Microclimates and the Distribution of Terrestrial Arthropods

Abstract

Just as plants and their habitats are closely related, so are animals and the microclimates they inhabit. Although it is possible for animals to survive for a while in infavorable circumstances, they differ from plants in their ability to move and seek out more favorable resting sites. For this reason, a study of microclimates and their influence on diurnal and seasonal rhythms of activity is of paramount importance in the understanding of animal ecology. Certain species are so dependent upon suitable habitats that they can be used to serve for the identification and classification of microclimates, just as macroclimates may often be associated with particular groups of plants. Insects are perhaps the best micro-climatic indicators of all, and Kuhnelt has cited them as "bioclimatic index forms." However, some species may be restricted to extreme habitats, not because there are advantageous per se, but because here the balance of competition with other species is favorable. Micrometeorology is the study of atmospheric processes at the earth''s surface. If the leaves of plants and the integuments of animals are regarded as extensions of that surface, micrometeorology principles can help the biologist investigate the influence of the physical background on living material. However, in addition to the meteorological variables of short-wave radiation, air temperature, ground temperature, vapour pressure, and so on must be added the biological variables of reflectivity and transmissivity, size and shape, internal diffusion resistance, and metabolism of the organism. Consequently, theoretical calculations can seldom be expected to agree with the few experimental measurements that have been made, and a practical approach is likely to be the more profitable for a long time to come. The mere accumulation of data will never solve problems. There is a great need for the distribution of arthropods to be studied in relation to their micro-habitats and not merely the microclimates to be studied without reference to the organisms within them. In his review of woodlice and the land habitat, Edney stressed the desirability of more information on microclimates in the habitats of woodlice so that the behavior and orientation mechanisms of these animals may be related to the conditions within the environments they inhabit. The same comment applies to all the terrestrial arthropods. It is clear from the considerations listed above that the study of microclimates is becoming an increasingly important branch of animal ecology. A more thorough knowledge of arthropods in relation to the microenvironments in which they are distributed is greatly needed.