LIFE HISTORY TRAITS OF AQUATIC ARTHROPODS IN SPRINGS

Springs are especially useful for examining questions related to life history because they are widespread, and because they include not only the most predictable of freshwater habitats but also the most adverse (hot springs). Permanent springs tend to be stable environments, particularly in terms of temperature, discharge, and substrate. Extreme habitats such as hot springs can be ideal for studying biotic responses to environmental features because they vary little in certain factors and so do not conceal the mechanisms at work. This paper reviews the known life history and associated community traits of spring arthropods in terms of broad categories of selection forces thought to be acting in these habitats, and also examines the biotic consequences of stable environmental temperature. The data, although limited, show most support for the deterministic view of life history evolution in that traits of cold and hot permanent spring faunas tend to conform to those of K- and A-selected species, respectively. Nonconformities exist however, and data are totally lacking for springs that flow intermittently. A model continuum of spring types from the stable to the unstable and from the benign to the adverse is proposed which predicts the biological properties of communities living in little-studied spring types. The stable and/or adverse temperature regimens of springs are thought to impinge on many aspects of the biology of their faunas but most relationships (e.g. physiological, phenological) are based on data that are correlative, circumstantial, or laboratory based. Manipulative field tests are advocated to establish definite causative links. Wide scope exists for further research on the life history and community traits of spring arthropods.