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Dispersal without drivers: Intrinsic and extrinsic variables have no impact on movement distances in a terrestrial amphibian


Jreidini, Nathalie; Green, David M. (2022), Dispersal without drivers: Intrinsic and extrinsic variables have no impact on movement distances in a terrestrial amphibian, Dryad, Dataset,


Dispersive movements are often thought to be multicausal and driven by individual body size, sex, conspecific density, environmental variation, personality and/or other variables. Yet such variables often do not account for most of the variation among dispersive movements in nature, leaving open the possibility that dispersion may be indeterministic. We assessed the amount of variation in 24 h movement distances that could be accounted for by potential drivers of displacement with a large empirical dataset of movement distances performed by Fowler’s Toads (Anaxyrus fowleri) on the northern shore of Lake Erie at Long Point, Ontario (2002–2021, incl.). These toads are easy to sample repeatedly, can be identified individually and move parallel to the shoreline as they forage at night, potentially dispersing to new refuge sites. Using a linear mixed-effect model that incorporated random effect terms to account for sampling variance and inter-annual variation, we found that all potential intrinsic and extrinsic drivers of movement accounted for virtually none of the variation observed among 24 h distances moved by these animals, whether over short or large spatial scales. We examined the idea of movement personality by testing variance per individual toad and found no evidence of individuality in movement distances. We conclude that deterministic variables, whether intrinsic or extrinsic, neither can be shown to nor are necessary to drive movements in this population over all spatial scales. Stochastic, short-timescale movements, such as daily foraging movements, can instead accumulate over time to produce large spatial-scale movements that are dispersive in nature.


The dataset comprises geo-referenced captures of individually identified Fowler's Toads (Anaxyrus fowleri) over 20 years (2002–2021, incl.), as well as environmental variation obtained for data extracted from the Environment Canada website ( for the Port Colborne, Ontario, weather station and US Army Corps of Engineers, Detroit District (


Natural Sciences and Engineering Research Council of Canada