but the rate of turnover of primary producer biomass that influences their
occurrence. Body size plays various roles which can be summarized thus:
(i) A large size disparity between predators and prey leads to strong interaction
strengths and less discrimination between prey types.
(ii) The trophic pyramid assumes a square or inverted triangle shape, associ-
ated with a trophic cascade, where the turnover of primary producer
biomass is high. High-turnover primary producers typically have small
body size, but the opposite is not true.
(iii) Large body size of primary producers leads to increased complexity of
habitat architecture, which in turn stabilizes the food web.
(iv) Facilitation can be of importance for trophic cascades and may affect body
size – trophic cascade relationships.
The often repeated dearth of cascades in terrestrial habitats, if true, may be a
consequence of a relatively large size and slow turnover of primary producers in
terrestrial environments. However, it is more likely to be a consequence of less
effort to demonstrate their presence. A directed search for cascades in commun-
ities where there is a large predator:prey body size and rapid turnover of
primary-producer biomass is likely to be fruitful. Nevertheless, we suggest
that effort is put into linking body size, biomass turnover, productivity and
trophic cascades, as by bringing these together we may be able to take our
understanding of this subject forward into new and exciting areas.Acknowledgements
We thank the British Ecological Society and Freshwater Biological Association
for their support, and the other contributors for stimulating discussions. EJ was
supported by Euro-limpacs (GOCE-CT-2003-505540), the Danish Natural Science
Research Council (CONWOY project), CLEAR and NORLAKE. JIJ was supported by
a NERC Fellowship, GT5/98/21/CB, and by NERC CEH. We are also indebted to the
Greenland team at NERI and the Freshwater Biological Laboratory, Hillerød and
to those who allowed us to use their data, particularly the Danish Counties,
Angela Beresford, Tom Davidson, Carl Sayer and Martin Perrow.References
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