The crustacean zooplankton community of Harp Lake, Ontario, Canada, has changed appreciably since the invasion by the spiny water flea, Bythotrephes. Crustacean species richness has declined, large-bodied Cladocera have replaced small-bodied ones, and there has been a downward trend in the total abundance of zooplankton because copepod abundance has remained stable while Cladoceran abundance has declined. Although the zooplankton community has now been stable for 4 years (1995–1998), the biology of the invader has changed dramatically. In particular, there have been 10-fold differences in the mean annual abundance of Bythotrephes in this 5-year period and substantial changes in the timing of population maxima. We attribute these changes to two factors: (i) transition from a summer to a fall switch from parthenogenesis to gametogenesis and (ii) interannual differences in the thickness of a warm, dark stratum in the lake. We hypothesize that this stratum provides a refuge for Bythotrephes from predation by lake herring, Coregonus artedii.

Domestication can change animal traits such as skull size and shape. Given that domestic American mink Neovison vison may escape from farms within the native range of wild mink, we were interested in determining whether 1) skull characteristics differed between wild and domestic mink, and 2) free ranging mink in Ontario had skull features characteristic of domestic animals. Contrary to previous research, we found no effect of domestication on braincase volume or muzzle length in mink. We did, however, find that skulls of domestic mink were larger than those of wild mink and that domestic skulls had narrowed postorbital constrictions (POC). A model using both condylobasal length (CBL) and POC correctly classified the origin of 100% of male skulls and 90% of female skulls in an external data set. A POC-only model was less successful, however, correctly classifying 68% and 70% of male and female skulls, respectively. In a field application of the two-term model, only one of 109 skulls was identifed as being of farm origin. With the POC-only model, however, 12 skulls were classified as being from domestic animals. Where size differences are expected (for example, with recently escaped animals), the model should be effective for identifying domestic mink. However, the utility of CBL and POC for identifying domestic-origin or hybrid animals that have been born in the wild depends on a key uncertainty, namely, the extent to which these traits have a genetic basis.

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A technique is presented for dispatching fossil-fueled electric generators which results in a reduction in the ground level SO2 concentrations. The dispatching schedules and ground level SO2 concentrations are determined for a sample but realistic problem, and are presented to illustrate the effectiveness of the proposed technique. The results of the sample problem clearly demonstrate the viability of dispatching generators using an environmental cost to ensure compliance with ambient air quality regulations. However, it is also pointed out that an accurate deterministic dispersion model must be used if useful results are to be obtained.