Animals frequently raise their heads to check for danger. In a group, individuals generally raise their heads independently. Earlier models suggest that all group members could gain by coordinating their vigilance, i.e., each member raising its head when others are not. We re-examine these...

Fruit color changes during ripening are typically viewed as an adaptation to increase signal efficacy to seed dispersers. Plants can increase signal efficacy by enhancing chromatic (wavelength related) and/or achromatic (intensity related) contrasts between fruit and background. To assess how...