title: Resources alter the structure and increase stochasticity in bromeliad microfauna communities.
abstract: Although stochastic and deterministic processes have been found to jointly shape structure of natural communities, the relative importance of both forces may vary across different environmental conditions and across levels of biological organization. We tested the effects of abiotic environmental conditions, altered trophic interactions and dispersal limitation on the structure of aquatic microfauna communities in Costa Rican tank bromeliads. Our approach combined natural gradients in environmental conditions with experimental manipulations of bottom-up interactions (resources), top-down interactions (predators) and dispersal at two spatial scales in the field. We found that resource addition strongly increased the abundance and reduced the richness of microfauna communities. Community composition shifted in a predictable way towards assemblages dominated by flagellates and ciliates but with lower abundance and richness of algae and amoebae. While all functional groups responded strongly and predictably to resource addition, similarity among communities at the species level decreased, suggesting a role of stochasticity in species-level assembly processes. Dispersal limitation did not affect the communities. Since our design excluded potential priority effects we can attribute the differences in community similarity to increased demographic stochasticity of resource-enriched communities related to erratic changes in population sizes of some species. In contrast to resources, predators and environmental conditions had negligible effects on community structure. Our results demonstrate that bromeliad microfauna communities are strongly controlled by bottom-up forces. They further suggest that the relative importance of stochasticity may change with productivity and with the organizational level at which communities are examined.
authors.affiliation: Institute of Biology, Freie Universität Berlin, Königin-Luise-Str. 1-3, D-14195, Berlin, Germany; Berlin-Brandenburg Institute of Advanced Biodiversity Research (BBIB), D-14195, Berlin, Germany; Department of Ecology and Evolution, University of Salzburg, Hellbrunnerstrasse 34, 5020, Salzburg, Austria.
authors.forename: Jana S
authors.initials: JS
authors.lastname: Petermann
authors.affiliation: School of Biological and Chemical Sciences, Queen Mary University of London, London, E1 4NS, United Kingdom.
authors.forename: Pavel
authors.initials: P
authors.lastname: Kratina
authors.affiliation: Department of Ecology, Biology Institute, Federal University of Rio de Janeiro (UFRJ), 7 Ilha do Fundão, Rio de Janeiro, RJ, PO Box 68020, Brazil.
authors.forename: Nicholas A C
authors.initials: NA
authors.lastname: Marino
authors.affiliation: Department of Zoology & Biodiversity Research Centre, University of British Columbia, 6270 University Blvd., Vancouver, BC, V6T 1Z4, Canada.
authors.forename: A Andrew M
authors.initials: AA
authors.lastname: MacDonald
authors.affiliation: Department of Zoology & Biodiversity Research Centre, University of British Columbia, 6270 University Blvd., Vancouver, BC, V6T 1Z4, Canada.
authors.forename: Diane S
authors.initials: DS
authors.lastname: Srivastava
mesh_terms: D000818:Animals; D044822:Biodiversity; D031229:Bromeliaceae / Q000502:physiology; D003364:Costa Rica; D004777:Environment; D008954:Models, Biological; D011156:Population Density; D011235:Predatory Behavior; D013269:Stochastic Processes