CHAPTER ELEVEN
Body size and diversity
in marine systems
RICHARD M.WARWICK
Plymouth Marine LaboratoryIntroduction
Much has been written concerning the relationship between body size and
biological traits, mostly concerning the terrestrial situation. There is no reason
to suppose that many of these relationships will be different in the sea; for
example quarter-power scaling with body mass applies to virtually all organisms
(West, Brown & Enquist, 1999 ). For marine animals, metabolic rate and produc-
tion scales at three-quarters power (e.g. Brey, 1990 ; Warwick & Price,1979),
while it is likely that life span increases in proportion to body mass raised to the
power of one quarter, although so little is known about the natural history of
marine animals that this latter relationship cannot yet be established. On the
other hand, the very different phyletic composition of terrestrial and marine
faunas, and the big differences in life-history characteristics, suggest that relation-
ships between body size and diversity will differ between these two realms.
The relationship between body size and diversity is fraught with uncertainties
and inconsistencies. Hutchinson (1959 ) suggested that ‘...small size, by permit-
ting animals to become specialised to the conditions offered by small diversified
elements of the environmental mosaic, clearly makes possible a degree of diver-
sity quite unknown among groups of larger organisms’. However, it is now
suggested that the spatial and temporal structure of the physical environment
is fractal (Bellet al., 1993and references therein; seeSchmid & Schmid-Araya,this
volume), and if habitat complexity largely determines species diversity this leads
to the prediction (for a single perfect fractal) that all organisms, regardless of size,
will perceive the environment as equally complex and should have equivalent
diversity. A comprehensive study by Ormeet al.(2002 ) did not support any
correlation between the median body size of a phylum and the number of species
in that phylum, contrary to the Hutchinsonian view that the smallest bodied taxa
are the most diverse (Van Valen,1973 ; May,1986 ;Kochmer&Wagner,1988 )or
more recent suggestions that diversity is highest in taxa of intermediate size (Dial &
Marzluff,1988 ;Fenchel,1993; Siemann, Tilman & Harrstad,1996 ; Etienne &
Olff,2004 ).Uncertaintyalsoexistsastowhether local diversity is controlled by
regional processes, involving biogeographic and evolutionary mechanisms, or
Body Size: The Structure and Function of Aquatic Ecosystems, eds. Alan G. Hildrew, David G. Raffaelli and Ronni
Edmonds-Brown. Published by Cambridge University Press.#British Ecological Society 2007.