Succession of macroinvertebrates in playas of the Southern High Plains, USA

Playas are seasonal wetlands that constitute the principal surface-water fe atures of the semiarid, Southern High Plains, USA. They are shallow pools t hat usually persist for 2-4 mo following inundation by spring rains. The de velopment of macroinvertebrate assemblages in 10 playas located in West Tex as was examined during the summer of 1994. Playas were sampled 3 times at a pproximately monthly intervals, beginning shortly after initial inundation in early May. All playas were dry within 90 d. Species richness and diversi ty (Fisher's log-series a) increased significantly over time (p < 0.05). Th irteen of the 16 species representing at least 1% of collected individuals, showed significant differences in abundances over time (p < 0.05). Some ta xa increased in abundance (especially insects), whereas others decreased (m ost crustaceans). Trophic structure of assemblages also changed over time, with a significant reduction in the abundances of detrivores (p < 0.05) and filter-feeders (p < 0.05) occurring concurrently with an increase in the a bundance of predators (p < 0.05). The composition of macroinvertebrate asse mblages became more similar among playas over time (Ochai's index, p < 0.05 ), and changes in composition within individual playas tended to decrease w ith time (p < 0.05). These results suggest a rapid development of macroinve rtebrate assemblages in playas, begining with early dominance of crustacean detritivores and filter-feeders leg., phyllopods and ostracods), followed by later dominance of herbivorous and predaceous insects (e.g., hydrophilid s and notonectids). Increases in species richness, diversity, and similarit y in assemblage composition among playas over time are consistent with a pa ttern of progressive colonization by a finite set of species capable of exp loiting these ephemeral habitats.