We characterized the early population dynamics of invasion by extending the range of guppies upstream, above barrier waterfalls. We compared their population dynamics with those from equivalent natural communities with guppies. Two of our streams had intact forest canopies and two had thinned canopies, which mimics a common form of habitat disturbance. The guppies attained population densities equivalent to those of natural streams in experimental streams with intact canopies but exceeded natural densities under thinned canopies. As density increased, guppies moved into less desirable habitat, but did so without sacrifice of fitness, suggesting that habitat use conformed to an ideal free distribution. These photographs illustrate the article “Experimental study of species invasion: early population dynamics and role of disturbance in invasion success” by David N. Reznick, Sebastiano De Bona, Andres Lopez-Sepulcre, Mauricio Torres, Ronald D. Bassar, Paul Bentzen, and Joseph Travis published in Ecological Monographs. https://doi.org/10.1002/ecm.1413