A Field Test of the Intermediate Disturbance Hypothesis in the Soft‐Bottom Intertidal

The intermediate disturbance hypothesis has had success in explaining changes in local diversity in many habitats. Recent laboratory work has shown that disturbance may act to increase diversity in soft‐bottom marine communities as predicted by the hypothesis. In this paper, we present the results of a field experiment which tested the impacts of physical disturbance on soft‐bottom, intertidal macrobenthic communities. Five disturbance treatments were used, differing in the frequency of applied disturbance events; the highest frequency treatments were dug every week, lowest every eight weeks. The experiment was run for a total of 25 weeks over the winter of 1997/98. Our experiment controlled for differences in recovery time after disturbances. Abundances of Pygospio elegans, Macoma balthica, Hydrobia ulvae and Streblospio benedicti were all significantly reduced in high disturbance treatments, as was the total number of species. No species showed significant increases in abundance in disturbed treatments, and there was no evidence of an increase in diversity in any treatments. These results are discussed in the context of the intermediate disturbance hypothesis. Our results suggest that the interspecific competitive effects postulated by the hypothesis are not important in structuring this low diversity, intertidal community. However, unequivocally rejecting the hypothesis is difficult because it contains many ambiguities, and acts more as a conceptual model than as a falsifiable hypothesis.     

Rapid clonal multiplication of Digitalis lanata in tissue culture

Shoot cultures of Digitalis lanata have been established by inoculating the shoot tip of seedlings germinated in aseptic culture, or of field-grown plants, onto Linsmaier and Skoog's RM medium supplemented with 1 mg 6-benzylaminopurine and 0.1 mg indolacetic acid 1^–1. On this medium formation of up to 30 new axillary shoots could be induced. Shoots could be grown into functional plants after root induction on a medium containing reduced amounts (one-fifth of normal) of nitrogen and indolebutyric acid (0.5 mg 1^–1).