The influence of slope aspect and soil type on immigration and emergence of some northern temperate dung beetles

Soil type is a habitat factor that influences both adult habitat choice and reproductive success in tropical dung beetles. However,soil type habitat preferences of northern temperate dung beetles have not been studied,nor has their reproduc- tive success in relation to habitat heterogeneity been investigated.The aim of this study was,firstly,to study the impact of slope aspect (southern vs.northern) and soil type (sand vs.clay) on immigration and subsequent emergence of dung bee- tle offspring.A second aim was to evaluate whether the soil type selection was reflected in reproductive success.The study was performed with cow dung during early summer in central Sweden. Beetle immigration was estimated using dung- baited pitfall traps and numbers of emerging beetles were assessed using specially designed emergence traps. Immigrating beetles collected represented 11 Aphodiusspecies (Scarabaeidae),three Sphaeridiumspecies (Hydrophilidae), and one Geotrupes species (Geotrupidae).Seven emerging species were caught,all from the genus Aphodius.Immigration was influenced by soil type, i.e. more individuals of A. ater, were caught on clay while more individuals of A. haemor- rhoidaliswere caught on sand.Slope aspect had no significant influence on immigration. Four species (A.ater,A.fimetarius,A.fossorand A.pusillus) dominated amongst the emerging beetles at both sites.Emer- gence was earlier on the south-facing slope for A.fimetariusand on both the south-facing slope and on sand for A.fossor. Emergence patterns were dependent on soil type.More individuals of A.ateremerged on clay while more individuals of A. fossorand A.pusillusemerged on sand.Slope aspect did not significantly influence the number of emerging beetles. We conclude that soil type influenced both adult habitat selection and reproduction, while slope aspect had less effect. Patterns of immigration and emigration corresponded for some species but not for others,hence selection of soil type may not directly correspond to reproductive success.Our results also indicate that Aphodiusreproduction may be risky in wet clay soils because of mortality in over-wintering individuals.