Centre of endemic?

[Bob Mesibov]

The recent posts by Norbert Hahn and Don McAllister were very
interesting but in one sense were at cross-purposes. Don suggested a
methodical and objective way to discover centres of endemism within
continental areas. Norbert was asking (in part) what to do if those
centres were nested.

For a thorough but ultimately unhelpful discussion of Norbert's
questions, with examples from the New Zealand trichopteran fauna, see:

Henderson, I.M. 1991. Biogeography without area? pp. 59-71 in Ladiges,
P.Y., Humphries, C.J. and Martinelli, L.W., AUSTRAL BIOGEOGRAPHY.
Melbourne: CSIRO.

Don's recommended approach is the one being used by at least a few
Australian biogeographers, including me. An increasingly worrying
problem is geographic scale. The island of Tasmania (ca. 70000 km2) is
generally thought of as a centre of endemism within Australia because of
the high proportion (among low-vagility invertebrates, nearly 100%) of
endemics. Very few of the Tasmanian endemics occupy the whole island.
Instead, they're endemic to more or less discrete regions on the island
(say, 10000 km2) . In turn, only a few of the regional endemics fully
occupy their regions. Instead, they're endemic to small areas within the
regions (2000 km2 or less).

Clearly, a fine scale grid is needed to detect these nested centres of
endemism. The great majority of Tasmanian records can be placed within a
100 m square, but at this grid fineness, there aren't enough filled
squares for useful analysis. For some of our narrow-range endemics,
aggregating records to fill 1 km squares is just about right for
revealing spatial relationships. To get well-filled grids for most areas
and most species, however, 10 km squares are needed, but at this scale
the within-region picture is blurred!

Island biogeography is wonderfully straightforward, since for
terrestrial organisms at least there's a natural definition of 'area'
for defining 'area of endemism'. As I've said elsewhere, it isn't yet
clear whether within-continental centres of endemism are real, or just
biogeographer's daydreams. See Ian Henderson's article!
--
Dr Robert Mesibov
Honorary Research Associate
Queen Victoria Museum and Art Gallery
Home contact: PO Box 101, Penguin, Tasmania, Australia 7316
(03) 6437 1195; international 61 3 6437 1195