A Removal Experiment with Darkling Beetles: Lack of Evidence for Interspecific Competition

A removal experiment tested for interspecific competition among darkling ground beetles (Tenebrionidae) in a montane New Mexico meadow. Adult Eleodes obscurus were removed from three fenced 0.1—ha plots from August 1975 through August 1978. This species account for >50% of the adult tenebrionid biomass in the community (Wise, in press). Adult E. obscurus numbers were rapidly reduced and were kept low throughout the experiment. Removing adults should also have reduced densities of the soil—dwelling larvae, though the extent of any reduction in larval numbers could not be measured directly. Three plots in which E. obscurus adults were not removed were controls. Adult population densities of the other species did not increase in response to reducing E. obscurus density. Adult size was also measured because increased size at eclosion from the pupa would reflect release from competition among larvae. Removing E. obscurus adults produced no consistent evidence that competition between larval E. obscurus and larvae of the other species was influencing their size at eclosion. Adult size differed more between years than between removal and control plots. The number of E. obscurus adults emerging in the removal plots had not declined by 1978. Thus, lack of evidence for larval competition may reflect failure to have reduced substantially densities of E. obscurus larvae rather than the absence of competition. However, adult E. obscurus densities were substantially reduced, yet the other species showed no evidence of competitive release. Interspecific competition between adults may not be a major interaction in tenebrionid communities.