5.3
Zoogeography of the Fishes of the Indian Ocean
D.M.COHEN
As a prelude to considering the present state of knowledge on the distribution of
Indian Ocean fishes and in order to interject some perspective, I propose to briefly discuss
a series of questions with which zoogeographers concern themselves and to discuss two
different approaches to zoogeography.
I. Zoogeographic Questions
A. Where does an animal or group of animals live? For fishes, this topic might appropriately be subtitled geography and taxonomy, for until recently the study of fish distribution has been pursued almost exclusively by systematists. Describing the where of an
animal requires information on the what of an animal. Ideally, knowledge of a regional
fauna should progress in the following sequence.
a) Species descriptions and range extensions
b) Regional checklists and keys based on a)
c) Supraregional group revisions
d) Regional checklists and keys based on c)
The scene then is set for the zoogeographer to delimit patterns of distribution and to
analyze them in the light of information from disciplines other than taxonomy. Unfortunately, for purposes of this Symposium, even the first category is imprecisely known
for most tropical fishes.
B. Why does an animal or group of animals live where it does and not elsewhere?
This question leads to a consideration of habitats, niches isolating mechanisms, and
competition, and the zoogeographer must use concepts drawn from evolution and ecology.
These data often are considered implicitly by fish zoogeographers, but for most kinds of
fishes much pertinent information is accumulated under the term natural history and
has yet to be suitably organized or quantified for use in zoogeography.
C. Whence and how did animals - or their ancestors arrive? Although there is no
doubt that some species or groups of species have evolved in situ, it is equally obvious
that some have arrived from elsewhere. Here again the zoogeographer must look to
ecology with an eye to answering problems of dispersal, and to taxonomy (and when
possible palaeontology) as a guide to phylogeny. Needless to say, information on the
past history of the land and of the sea is invaluable.
II. Approaches to Zoogeography
Although combinations of the above 3 general topics are inherent in virtually all
studies of animal distribution, zoogeographers tend to come in 2 fairly distinct varieties-
Zoogeography of the Fishes of the Indian Ocean
D.M.COHEN
As a prelude to considering the present state of knowledge on the distribution of
Indian Ocean fishes and in order to interject some perspective, I propose to briefly discuss
a series of questions with which zoogeographers concern themselves and to discuss two
different approaches to zoogeography.
I. Zoogeographic Questions
A. Where does an animal or group of animals live? For fishes, this topic might appropriately be subtitled geography and taxonomy, for until recently the study of fish distribution has been pursued almost exclusively by systematists. Describing the where of an
animal requires information on the what of an animal. Ideally, knowledge of a regional
fauna should progress in the following sequence.
a) Species descriptions and range extensions
b) Regional checklists and keys based on a)
c) Supraregional group revisions
d) Regional checklists and keys based on c)
The scene then is set for the zoogeographer to delimit patterns of distribution and to
analyze them in the light of information from disciplines other than taxonomy. Unfortunately, for purposes of this Symposium, even the first category is imprecisely known
for most tropical fishes.
B. Why does an animal or group of animals live where it does and not elsewhere?
This question leads to a consideration of habitats, niches isolating mechanisms, and
competition, and the zoogeographer must use concepts drawn from evolution and ecology.
These data often are considered implicitly by fish zoogeographers, but for most kinds of
fishes much pertinent information is accumulated under the term natural history and
has yet to be suitably organized or quantified for use in zoogeography.
C. Whence and how did animals - or their ancestors arrive? Although there is no
doubt that some species or groups of species have evolved in situ, it is equally obvious
that some have arrived from elsewhere. Here again the zoogeographer must look to
ecology with an eye to answering problems of dispersal, and to taxonomy (and when
possible palaeontology) as a guide to phylogeny. Needless to say, information on the
past history of the land and of the sea is invaluable.
II. Approaches to Zoogeography
Although combinations of the above 3 general topics are inherent in virtually all
studies of animal distribution, zoogeographers tend to come in 2 fairly distinct varieties-