Document: MAR-3-82-10

Predicting rarity in vascular plants: The roles of phylogeny and biogeography.

SCHWARTZ, M.W.*, C.A.BRIGHAM and K.G.LYONS

University of California, Davis, CA 95616 USA ¹

Abstract:
Rarity in plants is disproportionately distributed toward large groups (eg, genera, families). That is, small genera and families, in aggregate, contain fewer rare taxa than we would expect. This pattern is opposite of that in global vertebrates and birds. This taxonomic selectivity can be driven by at least three phenomena: (1) Artifacts of taxonomic designation (taxonomic splitting creates rarity while lumping does the opposite); (2) different extinction rates in large and small groups; or (3) different speciation rates in large and small groups. In order to discern whether this pattern is generally related to group size, we conducted a phylogenetic analysis comparing close relatives for group size and frequency of rarity. We used the Nature Conservancy's Natural Heritage Database to assign rarity values for the over 15,000 native species of the United States and Canada. We also examined patterns of group size and frequency of rarity on floras of relatively isolated islands. We used the IUCN Red Book assignation of rarity for these island floras. We found evidence that comparing close relatives through a phylogenetic analysis retains the pattern, thus the pattern is not likely a result of taxonomic artifacts. We do not find repeatable patterns among island floras, suggesting that the pattern may not be general.

Keywords: phylogeny, rarity,

This abstract is being presented at: 3:30 PM in session:
CONSERVATION ECOLOGY