Competition and Disturbance in Communities of Carrion-Breeding Diptera

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Abstract
Non-equilibrium theory predicts an inverse relationship between the importance of competition and disturbance in determining community structure. The prediction was tested in this field study of Diptera that breed in dead slugs and small mammal carrion. Results from adding food to carcasses colonized under field conditions and manipulation of data collected from 207 slug carcasses showed that competition is not strong among the species reared from dead slugs. Competition was stronger for small mammal carrion. Five species that previously had only colonized non-mammal carcass types were reared from mouse carcasses protected from Phaenicia caeruleiviridis Macquart (Calliphoridae), the most common and abundant species reared from small mammal carcasses exposed under natural conditions. Disturbance of the dipteran community arose primarily through feeding by non-dipteran scavengers. The impact of feeding by non-dipteran arthropods was much greater for slugs than small mammals but both were heavily disturbed when vulnerable to vertebrates and carrion-burying beetles. This study and others show that few species breed in mammal carrion compared to small non-mammal carcass types. Disturbance by non-dipteran scavengers helps maintain the high diversity in small non-mammalian carcasses reducing the importance of competitive interactions among dipteran species. The low diversity of flies breeding in small mammals may be explained by the superior competitive ability of P. caeruleiviridis. Whether disturbance by non-dipteran arthropods is sufficient to explain the coexistence of carrion-breeding Diptera is also discussed.