Rates of dispersal of cane toads during their global invasion

Invasions often accelerate through time, as dispersal-enhancing traits accumulate at the expanding range edge. How does the dispersal behaviour of individual organisms shift to increase rates of population spread? We collate data from 44 radio-tracking studies (in total, of 650 animals) of cane toads (Rhinella marina) to quantify distances moved per day, and the frequency of displacement in their native range (French Guiana) and two invaded areas (Hawai’i and Australia). Here we show that toads in their native-range, Hawai’i and eastern Australia are relatively sedentary, while toads dispersing across tropical Australia increased their daily distances travelled from 20 to 200 m per day. That increase reflects an increasing propensity to change diurnal retreat sites every day, as well as to move further during each nocturnal displacement. Daily changes in retreat site evolved earlier than did changes in distances moved per night, indicating a breakdown in philopatry before other movement behaviours were optimised to maximise dispersal.

Methods

Cane toads were radio-tracked using waistbelts holding small transmitters. Locations were recorded daily for 5 days, providing information on distances moved between successive diurnal retreat-sites, and the proportion of nights on which taods changed shelter-sites. For this paper, data were colelcted fro mmany such studies over a wide area, to explore changes in dispersal-related traits during the toad's invasion history.