PARENT SESSION
Poster Session # 1: Ecological Theory and Evolutionary Ecology.

Monday, August 4 Presentation from 5:00 PM to 6:30 PM. SITCC Exhibit Hall B.

GIS and path analysis: Examining associations between the birds, the bees and plant sex in Echinocereus coccineus (Cactaceae).

Scobell, Summer^*,1, ¹ University of Miami, Coral Gables, FL

ABSTRACT- In plant families that exhibit dioecy, an association between the predominant pollinator type and the plant′s mating system has often been reported. Plants with more specialized pollinators (e.g. birds, bats) are predominantly hermaphroditic while species with depauperate, generalist or small pollinator fauna tend to be dioecious. It is hypothesized that the latter pollinator types may increase self-fertilization rates of hermaphroditic plants, and the inbreeding depression in selfed seeds then selects for dioecy. An alternative hypothesis is that selection in arid environments favors dioecy because this system allows more efficient allocation of scarce water resources to male and female functions. There is also the possibility that the association between water resources and dioecy is indirect: A habitat shift to drier areas may be associated with loss of more effective pollinators, which is proposed to select for dioecy. Echinocereus coccineus (Cactaceae) is an excellent model system to test hypotheses about links between pollinator type, water resource gradients and dioecy because it possesses contemporaneously both hermaphroditic and dioecious populations growing over a wide rainfall gradient. E. coccineus flowers appear specialized to hummingbirds, but are also pollinated by small Halictid bees. Distribution and abundance of these pollinator types varies across the plant′s geographic range and dioecy appears to be associated with areas of low hummingbird abundance. Dioecious populations also appear to be associated with drier, low altitude areas. In order to better quantify these associations, a GIS database was compiled containing data from over 500 herbarium specimens of E. coccineus, annual rainfall, and hummingbird abundance. The data from each population was then analyzed using multiple regression and path analysis to assess the relative direct and indirect influence of the predominant pollinator type and mean annual rainfall on the presence of dioecious populations in this species.

Key words: Pollinators, Dioecy, GIS, Hummingbirds