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latitudinal diversity gradient that was just a spurious consequence of the
difference in depth sampling.
When the data from the North and South Atlantic were statistically
corrected to remove the effect of depth, using the residuals of the
regression of diversity against depth and latitude against depth, large-scale
horizontal patterns emerged.
Focussing on an area in the North Atlantic where the patterns were
more obvious, he cited a study of more than 100 species of Turridae, the
largest family of gastropods, collected over a century at 1300 stations in
just the eastern North Atlantic. Rather than looking at the diversity of
samples, he had documented the well-characterised latitudinal range of
each species, examined where the ranges overlapped and summed the
diversity. When averaged over large scales of time and space, the
calculation showed the same sharp latitudinal decline in diversity. The
implications for mining were that it made a difference where the deep sea
was disturbed, in terms of the impact on biodiversity.
Meiofaunal data from foraminiferans in the North and South Atlantic
also showed a decline in diversity toward the poles. However, John
Lambshead 34 , looking for large-scale patterns in the metazoan meiofauna,
had found that they were not at all clear; there was either no pattern or, in
some cases, evidence of a positive latitudinal gradient. Whatever the
causes, on large scales there was variation in patterns of coexistence.
Many of the large-scale patterns had an historical component as
well as an ecological one, as shown in an analysis by Thomas and Gooday
of foraminiferal diversity between the Antarctic and Equatorial Pacific
Oceans throughout much of the Cenozoic Era 35 . In the Eocene Epoch, when
the Earth’s climate changed from a greenhouse to an icehouse world, and
polar ice caps developed in the South Atlantic and on Antarctica, the
environment had become much more seasonal. Quantitative samples of
deep-sea forams showed a divergence in diversity between the equator and
the poles, similar to the latitudinal gradient displayed in the recent data,
thus establishing that diversity remained high at the equator and headed
south, as it were, toward Antarctica.
As another example of a lengthy historical component to these
large-scale patterns, Rex had recalculated data from G.D.F. Wilson for
typical deep-sea isopods of the suborder Asellota. They had invaded the
deep sea early, apparently as far back as the Mesozoic Era, and had
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