Figure 1.

Conceptual illustration of how species interactions can limit evolution at a range edge. (a) A species’ range (grey box) occurs along the portion of an environmental gradient where the species has a positive growth rate (i.e. above the dashed reference line) at low intra-specific density but in the presence of other species. The range edge (black vertical line) occurs where the growth rate of a (potentially locally adapted) range-edge population (orange) falls below 0. (b) Ecological release following the loss or reduction of an antagonist (e.g. a competing species) increases population growth (green), enabling the species to expand its niche/geographical range ecologically without evolution occurring (yellow arrow). (c) In the longer term, ecological release allows the population to maintain larger population sizes, experience new portions of the abiotic gradient and experience a weakening of any adaptive trade-offs between the antagonist and the abiotic environment, enabling evolution and further range expansion.