Tigers eating tigers: evidence of intraguild predation operating in an assemblage of tiger beetles


W. Wyatt Hoback, Department of Biology, University of Nebraska at Kearney, Kearney, NE 68849, U.S.A.
E-mail: hobackww@unk.edu


1. Co-occurrence of closely related predators in a prey-limited habitat appears to contradict the principle of competitive exclusion, however it may be explained through indirect effects, niche shifts, and intraguild predation.

2. The interactions between sympatric tiger beetle Cicindela species were examined. Cicindela circumpicta is the largest of three species (C. circumpicta, C. togata, C. fulgida) found in saline habitats throughout central North America. The temporal occurrence of these species overlaps, as does their spatial occurrence on exposed salt flats of saline marshes. During field observations, exoskeletal remains of C. togata were found at the study site in Nebraska, U.S.A.

3. In laboratory trials, male C. circumpicta ate C. togata in 38% of trials and female C. circumpicta ate C. togata in 50% of trials (n = 24).

4. In the field, potential prey, consisting mainly of small flies, was found mostly in shaded conditions but tiger beetles differed significantly in shade use, with C. circumpicta spending 70% of the time in the shade compared with ≈ 20% for C. togata. Differential habitat use was not explained by maximum temperature tolerances, which did not differ between the species.

5. Laboratory trials established that both tiger beetle species consumed small prey (apterous Drosophila) but C. togata was more efficient at capturing winged Drosophila.

6. Foraging efficiency, as measured by the time taken for a C. togata to capture three prey items, decreased significantly in the presence of other tiger beetles, especially C. circumpicta.

7. These results are an indication that intraguild predation and induced changes in foraging behaviour operate in the ecology of adult tiger beetles.