POPULATION-DYNAMICS OF A PLAYA COMMUNITY IN THE CHIHUAHUAN DESERT

Population responses of desert playa organisms were examined following two separate rain storms (spring and late summer-fall) that flooded a playa and stock tank located in southern New Mexico. Invertebrate species that appeared following both floods included the crustaceans Streptocephalus texanus, Thamnocephalus platyurus, Eulimnadia texana, Triops longicaudatus, Moina wierzejskii and the rotifers Brachionus sp., Polyarthra sp., and Pedalia sp. Moina wierzejskii produced three generations during the single spring flood while other species produced a single generation. Initial population levels for all species were very high. Fairy shrimp levels decreased quickly, and population levels of Moina wierzejskii were depressed until levels of all other species were low. Arthropod species did not produce large numbers of drought-resistant eggs in response to the lowering of the water level. Tadpoles of two species of anurans, the spadefoot toad (Scaphiopus multiplacatus) and the true toad (Bufo cognatus) occurred in the playa following spring flooding. Tadpoles of Bufo cognatus were not collected after the late summer rain. Tadpoles, particularly spadefoot toads, preyed on other tadpoles and fairy shrimp (Anostraca). Apparently, both biotic and abiotic factors were important in the population dynamics of playa organisms. Biotic interactions appeared more important during the second flood when the population densities of most species were higher.