DISHARMONY, FILTERS, AND REGIONAL BIOGEOGRAPHY 51Table 3.1Apparent limits to long-distance dispersal of selected taxonomic groups based on water gap
distances. Considerable caution should be observed when inferring dispersal capability from water gap
distances for the following reasons: (a) For continental fragments there is the possibility of a vicariance
explanation due to geotectonic processes rather than a dispersal event; (b) eustatic sea level changes may in
the past have diminished the distances between islands and the mainland, in the case of many continental
shelf islands removing the barrier altogether. (Data compiled from various sources, including: Carlquist 1965,
1974; Gorman 1979; Menard 1986.)
Taxonomic group Water gap (km) Example
Freshwater fishes* 5 British Columbia–Vancouver Island
Large mammals 70–150 Pliocene Mediterranean megafauna
Small mammals (excepting rodents) 410 Africa–Madagascar
Rodents, land tortoises, and snakes 920 South America–Galápagos
Amphibians 1265 Africa–Seychelles
(1641) (Australia–New Zealand
(Palaeoendemisms?) )
Gymnosperms 1356 Europe–Azores
Lizards (geckos) 1641 Australia–New Zealand
(Palaeoendemisms?)
Bats, land birds, snails, arthropods, fungi, 3650 North America–Hawaii
mosses, ferns, angiosperms
*Excluding diadromous fishes, for which almost anything appears possible (R. McDowall, personal
communication).
Animal-externalAnimal-internalAquatic-activeAquatic-passiveAerial-activeAerial-passiveFigure 3.2The various modes of dispersal by which species may naturally disperse to and colonize a remote island through or across a
sea-water gap (redrawn from Aguilera et al. 1994, based on an original in Rodríguez de la Fuente 1980). Alternative nomenclature for the top
three categories as they apply to plants: seed dispersal by wind = anemochory; in the gut of an animal = endozochory; attached to the fur or
feathers = exozoochory; flotation in the sea = thalassochory.