Interference competition occurs when access to an available resource is negatively affected by interactions with other individuals, where mutual interference involves individuals of the same species. The interactive phenomena among individuals may be size-dependent, since body size is a major factor that may alter prey consumption rates and ultimately the dynamics and structure of food webs. A study was initiated in order to evaluate the effect of mutual interference in the prey-specific attack rates and handling times of same size class predators, incorporating variation in consumer size. For this purpose, laboratory functional response experiments were conducted using same age predators, i.e. newly hatched (first instar) or mature (fifth instar) nymphs of the polyphagous mirid predator Macrolophus pygmaeus preying on Ephestia kuehniella (Lepidoptera: Pyralidae) eggs. The experiments involved four predator density treatments, i.e. one, two, three or four predators of same age, i.e. either first or fifth instar nymphs, which were exposed to several prey densities. The Crowley-Martin model, which allows for interference competition between foraging predators, was used to fit the data. The results showed that mutual interference between predator’s nymphs may occur that affect their foraging efficiency. The values of the attack rate coefficient were dependent on the predator density and for the first instar nymphs was significantly lower at the highest predator density than the lower predator densities, whereas for the fifth instar nymphs in all density treatments was significantly lower to that of the individual foragers’ ones. These results indicate that mutual interference is more intense for larger predators and is more obvious at low prey densities where the competition level is higher. The wider use of predator-dependent functional response models will help towards a mechanistic understanding of intraspecific interactions and its consequences on the stability and structure of food webs.

First column: initial prey density

Second column: number of prey eaten

Third column: proportion of prey eaten