[Taxacom] Meliaceae vicariance

[Kenneth Kinman]

Dear All,
      Much is being made here of the fact that Meliaceae are absent from SW Australia, Hawaii, etc. (except for recent introductions) in areas where Rutaceae are diverse.   I doubt that it has anything to do with vicariance.
         Instead it could simply be a case of competitive exclusion of Meliaceae by their relatives in Rutaceae.   Especially if Rutaceae spread to those areas first.   So this just seems like another case of panbiogeographers attacking dispersal wherever they can imagine a vicariance alternative.
                               ---------------Ken

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From: Taxacom <taxacom-bounces at mailman.nhm.ku.edu> on behalf of John Grehan via Taxacom <taxacom at mailman.nhm.ku.edu>
Sent: Wednesday, November 13, 2019 10:36 PM
To: taxacom <taxacom at mailman.nhm.ku.edu>
Subject: [Taxacom] Meliaceae vicariance

Hopefully the heading will alert Taxacomers to read this only if interested
in evidence of vicariance. The monograph on Meliaceae biogeography by Heads
presents some observations on how this nearly pantropical group along with
the Simaroubaceae shows evidence of vicariance with respect .to the
Rutaceae:

“Meliaceae have maximum species numbers in tropical Asia and Malesia (303
species), with fewer in the Neotropics (189 species), Madagascar (107
species), and tropical Africa (102 species). However, despite their
abundance in Malesia and parts of the south-west Pacific, such as Fiji,
Meliaceae are absent from a vast area of the central Pacific (Fig. 2). This
area of absence includes Hawaii (where there are five naturalised species),
the Galapagos (with one naturalised, invasive species), Juan Fernandez Islands,
the Marquesas Islands (one naturalised species), the Society Islands and
the Cook Islands. This absence exists despite the fact that the family
includes mangroves (X*ylocarpus *J.Koenig, which ranges east to Tonga) and
many weedy species.”

“Meliaceae (48 genera, 700 species) form a well-supported clade with the
smaller, pantropical family Simaroubaceae (22 genera, 100 species) (Koenen
et al., 2015; Muellner-Riehl et al., 2016). This pair is closest to
Rutaceae (153 genera, 1975 species). Simaroubaceae are ‘pantropical’, as
they are present in Africa, Asia and America. However, as with Meliaceae,
they are absent from Hawaii, the Galapagos, Juan Fernandez Islands, and SE
Polynesia. In contrast, native Rutaceae are present in all four of these
areas, and are notably diverse in Hawaii (58 species) and the Marquesas (7
species) (the Marquesas have only 4% of the land area of Hawaii). The absence
of Meliaceae from many very small islands in the central Pacific, such as
Rapa or Rarotonga, might be the result of regional extinction with
continuing subsidence (as the plate moves away from the central Pacific
spreading ridge and cools). However, the absence from Hawaii and the
Marquesas seems more significant, as the closely related Rutaceae are so
diverse there.”The central Pacific allopatry between the two clades,
Meliaceae + Simaroubaceae, vs Rutaceae, especially on the Hawaii–Marquesas
sector, can be explained as a trace of the original allopatry caused by
vicariance between the two clades. If this is correct, similar patterns
should occur in other groups.

The Hawaiian biota is well known for the high diversity of groups such
as honeycreepers,
drosophilids and lobeliads. However, there are also many conspicuous absences
(Heads, 2012). In the Hawaiian flora, many tropical plants, including
mangroves,
are absent, despite having very efficient means of dispersal. Other plants
that characterise tropical shorelines and small islands, either globally
(such as *Calophyllum *L., *Terminalia *L., *Hernandia *L., *Salicornia *L.,
and *Atriplex *L.) or through the Old World and Pacific (such as *Barringtonia
*J.R.Forst. & G.Forst.), are also absent from the Hawaiian indigenous
flora. Nevertheless, species of most of these genera thrive in Hawaii as
introduced weeds.

Transport to Hawaii in mud on birds’ feet is often proposed to explain
groups’ presence on the islands. Yet some of the most characteristic marsh
plants, such as Eriocaulaceae and *Juncus *L., are absent from the
indigenous flora (although several introduced *Juncus *species are now
widespread). In the same way, many diverse, pantropical groups that are
abundant in rain forest elsewhere are absent from the indigenous flora of
Hawaii. These include Cyatheaceae, Araceae sensu stricto, Zingiberales
(Zingiberaceae, Marantaceae etc.), Melastomataceae, *Ficus *L. (figs),
and *Piper
*L. (members of all these groups are naturalised). Thus, although the
absence of Meliaceae, including the mangrove *Xylocarpus*, from Hawaii
seems strange, it conforms to a standard pattern that requires a general
explanation, and regional vicariance is suggested here. Meliaceae are also
absent from southwestern Australia (as native plants), again, in a region
where Rutaceae have high diversity."
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