Fluctuations in the distribution and abundance of intertidal barnacles

It is well known that towards the limits of an animal's geographical range both its abundance and exact boundaries may fluctuate from time to time. These fluctuations can sometimes be correlated with environmental changes, and thus may help to assess the relative importance of the factors that control distribution. For example the distribution of the common intertidal barnacles Chthamalus stellatus (Poli) and Balanus balanoides (Linnaeus) underwent changes which were attributed to a general rise in temperature over several years (Southward & Crisp, 1954a). The abundance of these barnacles has fluctuated further since 1951–52, and we are now able to analyse more closely the relation between the population changes and environmental variations.