Tropical Forest Community Ecology

Explaining Geographic Range Size by Species Age 55

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0.5

1.0

1.5

2.0

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−3.0 −2.5 −2.0 −1.5 −1.0 −0.5

Log(relative species age)

Log(range size)

Figure 4.4 Linear regression of log-transformed relative species age and log-transformed range size;
y=0.9399x+2.6143,r^2 =0.252,P<0.001.

Species-rich genera likePiper have a wide
range of ages, based on the available evidence
from molecular dating.Piperis a member of the
basal angiosperms (Angiosperm Phylogeny Group
2003), and may be a rather old lineage (based
onPiper and Peperomiadivergence, ∼40 Ma;
Wikströmet al. 2001). In contrast, analysis of
the diverse legume genusIngasuggests that it is
a young genus and many species originated on
the scale of 2–10 Ma (Richardsonet al. 2001).
In light of evidence of the existence of rain-
forests from the late or mid-Cretaceous (∼100 Ma;
Morley 2000; Daviset al. 2005),Ingaspecies
mustbeconsideredquiteyoung(Berminghamand
Dick 2001). Despite its relatively recent origin,
this clade has spread throughout the forests of
South and Central America, and at many sites
Ingaspecies are important forest components in
terms of both number and biomass (Richardson
et al. 2001). In fact, legume clades in general
may be remarkably young given their widespread
distribution and numerical importance in tropi-
cal forests (∼4–16 Ma; Lavinet al. 2004). Other
speciose tropical clades are considerably older,
such as those in the Annonaceae (e.g.,Xylopia,
Annona) which appear to be on the scale of

approximately 15–25 Ma (Richardsonet al. 2004,

Pirieet al. 2006). LikePiper, many of these clades

have pantropical or even cosmopolitan distribu-

tions; in fact, one of the most widespread tropical

plant species,Symphonia globulifera(Clusiaceae),

also ages to the mid-Tertiary (∼28 Ma; Dicket al.

2003). In Africa, the origin of the herbaceous

begonias (Begoniaceae) is also on the scale of

approximately 30 Ma, but many of the species in

this grou pdiverged relatively recently (from∼1to

10 Ma; Planaet al. 2004).

In another widespread herbaceous genus,

Costus(Costaceae), the neotropical species appear

to have diversified rapidly and recently (Kayet al.

2005). In the case of very recent diversification

of clades likeIngaandCostus, widespread species

within these genera provide evidence that com-

mon members of these clades are not particularly

old. However, the relationships of age and area

within these and other genera have not been

assessed. In a rapidly diversifying genus, if more

widespread species were found to be older, the

expected slope of the age and area relationship

would simply be very steep. However, finding

young but common species would certainly not be

surprising in light of recent evidence confirming