Range Expansion of an Introduced Mantid Iris oratoria and Niche Overlap with a Native Mantid Stagmomantis limbata (Mantodea: Mantidae)

Abstract

Iris oratoria L. invaded southern California in the 1930s. We describe its subsequent northward and eastward expansion in the southwestern United States. The rate of expansion into Arizona suggests that human activities have played a part in its spread. This mantid has come into contact with a native species Stagmomantis limbata Hahn. We present 3 yr of field data on 2 components of niche overlap between these 2 species: overlap in habitat use over time and in diet. At a field site in Davis, CA, S. limbata hatched earlier in the season than did L. oratoria , and I. oratoria tended to persist longer into the year than did S. limbata . The diets of the species overlapped to a moderate extent, yet they differed with respect to prey type and length. S. limbata ate a greater proportion of orthopterans and mantids than did I. oratoria , and S. limbata ate longer prey than did I. oratoria . Additionally, S. limbata adults had longer pronota and forelegs than I. oratoria adults. This difference in body size might be an important cause of the dietary differences between the species. Furthermore, the earlier hatch date for S. limbata also might result in a reduction of size overlap and, consequently, diet overlap among nymphs of the 2 species. Thus, the differences in body size and phenology may be mechanisms that allow these species to coexist.