Ecological Studies of Seaweeds in McMurdo Sound, Antarctica

Three species of benthic marine macroalgae comprise the chiefcomponents of the seaweed flora of McMurdo Sound, Antarctica.Quantitative studies at Cape Evans demonstrate a depth-relateddistribution pattern, with Iridaea cordata (Turner) Bory inshallow water, Phyllophora antarctica A. and E. S. Gepp abundantand fertile at intermediate depths, and Leptophytum coulmanicum(Foslie) Adey dominant below 20 m. The vertical distributionof species is correlated with irradiance levels. At sites withthinner annual sea ice and less snow accumulation (e.g., CapeEvans, Cape Royds, and Granite Harbor), vertical distributionsare shifted downward relative to those at sites that remaincovered most of the year with thick or snow-covered fast ice(e.g., Cape Armitage and New Harbor). Disturbance caused byice scour and anchor ice probably determines the upper limitof algal distribution; herbivory is apparently absent. There is a disproportionate representation of cystocarpic femalegametophytes in populations of I. cordata and P. antarctica.Perennation via persistent basal crusts and apogamic recyclingof gametophytes are suggested as factors structuring phase distribution.Although the overall size of I. cordata blades is greater (andcystocarpic plants more abundant) at Cape Royds than at CapeEvans, cystocarpic blades are similar in minimum size at bothsites, indicating a threshhold size or age for the onset ofreproduction in this species.     

Comparative reproductive biology of Ariolimax californicus and A. dolichophallus (Gastropoda; Stylommiatophora)

Summary

Traits which differ among species in a genus are considered to be the product of relatively rapid evolution. Laboratory studies indicate that copulation differs between two species of the banana slug Ariolimax with A. dolichophallus having a pattern of a single, long duration (typically greater than 1 h) intromission which is simultaneously reciprocal, and A. californicus having mating encounters typically involving a bout of brief (typically 10–20 min) unilateral intromissions. Reciprocal apophallation was observed for both species. Field observations confirm simultaneously reciprocal copulation and apophallation in A. dolichophallus. Mating was more frequent in the spring and summer months. In laboratory studies the two species also differed in life history parameters; mean growth rate was greater in A. californicus than A. dolichophallus, whereas eggs are larger in A. dolichophallus (range = 0.33–0.5 g; n=59) than in A. californicus (range= 0.08–0.27 g; n=164).     

Correlation Between Nest and Duckling Survival of Mallards Breeding in Saskatchewan

Abstract: Few studies have estimated reproductive and survival parameters of breeding ducks simultaneously, although such efforts can reveal relationships among vital rates. We estimated survival of mallard (Anas platyrhynchos) nests and duckling on 8 study sites in south-central Saskatchewan during spring and summer 2000 and 2001. We observed a strong positive correlation between these parameters (r = 0.914) and through analysis of residual values found 14% of the relationship was explained by a predator-removal treatment, 26% by year effects, 44% by spatial variation, and 16% unexplained. Potential mechanisms include similar environmental factors influencing both parameters (e.g., predators) and positive density dependence. Information regarding covariation among vital rates is important in construction and interpretation of population growth models describing population dynamics of mallards and other upland-nesting ducks.