SPINES PROTECT PLANTS AGAINST BROWSING BY SMALL CLIMBING MAMMALS

The presence of spines on woody plants has been shown to limit the los s of foliage to large mammalian browsers by restricting both bite size and biting rate. We tested the hypothesis that plant spines are also an effective defense against browsing by small mammals, such as rodent s, that climb within the canopy of shrubs to harvest fruits, seeds, an d foliage. Tame southern plains woodrats (Neotoma micropus) were allow ed to harvest raisins impaled on the branches of blackbrush shrubs (Ac acia rigidula Benth.) in five categories of spinescence: naturally spi neless, moderately spiny, or very spiny branches, and moderately spiny and very spiny branches with the spines removed. Plant spinescence si gnificantly reduced the woodrats foraging efficiency (P = 0.0001). Alt hough plant spines are generally thought to be an evolved defense agai nst browsing by ungulate herbivores, they may also reduce browsing by small mammals.