“…Thus, there is a permanent evolutionary arms race between the plants and their herbivores, in which, on an evolutionary time scale, plants acquire better defenses and herbivores partly or fully overcome them (Cornell and Hawkins, 2003). Spines, thorns and prickles are well known as physical protection against herbivory (e.g., Cash and Fulbright, 2005;Cooper and Owen-Smith, 1986;Grubb, 1992;Gowda, 1996;Janzen, 1986;Janzen and Martin, 1982;Myers and Bazely, 1991;Rebollo et al, 2002) because they can wound mouth parts and digestive systems (Janzen and Martin, 1982;Janzen, 1986) as well as other body parts of the herbivores. In addition, spines inject pathogenic bacteria and fungi into large herbivores (Halpern et al, 2007a(Halpern et al, , 2007bLev-Yadun and Halpern, 2008).…”