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

1. Co-occurrence of closely related predators in a prey-limited habitat app ears to contradict the principle of competitive exclusion, however it may b e explained through indirect effects, niche shifts, and intraguild predatio n. 2. The interactions between sympatric tiger beetle Cicindela species were e xamined. Cicindela circumpicta is the largest of three species (C. circumpi cta, C. togata, C. fulgida) found in saline habitats throughout central Nor th America. The temporal occurrence of these species overlaps, as does thei r 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 foun d mostly in shaded conditions but tiger beetles differed significantly in s hade use, with C. circumpicta spending 70% of the time in the shade compare d with approximate to 20% for C. togata. Differential habitat use was not e xplained by maximum temperature tolerances, which did not differ between th e species. 5. Laboratory trials established that both tiger beetle species consumed sm all prey (apterous Drosophila) but C. togata was more efficient at capturin g winged Drosophila. 6. Foraging efficiency, as measured by the time taken for a C. togata to ca pture three prey items, decreased significantly in the presence of other ti ger beetles, especially C. circumpicta. 7. These results are an indication that intraguild predation and induced ch anges in foraging behaviour operate in the ecology of adult tiger beetles.