Simpson, Andrew , Schierenbeck, Kristina A. .
Multiple causal factors influence propagule size gradients in Arctostaphylos (Ericaceae).
The latitudinal gradient in propagule size (fruits and seeds) is an unexplained pattern in phytogeography and paleobotany. Proposed causes often focus on differences in biome structure or mode of seed dispersal. Here we present an analysis of latitude, altitude, and plant height as they affect fruit size in Arctostaphylos (Ericaceae), an animal-dispersed and primarily Californian chaparral shrub genus. Stepwise linear regression on multiple measures reveals a positive relationship between fruit size and plant height (R2=0.15; p=0.0001). In addition to and independent of plant height, we found a statistically significant negative correlation between fruit size and latitude (R2=0.08; p=0.0021) and a positive correlation between fruit size and altitude (R2=0.05; p=0.019). Species with burls typically range into comparatively low latitudes and yet have large fruits (1.13x larger fruit size, p < 0.0001). Our findings are consistent with other global patterns in propagule size, but are in contrast with previous work examining the relationship between propagule size and elevation. We conclude that the driving factor in the contrasting latitudinal and altitudinal fruit size gradients in Arctostaphylos is not temperature, and that the mechanisms responsible for the gradients in this genus therefore do not include length of the growing season. The statistical independence of the relationships between fruit size and plant height, altitude, and latitude imply that multiple factors are responsible for the global latitudinal propagule size gradient. Our observation that geographic variables other than latitudinal gradient affect propagule size and are statistically independent of latitude emphasizes the need for further research to determine what specific environmental variables (e.g. edaphism, rainfall) actually drive the gradient, instead of broad-scale geographic patterns.
Log in to add this item to your schedule
1 - California State University, Chico, Biological Sciences, 206 Holt Hall, Chico, California, 95926, United States of America
2 - California State University Chico, Department of Biological Sciences, Chico, California, 95929-0515, USA
Propagule size gradients
Presentation Type: Oral Paper:Papers for Topics
Date: Monday, July 28th, 2008
Time: 5:15 PM