Fig. 1.

Hypothesized effects of ecological barriers on community composition shift distance and direction. The icons in panels A–C illustrate ecological barriers: biome boundaries, coastlines, and elevation, respectively. In each map, the orange-outlined square indicates the hypothetical bird community of interest and the black arrows the hypothetical distances and directions of community composition shift. In panel A, terrestrial biome boundaries are indicated with different colored polygons. In panel B, the coastline is indicated with a black line. In panel C, elevation is indicated with a brown–yellow gradient (brown colors: high elevation). Each graph illustrates the hypothesized effect of a barrier on community composition shift distance and direction (X axis). For simplicity of the illustration, the X axis for direction is represented as a linear term, expressing a shift along the latitudinal (south–north) or longitudinal (west–east) axis (for details, see Materials and Methods).