Santiago-Vera, Josué D.

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    Are natural microcosms composed of community alternative stable states? Insights from a simple community of ciliates and testate amoebae within the phytotelma of Tillandsia utriculata L. (Bromeliaceae) in Guánica State Forest, Puerto Rico
    (2013) Santiago-Vera, Josué D.; Acosta Mercado, Dimaris; College of Arts and Sciences - Sciences; Alston, Dallas E.; Santos Flores, Carlos J.; Whitmire, Stefanie; Department of Biology; González Gill, Lizzette
    Changes in environmental parameters such as abiotic factors, trophic dynamics, and nutrient availability have been suggested as the primary drivers of stable alternate community shifts. Abiotic environmental thresholds, such as conductivity and nutrients can be important factors driving these shifts in bromeliad microcosms. Although primarily described for macrobiota, predation could also be an important factor, driving stable alternate microbial communities through density-mediated indirect interactions and direct predation effects. Furthermore, nutrient availability is also known to generate shifts in the community through bottom-up effects. Both a longitudinal study and a manipulation experiment were performed to determine whether conductivity, pH, nutrient availability, and the presence of a generalist predator were significant factors explaining community shifts of testate amoebae and ciliates in the phytotelma of Tillandsia utriculata. If abiotic parameters are the drivers of testate amoebae and ciliate alternate stable communities, then changes in such parameters should be concomitant with shifts in testate amoebae and ciliate species diversity and composition. If predation and nutrient availability are significant factors explaining the alternation of testate amoebae and ciliate communities, then testate amoebae and ciliate communities in the predator and nutrient inputs treatments should be significantly different in comparison with their repective controls. Microcosm experiments were conducted in a controlled environment; one experiment with Macrostomum tuba as the generalist predator and the other experiment with manipulation of NO3- and PO4-3. The testate amoebae community had low abundances and species richness, thus making their community analyses impossible. For the longitudinal study, a multivariate analysis showed a ciliate community shift between wet and dry seasons and a Repeated Measure ANOVA showed significant differences across time for conductivity and phosphate, moreover a PCA revealed that conductivity explains 96% of the ciliate abundance variation. For the predation experiment, an ANOSIM test revealed two different ciliate communities between treatments. Nutrient availability had no effect on the ciliate community as revealed by an ANOVA. In conclusion, I suggest that conductivity, phosphate, and predation could be important factors causing alternate stable-state ciliates communities of T. utriculata in the Guánica Dry Forest.