Patterns of Diel Flight Activity in Dung-Inhabiting Beetles: An Ecological Analysis

Abstract

The diel flight activity of dung-inhabiting beetles was monitored during the whole active season (May to October) in two localities in southern Finland, one exposed and one shaded using a baited Johnson-Taylor suction trap and a window trap. Altogether 49200 individuals were trapped, representing 148 species, of which 86 were included in the analysis. Ten different flight activity distributions, three unimodal and seven bimodal were distinguished, based on the hourly numbers of individuals captured. In the specialist coprophages, Sphaeridium and Aphodius, and the larger predators (subfamily Staphylininae) a unimodal pattern dominated, these being mostly day-flyers, while the generalist coprophages (genera Cercyon and Megarthrus and subfamily Oxytelinae) and the smaller predators (subfamily Aleocharinae) were mostly bimodal, and consequently more or less crepuscular. In most species the flight activity pattern changes characteristically by season and habitat. The duration of flight activity was the longest in summer, and shortest in autumn. The variance between the seasons was greatest at the beginning of the daily flight period than at the end. In most bimodal species the distributions overlapped totally in autumn resulting in a unimodal activity pattern. In the multivoltine species two different strategies was suggested as means of coping with the large seasonal temperature variations: (1) a flexible bimodal and (2) a broad unimodal activity pattern. In bimodal species a significant negative correlation was found between median flight temperature and macrohabitat niche width. Trends in the evolution of dispersal flight in dung-inhabiting beetles are discussed.