Tom S. Romdal, Robert K. Colwell, and Carsten Rakbek. 2005. The influence of band sum area, domain extent, and range sizes on the latitudinal mid-domain effect. Ecology 86:235–244.

Appendix B. Assumption of continuous ranges.

The empirical richness values analyzed in this study do not correspond precisely to actual empirical richness at specific latitude, because we assume complete ranges without gaps. MDE models so far do not incorporate the concept of gaps. The possible bias from ignoring gaps was assessed by a simple comparison of basic species richness patterns with and without gaps (Fig. B1). The lower curve shows the pattern when the empirical gaps are retained in the species distributions. A slight deviation is recorded, mainly at mid-latitude, but is negligible throughout.

FIG. B1. Comparison of the empirical latitudinal richness pattern for New World birds, assuming continuous ranges (Empirical S, upper curve) with the empirical pattern adjusted for gaps (Gap-adjusted S, lower curve). The x-axis shows latitude from 60ºS (-60) to 80ºN. Richness was adjusted for gaps of 3º or larger.