Is seed production affected by: male density ? male proximity? male to female ratio?

1. EFFECT OF MALE DENSITY AND PROXIMITY ON SEED PRODUCITON IN THE DIOECIOUS PLANT ATRIPLEX HYMENELYTRA Andrew Esterson1, Tina Hartney1 and Sara Garver2 1Department of Biological Science, California State Polytechnic University, Pomona 2Department of Geography and Anthropology, California State Polytechnic University, Pomona Background • Bract production is positively correlated to female size with females producing up to 20,000 bracts per plant. When fertilization is successful each bract bears one seed. Questions Addressed Conclusions • Is seed production affected by: • male density? • male proximity? • male to female ratio? • 8 • Desert holly (Atriplex hymenelytra: Chenopodiaceae), a common low growing shrub (<1m), is widely distributed at low elevations (<600m) throughout southwestern North America. • As a dioecious species, pollen generators (males) and seed producers (females) are separate individuals. • Pollen is wind-dispersed. • Preliminary findings are suggestive of : • A direct relationship between male density and seed production (Figure 1). • An inverse relationship between male proximity to female and seed production. That is, the closer a male is to a female the greater the seed production (Figure 2). • A positive correlation between male to female ratio and seed production (Figure 3). • Insignificant effects of the three factors on seed production (p>0.05). Methods 8 • Five females at each site were randomly tagged and dimensions measured (height, semi-major axis, semi-minor axis). • Tagged females were bagged in April 2009 for bract collection. • Geographic coordinates of all individuals within a 6 meter radius (113m2) of tagged females were determined using GPS. • All bracts were counted and 5% of the total were dissected to verify the presence of seeds. • Seed production was standardized as a function of plant volume. Female Male Bagged Female Future Research Directions • 8 Results 8 • Statistical Effects: Increase sample size in order to strengthen statistical analyses. • Temporal Effects: Analyze seed production over several years to determine if results are consistent or unique to 2009. • Spatial Effects: Examine whether the directional location of males relative to females influences seed production especially as it relates to prevailing wind direction and slope (uphill/downhill). Dissected Bract and Seed (Circled) Study Area Figure 2 Figure 1 Acknowledgments The authors would like to thank: California State University’s Desert Studies Center for providing logistical support, the U.S. National Park Service for permitting research efforts within the Mojave National Preserve, Dr. David Moriarity for statistical assistance and multiple field assistants including Jen Becker, Odara Pineda, Danny Head, Jill Walker, Chirag Jain and Ben Lucas. Site 2 Site 1 Figure 3