As range shifts coincident with climate change have become increasingly well documented, efforts to describe the causes of range boundaries have increased. Three mechanisms-genetic impoverishment, migration load, or a physical barrier to dispersal-are well described theoretically, but the data needed to distinguish among them have rarely been collected. We describe the distribution, abundance, ...

1. Fibres from adductor scutorum muscle of a barnacle Tetraclita squamosa were made to contract isometrically by electrical stimulation, and the change in the ability to shorten actively during the mechanical responses was examined by suddenly allowing the fibres to shorten under a very small load (<3 % of the force immediately before shortening) at various times after the onset of stimulation....

Mobile species may actively seek refuge from stressful conditions in biogenic habitats on rocky shores. In Hong Kong, the upper intertidal zone is extremely stressful, especially in summer when organisms are emersed for long periods in hot desiccating conditions. As a result, many species migrate downshore between winter and summer to reduce these stressful conditions. The littorinids Echinolit...