Does Male Density and Proximity Affect Seed Production in Desert Holly, Atriplex hymenelytra?
Author:
Andrew EstersonMentors:
- Kristine Hartney, Interim Associate Dean for Academic Programs, California State Polytechnic University Pomona
- Sara Garver, Geography Program Coordinator, California State Polytechnic University Pomona
A variety of ecological factors can influence the production of seeds by plants. Among dioecious species where pollen generators (males) and seed producers (females) are separate individuals and pollen is wind-dispersed, the density and proximity of males relative to females may be particularly important in determining pollination success and subsequent seed set. We investigated the potential effect of male density and abundance on the production of seeds in the dioecious species Atriplex hymenelytra, a common desert shrub. In this species, mature females produce bracts (fruits) during winter months (December through March) that at most contain a single seed if fertilization and development has been successful. At study sites in the Mojave National Preserve, the spatial distribution of all males within a 4.5-meter radius of each of 10 tagged females was determined using a handheld Global Positioning System (GPS). Female dimensions were measured and all bracts produced by each female were collected over the 2009 reproductive season. All bracts collected from each female were counted and a subset examined for the presence of fully formed seeds. Statistical analyses indicate that male density and the proximity of males to females has no significant effect on seed production. These results suggest that seed production is more likely limited by some other factor or combination of factors that could include water availability, soil salt concentration, wind direction, slope aspect, or female age. Determining the effect of these factors on reproductive success is particularly important to understanding the dynamics of this population that is undergoing a slow but certain decline in population size.