Simpson, Andrew , Schierenbeck, Kristina A. , Parker, V. Thomas .
Propagule size gradients in Arctostaphylos (Ericaceae) do not reflect the global trends.
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 between tropical forests and temperate grasslands or savannahs. Here we compare effects of latitude and altitude on fruit size in Arctostaphylos (Ericaceae), an animal-dispersed and primarily Californian chaparral shrub genus, using both a meta-analysis of published geographic and morphological ranges, and field analysis of three species in the Sierra Nevada foothills. Stepwise linear regression on multiple measures variables reveals a weak but statistically significant negative correlation between fruit size and latitude and a similarly weak positive correlation between fruit size and altitude. Species with burls typically have low minimum latitude and high maximum fruit size. By contrast, intraspecific field data reveal a positive relationship between fruit size and both elevation and latitude. These results reveal that Arctostaphylos does not exhibit the global propagule size gradients exhibited by other angiosperms, even within California. Possible mechanisms responsible for these anomalous results involve the reliance of Arctostaphylos on animal dispersal, the disturbance ecology of chaparral shrublands, or the locally inverted latitudinal gradient in precipitation characteristic of Mediterranean-type climates. Latitudinal propagule-size gradients so far been predominantly investigated using floristic-scale literature-based meta-analyses. More studies are needed at smaller taxonomic scales in order to determine the complexity and mechanisms underlying the global pattern.
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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
3 - San Francisco State University, Department of Biology, 1600 Holloway Avenue, San Francisco, California, 94132
Presentation Type: Oral Paper:Papers for Topics
Location: Cottonwood B/Snowbird Center
Date: Monday, July 27th, 2009
Time: 2:00 PM