Dispersal patterns and clumping behaviors in the beetle Trichoton sordidum

Although a significant number of behavioral studies of desert tenebrionids have been done, almost nothing is recorded of Trichoton sordidum (LeConte) (Coleoptera: Tenebrionidae), an inhabitant of the sunny, sparsely vegetated US/Mexican borderlands. For this small, flightless beetle successful predator evasion and adaptation to a desert environment has required development of complicated, quickly utilizable behavioral mechanisms for regulating exposure to extremes of heat, light, humidity, and habitat structure. In this study, T. sordidum was exposed to sudden changes in temperature, illumination, and habitat complexity, and some patterns representing its normal aggregation were recorded. Minimum Risk Distribution models (Floater 2001) predict changes in spatial distribution patterns of groups of individuals as they are exposed to environmental change. A successful species must have a large percentage of individuals adhering to changes with a set pattern of behaviors. All groups of T. sordidum tested demonstrated both rapid and cohesive dispersal patterns. They normally showed little tendency toward clustering, except clear adhesive aggregation patterns in cases of limited resources in a fragmented environment. Under conditions of extreme heat or light, aggregations in the form of clumping did occur. The formation of clumps from simple two-stacks to groups of up to ten is documented here. The sophistication, consistency of use, and rapid initiation of clumps suggest clumping might well be a highly evolved and successful mechanism for group threat evasion. The morphology of T. sordidum Abbreviation: / MRD: Minimum Risk Distribution: A model of spatial distribution of individuals that results in the minimum number of premature deaths in a population, and leads to maximized population growth (Floater 2001). C-value: A statistical measurement used in this study to quantify relative clump sizes for Trichoton sordidum rather than total number of individuals in a clump. Homogeneous environment: Environment composed only of uniform, similar features with no irregular detail. In this experiment, open areas of sand, cloth, or fine debris were used. Habitat complexity: Structural interference in a habitat which leads to spatial variability. The result is predicted to be a change in the spatial distribution of individuals within the habitat. In this study pebbles were added to the homogeneous environment to break up a uniform surface area.