and that the species occurring in any particular location are a more or less
random selection from that pool. This would account for the conservative
basic patterns encountered in marine habitats, which of course will be modified
to some degree by ecological constraints. Whilst the effects of these ecological
constraints can be examined experimentally, we cannot do manipulative
experiments over evolutionary time and we must rely on so-called ‘natural
experiments’, studying comparative situations where the invoked evolutionary
mechanisms differ. For example, it would be a good test for the importance of
the developmental mode if situations where the benthic/pelagic larval develop-
ment dichotomy does not exist, e.g. the deep-sea, could be compared. Although
no comprehensive size spectra yet exist for the deep sea, the model predicts a
unimodal species-size distribution if the developmental mode is the key trait
responsible for the size dichotomy.
Acknowledgements
The ideas summarized here result from interactions with a large number of
colleagues, and financial support from a large number of funding agencies over
the course of a long career (resulting in an embarrassing proportion of self-
citations). These are far too numerous to list, but I thank them all. The writing of
Table 11.3Adult dry weight of species that become very
abundant in organically enriched habitats. For sources of
data see Warwicket al.(1986).
Species Dry weight (mg)
Annelids
Capitella capitata 505
Polydora ciliata/ligni 125
Streblospio benedicti/shrubsolii 188
Tubificoides benedeni 306
Ophryotrocha hartmanni 50
Ophryotrocha puerilis 140
Raphidrilussp. 158
Protodorvillea kefersteini 108
Pholoe minuta 190
Nematodes
Metoncholaimus albidus 12
Metoncholaimus scanicus 23
Pontonemaspp. 64
Copepods
Tisbespp. 12
Bulbamphiascus imus 3
BODY SIZE AND DIVERSITY IN MARINE SYSTEMS 221