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Aphodius fossor (L.) (Coleoptera: Scarabaeidae), a common endocoprid dung beetle in southeastern Wyoming, may have a survival strategy to maintain dung pad integrity and moisture crucial to larval survival in an arid climate (annual precipitation <30 cm). Typically, A. fossor seems to contribute little to dung pad decomposition, because inhabited dung pads seem to be intact and weigh approximately the same as uninhabited pads, even after 1 yr on pasture. To assess the role of A. fossor in dung pad decomposition and nutrient recycling, artificially formed bovine dung pads were inoculated with five pairs of adult A. fossor. After 40 d, A. fossor activity had no measurable effect on external surface area or moisture retention within the dung pad cores. Pads inhabited by A. fossor weighed significantly more than did control pads on most weigh dates of the experiment, possibly because of incorporation of soil particles at the dung/soil interface. Externally, A. fossor-inhabited dung pads seemed intact; however extensive tunneling was evident throughout the core of the pad leaving an intact, protective crust. A. fossor activity increased microbial biomass carbon in the soil beneath the dung pad. Levels of total nitrogen (N) and carbon (C) decreased in the pads but increased in soil beneath the pads. Dung in the core and in the crust of pads with A. fossor had significantly less total N than pads with no beetles and total C was significantly lower in the crust.

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Selenium (Se) is an element of interest in plant and animal nutrition because of the narrow range between essential and toxic levels. Many areas being mined in the Powder River Basin of northeastern Wyoming contain pockets ofhigb Se concentrations within the overburden material. Therefore, it has become increasingly necessary for industcy and state regulatory personnel to ti)' to quantify relationships between pre-existing soil Se levels to postmining levels in both soils and plants. A study was initiated in 1991 to investigate the relationship of plant Se uptake • and soil/backfill Se levels at two active coal mines in the Powder River Basin, Wyoming. Soil and vegetation samples were collected in 1991 and 1992. Soil/backfill Se levels were determined by five methods: total Se and hot water, AB-DTP A, saturated paste, and dihydrogen phosphate extractable Se. Total plant Se was also determined. Plant Se levels of four vegetation lifeforms were regressed on eleven soil variables to construct appropriate models for assessing.plant-soil Se relationships. These regression analyses were conducted with soil depth, vegetation type (native versus reclaimed), and mine (large mine (Mine L) and (small mine (Mine S)) as important subcategories. Depth and type were significant in determining statistical relationships. Simple linear regression models were developed, but the majority of the slopes were not significantly different at the 0.05 probability level. Multiple linear regression models revealed that soil Se and pH were the most important predictors of plant Se levels for native areas; no specific parameter was dominant in reclaimed area analysis. The R 2 's for native areas were improved over the multiple linear models by deriving polynomial regression models. Polynomial regression models for the reclaimed areas resulted in marginal improvement ofR 2 values over the multiple linear regression models. Whereas hot water soluble Se appears to be a better predictor of plant Se concentrations, both AB-DTP A and phosphate extractable Se were also good predictors. The best statistical relationships were also determined with depths 2 and 3 of native areas. Inclusion of age of reclamation, however, improved the polynomial models for reclaimed areas.