Animal Color Vision

Herbivores use visual cues and signals as part of their complicated, multifactor way of selecting food plants (Arnold 1966; Krueger et al. 1974; Cahn and Harper 1976; Rausher 1978; Prokopy and Owens 1983; Reeves 2011). When discussing defensive plant coloration or any visual plant defense, it should be clear that the relevant herbivorous animals can see such visual cues, signals, deceptive coloration of various types, and distinguish (or not in crypsis) between these and backgrounds. It has been hotly debated whether mammalian or insect herbivores see colors or not, and if they do, which colors and to what degree. Reviews of this issue have provided conclusive proof that they do see colors (Jacobs 1993; Dafni et al. 1997; Kelber 2001; Kelber et al. 2003). While most large mammalian herbivores don’t see colors the way trichromatic humans do, there are still good reasons to conclude that even with the dichromatic vision characterizing many large mammalian herbivores, colorful plant parts look different from regular green tissues because of their hue, saturation, contrast, or brightness (see Sumner and Mollon 2000a, b; Kelber et al. 2003). The herbivores may also use reflectance cues of the colorful plant parts (see Schaefer et al. 2006; Motoyoshi et al. 2007). This view is supported by the case of “color-blind” cuttlefish that successfully camouflage themselves in various backgrounds (Marshall and Messenger 1996) and by the importance of the luminance contrast component of aposematic and other types of defensive plant coloration even for color-blind animals (Prudic et al. 2007). In any case, colors can be seen by animals both as chromatic (wavelength related) signals and achromatic (intensity related) signals (e.g., Schaefer et al. 2006) and this issue should also be studied on a larger scale in the context of visual plant defenses. Herbivore’s character of not seeing part of the spectrum may also be used by plants for defensive coloration. For instance, red appears black or very dark to certain insects. In such cases, “black” red coloration can be used to look dead, for mimicry, camouflage etc., while that red coloration can be used for signaling to animals that see red, or for physiological functions.