The Seasonal and Diurnal Activity of the Fauna Sampled by Pitfall Traps in Different Habitats

Abstract

Twenty-four hour rhythms of activity are widespread in the animal kingdom (Calhoun 1944-46), so much so that it has been suggested (Harker 1958) that there is a basic twenty-four hour rhythm in the cells of all animals even if this is not shown in overt behaviour. A great deal of research has been undertaken to establish the nature of the 'clock' which enables rhythms to persist under uniform conditions and which keeps time even in poikilotherms subject to widely fluctuating temperatures, and a number of physiological models have been proposed (Harker 1958, Hastings & Sweeney 1957, Pittendrigh & Bruce 1957). Research on the mechanism of time-keeping has overshadowed the ecological implications of the rhythms and extrapolation from the laboratory to the field has only been made to show how far the experimental results are pertinent to the particular animal's natural mode of life. The only discussion of the rhythms shown by communities has been that of Park (1941). Park argues, on theoretical grounds, that there is an evolution of communities from a primitive state in which activity is asymmetrical in the twenty-four hour cycle (or diel) to a more advanced state in which activity is symmetrically disposed around the diel. His argument may be paraphrased as follows: in community physiology, the unifying principle is that the available resources should be fully exploited, and a community which includes both nocturnal and diurnal animals is using the resources more efficiently than a community with a single phase of activity. Consequently, there is a development to the state where the total activity of the community is uniform throughout the diel, that is, where community activity is arhythmic despite rhythms of behaviour in the individual species which make up the assemblage. The idea is probably familiar to all animal ecologists as the well-known text book (Allee et al. 1949) provides its pictorial demonstration in human societies, a small village showing a rhythm of activity which follows the environmental change from day to night whereas in a city, activity is continuous throughout the twenty-four hours. The hypothesis seems to be reasonable when applied to natural communities, but no field observations have been directed specifically to test its validity and it was for this reason that the present observations were begun. The most convincing test would be an estimate of the total activity of communities selected from the extremes of possible community range, coinparing, for example, a raw quarry face with the climax woodland behind it. But to measure the total activity