P3.27 Friday, Jan. 6 Microcosm tests of interspecific competitive abilities and habitat monopolization WALSH, E.J.*; WOODS, M.A.; SCHROEDER, T.; Univ. of Texas, El Paso; Univ. of Texas, El Paso; Univ. of Texas, El Paso email@example.com
The Monopolization Hypothesis states that if a species establishes itself in an environment then other species will not be able to colonize the same habitat. This occurs due to resource monopolization and competitive numerical advantages of early colonists. Here we conduct a series of microcosm experiments to investigate competition between two rotifers (Epiphanes chihuahuaensis and Cephalodella sterea) commonly found in rock pools in the Chihuahuan Desert. In the first experiment, Epiphanes and Cephalodella were placed together in microcosms at a high and low food concentrations. At low food concentration, Cephalodella were nearly driven to extinction, but at high concentrations both species coexisted. Next, Epiphanes were limited to a population size of 3. Under these conditions, Cephalodella populations gradually increased to an average of 67 females per replicate. In the final experiment, Cephalodella was allowed to establish a population size of ~125 individuals before Epiphanes were introduced. Cephalodella grew exponentially until introduction of Epiphanes, then population growth rate slowed dramatically and eventually they became extinct in all but one replicate. Finally, observations were made to see how the two species interact. Surprisingly, observations indicated that Epiphanes, ingested Cephalodella, in more than 50% of trials at two ratios: 1 Epiphanes: 20 Cephalodella and 1 Epiphanes: 30 Cephalodella. These results indicate that competitive interactions between these two species is partially interference and not solely exploitative. Further, results did not support either the Monopolization Hypothesis. Epiphanes were superior competitors in every experiment.