Flowering phenologies of hummingbird plants from the temperate forest of southern South America: is there evidence of competitive displacement?

Authors

  • Marcelo A. Aizen,

  • Diego P. Vázquez


M. A. Aizen (marcito@crub.uncoma.edu.ar), Laboratorio Ecotono-CRUB, Universidad Nacional del Comahue, Quintral 1250, (8400) Bariloche, Río Negro, Argentina. – D. P. Vázquez, National Center for Ecological Analysis and Synthesis, Univ. of California, 735 State St., Suite 300, Santa Barbara, CA 93101, USA, (present address: Inst. Argentino de Investigaciones de las Zonas Áridas, Centro Nacional de Investigaciones Científicas y Tecnológicas, Av. Ruiz Leal s/n, (5500) Mendoza, Argentina).

Abstract

Plant species sharing pollinators may compete through pollination. This type of competition may lead to overdispersed flowering phenologies. However, phenological segregation is difficult to detect in seasonal climates. We compared patterns of phenological overlap in assemblages of ornithophilous plants from three localities of the temperate forest of southern South America with those generated by four different null models. These species were all visited and presumably pollinated by a single species, the hummingbird Sephanoides sephaniodes, which makes this situation ideal to evaluate the role of pollination-mediated competition. For one site, we compiled data on flowering phenologies for three different years. Three models considered the flowering period of the whole assemblage of ornithophilous plants as the phenological window within which flowering phenologies were randomized, but made no further assumptions on how species should be distributed within that temporal frame. The fourth model assigned differential probabilities to different time intervals based on the flowering onset of non-ornithophilous plant species. Observed mean pairwise overlaps for all localities and years were well within the interval defined by the 2.5 and 97.5% percentiles of the randomized distribution of expected mean pairwise overlaps according to models 1–3. However, model 4 showed a consistent trend towards overdispersion of ornihophilous phenologies, which show a shift towards mid- to late-summer flowering. Thus, to the extent that the distribution of flowering of non-ornithophilous species reflects the constraints imposed by a highly seasonal climate, our results provide support to the proposal that pollinator sharing may cause evolutionary displacement or ecological sorting of flowering phenologies. Other factors, such as phylogenetic inertia, could also contribute to explain extant phenological patterns in the highly endemic ornithophilous flora of the temperate forest of southern South America.

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