Life history traits (e.g., clutch size, life span) have mostly been
used in amphibians, whereas metabolic rate has been used as a dispersal
proxy in mammals. For vascular plants, proxies of dispersal are related
to the characteristics of the diaspore (e.g., seed size and number) and
dispersal mechanism (i.e., dispersal syndrome, such as wind, water or
animal). In freshwater animals, body size is also a common proxy of
dispersal (for fish, testudines and diatoms). Dispersal in parasitic
trematodes is assumed to be linked to the dispersal ability of the host
(e.g. fish, mammals, birds). See Appendix 1 in Suppl. Mat. for an
extended description.