Fig. 12

Large body size appears to confer numerous advantages on organisms within populations. Based on an analysis of various vertebrates, invertebrates, and plants, Kingsolver and Pfennig (2004) reported that larger body size (solid lines) tends to be associated with positive selection gradients (i.e., greater success relative to smaller individuals) within populations as measured in terms of survival (a), number of offspring (fecundity) (b), and mating success (c). By contrast, other morphological traits (dotted lines) unrelated to body size tend to exhibit positive and negative selection gradients in roughly equal frequencies (i.e., overall they confer no significant advantage, nor a cost, on individuals with especially high or low values for the traits). The authors argue that there is consistent selection within populations for larger size and that this could translate into large-scale trends toward increased body size (“Cope’s Rule”) over evolutionary timescales. Figure from Kingsolver and Pfennig (2004), reproduced by permission of Blackwell