Climate-mediated range shifts into eco-evolutionary novel habitats have the potential to alter the
ecology and behaviour of range-expanding species. Of particular concern are behaviours that have a
strong impact on the ecology and life history of expanding species. Behaviours that control the spatial
patterns of habitat use may be particularly important. We examined site fidelity and foraging foray
behaviour of the mangrove tree crab, Aratus pisonii, in its historic mangrove habitat and the recently
colonized eco-evolutionary novel salt marsh. In the mangrove, A. pisonii showed both strong site fi-
delity to individual trees and a foraging pattern wherein they made foraging forays that decreased in
frequency as their distance from the home tree increased; but they displayed neither behaviour in the
salt marsh. Chemical cues from faeces appear to be the mechanism behind site fidelity in the
mangrove and may suggest the mechanism for the loss of this behaviour in the salt marsh where
substrate is regularly submerged, potentially preventing establishment of such cues. The loss of site
fidelity may affect the foraging behaviour and predation risk of A. pisonii in the salt marsh, leading to a
shift in its ecology and bioenergetics. As more species are forced to shift ranges into eco-evolutionary
novel habitats, it is important to understand how this shift may affect their life history, behaviour and
ecology in indirect ways.