Spatial Use of an Equatorial Coastal System (East Africa) by an Arthropod Community in Relation to Periodically Varying Environmental Conditions

During the dry season (1971) and the wet season (1973) two field studies were conducted at Sar Uanle, a locality along the coast of Somalia (East Africa). The study analysed the beach–dune system considering ecological aspects in a dynamic way. During the two periods of study and for an entire synodic period, a system of traps (directional pitfall traps) was used. At the same time the climatic factors were registered. For the most abundant arthropod species mean zonations were calculated during surface activity and considered in relation to the season, diel, synodic and tidal phases. The variations in mean zonation were then correlated with the main environmental parameters. During the wet season, for some taxa orientation indices were calculated. The results indicate that two distinct subcommunities are present at Sar Uanle: a more dynamic one on the beach and another on the dune. Arthropod species living in this beach–dune system have evolved behavioural strategies in relation to cyclical environmental changes according to their physiological needs, locomotory capacities and zonation.