1 23 Oecologia ISSN 0029-8549 Volume 175 Number 1 Oecologia (2014) 175:129-138 DOI 10.1007/s00442-013-2876-4 Native insect herbivory limits population growth rate of a non-native thistle James O. Eckberg, Brigitte Tenhumberg & Svata M. Louda