ILSE, L.M.*; HELLGREN, E.C.: Porcupines, Pinyon Pines, and Pine Engravers: What’s the Connection?

Understanding linkages among different trophic levels is important to the conservation and management of ecosystems. The goal of this research was to test the hypothesis that porcupines, Erethizon dorsatum, predispose the papershell pinyon pine, Pinus remota, a Pleistocene-relict species, to colonization by pine engraver beetles of the genus Ips. We studied porcupine ecology, pinyon pine physiology and physiognamy, and beetle-pine associations on a study area in the southwestern Edwards Plateau from June 1997 to August 1999 to elucidate relationships among these 3 organisms. Porcupines primarily were located in pinyon pines. Pines damaged by porcupines were greater in girth (P < 0.006), taller, (P < 0.001), and had greater resin flow rates (P < 0.001) than paired undamaged trees (n = 183 pairs on 20 transects). The distribution of bark beetle infestations varied (P < 0.01) between damaged and undamaged trees. Although attacks by beetles were evident on both types of trees, successful colonization was greater on pines damaged by porcupines. Intensity of porcupine attack, indexed by number of feeding scars and amount of bark removed, was also associated with greater colonization rate by bark beetles. Our data on these interspecific relationships are of regional interest relative to conservation of this unique pinyon-juniper woodland, and of wider value as a model system showing the role of distinct phyla that define community structure in forest and woodland ecosystems.