58 John R. Paul and Stephen J. Tonsor
different spatial and temporal scales. If a positive
age and area relationshi pis found for a grou pof
taxa, this finding can point to valuable lines of
research for future studies ( Joneset al. 2005).
For example, if such a relationship is found in a
20 Ma clade of plants, could this be an indica-
tion that the range-size transformations within
this grou pare rather slow and potentially gov-
erned by the ecological drift? If only certain guilds
of plants (e.g., understory shrubs) show a positive
age and area relationship, could this be related
to the potential dispersal limitations imposed on
these plants through their canopy position and
reliable seed dispersers? In addition, how do clades
that have many old species with small ranges
differ from those clades likePiperwhich appar-
ently lack many old species with small ranges?
An updated view of the age-and-area hypothe-
sis thus allows researchers to inquire about much
more than whether the age and area relationship
in a given grou pof organisms is linear and posi-
tive. The shape of the relationship in a given clade
can be used to infer the importance of various fac-
tors in the range transformation of species, and
suggest if new species start with small range sizes.
CONCLUSIONS
An explanation for why many tropical forest
species are rare and endemic may simply be the
relatively young age of these species. We have
reviewed the limited empirical work addressing
age and area relationships, none of which came
from strictly tropical taxa, and showed that sup-
port for the traditional age-and-area hypothesis is
equivocal. Using neotropicalPiperspecies as a case
study, we conducted the first age and area analy-
sis for a tropical plant clade, and found significant
support for a positive age and area relationship
that explains a quarter of the variance in range
size among species. Speculation about the age
and area relationships within other taxonomic
groups is difficult, however, because species-level
data on either ages or ranges are sparse. Although
inferring species ages from molecular data and
phylogenetic trees can introduce difficulties when
interpreting results of age and area analyses, we
predict that in the near future broader analyses of
age and area will be plausible with many clades of
tropical plants.ACKNOWLEDGMENTS
We thank Walter Carson and Stefan Schnitzer
for inviting us to contribute this chapter. We
thank four anonymous reviewers, Anthony
Baumert, Anthony Bledsoe, James Cronin,
Richard Gomulkiewicz, Susan Kalisz, Mark
McPeek, April Randle, Scott Stark, John J. Wiens,
and the Wiens lab for their comments on earlier
versions of this chapter. We also thank the original
authors of thePipersequences for making these
data publicly available for use by the scientific
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