Habitat edges as a potential ecological trap for an insect predator


*Leslie Ries, Center for Environmental Sciences and Education, Northern Arizona University, Box 5694, Flagstaff, AZ 86011, U.S.A. E-mail: Leslie.Ries@nau.edu


Abstract.  1. Ecological traps, where animals actively select poor habitat for reproduction over superior habitat, are generally associated with birds at forest edges. This study examines oviposition preference, predation, and parasitism rates in the mantid Stagmomantis limbata to determine the potential generality of this phenomenon.

2. Egg case (oothecae) densities were measured across two edge types (cottonwood and desert scrub) within desert riparian ecosystems. A positive edge effect in oothecae density was found with an approximate three-fold increase in density at cottonwood (Xedge = 0.05 oothecae/100 m2 vs. Xinterior = 0.015 oothecae/100 m2) and desert scrub (Xedge = 0.20 oothecae/100 m2 vs. Xinterior = 0.06 oothecae/100 m2) edges (P < 0.01).

3. Rates of bird predation were significantly higher for oothecae at desert scrub edges and showed a trend of higher predation rates at cottonwood edges, suggesting that riparian habitat edges may be acting as an ecological trap for this mantid species. There was no effect of edges on oothecal parasitism rates.

4. These results provide an example of the effect of habitat edges on a generalist insect predator and indicate that an ecological trap may exist with respect to one of its natural enemies.