Habitat Selection in Two Species of Flour Beetles (Tribolium) on a Temperature Gradient

Abstract

The dispersion of adult flour beetles, Tribolium confusum and T. castaneum, was studied for single species populations along a temperature gradient (18.5 to 37.7 C) at varying densities (200-400-800 beetles). The distribution of beetles was used to calculate niche breadth values for each species at different densities. Niche breadth increases with increasing density in both species but at a faster rate in T. castaneum. At very high density, there is a reduction in niche breadth for T. confusum. At both low and high densities, T. confusum adults accumulate at the cold end of the thermal gradient, while adults of T. castaneum accumulate at the hot end. It is suspected that these flour beetles have different physiological preferences with respect to temperature, and that this preference is modified by density especially in T. castaneum which appears to be more sensitive to increased density of adults than T. confusum. INTRODUCTION The membership of a population of a mobile species is not evenly distributed across different adjacent habitats. Different animals vary greatly in vagility of individuals in populations, where vagility is the ability to move across ecological barriers (Allee et at., 1949). This study examines the effects of density on dispersion and habitat selection in laboratory populations olf flour beetles, Tribolium castaneum and T. confusum (Coleoptera: Tenebrionidae), where dispersion is the pattern of distribution of individuals, in a series of specified habitats. Because b,ody size is small and density of populations is easily manipulated, Tribolium is a useful exnerimental organism for studying the effects of density on dispersion (King and Dawson, 1972). Previous studies of flour beetles, have shown that interaction among individuals, in single species population influences dispersion (Naylor, 1959, 1961; Ghent, 1963; 1966; Lerner et al., 1966). A habitat of an organism. is determined primarily by three factors: (1) the physiological adaptations of the organism to the environment; (2) interactions among members of the same species (intraspecific) and among members, of different species (interspecific), and (3) heterogeneity of abiotic and biotic factors of the environment in time. For each species of flour beetle, this expieriment tests the following predictions: (1) there is an uneven distribution of the population's membership at low density owing to different physiological preferenda, 1 Address reprint requests to Dr. Young. 2 Present address: Division of Invertebrate Zoology, Milwaukee Public Museum, Milwaukee, Wisconsin 53233.