The effects of Hg2+, methyl mercury, and flufenamic acid, all of which inhibit mitochondria, were examined at frog motor nerve terminals. Unbiased estimates of m (no. of transmitter quanta released), n (no. of functional release sites), p (probability of release), and vars p (spatial variance in p) were obtained using K+-induced asynchronous neurosecretion (m, n and p not having the same definitions as with nerve-evoked release). Transient but significant increases in m, n, p and vars p were found with all three agents. These findings indicate that mitochondrial inhibition and release of sequestered Ca2+ can be detected as a real-time increase in vars p. The results also suggest that changes in vars p might be used to differentiate between cellular (membrane) and subcellular (organellar) actions of drugs at the nerve terminal.

Conserving structural and compositional diversity in Fescue Prairie requires reintroducing natural disturbances according to their historic regime. Fire is an important natural process that may be a source of spatial heterogeneity in Fescue Prairies. The effects of burning in all months of the year except January and February were evaluated in a Fescue Prairie in central Saskatchewan for 6 years following burning on 2 sites that had not been previously burned and 2 sites that had been burned 5 years earlier. Except for burning in March, burning reduced cover of litter (P<0.01) and <i>Festuca hallii </i> (Vasey) Piper (P=0.01) while increasing bare soil (P<0.01) for 1 to 5 years. Cover of <i>Elymus lanceolatus </i>(Scribn. & J.G. Sm.) Gould (P<0.01), graminoids (P=0.02), and species evenness (P=0.01) increased with burning frequency. Burning in late-summer reduced cover of graminoids (P=0.03), plants other than the dominant grasses (P=0.03), and total plant cover (P=0.02). Burning increased the spatial variance (s2) in litter cover (P<0.01) and bare soil (P<0.01) for 1 to 3 years. Aside from burning in early spring, burning reduced s2 in total standing crop (P=0.02) and <i>F. hallii</i> (P=0.01). Variability in the cover of <i>E. lanceolatus </i>(P<0.01) and graminoids (P=0.04) increased with burning frequency. Canonical correspondence analysis (CCA) indicated that pre-burn history had a dominant effect on plant community composition, explaining 13% of the variation (P<0.01). The cumulative effects of repeated burning, annual variability in weather, and exposure to temperature extremes may have caused a shift in the composition of the plant community. The first 4 ordination axes explained 22% of the variation in plant community composition after burning, indicating that many other environmental or site variables controlled community composition. A range of burning dates and frequencies should be reintroduced or maintained in Fescue Prairie to create a mosaic of plant communities in various stages of recovery after burning. A mosaic will increase the structural and compositional diversity in remnant Fescue Prairies.

Conserving structural and compositional diversity in Fescue Prairie requires reintroducing natural disturbances according to their historic regime. Fire is an important natural process that may be a source of spatial heterogeneity in Fescue Prairies. The effects of burning in all months of the year except January and February were evaluated in a Fescue Prairie in central Saskatchewan for 6 years following burning on 2 sites that had not been previously burned and 2 sites that had been burned 5 years earlier. Except for burning in March, burning reduced cover of litter (P<0.01) and <i>Festuca hallii </i> (Vasey) Piper (P=0.01) while increasing bare soil (P<0.01) for 1 to 5 years. Cover of <i>Elymus lanceolatus </i>(Scribn. & J.G. Sm.) Gould (P<0.01), graminoids (P=0.02), and species evenness (P=0.01) increased with burning frequency. Burning in late-summer reduced cover of graminoids (P=0.03), plants other than the dominant grasses (P=0.03), and total plant cover (P=0.02). Burning increased the spatial variance (s2) in litter cover (P<0.01) and bare soil (P<0.01) for 1 to 3 years. Aside from burning in early spring, burning reduced s2 in total standing crop (P=0.02) and <i>F. hallii</i> (P=0.01). Variability in the cover of <i>E. lanceolatus </i>(P<0.01) and graminoids (P=0.04) increased with burning frequency. Canonical correspondence analysis (CCA) indicated that pre-burn history had a dominant effect on plant community composition, explaining 13% of the variation (P<0.01). The cumulative effects of repeated burning, annual variability in weather, and exposure to temperature extremes may have caused a shift in the composition of the plant community. The first 4 ordination axes explained 22% of the variation in plant community composition after burning, indicating that many other environmental or site variables controlled community composition. A range of burning dates and frequencies should be reintroduced or maintained in Fescue Prairie to create a mosaic of plant communities in various stages of recovery after burning. A mosaic will increase the structural and compositional diversity in remnant Fescue Prairies.

No description available.