• ideal free distribution;
  • input matching;
  • rosyside dace;
  • yellowfin shiner;
  • interspecific competition


When members of a population choose patches that maximise individual net energy gain without interference, they are input matching, a strategy derived from the ideal free distribution (IFD) that results in equal rewards across all patches. We investigated the input matching abilities of yellowfin shiner, a recent invader, and rosyside dace, a common native minnow, found in Coweeta Creek, North Carolina, USA. To test the species' relative input matching abilities, we varied food abundance within the range found in the natural habitat in a two-patch laboratory stream to document the distribution of foragers when food densities differed in the ratio of 2:1. We then applied simple IFD model predictions to determine whether the observed distribution of foragers was best described by (i) the IFD, (ii) differing competitive abilities or (iii) the ideal despotic distribution and/or other unequal competitor models, and to ascertain whether the invader demonstrated a superior ability to track resource distributions. Yellowfin shiner was more likely to move between patches, which resulted in increased ability to match the distribution of food when prey abundance increased. The distribution of rosyside dace between patches did not change in response to increased food abundance. Despite a considerable range of competitive abilities within intraspecific groups, the ‘equal competitors’ IFD was as good at predicting fish distributions as ‘unequal competitor’ models. The ability to track local resource availability in highly variable environments facilitates maximising energy intake and likely promoted the establishment of yellowfin shiner in a southern Appalachian stream.