Figure 2.
Relationship between clutch size and coefficient of between-male variation in sperm total length (CVbm) for 31 Afrotropical (open circles) and 99 temperate zone (filled circles) passerine species. The association between clutch size and CVbm is significant in tropical species only (see §3 for further details) and is indicated by a solid line. Plotted points are species averages, and relationships are not controlled for phylogeny. Higher values of CVbm indicate lower values of EPP, and hence sperm competition (see the main text for further details).