Fig. 1

Model predicting overall species richness and diversity in local communities across the full range of environmental stress across which a regional biota can occur (see the “Introduction” for a rationale). The horizontal lines for northern Nova Scotia and Helgoland indicate the approximate stress range occurring on those two coasts relative to the full stress range across which the cold-temperate biotas from the NW Atlantic and NE Atlantic, respectively, can occur. On each coast, high stress is expected at high intertidal elevations, whereas low stress is expected at low elevations. The dotted sections of each line indicate the possible variation among local shores