Fig. 4.

Relationships between the richness of ruderal species at the Central Valley sites (WS, NS, RC) and the richness of both ruderal (A) and nonruderal (B) species in the Sierran sites (excluding SV) and both ruderal (C) and nonruderal (D) species in the Coast Range (GC). Values on both axes for all graphs are residuals from the relationship between richness and the number of visits per year (SI Text). Thus, these values have been corrected for variation in sampling effort among sites. Statistics reported in the upper portion of each graph are results of simple linear regressions. SV was excluded from these analyses, because the position of the site east of the Sierran crest (Fig. 1) makes it less likely to be connected via dispersal to the low elevations west of the Sierran crest.