Reproductive Interactions Between Sympatric Dalechampia Species: Are Natural Assemblages "Random" or Organized?

By considering patterns of species co—occurrence and pollinator use, I attempted to answer the question: are natural assemblages of Dalechampia species (Euphorbiaceae) organized in ways that reduce the amount of interspecific pollination and/or competition for pollinator service? The observed structure was tested against three null models, one operating by species assemblage processes, one operating by species evolution processes, and a third operating by both processes. Two alternative operations definitions of sympatry were used with each model. The outcome (rejection or acceptance of the null hypothesis) was sensitive to the null model employed and the definition of sympatry used. This underscores the importance of using biologically realistic null models, assumptions, and definitions. Using the biologically more reasonable definition of sympatry, tests against all three null models suggest that assemblages of Dalechampia are structured with respect to pollinator use; indirect evidence suggests that some of this structuring has occurred through evolution of component taxa.