Spatial Variation in the Timing of the Seasonal Occurrence in Coprophagous Beetles

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Abstract
Seasonal changes in the numbers of individuals in 2 groups of dung-inhabiting beetles, Aphodius (Scarabaeidae) and Hydrophilidae, vary substantially between similar pastures situated about 1.5 km apart. This may be related to seasonally constant quantity and quality of their habitat and resources (droppings); in the absence of this constraint, other factors, e.g., chance, history and interspecific interactions, may become decisive determinants of the spatio-temporal structure of populations. The seasonal mean overlap (percentage similarity) with the most similar species in the same field and the mean intraspecific between-field overlap were both about 50%; which shows the importance of examining spatial variation in studies of niche relations. Some species of Aphodius showed bimodal seasonal distribution in numbers, which is interpreted to reflect intraspecific variation in the stage of hibernation. The relation between spatial variance in numbers and in the timing of the seasonal occurrence is discussed. Due to spatial variation in the species composition, intraspecific diversity in the seasonal occurrence of different species may promote rather than displace interspecific diversity.

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